Patent Publication Number: US-2023151339-A1

Title: Engineered aryl sulfate-dependent enzymes

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The instant application is a continuation in-part of U.S. patent application Ser. No. 17/894,933, filed on Aug. 24, 2022, which was a continuation of U.S. patent application Ser. No. 17/376,332, filed on Jul. 15, 2021, which was a continuation-in-part of International Application No. PCT/US2020/013677, filed on Jan. 15, 2020, which claims of the benefit of U.S. Provisional Applications 62/792,440, filed on Jan. 15, 2019; 62/797,466, filed on Jan. 28, 2019; 62/808,074, filed on Feb. 20, 2019; and 62/853,261, filed May 28, 2019, the disclosures of which are hereby incorporated by reference in their entireties. The instant application is also a continuation of International Application No. PCT/US2021/041537, filed on Jul. 14, 2021, which claims the benefit of U.S. Provisional Application 63/051,764, filed on Jul. 14, 2020, the disclosures of which are hereby incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to methods for synthesizing non-anticoagulant heparan sulfate using non-natural sulfotransferase enzymes that are engineered to react with an aryl sulfate compound, instead of 3′-phosphoadenosine 5′-phosphosulfate, as a sulfo group donor. REFERENCE TO SEQUENCE LISTING 
     The present application is being filed along with a sequence listing in electronic format. The sequence listing is provided as a file entitled “OPT-001XRT-36CT_Sequence_Listing.xml” created on Aug. 23, 2022, and which is 555,100 bytes in size. The information in electronic format of the sequence listing is incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Although heparin and low-molecular weight heparin (LMWH) are commonly known and prescribed as anticoagulants to reduce or prevent blood clotting, they can also be useful during the treatment of conditions such as, for example: cancers; inflammation; thrombocytopenia; neutropenia; apoptosis; asthma; emphysema; bronchitis; adult respiratory distress syndrome; cystic fibrosis; and ischemia-reperfusion related conditions. However, for many patients, diminished blood coagulation is an unwanted side effect that in some instances can cause more problems than the treatment itself is designed to remedy. 
     One solution to this problem has been to develop 2-O, 3-O-desulfated heparin (ODSH) derivatives, which have a greatly diminished anticoagulant activity relative to heparin or LMWH. Generally, ODSH compositions are prepared by reacting unfractionated heparin or LMWH with a strong base, often at cold temperatures, to remove 2-O and 3-O sulfate groups from the heparan sulfate polysaccharide backbone. Methods of preparing ODSH and their use in the treatment of patients is described in U.S. Pat. Nos. 10,052,346, 9,271,999, 7,468,358, 6,489,311, 5,990,097, 5,912,237, 5,808,021, 5,668,118, and 5,296,471, the disclosures of which are incorporated by reference in their entireties (see also Mousavi, S. et al., (2015)  Advances in Pharmacological Sciences , Article ID 507151, available at http://dx.doi.org/10.1155/2015/507151, incorporated by reference in its entirety). However, although ODSH has been produced that has a reduction of up to 99% of anticoagulant activity relative to heparin, the complete removal of all anticoagulant activity, while maintaining the pharmacological benefits of ODSH, has never been reported. 
     Further, because ODSH is prepared from unfractionated heparin, which is isolated and purified from the internal organs of animals, such as pigs and cows, they are susceptible to disruptions in the worldwide supply due to potential contamination of heparin (over 200 people died as a result of contaminated compounds in 2007 in the United States alone), cross-species transmission of the flu and/or other animal viruses into humans, or geopolitical tensions with global suppliers, particularly China. As a result, there has been a recent push to try to synthesize heparin in vitro. 
     Generally, sulfated polysaccharides, including heparin, are synthesized by the catalytic transfer by multiple sulfotransferase enzymes of sulfate functional groups, also called “sulfo groups”, from a sulfo group donor to a polysaccharide, which acts as a sulfo group acceptor. Sulfotransferases are a vital class of enzymes that catalyze the transfer of a sulfo group from a sulfo group donor to a sulfo group acceptor. Sulfotransferases are nearly ubiquitous in nature, and they exist in nearly all types of organisms, including bacteria, yeast, and animals, including humans. Similarly, sulfotransferase enzymes play an integral role in the sulfation of a wide array of sulfo group acceptors, including many types of steroids, polysaccharides, proteins, xenobiotics, and other molecules. 
     There are several polysaccharides that can be utilized as sulfo group acceptors, including, for example, dermatan, keratan, heparosan, and chondroitin. In particular, heparosan comprises repeating disaccharide units of 1→4 glycosidically-linked, glucuronic acid and N-acetylated glucosamine ([β(1,4)GlcA-α(1,4)GlcNAc] n ) residues, any of which can be further modified by one or more enzyme-catalyzed deacetylation, sulfation, or epimerization reactions. Sulfation of heparosan-based polysaccharides can be catalyzed by up to four sulfotransferase enzymes to form heparan sulfate (HS), and when performed in a particular order along with deacetylation of one or more glucosamine residues and epimerization of one or more glucuronic acid residues, can be utilized to form heparin. 
     However, as wide-ranging and voluminous as the set of sulfo group acceptors can be, there are only a couple of molecules that can be utilized by sulfotransferase enzymes as sulfo group donors. The nearly ubiquitous sulfo group donor, including for each of the four HS sulfotransferases, is 3′-phosphoadenosine 5′-phosphosulfate (PAPS). These in vivo systems have evolved to exclusively utilize PAPS because it has a short half-life and can readily be synthesized and metabolized, as needed, by the organism. However, that same short half-life renders PAPS to be unsuitable for most in vitro syntheses, particularly in large scale syntheses, that utilize sulfotransferases because it can readily decompose into adenosine 3′,5′-diphosphate, which actively inhibits the sulfotransferases&#39; biological activity. In contrast, in vivo systems have evolved to exclusively and efficiently react with PAPS because adenosine 3′,5′-diphosphate can either readily be converted back into PAPS or be broken down into one or more compounds that do not inhibit sulfotransferase activity. As a result, the natural activity of sulfotransferase enzymes to exclusively utilize PAPS as a sulfo group donor presents a steep barrier to the in vitro synthesis of heparin, from which ODSH is prepared. 
     Aryl sulfate compounds, such asp-nitrophenyl sulfate (PNS) and 4-methylumbelliferyl sulfate (MUS) have been identified as cheap, widely-available compounds that can be useful as sulfo donors with a very limited number of sulfotransferases to synthesize certain small molecule products (see Malojcic, G., et al. (2008)  Proc. Nat. Acad. Sci.  105 (49):19217-19222 and Kaysser, L., et al., (2010)  J. Biol. Chem.  285 (17):12684-12694, the disclosures of which are incorporated by reference in their entireties). Yet, only a small number of bacterial sulfotransferases have been shown to react with aryl sulfate compounds as sulfo group donors, and none of these react with polysaccharides, let alone heparosan-based polysaccharides, as sulfo group acceptors. As a result, when sulfotransferases are used in the in vitro synthesis of sulfated polysaccharides, PAPS must be included in the reaction mixture to effectively catalyze sulfo group transfer, and aryl sulfate compounds can only be used indirectly, to repopulate the system with PAPS (see U.S. Pat. No. 6,255,088, the disclosure of which is incorporated by reference in its entirety). 
     Consequently, there is a need to develop sulfotransferase enzymes that react with aryl sulfate compounds as sulfo group donors, as well as polysaccharides as sulfo group acceptors. In particular, the development of sulfotransferase enzymes that are capable of both reacting with aryl sulfate compounds as sulfo group donors and with heparosan-based polysaccharides as sulfo group acceptors would present a large step forward toward the development of large-scale syntheses of heparin and non-anticoagulant ODSH analogs in vitro. 
     SUMMARY OF THE INVENTION 
     The present invention provides several engineered, biologically-active enzymes that are capable of recognizing, binding to, and reacting with aryl sulfate compounds as substrates. According to the present invention, the engineered enzyme can have sulfatase activity. According to the present invention, the engineered enzyme can have sulfotransferase activity. 
     According to the present invention, an engineered enzyme having sulfatase and/or sulfotransferase activity can react with an aryl sulfate compound, preferably selected from the group consisting of p-nitrophenyl sulfate (PNS), 4-methylumbelliferyl sulfate, 7-hydroxycoumarin sulfate, phenyl sulfate, 4-acetylphenyl sulfate, indoxyl sulfate, 1-naphthyl sulfate, 2-naphthyl sulfate (2NapS), and 4-nitrocatechol sulfate (NCS). According to the present invention, an engineered sulfotransferase can recognize, bind, and react with PNS as the sulfo group donor. According to the present invention, an engineered sulfotransferase can recognize, bind, and react with NCS as the sulfo group donor. According to the present invention, an engineered sulfotransferase can recognize, bind, and react with either PNS or NCS as the sulfo group donor. 
     In an aspect of the invention, an engineered enzyme of the present invention can have sulfatase biological activity. According to the present invention, sulfatase activity comprises the nucleophilic attack of a sulfur atom within an aryl sulfate compound, causing hydrolysis of a sulfate group and releasing the aromatic moiety from the active site. According to the present invention, the nucleophilic attack of the sulfur atom can be initiated by an amino acid residue within the active site of the engineered enzyme, particularly a histidine residue. According to the present invention, the reaction with the aryl sulfate compound can result in a sulfohistidine intermediate, in which a sulfate group is covalently bound to the amino acid nucleophile, particularly a histidine residue. 
     According to the present invention, an engineered enzyme of the present invention having sulfatase activity differs from other known sulfatases, which typically comprise greater than 500 amino acid residues, at least one cysteine or serine residue that is post-translationally modified to become α-formylglycine, and one or more characteristic signature sequences, C/S-X-P-S/X-R-X-X-X-L/X-T/X-G/X-R/X or G-Y/V-X-S/T-X-X-X-G-K-X-X-H, which correspond to SEQ ID NO: 271 and SEQ ID NO: 272 in the sequence listing, respectively, and direct the post-translational modification of the cysteine or serine into α-formylglycine. Thus, according to the present invention, engineered enzymes having sulfatase activity can comprise less than 500 amino acid residues. According to the present invention, engineered enzymes having sulfatase activity can have zero α-formylglycine residues. According to the present invention, engineered enzymes having sulfatase activity can have no amino acid sequence motifs comprising the amino acid sequences of either SEQ ID NO: 271 or SEQ ID NO: 272. 
     According to the present invention, engineered enzymes of the present invention that have sulfatase activity can comprise any amino acid sequence, so long as nucleophilic attack of the aryl sulfate compound is initiated by an active site amino acid residue, preferably a histidine residue. According to the present invention, an engineered enzyme having sulfatase activity can have an amino acid sequence selected from the group consisting of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151. According to the present invention, an engineered enzyme having sulfatase activity can have an amino acid sequence selected from the group consisting of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160. According to the present invention, an engineered enzyme having sulfatase activity can have comprise any amino acid sequence that is a biological equivalent of any of the amino acid sequences above. 
     In another aspect of the present invention, an engineered enzyme of the present invention can have sulfotransferase biological activity. According to the present invention, sulfotransferase activity comprises the enzymatic transfer of a sulfo group from an aryl sulfate compound to a sulfo group acceptor. According to the present invention, the sulfo group acceptor can be a polysaccharide. According to the present invention, the sulfo group acceptor polysaccharide can be a heparosan-based polysaccharide. According to the present invention, the heparosan-based polysaccharide can be N-deacetylated heparosan. According to the present invention, the heparosan-based polysaccharide can be N-sulfated heparosan (NS-HS). According to the present invention, the heparosan-based polysaccharide can be N-sulfated, 2-O sulfated heparan sulfate (N,2O-HS). According to the present invention, the heparosan-based polysaccharide can be N-sulfated, 2-O sulfated, 6-O sulfated heparan sulfate (N,2O,6O-HS). According to the present invention, the heparosan-based polysaccharide can be N-sulfated, 2-O sulfated, 3-O sulfated, 6-O sulfated heparan sulfate (N,2O,3O,6O-HS). According the present invention, and as described below, the N,2O,3O,6O-HS product can have one or more molecular weight properties and/or anticoagulant activity that are similar or equivalent to heparin. According to the present invention, the heparosan-based polysaccharide can be sulfated at any of the N-, 2-O, 3-O, and/or 6-O positions, within any of the disaccharide units comprising the heparosan-based polysaccharide. According to the present invention, the heparosan-based polysaccharide can comprise one or more iduronic acid residues substituted in place of a glucuronic acid residue. According to the present invention, one or more of the iduronic acid residues can be 2-O sulfated. 
     According to the present invention, the sulfotransfer reaction catalyzed by an engineered sulfotransferase enzyme can proceed via a reaction mechanism in which a sulfohistidine intermediate is first formed upon the reaction between the enzyme and an aryl sulfate compound, followed by the binding of a heparosan-based polysaccharide within the active site, and subsequent transfer of the sulfo group from the sulfohistidine intermediate to the polysaccharide. Alternatively, according to the present invention, the sulfotransfer reaction catalyzed by an engineered sulfotransferase enzyme can proceed via a reaction mechanism in which both an aryl sulfate compound and a heparosan-based polysaccharide are bound within the active site, and the enzyme catalyzes the direct transfer of the sulfo group from the aryl sulfate compound to the polysaccharide. 
     According to the present invention, an engineered sulfotransferase enzyme can have a biological activity based on the position within the heparosan-based polysaccharide that receives the sulfo group, including glucosaminyl N-sulfotransferase activity, hexuronyl 2-O sulfotransferase activity, glucosaminyl 6-O sulfotransferase activity, or glucosaminyl 3-O sulfotransferase activity. Each biological activity is described in further detail, below. 
     In an aspect of the invention, an engineered sulfotransferase enzyme can have glucosaminyl N-sulfotransferase activity, comprising the transfer of a sulfo group from an aryl sulfate compound to the N-position of an unsubstituted glucosamine residue within a heparosan-based polysaccharide. According to the present invention, an engineered glucosaminyl N-sulfotransferase (NST) enzyme can comprise any amino acid sequence, so long as the sulfo group donor is an aryl sulfate compound and the sulfo group acceptor is a heparosan-based polysaccharide. 
     According to the present invention, engineered NST enzymes can be mutants of the N-sulfotransferase domain of natural N-deacetylase/N-sulfotransferase (NDST) enzymes, which are members of enzyme class (EC) 2.8.2.8. In contrast to the engineered NST enzymes of the present invention, natural enzymes within EC 2.8.2.8 do not react with aryl sulfate compounds, and only react with 3′-phosphoadenosine 5′-phosphosulfate (PAPS) as a sulfo group donor. However, the engineered NST enzymes can retain the same biological activity as the natural enzymes within EC 2.8.2.8 with heparosan-based polysaccharides as sulfo group acceptors. According to the present invention, heparosan-based polysaccharides that can be utilized as sulfo acceptors with any of the engineered NST enzymes can comprise one or more disaccharide units having the structure of Formula II, below: 
     
       
         
         
             
             
         
       
     
     wherein n is an integer and R is selected from the group consisting of a hydrogen atom or a sulfo group. According to the present invention, both R groups within the disaccharide unit can be a hydrogen atom. According to the present invention, all of the R groups within the same polysaccharide molecule can be hydrogen atoms. When the sulfo acceptor polysaccharide comprises the structure of Formula II, upon transfer of the sulfo group from an aryl sulfate compound, the sulfated polysaccharide product comprises the structure of Formula III, below: 
     
       
         
         
             
             
         
       
     
     wherein n is an integer and R is selected from the group consisting of a hydrogen atom or a sulfo group. 
     According to the present invention, although the glucosamine residue that receives the sulfo group is N-unsubstituted, as illustrated in Formula II and Formula III above, other glucosamine residues within the same polysaccharide molecule can be N-acetylated, N-sulfated, or N-unsubstituted, 3-O sulfated, and/or 6-O sulfated. Similarly, hexuronic acid residues in other positions within the polysaccharide that are not adjacent to the glucosamine residue receiving the sulfo group can be glucuronic acid or iduronic acid residues, any of which can be optionally 2-O sulfated. According to the present invention, and in some preferred embodiments, the heparosan-based polysaccharide can be N-deacetylated heparosan, in which all of the glucosamine residues are N-unsubstituted, or are present as a mixture of N-acetylglucosamine and N-unsubstituted glucosamine. 
     According to the present invention, an engineered NST enzyme can consist of a single N-sulfotransferase domain that is capable of binding and reacting with an aryl sulfate compound as a sulfo group donor. However, most natural NDST enzymes within EC 2.8.2.8 have dual N-deacetylase/N-sulfotransferase activity, with one domain structurally configured for N-deacetylase activity and another domain structurally configured for N-sulfotransferase activity. Therefore, according to the present invention, the engineered NST enzyme can also comprise an N-deacetylase domain having either an identical or mutated amino acid sequence to the N-deacetylase domain of any of the NDST enzymes in EC 2.8.2.8. 
     To facilitate its exclusive reactivity with PAPS as the sulfo group donor, natural NDST enzymes typically comprise highly-conserved or identical amino acid sequences that define the active site and govern the enzyme&#39;s recognition, binding, and reactivity with PAPS. According to the present invention, the amino acid sequence of an engineered NST enzyme can comprise one or more mutations relative to the N-sulfotransferase domain of a natural NDST enzyme, in order to facilitate binding of an aryl sulfate compound instead of PAPS. According to the present invention, an engineered NST enzyme can comprise an amino acid sequence having at least one amino acid mutation relative to the N-sulfotransferase domain of a natural NDST enzyme, including at least two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, twenty, thirty, forty, fifty, up to at least one hundred amino acid mutations. According to the present invention, an engineered NST enzyme can comprise at least one amino acid mutation relative to the amino acid sequence of any of the NDST enzymes, in regions that are known to define the enzyme&#39;s active site, including at least two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, or fifteen amino acid mutations, up to at least twenty amino acid mutations. 
     According to the present invention, the amino acid sequence of an engineered NST enzyme can be expressed as a “percent identity” or “% identity” relative to the amino acid sequence of one or more of the natural NDST enzymes within EC 2.8.2.8, particularly relative to their N-sulfotransferase domains, and including biological functional fragments thereof. According to the present invention, an engineered NST enzyme can have at least 50% sequence identity, and up to at least 97% sequence identity, with the N-sulfotransferase domain of any of the enzymes within EC 2.8.2.8. In a non-limiting example, the amino acid sequence of the non-natural NST enzyme can have at least 80% sequence identity with the amino acid sequence of the N-sulfotransferase domain of a natural NDST enzyme, the natural NDST enzyme selected from the group consisting of: the human NDST1 enzyme (SEQ ID NO: 164, UniProtKB Accession No. P52848); the human NDST2 enzyme (SEQ ID NO: 177, UniProtKB Accession No. P52849); the human NDST3 enzyme (SEQ ID NO: 174, UniProtKB Accession No. 095803); and the human NDST4 enzyme (SEQ ID NO: 173, UniProtKB Accession No. Q9H3R1). According to the present invention, such engineered NST enzymes can also have an N-deacetylase domain that is either identical to, or contains one or more amino acid mutations relative to, any of the enzymes within EC 2.8.2.8. 
     According to the present invention, an engineered NST enzyme can comprise one or more mutated amino acid sequence motifs relative to conserved amino acid sequence motifs found in one or more natural NDST enzymes within EC 2.8.2.8. Each mutated amino acid sequence motif, when present, can have at least one amino acid mutation relative to the corresponding conserved amino acid sequence motif within the natural NDSTs. According to the present invention, an engineered NST enzyme can comprise one, two, three, four, or five mutated amino acid sequence motifs relative to the following conserved NST amino acid sequence motifs: (Q-K-T-G-T-T-A), (T-F-E-E), (F-E-K-S-A), (S-W-Y-Q-H), and (C-L-G-K/R-S-K-G-R), which correspond to SEQ ID NO: 221, SEQ ID NO: 222, SEQ ID NO: 223, SEQ ID NO: 224, and SEQ ID NO: 225 in the sequence listing, respectively. In some embodiments, within the amino acid sequence of the engineered NST enzyme, the conserved Q-K-T-G-T-T-A amino acid sequence motif (SEQ ID NO: 221) is mutated to an amino acid sequence motif selected from the group consisting of: H-X 1 -T-G-X 2 -H-A (SEQ ID NO: 226), wherein X 1  and X 2  are either both glycine (as indicated in SEQ ID NO: 227), or wherein X 1  is lysine and X 2  is valine (as indicated in SEQ ID NO: 228); and X 3 -K-T-G-A-W/F-A/L (SEQ ID NO: 234), wherein X 3  can optionally be mutated to a serine (as indicated in SEQ ID NO: 235) or alanine (as indicated in SEQ ID NO: 236). In some embodiments, when the mutated amino acid sequence motif H-X 1 -T-G-X 2 -H-A (SEQ ID NO: 226) is selected, the C-terminal lysine residue within the conserved C-L-G-K/R-S-K-G-R amino acid sequence motif (SEQ ID NO: 225) is mutated to either a leucine (as indicated in SEQ ID NO: 229) or valine (as indicated in SEQ ID NO: 230) residue, and the amino acid sequence of the non-natural NST enzyme contains at least one additional mutation to a histidine residue, at a position selected from the group consisting of: the C-terminal glutamic acid residue in the conserved T-F-E-E amino acid sequence (as illustrated in SEQ ID NO: 231); the lysine residue in the conserved F-E-K-S-A amino acid sequence (as illustrated in SEQ ID NO: 232); and the serine residue in the conserved C-L-G-K/R-S-K-G-R amino acid sequence (as illustrated in SEQ ID NO: 233). In some embodiments, when the mutated amino acid sequence motif X 3 -K-T-G-A-W/F-A/L (SEQ ID NO: 234) is selected, the final three residues in the conserved T-F-E-E amino acid sequence motif are mutated such that the C-terminal glutamic acid residue in SEQ ID NO: 222 is mutated to a serine residue, and the mutated amino acid sequence motif is selected from the group consisting of: T-H-G-S(SEQ ID NO: 237); T-G-H-S(SEQ ID NO: 238); the conserved C-L-G-K/R-S-K-G-R amino acid sequence motif (SEQ ID NO: 225) is mutated to include a histidine residue, at a position selected from the group consisting of the leucine residue, the serine residue, or the C-terminal lysine residue (as illustrated in SEQ ID NO: 239, SEQ ID NO: 240, or SEQ ID NO: 243, respectively), and if the histidine is substituted within the conserved C-L-G-K/R-S-K-G-R amino acid sequence motif at the leucine or serine residue, the C-terminal lysine residue is mutated to either a leucine (as illustrated in SEQ ID NO: 239 or SEQ ID NO: 240) or a tryptophan residue (as illustrated in SEQ ID NO: 241 or SEQ ID NO: 242). Additional non-limiting examples of mutated amino acid sequence motifs are described in further detail, below. 
     According to the present invention, an engineered NST enzyme can comprise an amino acid sequence selected from the group consisting of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, and SEQ ID NO: 25, each of which contains several amino acid mutations made relative to highly conserved amino acid sequences that define the N-sulfotransferase domain of natural enzymes within EC 2.8.2.8. According to the present invention, engineered NST enzymes utilized in accordance with any of the methods described herein can also comprise any amino acid sequence that is a biological equivalent, and/or a functional fragment, of an amino acid sequence selected from the group consisting of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, and SEQ ID NO: 25. 
     According to the present invention, any of the engineered NST enzymes described above can possess one or more residue differences or mutations as compared to the amino acid sequences disclosed by an amino acid sequence selected from the group consisting of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, and SEQ ID NO: 25. Non-limiting examples of such residue differences include amino acid insertions, deletions, substitutions, or any combination of such changes. According to the present invention, differences from the disclosed amino acid sequences in an amino acid sequence selected from the group consisting of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, and SEQ ID NO: 25 can comprise non-conservative substitutions, conservative substitutions, as well as combinations of conservative and non-conservative amino acid substitutions. According to the present invention, an amino acid mutation can be made at any position within SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, and SEQ ID NO: 25, so long as the mutated enzyme retains its NST activity with an aryl sulfate compound as a sulfo group donor and a heparosan-based polysaccharide comprising the structure of Formula II as the sulfo group acceptor. 
     According to the present invention, an engineered NST enzyme can comprise the amino acid sequence of SEQ ID NO: 18. Within SEQ ID NO: 18, residues having the designation, “Xaa,” illustrate known instances in which there is a lack of identity at a particular position within the amino acid sequences of SEQ ID NO: 5, SEQ ID NO: 7, and SEQ ID NO: 15. Thus, an “Xaa” designation indicates the amino acid at that position can be selected from a group of two or more amino acids, as defined by SEQ ID NO: 18. 
     According to the present invention, an engineered NST enzyme can comprise the amino acid sequence of SEQ ID NO: 19. Within SEQ ID NO: 19, residues having the designation, “Xaa,” illustrate known instances in which there is a lack of identity at a particular position within the amino acid sequences of SEQ ID NO: 9, SEQ ID NO: 11, and SEQ ID NO: 13. Thus, an “Xaa” designation indicates the amino acid at that position can be selected from a group of two or more amino acids, as defined by SEQ ID NO: 19. 
     Additionally, and according to the present invention, amino acid mutations can be made at one or more positions within SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, and SEQ ID NO: 25 so long as the mutated enzyme retains its glucosaminyl N-sulfotransferase activity with an aryl sulfate compound as a sulfo group donor. According to the present invention, an aryl sulfate-dependent enzyme comprising the amino acid sequence of SEQ ID NO: 18 or SEQ ID NO: 19 can optionally comprise one or more amino acid mutations at positions not designated as “Xaa,” while still retaining its glucosaminyl N-sulfotransferase activity with an aryl sulfate compound as a sulfo group donor. 
     In an aspect of the invention, an engineered sulfotransferase enzyme can have hexuronyl 2-O sulfotransferase activity, comprising the transfer of a sulfo group from an aryl sulfate compound to the 2-O position of a hexuronic acid residue within a heparosan-based polysaccharide. According to the present invention, an engineered 2OST can comprise any amino acid sequence, so long as the sulfo group donor is an aryl sulfate compound and the sulfo group acceptor is a heparosan-based polysaccharide. 
     According to the present invention, engineered 2OST enzymes can be mutants of natural sulfotransferases that have 2OST activity, which are members of enzyme class (EC) 2.8.2.—. In contrast to the engineered 2OST enzymes of the present invention, natural 2OST enzymes within EC 2.8.2.—do not react with aryl sulfate compounds, and only react with PAPS as a sulfo group donor. However, the engineered 2OST enzymes can retain the same biological activity as the natural 2OST enzymes within EC 2.8.2.—with heparosan-based polysaccharides as sulfo group acceptors. According to the present invention, heparosan-based polysaccharides that can be utilized as sulfo acceptors with any of the engineered 2OST enzymes can comprise one or more structural motifs having the structure of Formula IV, below: 
     
       
         
         
             
             
         
       
     
     As indicated in Formula IV, the hexuronic acid residue is glucuronic acid. According to the present invention, and in another non-limiting example, when the hexuronic acid residue is iduronic acid, the heparosan-based polysaccharide comprises the structure of Formula V, below: 
     
       
         
         
             
             
         
       
     
     According to the present invention, when the heparosan-based polysaccharide comprises the structure of Formula IV, the 2-O sulfated polysaccharide product comprises the structure of Formula VI, below: 
     
       
         
         
             
             
         
       
     
     According to the present invention, when the heparosan-based polysaccharide comprises the structure of Formula V, the 2-O sulfated polysaccharide product comprises the structure of Formula VII, below: 
     
       
         
         
             
             
         
       
     
     According to the present invention, the heparosan-based polysaccharide comprising the structure of Formula IV or Formula V can be N-sulfated heparosan. According to the present invention, a sulfo group acceptor for an engineered 2OST enzyme can comprise multiple motifs comprising the structure of Formula IV and/or Formula V, any or all of which can be sulfated by the enzyme. According to the present invention, and as illustrated in Formula IV and Formula V above, both of the glucosamine residues adjacent to the hexuronic acid residue that receives the sulfo group are N-sulfated. According to the present invention, a sulfo group acceptor for an engineered 2OST enzyme can be the sulfated polysaccharide product of an engineered NST enzyme, described above. According to the present invention, a sulfated polysaccharide product formed by an engineered 2OST enzyme, and comprising the structure(s) of Formula VI and/or Formula VII, is an N,2O-HS product. 
     According to the present invention, glucosamine residues within the polysaccharide that are not adjacent to the hexuronic acid residue receiving the sulfo group can optionally be N-, 3-O, and/or 6-O sulfated, N-acetylated, or N-unsubstituted. Similarly, hexuronic acid residues in other positions within the polysaccharide that are not adjacent to the glucosamine residue receiving the sulfo group can be glucuronic acid or iduronic acid residues, any of which can be optionally 2-O sulfated. 
     According to the present invention, polysaccharides comprising the structures of Formula IV and/or Formula V can be reacted with a glucuronyl C 5 -epimerase enzyme to reversibly invert the stereochemistry of the C 5 -carbon to form iduronic acid from glucuronic acid, and vice versa. However, once a hexuronic acid residue has been 2-O sulfated, it can no longer react with the glucuronyl C 5 -epimerase. In some preferred embodiments, a glucuronyl C 5 -epimerase enzyme can be used to invert the stereochemistry of hexuronic acid residues within N-sulfated heparosan polysaccharides comprising the structure of Formula III and form a structural motif comprising the structure of Formula V, prior to reacting with a 2OST enzyme. According to the present invention, the glucuronyl C 5 -epimerase enzyme can comprise the amino acid sequence of SEQ ID NO: 67, preferably residues 34-617 of SEQ ID NO: 67. According to the present invention, the glucuronyl C 5 -epimerase enzyme can be used to catalyze the conversion of one or more glucuronic acid residues within N-sulfated heparosan to iduronic acid residues, prior to reacting with an engineered 2OST enzyme. 
     To facilitate its exclusive reactivity with PAPS as the sulfo group donor, natural 2OST enzymes within EC 2.8.2.—typically comprise highly-conserved or identical amino acid sequences that define the active site and govern the enzyme&#39;s recognition, binding, and reactivity with PAPS. According to the present invention, the amino acid sequence of an engineered 2OST enzyme can comprise one or more mutations relative to one or more natural 2OST enzymes within EC 2.8.2.—, in order to facilitate binding of an aryl sulfate compound instead of PAPS. According to the present invention, an engineered 2OST enzyme can comprise an amino acid sequence having at least one amino acid mutation relative to any of the natural 2OST enzymes within EC 2.8.2.—, including at least two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, twenty, thirty, forty, fifty, up to at least one hundred amino acid mutations. According to the present invention, an engineered 2OST enzyme can comprise at least one amino acid mutation relative to the amino acid sequence of any of the natural 2OST enzymes within EC 2.8.2.—, in regions that are known to define the enzyme&#39;s active site, including at least two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, or fifteen amino acid mutations, up to at least twenty amino acid mutations. 
     According to the present invention, the amino acid sequence of an engineered 2OST enzyme can be expressed as a “percent identity” or “% identity” relative to the amino acid sequence of one or more of the natural 2OST enzymes within EC 2.8.2.—, including biological functional fragments thereof. According to the present invention, an engineered 2OST enzyme can have at least 50% sequence identity, and up to at least 97% sequence identity, with any of the 2OST enzymes within EC 2.8.2.—. In a non-limiting example, the amino acid sequence of the engineered 2OST enzyme can have at least 80% sequence identity with the amino acid sequence of the chicken 2OST1 enzyme (SEQ ID NO: 179, UniProtKB Accession No. Q76KB1). 
     According to the present invention, an engineered 2OST enzyme can comprise one or more mutated amino acid sequence motifs relative to conserved amino acid sequence motifs found in one or more natural 2OST enzymes within EC 2.8.2.—. Each mutated amino acid sequence motif, when present, can have at least one amino acid mutation relative to the corresponding conserved amino acid sequence motif within the natural 2OST enzymes within EC 2.8.2.—. According to the present invention, an engineered 2OST enzyme can comprise one, two, three, four, five, or six mutated amino acid sequence motifs relative to the following conserved 2OST amino acid sequence motifs: (R-V-P-K-T-A/G-S-T), (N-T-S/T-K-N), (Y-H-G-H), (F-L-R-F/H-G-D-D/N-F/Y), (R-R-K/R-Q-G), and (S-H-L-R-K/R-T), which correspond to SEQ ID NO: 244, SEQ ID NO: 273, SEQ ID NO: 274, SEQ ID NO: 245, SEQ ID NO: 246, and SEQ ID NO: 247 in the sequence listing, respectively. In some embodiments, within the amino acid sequence of the engineered 2OST enzyme, the conserved R-V-P-K-T-A/G-S-T amino acid sequence motif (SEQ ID NO: 244) is mutated to the amino acid sequence motif R-V-X 1 -X 2 -T-A-S-X 3 , wherein the amino acid sequence motif R-V-X 1 -X 2 -T-A-S-X 3  is selected from the group consisting of R-V-P-H-T-A-S-T and R-V-H-R-T-A-S-H (corresponding to SEQ ID NO: 248 and SEQ ID NO: 249 in the sequence listing, respectively), and the conserved S-H-L-R-K/R-T amino acid sequence motif (SEQ ID NO: 247) is mutated to S-H-L-H-K-T (SEQ ID NO: 250). In a further embodiment, when the amino acid sequence R-V-P-H-T-A-S-T (SEQ ID NO: 248) is selected, the conserved F-L-R-F/H-G-D-D/N-F/Y sequence motif (SEQ ID NO: 245) can be mutated to H-L-R-F-G-D-D-Y (SEQ ID NO: 251). Additional non-limiting examples of mutated amino acid sequence motifs are described in further detail, below. 
     According to the present invention, an engineered 2OST enzyme can comprise an amino acid sequence selected from the group consisting of SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 68, and SEQ ID NO: 69, each of which contains several amino acid mutations made relative to highly conserved amino acid sequences that define the natural 2OST enzymes within EC 2.8.2.—. According to the present invention, engineered 2OST enzymes utilized in accordance with any of the methods described herein can also comprise any amino acid sequence that is a biological equivalent, and/or a functional fragment, of an amino acid sequence selected from the group consisting of SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 68, and SEQ ID NO: 69. 
     According to the present invention, any of the engineered 2OST enzymes described above can possess one or more residue differences or mutations as compared to the amino acid sequences disclosed by an amino acid sequence selected from the group consisting of SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 68, and SEQ ID NO: 69. Non-limiting examples of such residue differences include amino acid insertions, deletions, substitutions, or any combination of such changes. According to the present invention, differences from the disclosed amino acid sequences in an amino acid sequence selected from the group consisting of SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 68, and SEQ ID NO: 69 can comprise non-conservative substitutions, conservative substitutions, as well as combinations of conservative and non-conservative amino acid substitutions. According to the present invention, an amino acid mutation can be made at any position within SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 68, or SEQ ID NO: 69, so long as the mutated enzyme retains its hexuronyl 2-O sulfotransferase activity with an aryl sulfate compound as a sulfo group donor and a heparosan-based polysaccharide comprising the structure of Formula IV and/or Formula V as the sulfo group acceptor. 
     In an aspect of the invention, an engineered sulfotransferase enzyme can have glucosaminyl 6-O sulfotransferase activity, comprising the transfer of a sulfo group from an aryl sulfate compound to the 6-O position of a glucosamine residue within a heparosan-based polysaccharide. According to the present invention, an engineered 6OST enzyme can comprise any amino acid sequence, so long as the sulfo group donor is an aryl sulfate compound and the sulfo group acceptor is a heparosan-based polysaccharide. 
     According to the present invention, engineered 6OST enzymes can be mutants of natural sulfotransferases that have glucosaminyl 6-O sulfotransferase activity, which are members of EC 2.8.2.—. In contrast to the engineered 6OST enzymes of the present invention, natural 6OST enzymes within EC 2.8.2.—do not react with aryl sulfate compounds, and only react with PAPS as a sulfo group donor. However, the engineered 6OST enzymes can retain the same biological activity as the natural 6OST enzymes within EC 2.8.2.—with heparosan-based polysaccharides as sulfo group acceptors. 
     According to the present invention, the glucosamine residue receiving the sulfo group at the 6-O position can be N-sulfated, N-unsubstituted, N-acetylated, and/or 3-O sulfated, prior to reacting with the enzyme. According to the present invention, any other glucosamine residue within the sulfo acceptor polysaccharide can be optionally be N-, 3-O, and/or 6-O sulfated, N-acetylated, or N-unsubstituted. According to the present invention, any of the hexuronic acid residues within the heparosan-based polysaccharide, including hexuronic acid residues adjacent to the glucosamine residue receiving the sulfo group, can optionally be iduronic acid or glucuronic acid, and can optionally be 2-O sulfated, prior to reacting with the 6OST enzyme. 
     One non-limiting example of a heparosan-based polysaccharide that can be utilized as a sulfo acceptor with any of the engineered 6OST enzymes is a heparosan-based polysaccharide comprising one or more structural motifs having the structure of Formula VIII, below: 
     
       
         
         
             
             
         
       
     
     wherein X comprises any of the hexuronic acid residues depicted in Formula VIII above. When the sulfo acceptor polysaccharide comprises the structure of Formula VIII, upon transfer of the sulfo group from an aryl sulfate compound, the sulfated polysaccharide product comprises the structure of Formula IX, below: 
     
       
         
         
             
             
         
       
     
     wherein X comprises any of the hexuronic acid residues depicted in Formula IX, above. 
     According to the present invention, the sulfo group acceptor for the engineered 6OST enzyme can comprise multiple structural motifs comprising the structure of Formula VIII, any or all of which can be sulfated by an engineered 6OST enzyme. According to the present invention, the sulfo group acceptor can be N-deacetylated heparosan. According to the present invention, the sulfo group acceptor can be N-sulfated heparosan. According to the present invention, the sulfo group acceptor for the engineered 6OST can be N,2O-HS. According to the present invention, the sulfo group acceptor for the engineered 6OST enzyme can be a sulfated polysaccharide product formed by an engineered NST enzyme, described above. According to the present invention, the sulfo group acceptor for the engineered 6OST enzyme can be a sulfated polysaccharide product formed by an engineered 2OST enzyme, as described above. According to the present invention, the sulfated polysaccharide product of an engineered 6OST enzyme is an N,2O,6O-HS product. 
     To facilitate its exclusive reactivity with PAPS as the sulfo group donor, natural 6OST enzymes within EC 2.8.2.—typically comprise highly-conserved or identical amino acid sequences that define the active site and govern the enzyme&#39;s recognition, binding, and reactivity with PAPS. According to the present invention, the amino acid sequence of an engineered 6OST enzyme can comprise one or more mutations relative to natural 6OST enzymes within EC 2.8.2.—, in order to facilitate binding of an aryl sulfate compound instead of PAPS. According to the present invention, an engineered 6OST enzyme can comprise an amino acid sequence having at least one amino acid mutation relative to any of the natural 6OST enzymes within EC 2.8.2.—, including at least two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, twenty, thirty, forty, fifty, up to at least one hundred amino acid mutations. According to the present invention, an engineered 6OST enzyme can comprise at least one amino acid mutation relative to the amino acid sequence of any of the natural 6OST enzymes within EC 2.8.2.—, in regions that are known to define the enzyme&#39;s active site, including at least two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, or fifteen amino acid mutations, up to at least twenty amino acid mutations. 
     According to the present invention, the amino acid sequence of an engineered 6OST enzyme can be expressed as a “percent identity” or “% identity” relative to the amino acid sequence of one or more of the natural 6OST enzymes within EC 2.8.2.—, particularly relative to one or more of the natural 6OST enzymes within EC 2.8.2.—, and including biological functional fragments thereof. According to the present invention, an engineered 6OST enzyme can have at least 50% sequence identity, and up to at least 97% sequence identity, with any of the natural 6OST enzymes within EC 2.8.2.—. In a non-limiting example, the amino acid sequence of the non-natural 6OST enzyme can have at least 80% sequence identity with the amino acid sequence of a natural 6OST enzyme, the natural 6OST enzyme selected from the group consisting of the mouse 6OST1 enzyme (SEQ ID NO: 191, UniProtKB Accession No. Q9QYK5), the mouse 6OST2 enzyme (SEQ ID NO: 199, UniProtKB Accession No. Q80UW0), and the mouse 6OST3 enzyme (SEQ ID NO: 201, UniProtKB Accession No. Q9QYK4). 
     According to the present invention, an engineered 6OST enzyme can comprise one or more mutated amino acid sequence motifs relative to conserved amino acid sequence motifs found in one or more natural 6OST enzymes within EC 2.8.2.—. Each mutated amino acid sequence motif, when present, can have at least one amino acid mutation relative to the corresponding conserved amino acid sequence motif within the natural 6OST enzymes within EC 2.8.2.—. According to the present invention, an engineered 6OST enzyme can comprise one, two, three, four, or five mutated amino acid sequence motifs relative to the following conserved 6OST amino acid sequence motifs: (Q-K-T-G-G-T), (C-G-L-H-A-D), (L-R-D-V-P-S), (S-E-W-R/K-H-V-Q-R-G-A-T-W-K), or (L-T-E-F/Y-Q), which correspond to SEQ ID NO: 254, SEQ ID NO: 255, SEQ ID NO: 275, SEQ ID NO: 256, and SEQ ID NO: 276 in the sequence listing, respectively. In some embodiments, the conserved Q-K-T-G-G-T amino acid sequence motif (SEQ ID NO: 254) is mutated to G-H-T-G-G-T (SEQ ID NO: 257); the leucine residue within the conserved C-G-L-H-A-D amino acid sequence motif (SEQ ID NO: 255) is mutated to a alcohol residue selected from the group consisting of a threonine and a serine (as indicated in SEQ ID NO: 258 or SEQ ID NO: 259, respectively), and the conserved S-E-W-R/K-H-V-Q-R-G-A-T-W-K amino acid sequence motif (SEQ ID NO: 256) is mutated to the amino acid sequence motif X 1 -X 2 -W-R-H-X 3 -Q-R-G-G-X 4 -N-K (SEQ ID NO: 260), wherein: X 1  can be selected from the group consisting of serine or glycine; X 2  can be selected from the group consisting of glycine and histidine; X 3  can be selected from the group consisting of threonine and histidine; and X 4  can be selected from the group consisting of threonine and alanine. In some further embodiments, the identity of X 1  and X 4  are dependent on each other such that when X 1  is glycine, X 4  is threonine (as illustrated in SEQ ID NO: 261), and when X 1  is serine, X 4  is alanine (as illustrated in SEQ ID NO: 262). In other further embodiments, the identity of X 2  and X 3  are dependent on each other such that when X 2  is glycine, X 3  is histidine (as illustrated in SEQ ID NO: 263), and when X 2  is histidine, X 3  is threonine (as illustrated in SEQ ID NO: 264). Additional non-limiting examples of mutated amino acid sequence motifs are described in further detail, below. 
     According to the present invention, an engineered 6OST enzyme can comprise an amino acid sequence selected from the group consisting of SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122, each of which contains several amino acid mutations made relative to highly conserved amino acid sequences of natural 6OST enzymes within EC 2.8.2.—. According to the present invention, engineered 6OST enzymes utilized in accordance with any of the methods described herein can also comprise any amino acid sequence that is a biological equivalent, and/or a functional fragment, of an amino acid sequence selected from the group consisting of SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122. 
     According to the present invention, any of the engineered 6OST enzymes described above can possess one or more residue differences or mutations as compared to the amino acid sequences disclosed by an amino acid sequence selected from the group consisting of SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122. Non-limiting examples of such residue differences include amino acid insertions, deletions, substitutions, or any combination of such changes. According to the present invention, differences from the disclosed amino acid sequences in an amino acid sequence selected from the group consisting of SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122 can comprise non-conservative substitutions, conservative substitutions, as well as combinations of conservative and non-conservative amino acid substitutions. According to the present invention, an amino acid mutation can be made at any position within SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122, so long as the mutated enzyme retains its 6OST activity with an aryl sulfate compound as a sulfo group donor and any of the heparosan-based polysaccharides described above as a sulfo group acceptor. 
     According to the present invention, an engineered 6OST enzyme can comprise the amino acid sequence of SEQ ID NO: 112. Within SEQ ID NO: 112, residues having the designation, “Xaa,” illustrate known instances in which there is a lack of identity at a particular position within the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, and SEQ ID NO: 108. Thus, an “Xaa” designation indicates the amino acid at that position can be selected from a group of two or more amino acids, as defined by SEQ ID NO: 112. 
     According to the present invention, an engineered 6OST enzyme can comprise the amino acid sequence of SEQ ID NO: 113. According to the present invention, within SEQ ID NO: 113, residues having the designation, “Xaa,” illustrate known instances in which there is a lack of identity at a particular position within the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, and SEQ ID NO: 108. According to the present invention, SEQ ID NO: 113 also comprises N-terminal residues 1-66, and C-terminal residues 378-411, of several full-length 6OST enzymes within EC 2.8.2.—, including, as non-limiting examples, the mouse, human, and pig 6OST enzymes. Thus, an “Xaa” designation indicates the amino acid at that position can be selected from a group of two or more amino acids, as defined by SEQ ID NO: 113. 
     Additionally, and according to the present invention, amino acid mutations can be made at one or more positions within SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122 so long as the mutated enzyme retains its glucosaminyl 6-O sulfotransferase activity with an aryl sulfate compound as a sulfo group donor. According to the present invention, an aryl sulfate-dependent enzyme comprising the amino acid sequence of SEQ ID NO: 132 or SEQ ID NO: 133 can optionally comprise one or more amino acid mutations at positions not designated as “Xaa,” while still retaining its glucosaminyl 6-O sulfotransferase activity with an aryl sulfate compound as a sulfo group donor. 
     In an aspect of the invention, an engineered sulfotransferase enzyme can have glucosaminyl 3-O sulfotransferase activity, comprising the transfer of a sulfo group from an aryl sulfate compound to the 3-O position of a glucosamine residue within a heparosan-based polysaccharide. According to the present invention, an engineered 3OST can comprise any amino acid sequence, so long as the sulfo group donor is an aryl sulfate compound and the sulfo group acceptor is a heparosan-based polysaccharide. 
     According to the present invention, engineered 3OST enzymes can be mutants of natural sulfotransferases that have 3OST activity, which are members of EC 2.8.2.23. In contrast to the engineered 3OST enzymes of the present invention, natural 3OST enzymes within EC 2.8.2.23 do not react with aryl sulfate compounds, and only react with PAPS as a sulfo group donor. However, the engineered 3OST enzymes can retain the same biological activity as the natural 3OST enzymes within EC 2.8.2.23 with heparosan-based polysaccharides as sulfo group acceptors. 
     According to the present invention, glucosamine residues within the heparosan-based polysaccharide that can receive a sulfo group at the 3-O position are N-sulfated, and can optionally comprise a 6-O sulfo group as well. According to the present invention, any other glucosamine residue within the sulfo acceptor polysaccharide can be optionally be N-, 3-O, and/or 6-O sulfated, N-acetylated, or N-unsubstituted. According to the present invention, one or more of the glucosamine residues within the heparosan-based polysaccharide, including the glucosamine residue being 3-O sulfated, can be both N-sulfated and 6-O sulfated. According to the present invention, the glucosamine residue being 3-O sulfated can be adjacent to an unsulfated glucuronic acid residue at the non-reducing end and an iduronic acid residue at the reducing end. According to the present invention, the iduronic acid residue at the reducing end of the glucosamine residue being 3-O sulfated can optionally be 2-O sulfated. According to the present invention, any of the other hexuronic acid residues within the heparosan-based polysaccharide acting as the sulfo group acceptor for the 3OST can optionally be iduronic acid or glucuronic acid, and can optionally be 2-O sulfated. One non-limiting example of a heparosan-based polysaccharide that can be utilized as a sulfo acceptor with any of the engineered 3OST enzymes is a heparosan-based polysaccharide comprising one or more structural motifs having the structure of Formula X, below: 
     
       
         
         
             
             
         
       
     
     wherein X is either a sulfo group or an acetate group and Y is either a sulfo group or a hydroxyl group. According to the present invention, in some preferred embodiments, X can be a sulfo group and Y can be a sulfo group. When the heparosan-based polysaccharide comprises the structure of Formula X, the 3-O sulfated polysaccharide product comprises the structure of Formula I, below: 
     
       
         
         
             
             
         
       
     
     wherein X is either a sulfo group or an acetate group and Y is either a sulfo group or a hydroxyl group. According to the present invention, in some preferred embodiments, X can be a sulfo group and Y can be a sulfo group. According to the present invention, an N,2O,3O,6O-HS products comprising the structure of Formula I and which are formed upon reacting with an engineered 3OST enzyme can have anticoagulant activity and have similar or equivalent physical properties to heparin. The anticoagulant activity of heparin and other N,2O,3O,6O-HS polysaccharides is described in further detail, below. 
     According to the present invention, the sulfo group acceptor for the engineered 3OST enzyme can comprise multiple structural motifs comprising the structure of Formula X, any or all of which can be sulfated by an engineered 3OST enzyme. According to the present invention, the sulfo group acceptor for the engineered 3OST can be N,2O,6O-HS. According to the present invention, the sulfo group acceptor for the engineered 3OST enzyme can be a sulfated polysaccharide product formed by an engineered 6OST enzyme, described above. 
     To facilitate its exclusive reactivity with PAPS as the sulfo group donor, natural 3OST enzymes within EC 2.8.2.23 typically comprise highly-conserved or identical amino acid sequences that define the active site and govern the enzyme&#39;s recognition, binding, and reactivity with PAPS. According to the present invention, the amino acid sequence of an engineered 3OST enzyme can comprise one or more mutations relative to natural 3OST enzymes within EC 2.8.2.23, in order to facilitate binding of an aryl sulfate compound instead of PAPS. According to the present invention, an engineered 3OST enzyme can comprise an amino acid sequence having at least one amino acid mutation relative to any of the natural 3OST enzymes within EC 2.8.2.23, including at least two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, twenty, thirty, forty, fifty, up to at least one hundred amino acid mutations. According to the present invention, an engineered 3OST enzyme can comprise at least one amino acid mutation relative to the amino acid sequence of any of the natural 3OST enzymes within EC 2.8.2.23, in regions that are known to define the enzyme&#39;s active site, including at least two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, or fifteen amino acid mutations, up to at least twenty amino acid mutations. 
     According to the present invention, the amino acid sequence of an engineered 3OST enzyme can be expressed as a “percent identity” or “% identity” relative to the amino acid sequence of one or more of the natural 3OST enzymes within EC 2.8.2.23, particularly relative to one or more of the natural 3OST enzymes within EC 2.8.2.23, and including biological functional fragments thereof. According to the present invention, an engineered 3OST enzyme can have at least 50% sequence identity, and up to at least 97% sequence identity, with any of the natural 3OST enzymes within EC 2.8.2.23. In a non-limiting example, the amino acid sequence of the engineered 3OST enzyme can have at least 80% sequence identity with the amino acid sequence of a natural 3OST enzyme, the natural 3OST enzyme selected from the group consisting of the human 3OST1 enzyme (SEQ ID NO: 206, UniProtKB Accession No. 014792) and the human 3OST5 enzyme (SEQ ID NO: 220, UniProtKB Accession No. Q8IZT8). 
     According to the present invention, an engineered 3OST enzyme can comprise one or more mutated amino acid sequence motifs relative to conserved amino acid sequence motifs found in one or more natural 3OST enzymes within EC 2.8.2.23. Each mutated amino acid sequence motif, when present, can have at least one amino acid mutation relative to the corresponding conserved amino acid sequence motif within the natural 3OST enzymes within EC 2.8.2.23. According to the present invention, an engineered 3OST enzyme can comprise one, two, three, or four mutated amino acid sequence motifs relative to the following conserved 3OST amino acid sequence motifs: (G-V-R-K-G-G), (P-A/G-Y-F), (S-D-Y-T-Q-V), or (Y-K-A). The conserved amino acid sequence motifs G-V-R-K-G-G, P-A/G-Y-F, and S-D-Y-T-Q-V correspond to SEQ ID NO: 265, SEQ ID NO: 266, and SEQ ID NO: 267 in the sequence listing, respectively. In some embodiments, within the amino acid sequence of the engineered 3OST enzyme, the conserved G-V-R-K-G-G amino acid sequence motif (SEQ ID NO: 265) is mutated to G-V-G-H-G-G (SEQ ID NO: 268), the conserved P-A/G-Y-F amino acid sequence motif (SEQ ID NO: 266) is mutated to H-S-Y-F (SEQ ID NO: 269), and the conserved Y-K-A amino acid sequence motif is mutated to Y-V/T-G. Additional non-limiting examples of mutated amino acid sequence motifs are described in further detail, below. 
     According to the present invention, an engineered 3OST enzyme can comprise an amino acid sequence selected from the group consisting of SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160, each of which contains several amino acid mutations made relative to highly conserved amino acid sequences of natural 3OST enzymes within EC 2.8.2.23. According to the present invention, engineered 3OST enzymes utilized in accordance with any of the methods described herein can also comprise any amino acid sequence that is a biological equivalent, and/or a functional fragment, of an amino acid sequence selected from the group consisting of SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160. 
     According to the present invention, any of the engineered 3OST enzymes described above can possess one or more residue differences or mutations as compared to the amino acid sequences disclosed by an amino acid sequence selected from the group consisting of SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160. Non-limiting examples of such residue differences include amino acid insertions, deletions, substitutions, or any combination of such changes. According to the present invention, differences from the disclosed amino acid sequences in an amino acid sequence selected from the group consisting of SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160 can comprise non-conservative substitutions, conservative substitutions, as well as combinations of conservative and non-conservative amino acid substitutions. According to the present invention, an amino acid mutation can be made at any position within SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160, so long as the mutated enzyme retains its glucosaminyl 3-O sulfotransferase activity with an aryl sulfate compound as a sulfo group donor and any of the heparosan-based polysaccharides described above as a sulfo group acceptor. 
     According to the present invention, an engineered 3OST enzyme can comprise the amino acid sequence of SEQ ID NO: 154. Within SEQ ID NO: 154, residues having the designation, “Xaa,” illustrate known instances in which there is a lack of identity at a particular position within the amino acid sequences of SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151. Thus, an “Xaa” designation indicates the amino acid at that position can be selected from a group of two or more amino acids, as defined by SEQ ID NO: 154. 
     Additionally, and according to the present invention, amino acid mutations can be made at one or more positions within SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160 so long as the mutated enzyme retains its glucosaminyl 3-O sulfotransferase activity with an aryl sulfate compound as a sulfo group donor. According to the present invention, an aryl sulfate-dependent enzyme comprising the amino acid sequence of SEQ ID NO: 154 can optionally comprise one or more amino acid mutations at positions not designated as “Xaa,” while still retaining its glucosaminyl 3-O sulfotransferase activity with an aryl sulfate compound as a sulfo group donor. 
     In another aspect, the invention provides methods for enzymatically transferring a sulfo group from an aryl sulfate compound to a polysaccharide to form a sulfated polysaccharide product. According to the present invention, the polysaccharide can be a heparosan-based polysaccharide. According to the present invention, a method for enzymatically transferring a sulfo group from an aryl sulfate compound to a heparosan-based polysaccharide can comprise the following steps: (a) providing an aryl sulfate compound; (b) providing any of the engineered sulfotransferase enzymes described above, wherein the engineered sulfotransferase enzyme has biological activity with an aryl sulfate compound as a sulfo group donor; (c) providing a heparosan-based polysaccharide; (d) combining the aryl sulfate compound, the sulfotransferase enzyme, and the heparosan-based polysaccharide into a reaction mixture; and (e) transferring the sulfo group from the aryl sulfate compound to the heparosan-based polysaccharide, using the sulfotransferase enzyme, thereby forming the sulfated polysaccharide product. According to the present invention, the aryl sulfate compound can be selected from the consisting of PNS, 4-methylumbelliferyl sulfate, 7-hydroxycoumarin sulfate, phenyl sulfate, 4-acetylphenyl sulfate, indoxyl sulfate, 1-naphthyl sulfate, 2NapS, and NCS. According to the present invention, the aryl sulfate compound can be PNS. According to the present invention, the aryl sulfate compound can be NCS. 
     According to the present invention, the engineered sulfotransferase can be any of the engineered NST enzymes described above, preferably an engineered NST enzyme comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, and SEQ ID NO: 25. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the heparosan-based polysaccharide can be N-deacetylated heparosan. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the heparosan-based polysaccharide can comprise one or more disaccharide units comprising the structure of Formula II. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the sulfated polysaccharide product comprises the structure of Formula III. 
     According to the present invention, the engineered sulfotransferase can be any of the engineered 2OST enzymes described above, preferably an engineered 2OST enzyme comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 67, and SEQ ID NO: 69. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the heparosan-based polysaccharide can be N-sulfated heparosan. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the heparosan-based polysaccharide can comprise one or more structural motifs comprising the structure of Formula IV and/or Formula V, and preferably at least one structural motif comprising the structure of Formula V. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the method can further comprise the step of providing a glucuronyl C 5 -epimerase, preferably a glucuronyl C 5 -epimerase comprising the amino acid sequence of SEQ ID NO: 67, and more preferably residues 34-617 of SEQ ID NO: 67. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the sulfated polysaccharide product comprises the structure of Formula VI and/or Formula VII. 
     According to the present invention, the engineered sulfotransferase can be any of the engineered 6OST enzymes described above, preferably an engineered 6OST enzyme comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the heparosan-based polysaccharide can be any of the heparosan-based polysaccharides described above that are suitable sulfo acceptors for an engineered 6OST enzyme. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the heparosan-based polysaccharide can be N,2O-HS. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the heparosan-based polysaccharide can comprise one or more structural motifs comprising the structure of Formula VIII. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the sulfated polysaccharide product comprises the structure of Formula IX. 
     According to the present invention, the engineered sulfotransferase can be any of the engineered 3OST enzymes described above, preferably an engineered 3OST enzyme comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the heparosan-based polysaccharide can be N,2O,6O-HS. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the heparosan-based polysaccharide can comprise one or more structural motifs comprising the structure of Formula X. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the sulfated polysaccharide product comprises the structure of Formula I. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the sulfated polysaccharide product comprising the structure of Formula I can have anticoagulant activity. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the sulfated polysaccharide product comprising the structure of Formula I can have one or more similar or equivalent molecular weight properties and/or anticoagulant activity relative to heparin. 
     The present invention also provides methods for producing non-anticoagulant N-, 6-O sulfated heparan sulfate (N,6O-HS) products that are structural analogs of ODSH, which when prepared from heparin according to known techniques, retain some of the heparin&#39;s glucosamine 3-O sulfation and accordingly, low-level anticoagulant activity. On the other hand, N,6O-HS products can contain no 3-O sulfated glucosamine residues, and optionally, no 2-O sulfated hexuronic acid residues. Such fully non-anticoagulant N,6O-HS compositions can be utilized in the treatment of several medical conditions, including, as non-limiting examples, cancers; inflammation; thrombocytopenia; neutropenia; apoptosis; asthma; emphysema; bronchitis; adult respiratory distress syndrome; cystic fibrosis; and ischemia-reperfusion related conditions. Such treatments are described in further detail, below. 
     In another aspect of the invention, N,6O-HS can be synthesized using a method comprising the following steps: (a) providing a starting polysaccharide composition comprising N-deacetylated heparosan; (b) reacting the starting polysaccharide composition within a reaction mixture comprising an N-sulfation agent, to form an N-sulfated heparan sulfate (NS-HS) product; and (c) reacting the NS-HS product within a reaction mixture comprising an aryl sulfate compound and an engineered glucosaminyl 6-O sulfotransferase (6OST) enzyme, thereby forming the N,6O-HS product; wherein the biological activity of the engineered 6OST enzyme comprises the transfer of a sulfo group from an aryl sulfate compound to a heparosan-based polysaccharide. 
     In various embodiments, NS-HS polysaccharides can be isolated and purified prior to reacting with the 6OST in a separate reaction mixture. In other embodiments, 6-O sulfation of glucosamine residues can take place in the same reaction mixture as the N-sulfation of N-deacetylated heparosan. 
     In various embodiments, the step of providing the starting polysaccharide reaction mixture can comprise the chemical synthesis of N-sulfated heparosan, comprising the following sub-steps: (i) providing a precursor polysaccharide composition comprising heparosan; (ii) combining the precursor polysaccharide composition with a reaction mixture comprising a base, preferably lithium hydroxide or sodium hydroxide, for a time sufficient to N-deacetylate at least one of the N-acetylated glucosamine residues within the heparosan to form the starting polysaccharide composition. 
     In various embodiments, the step of providing the precursor polysaccharide composition comprising heparosan can further comprise the sub-step of isolating heparosan from a bacterial or eukaryotic cell culture, preferably a bacterial cell culture, and more preferably a bacterial cell culture comprising bacteria selected from the group consisting of the K5 strain of  Escherichia coli  ( E. coli ) and the BL21 strain of  E. coli . Heparosan can be isolated from  E. coli  as a polydisperse mixture of polysaccharides having a weight-average molecular weight of at least 10,000 Da, and up to at least 1,000,000 Da. In various embodiments, at least 90% of the glucosamine residues within the heparosan are N-acetylated. 
     Treating heparosan with a base, such as lithium hydroxide or sodium hydroxide, removes acetyl groups from N-acetyl glucosamine residues, forming N-unsubstituted glucosamine residues that can subsequently be N-sulfated by an N-sulfation agent. In various embodiments, precursor polysaccharides can be treated with a base for a time sufficient to reduce the relative number of N-acetylated glucosamine residues to a desired level. The reaction time can be dependent on factors such as the average molecular weight of the heparosan within the precursor polysaccharide composition, the N-acetyl glucosamine content of the heparosan prior to reacting with the base, the desired N-acetyl content within the N-deacetylated heparosan composition, and the concentration and identity of the base itself. In various embodiments, the time sufficient to N-deacetylate the heparosan within the precursor polysaccharide composition can be the time sufficient to form an N-deacetylated heparosan composition in which less than 60%, down to less than 5%, preferably in the range of 12% to 18%, and more preferably 15%, of the glucosamine residues remain N-acetylated. 
     Additionally, treating the precursor polysaccharide composition with a base to reduce the number of N-acetylated glucosamine residues can also have the effect of depolymerizing the heparosan, causing the N-deacetylated heparosan composition to have a lower average molecular weight relative to the precursor polysaccharide composition. Accordingly, in various embodiments, the precursor polysaccharide composition can be treated with a base for a time sufficient to form an N-deacetylated heparosan composition having a desired average molecular weight. As with above, the reaction time can depend on several factors, including the average molecular weight of the heparosan within the precursor polysaccharide composition, and the desired average molecular weight of the polysaccharides within the N-deacetylated heparosan composition itself. In various embodiments, the time sufficient to N-deacetylate the heparosan within the precursor polysaccharide composition can be the time sufficient to form an N-deacetylated polysaccharide composition having a weight-average molecular weight in a range from 1,500 Da to 100,000 Da, for example, from at least 9,000 Da, and up to 12,500 Da. 
     In various embodiments, once the N-deacetylated heparosan is formed, the resulting N-unsubstituted glucosaminyl residues can then receive a sulfo group upon reacting within a reaction mixture comprising an N-sulfation agent, to form NS-HS. In various embodiments, one or more of the N-unsubstituted glucosamine residues within N-deacetylated heparosan can be chemically N-sulfated. A non-limiting example of a chemical N-sulfation agent can comprise a reaction mixture comprising a sulfur trioxide-containing compound or adduct, particularly a sulfur trioxide-trimethylamine adduct. 
     In various embodiments, the N-sulfation agent is an engineered NST or natural NDST enzyme. In various embodiments, enzymatic N-sulfation can either supplement or replace chemical N-sulfation of N-deacetylated heparosan. 
     In another aspect of the invention, a non-anticoagulant N-sulfated, 2-O sulfated, 6-O sulfated heparan sulfate polysaccharide (N,2O,6O-HS) product can be synthesized by a method comprising the following steps: (a) providing a starting polysaccharide reaction mixture comprising N-deacetylated heparosan; (b) reacting the starting polysaccharide composition within a reaction mixture comprising an N-sulfation agent, to form an NS-HS product; (c) combining the NS-HS product with a reaction mixture comprising a sulfo group donor and an intermediate sulfotransferase enzyme selected from the group consisting of a hexuronyl 2-O sulfotransferase (2OST) enzyme and a 6OST enzyme, to form an intermediate HS product; (d) combining the intermediate HS product with a reaction mixture comprising a finishing sulfotransferase enzyme, wherein the finishing sulfotransferase enzyme is the enzyme that was not selected in step (c), to form the N,2O,6O-HS product; wherein (i) at least one of the sulfotransferase enzymes is an engineered sulfotransferase enzyme that is dependent on reacting with an aryl sulfate compound as a sulfo group donor to catalyze a sulfotransfer reaction, and (ii) in a reaction mixture comprising an engineered sulfotransferase enzyme, the reaction mixture consists of an aryl sulfate compound as a sulfo group donor. In various embodiments, the intermediate sulfotransferase enzyme is a 2OST enzyme and the finishing sulfotransferase enzyme is a 6OST enzyme. In various embodiments, all of the sulfotransferase enzymes are engineered aryl sulfate-dependent sulfotransferase enzymes, and each of the sulfotransfer reactions can be performed in the absence of PAPS. 
     In various embodiments, the non-anticoagulant N,2O,6O-HS product can be utilized directly in the treatment of a subject having a medical condition, including, as non-limiting examples, cancers; inflammation; thrombocytopenia; neutropenia; apoptosis; asthma; emphysema; bronchitis; adult respiratory distress syndrome; cystic fibrosis; and ischemia-reperfusion related conditions. In other embodiments, the non-anticoagulant N,2O,6O-HS product can be modified by cold alkaline hydrolysis for a time sufficient to remove at least a portion of, and in some embodiments substantially all, of the 2-O sulfate groups from the non-anticoagulant N,2O,6O-HS product, according to the methods described in Fryer, A. et al., 1997 , J. Pharmacol. Exp. Ther.  282: 208-219, and U.S. Pat. Nos. 10,052,346 and 9,271,999. 
     In another aspect of the invention, an ODSH polysaccharide composition can be formed from an N-, 2-O-, 3-O-, 6-O-sulfated heparan sulfate (N,2O,3O,6O-HS) product that is synthesized by a method that utilizes at least one engineered, aryl sulfate-dependent sulfotransferase, the method comprising the following steps: (a) providing a starting polysaccharide reaction mixture comprising N-deacetylated heparosan; (b) reacting the starting polysaccharide composition within a reaction mixture comprising an N-sulfation agent, to form an NS-HS product; (c) combining the NS-HS product with a reaction mixture comprising a sulfo group donor and a first intermediate sulfotransferase enzyme selected from the group consisting of a 2OST enzyme and a 6OST enzyme, to form a first intermediate HS product; (d) combining the first intermediate HS product with a reaction mixture comprising a second intermediate sulfotransferase enzyme, wherein the second intermediate sulfotransferase enzyme is the enzyme that was not selected in step (c), to form a second intermediate HS product; and (e) combining the second intermediate HS product with a reaction mixture comprising a sulfo group donor and a glucosaminyl 3-O sulfotransferase (3OST) enzyme, to form the N,2O,3O,6O-HS product; wherein (i) at least one of the sulfotransferase enzymes is an engineered sulfotransferase enzyme that is dependent on reacting with an aryl sulfate compound as a sulfo group donor to catalyze a sulfotransfer reaction, and (ii) in a reaction mixture comprising an engineered sulfotransferase enzyme, the reaction mixture consists of an aryl sulfate compound as a sulfo group donor. In various embodiments, the first intermediate sulfotransferase enzyme is a 2OST enzyme and the second intermediate sulfotransferase enzyme is a 6OST enzyme. In various embodiments, all of the sulfotransferase enzymes are engineered aryl sulfate-dependent sulfotransferase enzymes, and each of the sulfotransfer reactions are performed in the absence of PAPS. In various embodiments, the N,2O,3O,6O-HS product has anticoagulant activity. In various embodiments, the N,2O,3O,6O-HS product is substantially equivalent in molecular weight, purity, and anticoagulant activity to any of the heparin compounds described by CAS NO: 9005-49-6 or CAS NO: 9041-08-1. In various embodiments, once the N,2O,3O,6O-HS product is formed, it can be modified by cold alkaline hydrolysis for a time sufficient to remove at least a portion of, and in some embodiments substantially all, of the 2-O and 3-O sulfate groups to form an ODSH polysaccharide composition. In various embodiments, the N,2O,3O,6O-HS product can be modified by any method known in the art for forming an ODSH polysaccharide composition and/or until the synthesized ODSH polysaccharide composition is substantially equivalent to any ODSH polysaccharide composition described in the art. Such prior art compositions and methods for forming them are described above. 
     In various embodiments, N,2O,6O-HS polysaccharides can be isolated and purified prior to reacting with the 3OST in a separate reaction mixture. In other embodiments, 3-O sulfation can take place in the same reaction mixture as the 6-O sulfation of N,2O-HS. 
     In various embodiments, heparosan-based polysaccharides that can be used as sulfo group acceptors in any of the sulfotransfer reactions described herein can generally be any molecular weight greater than 1,000 Da, including greater than 1,000,000 Da. In various embodiments, compositions or mixtures comprising N-deacetylated heparosan polysaccharides can preferably have a weight-average molecular weight in the range of at least 9,000 Da, and up to 12,500 Da. In various embodiments, sulfated polysaccharide products of any of the reactions described herein any of the methods described above can comprise molecular weights associated with the addition of a single sulfo group (about 80 Da), and up to the addition of sulfo groups to all available N, 2-O, 3-O, and/or 6-O positions, based on the molecular weight of the polysaccharide used as the sulfo group acceptor. 
     According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, within any reaction mixture or composition comprising a heparosan-based polysaccharide used as a starting material or a sulfated polysaccharide product, the polysaccharides can be present as a polydisperse mixture of polysaccharides having variable chain lengths, molecular weights, N-acetylation, and/or N-, 2-O, 6-0, or 3-O sulfation. Alternatively, according to the present invention, any of the polysaccharides described above can be present as a homogeneous composition comprised of polysaccharides having identical chain lengths, molecular weights, N-acetylation, and/or N-, 2-O, 6-0, or 3-O sulfation. 
     In various embodiments, the anticoagulant effect of antithrombin activation can be quantified for any of the heparosan-based polysaccharide starting materials or products described herein, particularly as a function of its subsequent effect on the activity of Factor IIa and Factor Xa, in terms of International Units of activity per milligram (IU mg −1 ). In one non-limiting example, N,2O,3O,6O-HS synthesized by any of the methods of the present invention can have a Factor IIa and/or Factor Xa activity of at least about 10, or 20, or 40, or 60, or 80, or 100, or 125, or 150, or 175 IU mg −1 . In another non-limiting example, N,6O-HS, and N,2O,6O-HS synthesized by any of the methods of the present invention can have zero anti-IIa or anti-Xa activity. 
     In various embodiments, any of the HS product mixtures produced by any of the methods above can have an average molecular weight of at least about 1,500 Da, depending on the weight average molecular weight of polysaccharides utilized as sulfo group acceptors, as described above. In various embodiments, non-anticoagulant HS products, particularly N,6O-HS products, can have a weight-average molecular weight in the range of about 2,000 Da to about 15,000 Da. In embodiments which an ODSH product is generated by modifying an N,2O,3O,6O-HS product using cold alkaline hydrolysis, the N,2O,3O,6O-HS product can have a molecular weight profile such that: (a) the weight-average molecular weight of the N,2O,3O,6O-HS product is at least 15,000 Da, and up to 19,000 Da; (b) less than or equal to 20% of the polysaccharides within the N,2O,3O,6O-HS product have a molecular weight greater than 24,000 Da; and (c) the number of polysaccharide chains within the N,2O,3O,6O-HS product having a molecular weight between 8,000 Da and 16,000 Da is greater than the number of polysaccharide chains having a molecular weight between 16,000 Da and 24,000 Da. 
     In another aspect of the invention, any of the HS products produced by any of the methods described above can be further modified by one or more subsequent processes to depolymerize and/or modify the HS product to form a low molecular weight (LMW)-HS product. In various embodiments, a non-anticoagulant LMW-HS composition can be synthesized from compositions comprising non-anticoagulant NS-HS, N,2O-HS, N,6O-HS, N,2O,6O-HS, or N,2O,3O,6O-HS. In various embodiments, the LMW-HS composition is an LMW-N,6O-HS composition. In various embodiments, an anticoagulant LMW-HS composition can be synthesized from anticoagulant N,2O,3O,6O-HS and subsequently subjected to cold alkaline hydrolysis to form LMW-ODSH. In other embodiments, an anticoagulant N,2O,3O,6O-HS composition can be modified using cold alkaline hydrolysis to form an ODSH composition, which can subsequently depolymerized to form LMW-ODSH. 
     In various embodiments, an HS product produced by any method described above can be referred to as an “unfractionated” HS product, relative to an LMW-HS product or LMW-ODSH product. Unfractionated HS products can include one or more non-anticoagulant NS-HS, N,2O-HS, N,6O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS products, and/or anticoagulant N,2O,6O,3O-HS. 
     Generally, methods of the present invention for synthesizing an LMW-HS or LMW-ODSH product can comprise the following steps: (a) synthesizing an unfractionated HS product according to any of the above methods; (b) providing one or more depolymerization agents; and (c) treating the unfractionated HS product with the one or more depolymerization agents for a time sufficient to depolymerize at least a portion of the polysaccharides within the unfractionated HS product, thereby forming the LMW-HS or LMW-ODSH product. In various embodiments, the weight-average molecular weight of the LMW-HS or LMW-ODSH product is at least 2,000 Da, and up to 12,000 Da, and preferably at least 3,000 Da, and up to 8,000 Da. 
     In various embodiments, the one or more depolymerization agents can be formed by, and/or be comprised of, one or more reaction components within one or more reaction mixtures, that can be combined with an unfractionated HS product to chemically and/or enzymatically depolymerize the unfractionated HS product and form an LMW-HS or LMW-ODSH product. In various embodiments, the selection of the depolymerization agent can determine which chemical or enzymatic depolymerization process occurs, as well as the chemical structure and/or anticoagulant activity of the depolymerized product. Such depolymerization processes can include, but are not limited to: chemical and/or enzymatic P-elimination reactions; deamination reactions; and oxidation reactions, including combinations thereof. In various embodiments, an unfractionated HS product can be treated with any combination of depolymerization agents in order to form an LMW-HS or LMW-ODSH product. 
     In various embodiments, the amount of time that an unfractionated HS product is treated with the one or more depolymerization agents can be controlled to form an LMW-HS or LMW-ODSH product with a desired molecular weight and/or chemical structure. According to the present invention, with respect to the same depolymerization agent, the amount of time that an unfractionated HS product is treated with the depolymerization agent can be varied to form products with similar chemical structures, but different molecular weights relative to each other. 
     In one-non-limiting example, an unfractionated HS product can be depolymerized by an enzymatic P-elimination reaction to form an LMW-HS or LMW-ODSH product. In various embodiments, the depolymerization agent can comprise a heparinase reaction mixture comprising at least one heparinase enzyme, and the unfractionated HS product can be treated with the heparinase reaction mixture for a time sufficient to catalyze β-eliminative cleavage of the unfractionated HS product and form an enzymatically-depolymerized LMW-HS or LMW-ODSH product. In various embodiments, the weight-average molecular weight of the enzymatically-depolymerized LMW-HS or LMW-ODSH product can be in the range of 2,000 Da to 10,000 Da, preferably 5,500 Da to 7,500 Da, and more preferably 6,500 Da. In various embodiments, the enzymatically-depolymerized LMW-HS or LMW-ODSH product can comprise polysaccharides having a 4,5-unsaturated uronic acid residue at the non-reducing end. 
     In another non-limiting example, an unfractionated HS product can be depolymerized by a chemical P-elimination reaction. In various embodiments, the depolymerization agent for a chemical P-elimination reaction can comprise a base, preferably a base selected from the group consisting of sodium hydroxide, a quaternary ammonium hydroxide, and a phosphazene base, including any combination thereof, and the unfractionated HS product can be treated with the base for a time sufficient to cause β-eliminative cleavage of the unfractionated HS product and form a chemically β-eliminative, LMW-HS or LMW-ODSH product. 
     In various embodiments, a benzethonium salt can be formed prior to reacting the unfractionated HS product with the base. Accordingly, in various embodiments, the step of treating the unfractionated HS product with the depolymerization agent can comprise the following sub-steps: (i) reacting the unfractionated HS product with a benzethonium salt, preferably benzethonium chloride, to form a benzethonium HS salt; and (ii) combining the benzethonium HS salt with a reaction mixture comprising the base for a time sufficient to form the chemically β-eliminative, LMW-HS or LMW-ODSH product. In various embodiments, the weight-average molecular weight of the chemically 3-eliminative, LMW-HS or LMW-ODSH product can be at least 2,000 Da, up to 10,000 Da, and preferably in the range of 2,000 Da to 6,000 Da. In various embodiments, the chemically β-eliminative, LMW-HS or LMW-ODSH product can comprise polysaccharides having a 4,5-unsaturated uronic acid residue at the non-reducing end. 
     In various embodiments, once the benzethonium HS salt is formed, it can be subsequently treated with a base for a time sufficient to form the chemically β-eliminative, LMW-HS or LMW-ODSH product. In various embodiments, the base can be a quaternary ammonium hydroxide, preferably benzyl trimethylammonium hydroxide (Triton® B). In various embodiments, the weight-average molecular weight of the chemically β-eliminative, LMW-HS or LMW-ODSH product can be in the range of 3,000 Da to 4,200 Da, and preferably 3,600 Da. 
     In various embodiments, the benzethonium HS salt can be further modified prior to reacting with the base. In one non-limiting example, the benzethonium HS salt can be converted to a benzyl ester form of HS upon reacting with a benzyl halide, particularly benzyl chloride. In various embodiments, the conversion to the benzyl ester can take place within a chlorinated solvent, including but not limited to methylene chloride and chloroform. 
     In various embodiments, once the benzyl ester HS is formed, it can be subsequently reacted with a base to initiate depolymerization. In various embodiments, the base can be sodium hydroxide. In various embodiments, the chemically β-eliminative, LMW-HS or LMW-ODSH product can comprise polysaccharides having a 1,6-anhydromannose or 1,6-anhydroglucosamine residue at the reducing end in addition to the 4,5-unsaturated uronic acid residue at the non-reducing end. In various embodiments, the weight-average molecular weight of the chemically β-eliminative, LMW-HS or LMW-ODSH product can be in the range of 3,800 Da to 5,000 Da, preferably 4,500 Da. 
     In various embodiments, the benzyl ester HS can instead be transalified in the presence of a benzethonium salt, preferably benzethonium chloride, in order to form a benzethonium benzyl ester HS, which can then be subsequently depolymerized using a base. In various embodiments, the base is a phosphazene base, preferably 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,2,3-diaza-phosphorine (BEMP). After depolymerization is complete, the remaining benzyl esters within the chemically β-eliminative, LMW-HS or LMW-ODSH product can be saponified and removed. In various embodiments, the weight-average molecular weight of the chemically β-eliminative, LMW-HS or LMW-ODSH product can be in the range of 2,000 Da to 3,000 Da, and is preferably 2,400 Da. 
     In another non-limiting example, an unfractionated HS product can be depolymerized by a deamination reaction. In various embodiments, the depolymerization agent can comprise a deamination reaction mixture comprising a deamination agent, preferably a deamination agent selected from the group consisting of isoamyl nitrate and nitrous acid, for a time sufficient to cause deaminative cleavage of the unfractionated HS product, thereby forming a deaminated LMW-HS or LMW-ODSH product. 
     In various embodiments, the deamination agent can be nitrous acid. In various embodiments, the deamination reaction mixture can comprise stoichiometric quantities of an acid, preferably acetic acid or hydrochloric acid, and an alkali or alkaline earth metal nitrite salt, preferably sodium nitrite, to form nitrous acid in situ. In various embodiments, the deaminated LMW-HS or LMW-ODSH product can comprise polysaccharides having a 2,5-anhydro-D-mannose residue at the reducing end. In various embodiments, the weight-average molecular weight of the deaminated LMW-HS or LMW-ODSH product can be in the range of 2,000 Da to 10,000 Da, preferably in the range of 4,000 Da to 6,000 Da. 
     In another non-limiting example, the deamination agent is isoamyl nitrate, and the weight-average molecular weight of the deaminated LMW-HS or LMW-ODSH product can be in the range of 5,000 Da to 5,600 Da, preferably 5,400 Da. 
     In another non-limiting example, an unfractionated HS product can be depolymerized by an oxidation reaction. In various embodiments, the depolymerization agent can comprise an oxidation agent, preferably an oxidation agent selected from the group consisting of a peroxide or a superoxide, and more preferably hydrogen peroxide to form an oxidized LMW-HS or LMW-ODSH product. In various embodiments, the step of treating an unfractionated HS product with the oxidation agent can comprise the following sub-steps: (i) acidifying the unfractionated HS product to form an acidified HS product; (ii) combining the acidified HS product with the oxidation reaction mixture; and (iii) incubating the acidified HS product within the oxidation reaction mixture at a temperature of at least than 50° C. for a time sufficient to form the oxidized LMW-HS or LMW-ODSH product. 
     In various embodiments, the sub-step of acidifying the unfractionated HS product can comprise the addition of a reaction mixture comprising an acid, preferably ascorbic acid, to the HS product to form the acidified HS product. Alternatively, the sub-step of acidifying the unfractionated HS product can further comprise the sub-steps of: loading the unfractionated HS product into a cation exchange resin, preferably a cation exchange resin suspended within a chromatography column; and eluting the unfractionated HS product from the cation exchange resin, forming the acidified HS product. In various embodiments, the pH of the acidified HS product can be at least 3.0, and up to 5.0, and preferably in a range of 3.0 to 3.5. 
     In various embodiments, the weight-average molecular weight of the oxidized LMW-HS or LMW-ODSH product can be in the range of 2,000 Da to 12,000 Da, preferably in the range of 4,000 Da to 6,000 Da. 
     According to the present invention, and useful in combination with one or more of the above aspects and embodiments, an engineered enzyme of the present invention having sulfatase and/or sulfotransferase activity with an aryl sulfate compounds as a substrate can be expressed from a nucleic acid comprising any nucleotide sequence that encodes for a polypeptide having the amino acid sequence of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, SEQ ID NO: 160. According to the present invention, such nucleotide sequences can be selected from the group consisting of SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56, SEQ ID NO: 58, SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 71, SEQ ID NO: 73, SEQ ID NO: 75, SEQ ID NO: 77, SEQ ID NO: 79, SEQ ID NO: 81, SEQ ID NO: 83, SEQ ID NO: 85, SEQ ID NO: 87, SEQ ID NO: 89, SEQ ID NO: 91, SEQ ID NO: 93, SEQ ID NO: 95, SEQ ID NO: 97, SEQ ID NO: 99, SEQ ID NO: 101, SEQ ID NO: 103, SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 109, SEQ ID NO: 124, SEQ ID NO: 126, SEQ ID NO: 128, SEQ ID NO: 130, SEQ ID NO: 132, SEQ ID NO: 134, SEQ ID NO: 136, SEQ ID NO: 138, SEQ ID NO: 140, SEQ ID NO: 142, SEQ ID NO: 144, SEQ ID NO: 146, SEQ ID NO: 148, SEQ ID NO: 150, and SEQ ID NO: 152, which encode for the amino acid sequences SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, or SEQ ID NO: 151, respectively. Persons skilled in the art can determine appropriate nucleotide sequences that encode for polypeptides having the amino acid sequence of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 66, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160, based on the nucleotide sequences listed above and the identity of the desired engineered enzyme. 
     According to the present invention, and useful in combination with one or more of the above aspects and embodiments, a nucleic acid comprising a nucleotide sequence encoding for any of the engineered enzymes described above can be inserted into an expression vector that is engineered to be inserted into biological host cells configured to retain the expression vector and overexpress the desired enzyme. According to the present invention, the nucleic acid inserted into an expression vector can comprise any nucleotide sequence encoding for any of the engineered enzymes described above, particularly those comprising the amino acid sequences of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160. According to the present invention, the nucleic acid inserted into an expression vector can comprise any nucleotide sequence selected from the group consisting of SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56, SEQ ID NO: 58, SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 71, SEQ ID NO: 73, SEQ ID NO: 75, SEQ ID NO: 77, SEQ ID NO: 79, SEQ ID NO: 81, SEQ ID NO: 83, SEQ ID NO: 85, SEQ ID NO: 87, SEQ ID NO: 89, SEQ ID NO: 91, SEQ ID NO: 93, SEQ ID NO: 95, SEQ ID NO: 97, SEQ ID NO: 99, SEQ ID NO: 101, SEQ ID NO: 103, SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 109, SEQ ID NO: 124, SEQ ID NO: 126, SEQ ID NO: 128, SEQ ID NO: 130, SEQ ID NO: 132, SEQ ID NO: 134, SEQ ID NO: 136, SEQ ID NO: 138, SEQ ID NO: 140, SEQ ID NO: 142, SEQ ID NO: 144, SEQ ID NO: 146, SEQ ID NO: 148, SEQ ID NO: 150, and SEQ ID NO: 152. 
     According to the present invention, and useful in combination with one or more of the above aspects and embodiments, the expression vector can optionally further comprise one or more nucleic acid sequences or genes encoding for proteins or host recognition sites that supplement the production of engineered enzymes of the present invention. Non-limiting examples include promoter sequences, antibiotic resistance genes, and genes encoding for fusion proteins that assist in the folding and stability of the engineered sulfotransferase enzyme. According to the present invention, any of the expression vectors described above can further comprise the malE gene from  Escherichia coli , which encodes for maltose binding protein (MBP). According to the present invention, any of the expression vectors described above can further comprise a gene encoding for a small ubiquitin-related modifier (SUMO) protein, preferably the SUMO1 gene, which encodes for the SUMO1 protein. As a result, and according to the present invention, once protein expression is initiated, a fusion protein can be formed that comprises either MBP or SUMO, as well as an engineered enzyme having an amino acid sequence selected from the group consisting of: SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160. 
     Expression vectors are typically transformed into host cells from which the enzyme can be overexpressed and extracted. According to the present invention, and useful in combination with one or more of the above aspects and embodiments, host cells can be transformed with expression vectors containing a nucleic acid sequence set forth in SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56, SEQ ID NO: 58, SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 71, SEQ ID NO: 73, SEQ ID NO: 75, SEQ ID NO: 77, SEQ ID NO: 79, SEQ ID NO: 81, SEQ ID NO: 83, SEQ ID NO: 85, SEQ ID NO: 87, SEQ ID NO: 89, SEQ ID NO: 91, SEQ ID NO: 93, SEQ ID NO: 95, SEQ ID NO: 97, SEQ ID NO: 99, SEQ ID NO: 101, SEQ ID NO: 103, SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 109, SEQ ID NO: 124, SEQ ID NO: 126, SEQ ID NO: 128, SEQ ID NO: 130, SEQ ID NO: 132, SEQ ID NO: 134, SEQ ID NO: 136, SEQ ID NO: 138, SEQ ID NO: 140, SEQ ID NO: 142, SEQ ID NO: 144, SEQ ID NO: 146, SEQ ID NO: 148, SEQ ID NO: 150, SEQ ID NO: 152, or any sequence that encodes for an enzyme having the amino acid sequence of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160. According to the present invention, any of the above expression vectors transformed into the host cell can further comprise the malE or SUMO1 gene. According to the present invention, the transformed host cells can be bacterial, yeast, insect, or mammalian cells. According to the present invention, the host cells can be bacterial cells. According to the present invention, the bacterial cells can be from a non-pathogenic strain of  Escherichia coli  ( E. coli ). 
     In another aspect of the invention, kits for forming a sulfated polysaccharide product, particularly N,2O,3O,6O-HS products having anticoagulant activity similar or equivalent to heparin, according to any of the methods described above, are provided. According to the present invention, the kit can comprise at least one engineered aryl sulfate-dependent sulfotransferase and at least one aryl sulfate compound, preferably PNS or NCS. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the kit can comprise an engineered NST, an engineered 2OST, an engineered 6OST, and/or an engineered 3OST, each of which is dependent on reacting with an aryl sulfate compound as a sulfo group donor to catalyze a transfer of the sulfo group to a polysaccharide, preferably a heparosan-based polysaccharide. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the kit can further comprise any of the heparosan-based polysaccharides described above as sulfo group donor. According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, the kit can further comprise a glucuronyl C 5 -epimerase, preferably an epimerase comprising the amino acid sequence of SEQ ID NO: 67, and more preferably an epimerase comprising amino acid residues 34-617 of SEQ ID NO: 67. 
     According to the present invention, and useful in combination with any one or more of the above aspects and embodiments, any of the sulfated polysaccharide products, including anticoagulant N,2O,3O,6O-HS products, prepared according to any of the methods described above can be prepared as pharmaceutically-acceptable salts, particularly alkali or alkali earth salts including, but not limited to, sodium, lithium, or calcium salts. 
     These and other embodiments of the present invention will be apparent to one of ordinary skill in the art from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    shows the sulfatase activity catalyzed by one of the engineered enzymes of the present invention, when PNS is the substrate. 
         FIG.  2    shows a theoretical reaction mechanism for the hydrolysis of the sulfate ester linkage and formation of a sulfohistidine intermediate. 
         FIG.  3 A  and  FIG.  3 B  show two proposed reaction mechanisms for natural sulfatase enzymes, catalyzed using an α-formylglycine residue. 
         FIG.  4 A ,  FIG.  4 B , and  FIG.  4 C  show a proposed reaction mechanism, transition state, and products formed as a result of a sulfotransfer reaction between the natural human 3OST enzyme, PAPS, and a heparosan-based polysaccharide. 
         FIG.  5    shows a non-limiting example of a heparosan-based polysaccharide that can be used as a sulfo group acceptor with engineered NST enzymes of the present invention. 
         FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C  show a multiple sequence alignment for the N-sulfotransferase domains of fifteen wild type EC 2.8.2.8 enzymes, illustrating conserved amino acid sequence motifs that are present regardless of overall sequence identity. 
         FIG.  7 A ,  FIG.  7 B , and  FIG.  7 C  show a proposed reaction mechanism, transition state, and products formed as a result of a sulfotransfer reaction between a natural NDST enzyme, PAPS, and N-deacetylated heparosan. 
         FIG.  8    shows a three-dimensional model of PNS bound within the active site of an engineered NST enzyme, superimposed over the crystal structure of the N-sulfotransferase domain of a natural enzyme from the EC. 2.8.2.8 enzyme class. 
         FIG.  9    shows a three-dimensional model of the engineered enzyme modeled in  FIG.  8   , illustrating amino acid mutations present within the active site. 
         FIG.  10    shows another three-dimensional model of PNS bound within the active site of an engineered NST enzyme, superimposed over the crystal structure of the N-sulfotransferase domain of a natural enzyme from the EC. 2.8.2.8 enzyme class. 
         FIG.  11    shows a three-dimensional model of the engineered enzyme modeled in  FIG.  10   , illustrating amino acid mutations present within the active site. 
         FIG.  12    shows a sequence alignment of polypeptides comprising the amino acid sequences of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, and SEQ ID NO: 15, respectively, depicting the position and identity of amino acid residues differences between each of the illustrated sequences. 
         FIG.  13    shows a non-limiting example of a heparosan-based polysaccharide that can be used as a sulfo group acceptor with engineered 2OST enzymes of the present invention. 
         FIG.  14    shows another non-limiting example of a heparosan-based polysaccharide that can be used as a sulfo group acceptor with engineered 2OST enzymes of the present invention, where a sulfate group is transferred to the 2-O position of a glucuronic acid residue within the heparosan-based polysaccharide. 
         FIG.  15    shows another non-limiting example of a heparosan-based polysaccharide that can be used as a sulfo group acceptor with engineered 2OST enzymes of the present invention, where a sulfate group is transferred to the 2-O position of an iduronic acid residue within the polysaccharide. 
         FIG.  16    shows another non-limiting example of a heparosan-based polysaccharide that can be used as a sulfo group acceptor with engineered 2OST enzymes of the present invention, where a sulfate group is transferred to both the 2-O position of a glucuronic acid residue and the 2-O position of an iduronic acid residue within the polysaccharide. 
         FIG.  17 A ,  FIG.  17 B ,  FIG.  17 C , and  FIG.  17 D  show a multiple sequence alignment for twelve wild-type 2OST enzymes within EC 2.8.2.—, illustrating conserved amino acid sequence motifs that are present regardless of overall sequence identity. 
         FIG.  18 A ,  FIG.  18 B , and  FIG.  18 C  show a proposed reaction mechanism, transition state, and products formed as a result of a sulfotransfer reaction between conserved residues within natural 2OST enzymes, PAPS, and a heparosan-based polysaccharide. 
         FIG.  19    shows a three-dimensional model of a mutated amino acid sequence motif enabling binding of NCS within the active site of an engineered 2OST enzyme, superimposed over the crystal structure of a natural 2-O sulfotransferase enzyme. 
         FIG.  20    shows a non-limiting example of a heparosan-based polysaccharide that can be used as a sulfo group acceptor with engineered 6OST enzymes of the present invention, in which the 6-O position of multiple glucosamine residues can receive a sulfo group. 
         FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C  show a multiple sequence alignment for fifteen wild-type 6OST enzymes within EC 2.8.2.—, illustrating conserved amino acid sequence motifs that are present regardless of overall sequence identity. 
         FIG.  22 A ,  FIG.  22 B , and  FIG.  22 C  show a proposed reaction mechanism, transition state, and products formed as a result of a sulfotransfer reaction between conserved residues within natural 6OST enzymes, PAPS, and a heparosan-based polysaccharide. 
         FIG.  23    shows a three-dimensional model of a mutated amino acid sequence motif enabling binding of PNS within the active site of an engineered 6OST enzyme, superimposed over the crystal structure of a natural 6OST enzyme. 
         FIG.  24    shows a sequence alignment of polypeptides comprising the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, and SEQ ID NO: 108, respectively, depicting the position and identity of amino acid residues differences between each of the illustrated sequences. 
         FIG.  25    shows a non-limiting example of a heparosan-based polysaccharide that can be used as a sulfo group acceptor with engineered 3OST enzymes of the present invention, to form an N,2O,3O,6O-HS product comprising a polysaccharide sequence motif having the structure of Formula I. 
         FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C  show a multiple sequence alignment for fifteen wild-type 3OST enzymes within EC 2.8.2.23, illustrating conserved amino acid sequence motifs that are present regardless of overall sequence identity. 
         FIG.  27    shows a three-dimensional model of a mutated amino acid sequence motif enabling binding of PNS within the active site of an engineered 3OST enzyme, superimposed over the crystal structure of a natural 3OST enzyme. 
         FIG.  28    shows a sequence alignment of polypeptides comprising the amino acid sequences of SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151, respectively, depicting the position and identity of amino acid residues differences between each of the illustrated sequences. 
         FIG.  29    shows a series of overlaid SAX-HPLC chromatograms of N-sulfated polysaccharide products synthesized using an engineered NST enzyme, compared to commercial standards. 
         FIG.  30 A  and  FIG.  30 B  show LCMS chromatograms of 2-O sulfated polysaccharide products synthesized using engineered 2OST enzymes having the amino acid sequence of SEQ ID NO: 63 and SEQ ID NO: 65, respectively. 
         FIG.  31 A ,  FIG.  31 B , and  FIG.  31 C  show LCMS chromatograms of a 6-O sulfated polysaccharide product synthesized using an engineered 6OST having the amino acid sequence SEQ ID NO 104, SEQ ID NO: 106, and SEQ ID NO: 108, respectively. 
         FIG.  32 A  and  FIG.  32 B  show a series of six LCMS chromatograms of sulfated polysaccharide products synthesized using engineered 3OST enzymes, compared to a series of disaccharide and polysaccharide standards. 
         FIG.  33    shows the reaction scheme for deuterium labeling of protons of interest for nuclear magnetic resonance (NMR) studies. 
         FIG.  34    shows  1 H-NMR spectra for sulfated polysaccharide products formed by the engineered 3OST enzymes of the present invention, upon reacting with either PNS or NCS. 
         FIG.  35    shows a magnified view of the 3.5 ppm to 4.5 ppm region of the  1 H-NMR spectra from  FIG.  34   . 
         FIG.  36    shows a SAX-HPLC chromatogram of a chemically N-sulfated polysaccharide product, compared to a commercial standard. 
         FIG.  37    shows a SAX-HPLC chromatogram of an enzymatically 2-O sulfated polysaccharide product prepared using the chemically N-sulfated polysaccharide product of Example 8 as the sulfo acceptor polysaccharide, compared to a commercial standard. 
         FIG.  38    shows a SAX-HPLC chromatogram of an enzymatically 2-O sulfated polysaccharide product prepared using the chemically N-sulfated polysaccharide product of Example 8 as the sulfo acceptor polysaccharide and with a C 5 -hexuronyl epimerase included in the reaction mixture, compared to a commercial standard. 
         FIG.  39    shows a SAX-HPLC chromatogram of an enzymatically 6-O sulfated polysaccharide product prepared using a 2-O sulfated polysaccharide product of Example 9 as the sulfo group acceptor, compared to a commercial standard. 
     
    
    
     DEFINITIONS 
     The term, “active site,” refers to sites in catalytic proteins, in which catalysis occurs, and can include one or more substrate binding sites. Active sites are of significant utility in the identification of compounds that specifically interact with, and modulate the activity of, a particular polypeptide. The association of natural ligands or substrates with the active sites of their corresponding receptors or enzymes is the basis of many biological mechanisms of action. Similarly, many compounds exert their biological effects through association with the active sites of receptors and enzymes. Such associations may occur with all or any parts of the active site. An understanding of such associations helps lead to the design of engineered active sites within sulfotransferases that are capable of binding to and reacting with aryl sulfate compounds instead of PAPS. 
     The term, “amino acid,” refers to a molecule having the structure wherein a central carbon atom (the alpha-carbon atom) is linked to a hydrogen atom, a carboxylic acid group (the carbon atom of which is referred to herein as a “carboxyl carbon atom”), an amino group (the nitrogen atom of which is referred to herein as an “amino nitrogen atom”), and a side chain group, R. When incorporated into a peptide, polypeptide, or protein, an amino acid loses one or more atoms of its amino and carboxylic groups in the dehydration reaction that links one amino acid to another. As a result, when incorporated into a protein, an amino acid is referred to as an “amino acid residue.” In the case of naturally occurring proteins, an amino acid residue&#39;s R group differentiates the 20 amino acids from which proteins are synthesized, although one or more amino acid residues in a protein may be derivatized or modified following incorporation into protein in biological systems (e.g., by glycosylation and/or by the formation of cysteine through the oxidation of the thiol side chains of two non-adjacent cysteine amino acid residues, resulting in a disulfide covalent bond that frequently plays an important role in stabilizing the folded conformation of a protein, etc.). Additionally, when an alpha-carbon atom has four different groups (as is the case with the 20 amino acids used by biological systems to synthesize proteins, except for glycine, which has two hydrogen atoms bonded to the carbon atom), two different enantiomeric forms of each amino acid exist, designated D and L. In mammals, only L-amino acids are incorporated into naturally occurring polypeptides. Engineered enzymes utilized of the present invention can incorporate one or more D- and L-amino acids, or can be comprised solely of D- or L-amino acid residues. 
     Non-naturally occurring amino acids can also be incorporated into any of the engineered enzymes of the present invention, particularly engineered sulfotransferase enzymes having aryl sulfate-dependent activity. Non-limiting examples of such amino acids include: alpha-amino isobutyric acid, 4-amino butyric acid, L-amino butyric acid, 6-amino hexanoic acid, 2-amino isobutyric acid, 3-amino propionic acid, ornithine, norleucine, norvaline, hydroxyproline, sarcosine, citrulline, cystic acid, t-butyl glycine, t-butyl alanine, phenylglycine, cyclohexyl alanine, beta-alanine, fluoro-amino acids, designer amino acids (e.g., beta-methyl amino acids, alpha-methyl amino acids, alpha-methyl amino acids) and amino acid analogs in general. 
     The term, “and/or,” when used in the context of a listing of entities, refers to the entities being present singly or in combination. Thus, for example, the phrase “A, B, C, and/or D” includes A, B, C, and D individually, but also includes any and all combinations and sub-combinations of A, B, C, and D. 
     The term, “API heparin,” refers to the form of heparin that is regulated for administering to patients, and which conforms to the United States Pharmacopeia (USP) reference standard with respect to identity, strength, quality, purity, and potency. Properties defined by the USP monograph for heparin sodium include: a characteristic  1 H-NMR spectrum; chromatographic purity, particularly with respect to dermatan sulfate and oversulfated chondroitin sulfate; anti-Factor Xa activity; anti-Factor IIa activity; the ratio of anti-factor Xa activity relative to anti-factor IIa activity; the presence or absence of inorganic and inorganic impurities; and a characteristic molecular weight distribution or profile. In particular, the USP Heparin Sodium standard has an anti-Factor Xa activity of not less than 180 IU mg −1 ; an anti-factor IIa activity of not less than 180 IU mg −1 ; a ratio of anti-Factor Xa activity to anti-Factor IIa activity of 0.9-1.1; the amount of polysaccharide chains greater than 24,000 Da is less than 20% of a heparin sample; the amount of polysaccharide chains between 8,000 Da and 16,000 Da being greater than the amount of polysaccharide chains between 16,000 Da and 24,000 Da within the heparin sample; and a weight average molecular weight of the heparin sample in the range of at least 15,000 Da and up to 19,000 Da. 
     The terms, “aryl sulfate” or “aryl sulfate compound,” refer to any compound, functional group, or substituent derived from an aromatic ring in which one or more of the hydrogen atoms directly bonded to the aromatic ring is replaced by a sulfate functional group. Typically, the sulfate functional group is covalently bound to the aromatic moiety of an aryl sulfate compound through a sulfate ester linkage. Non-limiting examples of aryl sulfate compounds that can be used as substrates with any of the engineered enzymes of the present invention include, but are not limited to, PNS, 4-methylumbelliferyl sulfate, 7-hydroxycoumarin sulfate, phenyl sulfate, 4-acetylphenyl sulfate, indoxyl sulfate, 1-naphthyl sulfate, 2NapS, and NCS. 
     The term, “aryl sulfate-dependent sulfotransferase,” refers to the collective group of engineered sulfotransferases that possess biological or catalytic activity with aryl sulfate compounds as sulfo donors. Non-limiting examples of aryl sulfate compounds upon which the biological activity of the sulfotransferase can be dependent include PNS and NCS. As described herein, engineered sulfotransferases having biological activity with aryl sulfate compounds as sulfo group donors can possess biological activity with polysaccharides, particularly heparosan-based polysaccharides, as sulfo group acceptors. “Aryl sulfate-dependent sulfotransferase” also includes both nucleic acids and polypeptides encoding for any aryl sulfate-dependent sulfotransferase, including mutants derived from the sequences disclosed herein. 
     The term, “average molecular weight,” with respect to any of the polysaccharide starting materials, intermediates, and/or products used or generated according to any of the methods of the present invention, and unless otherwise indicated, can refer to any accepted measure of determining the molar mass distribution or molar mass average of a mixture of polymers having varying degrees of polymerization, functionalization, and molar mass, including but not limited to “number-average molecular weight,” “mass-average molecular weight,” “weight-average molecular weight,” “Z (centrifugation) average molar mass,” or “viscosity average molar mass.” 
     The term, “weight-average molecular weight,” refers to a method of reporting the average molecular weight of polysaccharides in a mixture, calculated using the mole fraction distribution of the polysaccharides within the sample, using the equation 
     
       
         
           
             
               
                 
                   M 
                   _ 
                 
                 w 
               
               = 
               
                 
                   
                     ∑ 
                     i 
                   
                   
                     
                       N 
                       i 
                     
                     ⁢ 
                     
                       M 
                       i 
                       2 
                     
                   
                 
                 
                   
                     ∑ 
                     i 
                   
                   
                     
                       N 
                       i 
                     
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                       M 
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             , 
           
         
       
     
     wherein N i  is the number of polysaccharides of molecular mass M i . 
     The term, “number-average molecular weight,” refers to a method of reporting the average molecular weight of polysaccharides in a mixture, calculated by dividing the total weight of all of the polysaccharides in the sample divided by the number of polysaccharides in a sample, using the equation, 
     
       
         
           
             
               
                 
                   M 
                   _ 
                 
                 N 
               
               = 
               
                 
                   
                     ∑ 
                     i 
                   
                   
                     
                       N 
                       i 
                     
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                       M 
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                     ∑ 
                     i 
                   
                   
                     N 
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             , 
           
         
       
     
     wherein N i  is the number of polysaccharides of molecular mass M i . Accordingly, the weight-average molecular weight,  M   w , is necessarily skewed toward higher values corresponding to polysaccharides within the sample that are larger than other polysaccharides within the same mixture, and will always be larger than the number-average molecular weight,  M   n , except when the sample is monodisperse, and  M   w  equals  M   n . If a particular sample of polysaccharides within the sample has a large dispersion of actual weights, then  M   w  will be much larger than  M   n . Conversely, as the weight dispersion of polysaccharides in a sample narrows,  M   w  approaches  M   n . 
     The terms, “relative molecular weight” or “relative molar mass” (M r ), refers to another method of reporting the average molecular weight of polysaccharides in a mixture as a unitless quantity, most broadly determined by dividing the average mass of the molecule by an atomic mass constant, such as 1 atomic mass unit (amu) or 1 Dalton (Da). With respect to polysaccharides, M r  does not take into account the different chain-lengths, functionalization, and/or weight distribution of the polysaccharides in the sample, and instead simply represents the true average mass of the polysaccharides in the sample in a manner similar to small molecules. 
     The terms, “biological activity” or “catalytic activity,” refer to the ability of an enzyme to catalyze a particular chemical reaction by specific recognition of a particular substrate or substrates to generate a particular product or products. In some embodiments, the engineered enzymes of the present invention possess a biological or catalytic activity that is dependent on binding and reacting with aryl sulfate compounds, particularly PNS or NCS, as substrates. Additionally, some engineered enzymes are capable of having promiscuous catalytic activity with one or more alternate aryl sulfate compounds in addition to PNS, including but not limited to MUS, 7-hydroxycoumarin sulfate, phenyl sulfate, 4-acetylphenyl sulfate, indoxyl sulfate, 1-naphthyl sulfate, and 2NapS. 
     The term, “coding sequence,” refers to that portion of a nucleic acid, for example, a gene, that encodes an amino acid sequence of a protein. 
     The term, “codon-optimized” refers to changes in the codons of the polynucleotide encoding a protein to those preferentially used in a particular organism such that the encoded protein is efficiently expressed in the organism of interest. Although the genetic code is degenerate in that most amino acids are represented by several codons, it is well known that codon usage by particular organisms is non-random and biased toward particular codon triplets. In some embodiments of the invention, the polynucleotide encoding for an engineered enzyme may be codon optimized for optimal production from the host organism selected for expression. 
     The terms, “corresponding to,” “reference to,” or “relative to,” when used in the context of the numbering of a given amino acid or polynucleotide sequence, refers to the numbering of the residues of a specified reference sequence when the given amino acid or polynucleotide sequence is compared to the reference sequence. In other words, the residue number or residue position of a given polymer is designated with respect to the reference sequence rather than by the actual numerical position of the residue within the given amino acid or polynucleotide sequence. 
     The term, “deletion,” refers to modification of a polypeptide by removal of one or more amino acids from the reference polypeptide. Deletions can comprise removal of 1 or more amino acids, the net result of which is retaining the catalytic activity of the reference polypeptide. Deletions can be directed to the internal portions and/or terminal portions of a polypeptide. Additionally, deletions can comprise continuous segments or they can be discontinuous. 
     The term, “disaccharide unit,” refers to the smallest repeating backbone unit within many polysaccharides, including linear polysaccharides, in which the smallest repeating unit consists of two sugar residues. With respect to a heparosan-based polysaccharide, the disaccharide unit consists of a hexuronic acid residue and a glucosamine residue, either of which can be functionalized and in which the hexuronic acid residue can either be glucuronic acid or iduronic acid. Each disaccharide unit within the heparosan-based polysaccharide can be described by its backbone structure and by the number and position of sulfo groups that are present. Further, the relative abundance of disaccharide units having the same structure within the same polysaccharide, and/or within the same sample of polysaccharides, can be characterized to determine the amount of sulfation at a particular position as a result of reacting with any of the sulfotransferases described herein. 
     The terms, “fragment” or “segment,” refer to a polypeptide that has an amino- or carboxy-terminal deletion, but where the remaining amino acid sequence is identical to the corresponding positions in a reference sequence. Fragments can be at least 50 amino acids or longer, and comprise up to 70%, 80%, 90%, 95%, 98%, and 99% of the amino acid sequence of an enzyme. 
     The terms, “functional site” or “functional domain,” generally refer to any site in a protein that confers a function on the protein. Representative examples include active sites (i.e., those sites in catalytic proteins where catalysis occurs) and ligand binding sites. Ligand binding sites include, but are not limited to, metal binding sites, co-factor binding sites, antigen binding sites, substrate channels and tunnels, and substrate binding domains. In an enzyme, a ligand binding site that is a substrate binding domain may also be an active site. Functional sites may also be composites of multiple functional sites, wherein the absence of one or more sites comprising the composite results in a loss of function. As a non-limiting example, the active site of a particular sulfotransferase enzyme may include multiple binding sites or clefts, including one site for the sulfo donor and one site for the sulfo acceptor. 
     The terms, “gene,” “gene sequence,” and “gene segment,” refer to a functional unit of nucleic acid unit encoding for a functional protein, polypeptide, or peptide. As would be understood by those skilled in the art, this functional term includes both genomic sequences and cDNA sequences. The terms, “gene,” “gene sequence,” and “gene segment,” additionally refer to any DNA sequence that is substantially identical to a polynucleotide sequence disclosed herein encoding for engineered enzyme gene product, protein, or polysaccharide, and can comprise any combination of associated control sequence. The terms also refer to RNA, or antisense sequences, complementary to such DNA sequences. As used herein, the term “DNA segment” includes isolated DNA molecules that have been isolated free of recombinant vectors, including but not limited to plasmids, cosmids, phages, and viruses. 
     The term, “glycosaminoglycan,” refers to long, linear polysaccharides consisting of repeating disaccharide units. Examples of glycosaminoglycans (GAGs) include chondroitin, dermatan, heparosan, hyaluronic acid, and keratan. GAGs are generally heterogeneous with respect to mass, length, disaccharide unit structure and functionalization, degree of sulfation. 
     The term, “heparosan,” refers to a particular GAG having repeating [β(1,4)GlcA-α(1,4)GlcNAc]n disaccharide units, in which GlcA is glucuronic acid and GlcNAc is N-acetyl glucosamine. 
     The term, “heparosan-based polysaccharide,” refers to polysaccharides having the same backbone structure as heparosan, in which the disaccharide unit contains 1→4 glycosidically-linked hexuronic acid and glucosamine residues. The hexuronic acid residue can either be glucuronic acid, as in heparosan, or iduronic acid, and can optionally have a sulfo group at the 2-O position. The glucosamine residue can either be N-acetylated, as in heparosan, N-sulfated, or N-unsubstituted, and can optionally be sulfated at the N-, 3-O, or 6-O position. As used herein, the term “N-unsubstituted,” with respect to a glucosamine residue, is equivalent to an “N-deacetylated” glucosamine residue, and refers to an amine functional group that is capable of receiving a sulfo group either chemically, or enzymatically using a NST. According to the present invention, heparosan-based polysaccharides can be utilized as starting materials, formed as intermediates, acting as sulfo group acceptors and/or synthesized as products according to any of the methods described herein. 
     The term, “insertion,” refers to modifications to the polypeptide by addition of one or more amino acids to the reference polypeptide. Insertions can be in the internal portions of the polypeptide, or to the C- or N-termini of the polypeptide. Insertions can include fusion proteins as is known in the art and described below. The insertions can comprise a continuous segment of amino acids or multiple insertions separated by one or more of the amino acids in the reference polypeptide. 
     The term, “isolated nucleic acid” as used herein with respect to nucleic acids derived from naturally-occurring sequences, means a ribonucleic or deoxyribonucleic acid which comprises a naturally-occurring nucleotide sequence and which can be manipulated by standard recombinant DNA techniques, but which is not covalently joined to the nucleotide sequences that are immediately contiguous on its 5′ and 3′ ends in the naturally-occurring genome of the organism from which it is derived. As used herein with respect to synthetic nucleic acids, the term “isolated nucleic acid” means a ribonucleic or deoxyribonucleic acid which comprises a nucleotide sequence which does not occur in nature and which can be manipulated by standard recombinant DNA techniques. An isolated nucleic acid can be manipulated by standard recombinant DNA techniques when it may be used in, for example, amplification by polymerase chain reaction (PCR), in vitro translation, ligation to other nucleic acids (e.g., cloning or expression vectors), restriction from other nucleic acids (e.g., cloning or expression vectors), transformation of cells, hybridization screening assays, or the like. 
     The terms, “naturally occurring” or “wild-type,” refer to forms of an enzyme found in nature. For example, a naturally occurring or wild-type polypeptide or polynucleotide sequence is a sequence present in an organism that can be isolated from a source in nature and which has not been intentionally modified by human manipulation. A wild-type polypeptide or polynucleotide sequence can also refer to recombinant proteins or nucleic acids that can be synthesized, amplified, and/or expressed in vitro, and which have the same sequence and biological activity as an enzyme produced in vivo. In contrast to naturally occurring or wild-type sulfotransferase enzymes, the engineered sulfotransferase enzymes utilized in accordance with methods of the present invention have unique amino acid and nucleic acid sequences, have biological activity with aryl sulfate compounds as sulfo group donors instead of PAPS, and cannot be found in nature. 
     The term, “oligosaccharide,” refers to saccharide polymers containing a small number, typically three to nine, sugar residues within each molecule. 
     The term, “percent identity,” refers to a quantitative measurement of the similarity between two or more nucleic acid or amino acid sequences. As a non-limiting example, the percent identity can be assessed between two or more engineered enzymes of the present invention, two or more naturally occurring enzymes, or between one or more engineered enzymes and one or more naturally occurring enzymes. Percent identity can be assessed relative to two or more full-length sequences, two or more truncated sequences, or a combination of full-length sequences and truncated sequences. 
     The term, “polysaccharide,” refers to polymeric carbohydrate structures formed of repeating units, typically monosaccharide or disaccharide units, joined together by glycosidic bonds, and which can range in structure from a linear chain to a highly-branched three-dimensional structure. Although the term “polysaccharide,” as used in the art, can refer to saccharide polymers having more than ten sugar residues per molecule, “polysaccharide” is used within this application to describe saccharide polymers having more than one sugar residue, including saccharide polymers that have three to nine sugar residues that may be defined in the art as an “oligosaccharide.” According to the present invention, the term “polysaccharide,” is also used to generally describe GAGs and GAG-based compounds, including chondroitin, dermatan, heparosan, hyaluronic acid, and keratan compounds. 
     The terms, “protein,” “gene product,” “polypeptide,” and “peptide” can be used interchangeably to describe a biomolecule consisting of one or more chains of amino acid residues. In addition, proteins comprising multiple polypeptide subunits (e.g., dimers, trimers or tetramers), as well as other non-proteinaceous catalytic molecules will also be understood to be included within the meaning of “protein” as used herein. Similarly, “protein fragments,” i.e., stretches of amino acid residues that comprise fewer than all of the amino acid residues of a protein, are also within the scope of the invention and may be referred to herein as “proteins.” Additionally, “protein domains” are also included within the term “protein.” A “protein domain” represents a portion of a protein comprised of its own semi-independent folded region having its own characteristic spherical geometry with hydrophobic core and polar exterior. 
     The term, “recombinant,” when used with reference to, for example, a cell, nucleic acid, or polypeptide, refers to a material that has been modified in a manner that would not otherwise exist in nature. Non-limiting examples include, among others, recombinant cells expressing genes that are not found within the native (non-recombinant) form of the cell or express native genes that are otherwise expressed at a different level. 
     The term, “reference sequence,” refers to a disclosed or defined sequence used as a basis for sequence comparison. A reference sequence may be a subset of a larger sequence, for example, a segment of a full-length gene or polypeptide sequence. Generally, a reference sequence refers to at least a portion of a full-length sequence, typically at least 20 amino acids, or the full-length sequence of the nucleic acid or polypeptide. 
     The term, “saccharide,” refers to a carbohydrate, also known as a sugar, which is a broad term for a chemical compound comprised of carbon, hydrogen, and oxygen, wherein the number of hydrogen atoms is essentially twice that of the number of oxygen atoms. Often, the number of repeating units may vary in a saccharide. Thus, disaccharides, oligosaccharides, and polysaccharides are all examples of chains composed of saccharide units that are recognized by the engineered sulfotransferase enzymes of the present invention as sulfo group acceptors. 
     The term, “substantially equivalent,” with respect to polysaccharides utilized as starting materials, formed as intermediates, acting as sulfo group acceptors, and/or synthesized as products according to any of the methods described herein, refers to one or more properties of a polysaccharide sample that are identical to those found in a polysaccharide sample characterized in the prior art. Such properties may include, but are not limited to, chemical structure, sulfation frequency and location, disaccharide unit composition, molecular weight profile, and/or anticoagulant activity. Even if the two polysaccharide samples have additional properties that may be different, such differences do not significantly affect their substantial equivalence. In a non-limiting example, anticoagulant N,2O,3O,6O-HS products synthesized using engineered 3OSTs according to methods of the present invention can be substantially equivalent to the United States Pharmacopeia (USP) reference standard (CAS No: 9041-08-1) with respect to chemical structure, molecular weight profile, and/or anticoagulant activity, but can be produced at a different purity than the USP reference standard, which is isolated from natural sources and can contain non-trace amounts of other GAGs in the same sample. 
     The term, “substantially pure,” with respect to protein preparations, refers to a preparation which contains at least 60% (by dry weight) the protein of interest, exclusive of the weight of other intentionally included compounds. Particularly the preparation is at least 75%, more particularly at least 90%, and most particularly at least 99%, by dry weight the protein of interest, exclusive of the weight of other intentionally included compounds. Purity can be measured by any appropriate method, e.g., column chromatography, gel electrophoresis, or high-performance liquid chromatography (HPLC) analysis. If a preparation intentionally includes two or more different proteins of the invention, a “substantially pure” preparation means a preparation in which the total dry weight of the proteins of the invention is at least 60% of the total dry weight, exclusive of the weight of other intentionally included compounds. Particularly, for such preparations containing two or more proteins of the invention, the total weight of the proteins of the invention can be at least 75%, more particularly at least 90%, and most particularly at least 99%, of the total dry weight of the preparation, exclusive of the weight of other intentionally included compounds. 
     The terms, “sulfo” or “sulfuryl” refer to a functional group, substituent, or moiety having the chemical formula SO 3 H −  that can be removed from an aryl sulfate compound and/or be transferred from a donor compound to an acceptor compound. In some embodiments, the engineered sulfotransferases of the present invention catalyze the transfer of sulfo groups from aryl sulfate compounds to a polysaccharide, particularly heparosan and/or heparosan-based polysaccharides. 
     The term, “sulfotransferase,” refers to any enzyme in an in vivo or in vitro process that is used to catalyze the transfer of a sulfo group from a sulfo donor compound to a sulfo acceptor compound. “Sulfotransferase” can be used interchangeably to describe enzymes that catalyze sulfotransfer reactions in vivo or to describe engineered enzymes of the present invention that catalyze sulfotransfer reactions in vitro. 
     The term, “transformation,” refers to any method of introducing exogenous a nucleic acid into a cell including, but not limited to, transformation, transfection, electroporation, microinjection, direct injection of naked nucleic acid, particle-mediated delivery, viral-mediated transduction or any other means of delivering a nucleic acid into a host cell which results in transient or stable expression of said nucleic acid or integration of said nucleic acid into the genome of said host cell or descendant thereof. 
     The term, “unfractionated heparin,” refers to any synthesized or isolated heparin that has not been modified and/or partially depolymerized to form low molecular weight heparin. With respect to naturally-obtained heparin, the term “unfractionated heparin” generally represents the form of the heparin isolated from the animal, typically from porcine or bovine sources, prior to purification to meet USP reference standards. With respect to products synthesized by methods of the present invention, the term “unfractionated heparin” can refer to the N,2O,3O,6O-HS product having polysaccharides comprising the pentasaccharide sequence of Formula I, prior to purification to form API heparin or low-molecular-weight heparin. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present disclosure describes engineered enzymes that are configured to recognize, bind, and react with aryl sulfate compounds as substrates. The enzymes of the present invention are especially useful because many sulfate-containing compounds that are common substrates for bacterial and eukaryotic enzymes in vivo, including sulfatases and sulfotransferases, are often impractical to use as substrates for those same reactions in vitro. Aryl sulfate compounds are ubiquitous, cheap, stable, and comparatively easy to work with in a laboratory setting, but they are can react with very few enzymes in vivo. In particular, eukaryotic sulfotransferases cannot bind or react with aryl sulfate compounds as sulfo group donors, and instead can only react with 3′-phosphoadenosine 5′-phosphosulfate (PAPS) as a sulfo group donor. As a result, the sulfotransferases&#39; nearly universal reliance on PAPS has been an insurmountable roadblock to the large-scale chemoenzymatic or enzymatic in vitro synthesis of sulfated products, particularly sulfated polysaccharide products. 
     The engineered enzymes of the present invention, disclosed below, are mutants of natural sulfotransferase enzymes that exclusively recognize, bind, and react with PAPS, but instead are engineered to bind and react with aryl sulfate compounds as substrates. In an embodiment of the invention, many of the engineered enzymes possess sulfatase activity, in which the enzyme catalyzes hydrolysis of a sulfo group from an aryl sulfate compound. Without being limited by a particular theory, it is believed that the reaction mechanism for the sulfatase is unique relative to known natural sulfatases, which possess conserved signal sequences and post-translationally modified amino acids. The sulfatase activity of both natural enzymes and the engineered enzymes of the present invention is described in further detail below. 
     In another embodiment of the invention, several of the engineered enzymes possess sulfotransferase activity, in which the enzyme catalyzes the transfer of a sulfo group from an aryl sulfate compound to a sulfo group acceptor. In another embodiment, the sulfo group acceptor is a polysaccharide, particularly a heparosan-based polysaccharide. Without being limited by a particular theory, it is believed that sulfotransferase enzymes that recognize polysaccharides as sulfo group acceptors, but also bind and react with aryl sulfate compounds as sulfo donors, have neither been observed in nature nor described previously. Those skilled in the art will appreciate that the engineered aryl sulfate-dependent sulfotransferase enzymes of the present invention have several advantages over in vitro and in vivo reaction mechanisms that are unable to bind and react with aryl sulfate compounds in order to catalyze sulfo transfer. 
     It should be understood that while reference is made to exemplary embodiments and specific language is used to describe them, no limitation of the scope of the invention is intended. Further modifications of the methods described herein, as well as additional applications of the principles of those inventions as described, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of this invention. Furthermore, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of this particular invention pertain. The terminology used is for the purpose of describing those embodiments only, and is not intended to be limiting unless specified as such. Headings are provided for convenience only and are not to be construed to limit the invention in any way. Additionally, throughout the specification and claims, a given chemical formula or name shall encompass all optical isomers and stereoisomers, as well as racemic mixtures where such isomers and mixtures exist. 
     Aryl Sulfate-Dependent Sulfatases 
     In an embodiment of the invention, several of the engineered enzymes disclosed herein have sulfatase activity, and are capable of hydrolyzing the sulfate ester within an aryl sulfate compound (see Recksiek, et al., (1998)  J. Biol. Chem.  273 (11):6096-6103, the disclosure of which is incorporated by reference in its entirety). Upon binding with an aryl sulfate compound in an aqueous solution, engineered enzymes having sulfatase activity can catalyze the hydrolysis of the aryl sulfate compound to produce an aromatic compound and a sulfate ion. Non-limiting examples of aryl sulfate compounds include p-nitrophenyl sulfate (PNS), 4-methylumbelliferyl sulfate, 7-hydroxycoumarin sulfate, phenyl sulfate, 4-acetylphenyl sulfate, indoxyl sulfate, 1-naphthyl sulfate, 2-naphthyl sulfate (2NapS), and 4-nitrocatechol sulfate (NCS). As a non-limiting example and as illustrated in  FIG.  1   , when the aryl sulfate compound is PNS, the products are p-nitrophenol and a sulfate ion. In reactions conducted at a pH greater than the pKa of p-nitrophenol, the aromatic product is the p-nitrophenolate ion. 
     Without being limited by any particular theory, the hydrolysis of the sulfate ester catalyzed by an engineered enzyme of the present invention can occur upon binding of an aryl sulfate compound within the active site of the enzyme. As illustrated in  FIG.  2   , the lone pair of the basic nitrogen atom within the imidazole ring of an active site histidine residue initiates a nucleophilic attack of the sulfur atom within PNS, causing hydrolysis of the adjacent C—O bond and formation of a sulfohistidine intermediate. In a second step, the sulfohistidine intermediate itself can be nucleophilically attacked by a water molecule within the active site to cause a release of the sulfo group from the histidine side chain and restore the enzyme to its pre-reaction state. 
     Proceeding through a reaction mechanism that utilizes a histidine residue within the active site to hydrolyze the sulfate ester creates a unique niche for the engineered enzymes of the present invention relative to other known sulfatases. In nature, sulfatases comprise a class of enzymes (EC 3.1.5.6) that are highly conserved sequentially, structurally, and mechanistically across both prokaryotic and eukaryotic species, having functions such as cell development and detoxification, sulfur scavenging, degradation of compounds, and osmoprotection. Such similarities among natural sulfatases include a highly conserved N-terminal sequence region containing consensus sequence motifs, as well as unique, post-translationally modified active-site aldehyde residue, α-formylglycine, which is necessary for natural sulfatase activity (see Hanson, S. R., et al., (2004)  Agnew. Chem. Int. Ed.  43:5736-5763, the disclosure of which is incorporated by reference in its entirety). Additionally, natural sulfatases are typically large proteins that often comprise more than 500 amino acid residues, including up to about 800 amino acid residues for some eukaryotic sulfatases. 
     Without being limited by a particular theory, it is believed that all known natural hydrolytic sulfatases contain two highly homologous amino acid motifs that have been previously identified as sulfatase signature sequences I and II, both of which are found in the N-terminal sequence region (see Hanson, S. R., et al., above). Signature sequence I comprises the amino acids C/S-X-P-S/X-R-X-X-X-L/X-T/X-G/X-R/X, whereas signature sequence II comprises the amino acids G-Y/V-X-S/T-X-X-X-G-K-X-X-H. Both signature sequences correspond to SEQ ID NO: 271 and SEQ ID NO: 272 in the sequence listing, respectively, and play a vital role in the natural sulfatase enzyme activity. Signature sequence I is necessary for directing the post-translational modification of the active site to contain an α-formylglycine residue (described in further detail below) and signature sequence II contains important binding contacts that are important for optimizing sulfate ester catalysis within the α-formylglycine-containing active site. 
     In particular, the presence of α-formylglycine within the active site is the most salient feature within natural sulfatases, having been found in every characterized prokaryotic and eukaryotic sulfatase to date (see Uhlhorn-Dierls, G., et al., (1998)  Agnew. Chem.  37:2453, and Uhlhorn-Dierls, G., et al., (1998)  Agnew. Chem.  110:2591, the disclosures of which are incorporated by reference in their entireties). α-formylglycine residues can be formed from cysteine (most common) or serine residues within the active site, the modification of which has been determined to be directed by signature sequence I. 
     Based on the crystal structures of several natural sulfatases, two reaction mechanisms that prominently utilize the α-formylglycine residue for catalysis have been proposed. A first mechanism, illustrated in  FIG.  3 A , has been proposed in which the α-formylglycine residue, in its aldehyde form, is nucleophilically attacked by one of the sulfate group oxygen atoms within the substrate to form a sulfate diester. The alcohol conjugate is then released through the action of a nucleophile, such as an activated water molecule to form a sulfate hemiacetal. Subsequent attack by the alcohol of the nucleophilic center within the sulfate hemiacetal causes the release of the sulfate molecule from the active site, regenerating the enzyme for future catalysis. A second mechanism, illustrated in  FIG.  3 B , the α-formylglycine in its hydrated form can nucleophilically attack the sulfate atom via an S N 2 reaction to form the sulfate hemiacetal, and ultimately release the sulfate group from the active site, similar to the mechanism in  FIG.  3 A . Subsequent addition of water rehydrates the α-formylglycine aldehyde to reform the hydrated α-formylglycine residue. 
     However, and in another embodiment, the engineered enzymes of the present invention can be synthesized without signature sequence I, signature sequence II, and/or any α-formylglycine residues being present. In another embodiment, an enzyme that does not contain signature sequence I, signature sequence II, and/or any α-formylglycine residues, and which has been shown to have sulfatase activity (see the Examples, below) can be selected from the group consisting of: SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, or SEQ ID NO: 151. In another embodiment, an engineered enzyme having sulfatase activity can comprise an amino acid sequence that is substantially identical, or is a biological equivalent, to the amino acid sequence of any of the above polypeptides having sulfatase activity, as defined in the “Nucleic Acid and Polypeptide Preparation” section, below. 
     Accordingly, in another embodiment, the invention provides a method for enzymatically hydrolyzing an aryl sulfate compound, comprising the steps of: providing an aryl sulfate compound; providing an engineered enzyme having an active site configured to bind with an aryl sulfate compound and a polysaccharide, preferably a heparosan-based polysaccharide; combining the aryl sulfate compound and the engineered enzyme into a reaction mixture; and catalyzing the hydrolysis of the aryl sulfate compound using the engineered enzyme. In another embodiment, the aryl sulfate compound is selected from the group consisting of PNS, 4-methylumbelliferyl sulfate, 7-hydroxycoumarin sulfate, phenyl sulfate, 4-acetylphenyl sulfate, indoxyl sulfate, 1-naphthyl sulfate, 2NapS, and NCS. In another embodiment, the aryl sulfate compound is PNS. In another embodiment, the aryl sulfate compound is NCS. In another embodiment, the aryl sulfate compound is 2NapS. In another embodiment, hydrolysis of the aryl sulfate compound proceeds by a mechanism comprising the nucleophilic attack of the sulfur atom within the aryl sulfate compound, causing hydrolysis of the adjacent C—O bond and formation of a sulfohistidine intermediate. In another embodiment, the nucleophilic attack is initiated by a histidine residue. 
     Aryl Sulfate-Dependent Sulfotransferases 
     In another embodiment, and as described above, several of the engineered enzymes of the present invention have sulfotransferase activity with aryl sulfate compounds as sulfo group donors. In another embodiment, the sulfo group donor is a polysaccharide, preferably a heparosan-based polysaccharide. In each sulfotransfer reaction, the aryl sulfate compound participates as a sulfo group donor, while the polysaccharide participates as a sulfo group acceptor. Sulfotransferase enzymes that recognize polysaccharides as sulfo group acceptors, but also bind and react with aryl sulfate compounds as sulfo group donors, have neither been observed in nature nor described previously. 
     One particular polysaccharide, heparosan, is a starting material in the synthesis of a multitude of sulfated polysaccharides in vivo, particularly within eukaryotic organisms. Typically, heparosan is synthesized as a glycosaminoglycan (GAG) by the organism within the Golgi apparatus, and comprises repeating co-polymers of [β(1,4)GlcA-α(1,4)GlcNAc] n  disaccharide units, in which GlcA is glucuronic acid and GlcNAc is N-acetyl glucosamine. Heparosan GAGs can then be modified, particularly by one or more heparan sulfate (HS)-sulfotransferase enzymes, to form functionalized heparosan-based polysaccharide products, particularly HS and heparin. Such modifications to heparosan includes N-deacetylation and N-sulfation of glucosamine, C 5 -epimerization of glucuronic acid to form iduronic acid, 2-O-sulfation of iduronic and/or glucuronic acid, as well as 6-O-sulfation and 3-O-sulfation of glucosamine residues. The natural sulfotransferases that catalyze N-acetylation and N-sulfation, 2-O-sulfation, 6-O-sulfation, and 3-O-sulfation of heparosan and heparosan-based polysaccharides in vivo exclusively recognize and bind with PAPS as the sulfo group donor. Without being limited by a particular theory, it is believed that none of the four natural HS sulfotransferase enzymes—NDST, 2OST, 6OST, and 3OST—are active with any aryl sulfate compounds as a sulfo group donor. 
     Each of the four natural HS sulfotransferase enzymes generally catalyze the direct transfer of a sulfo group from PAPS to a heparosan-based polysaccharide in a single step. An example of a typical sulfotransfer reaction mechanism catalyzed by an HS sulfotransferase enzyme is illustrated in  FIG.  4 A ,  FIG.  4 B , and  FIG.  4 C , which collectively show a proposed mechanism, transition state, and products formed in a reaction between the human 3OST enzyme, PAPS, and a heparosan-based polysaccharide. In particular, the glutamic acid residue at position 43 abstracts the proton from the 3-O position of an N-, 6-O sulfated sulfoglucosamine residue within the heparosan-based polysaccharide, enabling the nucleophilic attack and removal of the sulfo group from PAPS, whereas His-45 and Asp-48 coordinate to stabilize the transition state of the enzyme before the sulfated polysaccharide product is released from the active site. 
     However, although PAPS is the exclusive sulfo donor in eukaryotes, it has a short half-life and can readily decompose into adenosine 3′,5′-diphosphate, which acts as a competitive inhibitor during sulfotransfer reactions. Animals can efficiently utilize PAPS because they can metabolize adenosine 3′,5′-diphosphate to prevent competitive inhibition and also replenish PAPS for each sulfotransfer reaction, as needed. On the other hand, aryl sulfate compounds, which can be utilized as sulfo donors in a limited number of bacterial systems (see Malojcic, G., et al., above), cannot react with any of the known native sulfotransferase enzymes in eukaryotes, including those that are involved in synthesizing HS and other heparosan-based polysaccharides in vivo. Without being limited by a particular theory, it is believed that the binding pockets for PAPS within the active sites of eukaryotic sulfotransferases either do not have a high enough affinity for aryl sulfate compounds to facilitate binding, and/or that the aryl sulfate compounds are sterically hindered from entering the active site at all. 
     Heparin, HS, and other heparosan-based polysaccharides play critical roles in a variety of important biological processes in vivo, including assisting viral infection, regulating blood coagulation and embryonic development, suppressing tumor growth, and controlling the eating behavior of test subjects by interacting with specific regulatory proteins. Depending on their role, heparosan polysaccharides can contain one or more unique patterns or motifs recognized by specific protein(s) involved in the particular biological process. In particular, heparin and other heparan sulfate polysaccharides, as well as routes to synthesizing such polysaccharides in vitro, are topics of extreme interest within the pharmaceutical industry. 
     However, the same anticoagulant activity that makes heparin so effective in many instances may not be desired in others, including situations where heparin may potentially cause dangerous side effects, including heparin-induced thrombocytopenia and increased risk of uncontrolled bleeding. To mitigate that risk, polysaccharide compositions that can still interact with various targets within the body while having reduced anticoagulant activity are prepared from heparin. Examples of such targets are described in further detail below. Heparin derivatives (also known as “heparinoids”) are typically prepared by O-desulfation of heparin, to form O-desulfated heparin (ODSH). The generated ODSH heparinoids are substantially desulfated at the 2-O position of hexuronic acid residues and/or the 3-O position of glucosamine residues within each polysaccharide, while retaining the N- and 6-O glucosamine sulfation commonly found in heparin. Methods of preparing and controlling the desulfation of heparin to form ODSH are described in U.S. Pat. Nos. 5,990,097, 5,912,237, 5,808,021, 5,668,118, and 5,296,471. 
     Although ODSH heparinoids prescribed in medical treatments are often substantially 2-O and 3-O desulfated, from at least 85% and up to at least 99% 2-O and 3-O desulfation, the ODSH products nonetheless retain some of the anticoagulant activity from heparin, indicating that not all of the 2-O and 3-O positions are desulfated. For example, U.S. Pat. Nos. 5,296,471 and 5,808,021 both describe the production of 2-O and 3-O desulfated ODSH compositions having between 1.2 and 10% of the anticoagulant activity of heparin using an activated partial thromboplastin time (aPTT) assay. Both patents also describe references which are referred to as “non-anticoagulant” depolymerized heparins, although these similarly only describe low molecular weight heparins (LMWH) having reduced anticoagulant potency under United States Pharmacopeia (USP) assay reaction conditions (see, e.g. Jaseja, M., et al.,  Can J. Chem  (1989) 67: 1449-1456 (&lt;5 IU/mg) and U.S. Pat. No. 6,150,342 (APTT: 54-102 IU/mg; Anti-Factor Xa: 3-8 IU/mg), the disclosures of which are incorporated by reference in their entireties). Similarly, U.S. Pat. Nos. 5,668,118, 5,912,237, and 5,990,097 describe the production of 2-O desulfated heparin with “much reduced anti-coagulant activity” when compared to heparin, while U.S. Pat. Nos. 6,489,311, 7,468,358, 9,271,999, and 10,052,346 describe the use of substantially 2-O and 3-O desulfated ODSH compositions having from 6-10 IU/mg of USP activity, 1.9-10 IU/mg of Anti-Factor Xa activity, and 2 IU/mg of Anti-Factor IIa activity. As a result, there is still potential for severe health risks associated with anticoagulant heparin when using ODSH heparinoids derived from anticoagulant heparin. 
     In contrast, heparan sulfate compounds that have no aPTT, USP, anti-Factor Xa (anti-Xa), and/or anti-Factor IIa (anti-IIa) anticoagulant activity can be synthesized by constructing such compounds in vitro, rather than depolymerizing heparin isolated from natural sources. 
     The present disclosure includes engineered sulfotransferase enzymes, described in further detail below, which have activity with aryl sulfate compounds as sulfo group donors and heparosan-based polysaccharides as sulfo group acceptors. Each of the engineered sulfotransferase enzymes is designed to be a mutant of a corresponding natural HS sulfotransferase: glucosaminyl N-deacetylase/N-sulfotransferase (NDST) (via its N-sulfotransferase (NST) domain), hexuronyl 2-O sulfotransferase (2OST), glucosaminyl 6-O sulfotransferase (6OST), and glucosaminyl 3-O sulfotransferase (3OST). In each instance, the engineered sulfotransferase enzyme has activity with one or more aryl sulfate compounds (instead of PAPS) as a sulfo group donor, but retains the affinity of the native HS-sulfotransferase enzyme for a particular heparosan-based polysaccharide as a sulfo group acceptor. As a non-limiting example, an engineered 2OST enzyme has sulfotransferase activity with an aryl sulfate compound as a sulfo group donor and N-sulfated heparosan as a sulfo group acceptor. In contrast, natural 2OST enzymes have sulfotransferase activity with PAPS as the sole sulfo group donor and N-sulfated heparosan as a sulfo group acceptor. Each of the engineered sulfotransferase enzymes, including their sequences, structures, and biological activities, are described in further detail below. Methods of synthesizing sulfated heparosan-based polysaccharides in vitro using an engineered sulfotransferase enzyme and an aryl sulfate compound are also described below. In some embodiments of the invention, HS polysaccharides having anticoagulant activity, including those having anticoagulant activity similar or equivalent to heparin, can be synthesized in vitro. In another embodiment, HS polysaccharides produced by any of the methods described herein can have zero anticoagulant activity. 
     Engineered NSTs 
     In nature, HS NDST enzymes have dual N-deacetylase and N-sulfotransferase activity, in which the same enzyme first catalyzes the removal of an N-acetyl group from a glucosamine residue within heparosan, and then catalyzes the transfer of a sulfo group from PAPS to the same glucosamine residue that was N-deacetylated in the first step. The dual N-deacetylase and N-sulfotransferase activity of the enzymes is achieved via two separate structural domains—an N-deacetylase domain and an N-sulfotransferase domain. However, the activity of one of the domains is not a pre-requisite for the activity of the other domain, and recombinant single-domain enzymes comprising either N-deacetylase or N-sulfotransferase activity can be expressed and purified. Similarly, and in an embodiment of the invention, engineered enzymes with NST activity can be expressed and purified as a single N-sulfotransferase domain, without additionally comprising an N-deacetylase domain. 
     Naturally-occurring NDST enzymes that utilize PAPS as the sulfo group donor are members of the EC 2.8.2.8 enzyme class. Generally, the N-deacetylase domain of an NDST enzyme can deacetylate one or more of the N-acetyl glucosamine residues within heparosan to form N-deacetylated heparosan, which can then be recognized as a sulfo group acceptor by the enzyme&#39;s N-sulfotransferase domain. However, the N-sulfotransferase domains of NDST enzymes have been shown to have sulfotransferase activity with N-deacetylated heparosan having one or more disaccharide units comprising the structure of Formula II, below: 
     
       
         
         
             
             
         
       
     
     wherein n is an integer and R is selected from the group consisting of a hydrogen atom or a sulfo group. Further, although the portion of the N-deacetylated heparosan that reacts with the enzyme comprises the structure of Formula II, other glucosamine residues within the polysaccharide can be N-sulfated, N-acetylated, 3-O sulfated, and/or 6-O sulfated, and hexuronyl residues can be glucuronic acid or iduronic acid, either of which can be 2-O sulfated. Typically, N-deacetylated heparosan and other heparosan-based polysaccharides comprising the structure of Formula II comprise at least four disaccharide units, or at least eight sugar residues total. Sulfotransfer reactions in which N-deacetylated heparosan is utilized as the sulfo group acceptor for NDST enzymes are discussed in Sheng, J., et al., (2011)  J. Biol. Chem.  286 (22):19768-76, as well as Gesteira, T. F., et al., (2013)  PLoS One  8 (8):e70880, the disclosures of which are incorporated by reference in their entireties. 
     Upon successfully binding PAPS and N-deacetylated heparosan, the N-sulfotransferase domain of natural NDST enzymes can catalyze transfer of the sulfo group to an unsubstituted glucosamine residue, forming an N-sulfated heparosan product comprising the structure of Formula III, below: 
     
       
         
         
             
             
         
       
     
     wherein n is an integer and R is selected from the group consisting of a hydrogen atom or a sulfo group. 
     In another embodiment, each of the repeating disaccharide units within the N-deacetylated heparosan comprises the structure of Formula II. In another embodiment, both of the R groups at the 6-O position of the glucosaminyl residues and the 2-O position of the glucuronic acid residues are hydrogen atoms, in one or more, including all, of the disaccharide units within the polysaccharide. In another embodiment, in some locations within the polysaccharide, at least a portion of the glucosamine residues are still N-acetylated, as shown in  FIG.  5   , although glucosaminyl residues within the polymer that are N-acetylated cannot directly participate as sulfo group acceptors with the engineered sulfotransferases of the present invention. However, the presence of N-acetylated residues within the polysaccharide does not affect the binding affinity that the engineered sulfotransferases have for non-acetylated glucosamine residues within the same polysaccharide. In another embodiment, regardless of the structure of the heparosan-based polysaccharide, a disaccharide unit comprising the structure of Formula II can be recognized as a sulfo acceptor by an engineered NST enzyme and an aryl sulfate compound to generated an N-sulfated product comprising the structure of Formula III. 
     In another embodiment, when there are multiple disaccharide units within the N-deacetylated heparosan that comprise the structure of Formula II, the glucosamine residue within any of those disaccharide units can be N-sulfated. Similarly, and in another embodiment, within a polysaccharide comprising multiple disaccharide units having the structure of Formula II, a plurality of glucosamine residues can be N-sulfated, including and up to all of the available glucosamine residues within the polysaccharide. 
     The N-sulfotransferase domains of natural NDST enzymes typically comprise approximately 300 to 350 amino acid residues that can vary greatly in their sequence, yet ultimately have the exact same function, namely, to catalyze the N-sulfation of unsubstituted glucosamine residues within N-deacetylated heparosan. Without being limited by a particular theory, it is believed that each of the natural NDST enzymes can catalyze the same chemical reaction because there are multiple amino acid sequence motifs and secondary structures that are either identical or highly conserved across all species. 
     Further, it is believed that several of the conserved amino acid sequence motifs within the natural N-sulfotransferase domains are directly involved in binding of either PAPS and/or the polysaccharide, or participate in the chemical reaction itself. The identity of conserved amino acid sequence motifs can be demonstrated by comparing the amino acid sequence of the N-sulfotransferase domain (SEQ ID NO: 164) of the human NDST enzyme, which has a known crystal structure (PDB code: 1NST) in which amino acid residues within the active site have been identified, alongside the amino acid sequences of the N-sulfotransferase domains of other natural NDST enzymes. A multiple sequence alignment of the amino acid sequences of the N-sulfotransferase domains of fifteen NDST enzymes, including several eukaryotic organisms and several isoforms of the human NDST enzyme, is shown in  FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C , along with percent identity relative to the N-sulfotransferase domain of human NDST1 (UniProtKB Accession No. P52848). As illustrated in  FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C , each amino acid sequence, corresponding to SEQ ID NOs: 164-178, ranges from having 98.4% sequence identity with the P52848 reference sequence (SEQ ID NO: 165, entry sp|Q02353|NDST1_RAT) for the rat N-sulfotransferase domain down to 55.6% sequence identity (SEQ ID NO: 178, entry sp|Q9V3L1|NDST_DROME) for the fruit fly N-sulfotransferase domain. Those skilled in the art would appreciate that the multiple sequence alignment was limited to fifteen sequences for clarity, and that there are hundreds of amino acid sequences encoding for the N-sulfotransferase domains of other wild-type NDST enzymes that have been identified and that have highly conserved active site and/or binding regions as well. 
     Within  FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C , amino acids that are depicted in white with a black background at a particular position, are 100% identical across all sequences. Amino acids that are highly conserved at a particular position, meaning that the amino acids are either identical or chemically or structurally similar, are enclosed with a black outline. Within highly conserved regions, consensus amino acids that are present in a majority of the sequences are in bold. Amino acids at a particular position that are not identical or highly conserved are typically variable. A period within a sequence indicates a gap that has been inserted into the sequence in order to facilitate the sequence alignment with other sequence(s) that have additional residues between highly conserved or identical region. Finally, above each block of sequences are a series of arrows and coils that indicate secondary structure that is conserved across all sequences, based on the identity of the amino acids within the alignment and using the structure of the N-sulfotransferase domain of the human NDST1 enzyme as a reference. The β symbol adjacent to an arrow refers to a β-sheet, whereas a coil adjacent to an α symbol or a η symbol refers to a helix secondary structure. 
     Within the fifteen aligned sequences in  FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C , there are several conserved amino acid motifs that include one or more amino acids that comprise the active site, based on the crystal structure of the N-sulfotransferase domain of human NDST1. These conserved amino acid sequence motifs, based on the numbering of the amino acid residues within  FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C  include residues 40-46 (Q-K-T-G-T-T-A); residues 66-69 (T-F-E-E); residues 101-105 (F-E-K-S-A); residues 139-143 (S-W-Y-Q-H); and residues 255-262 (C-L-G-K/R-S-K-G-R) which correspond to SEQ ID NO: 221, SEQ ID NO: 222, SEQ ID NO: 223, SEQ ID NO: 224, and SEQ ID NO: 225 in the sequence listing, respectively. In further embodiments, some NDST enzymes that comprise the conserved amino acid sequence motif Q-K-T-G-T-T-A (SEQ ID NO: 221) further comprise the conserved amino acids L-Y-L, from residues 47-49. 
     Without being limited by a particular theory, it is believed that these residues either facilitate or participate in the chemical reaction, or enable binding of PAPS or the polysaccharide within the active site. In particular and as illustrated in  FIG.  7 A ,  FIG.  7 B , and  FIG.  7 C , the histidine residue at position 143 of the N-sulfotransferase domain (SEQ ID NO: 164) of the human NDST1 enzyme is in position to abstract one of the two protons within the amine functional group of an unsubstituted glucosaminyl residue, enabling the nitrogen atom to initiate the nucleophilic attack of PAPS and remove the sulfate functional group. Additionally, lysine residues at position 41 and 260 are also universally conserved, and are thought to coordinate with the sulfate moiety, driving binding of PAPS within the active site as well as stabilizing the transition state during the course of the reaction (see Gesteira, T. F., et al., above, as well as Sueyoshi, T., et al., (1998)  FEBS Letters  433:211-214, the disclosure of which is incorporated by reference in its entirety). 
     However, as described above, natural NDST enzymes are unable to catalyze the transfer of the sulfate group from an aryl sulfate compound to the polysaccharide, because it is believed that the binding pocket for PAPS within the natural active site either does not have a high enough affinity for aryl sulfate compounds to facilitate binding and/or that the aryl sulfate compounds are sterically hindered from entering the active site altogether. Consequently, and in another embodiment, the N-sulfotransferase domain of a natural NDST enzyme can be mutated in several locations to enable binding of the aryl sulfate compound within the active site and/or to optimally position the aryl sulfate compound so transfer of the sulfate group to the polysaccharide can occur. 
     Accordingly, and in another embodiment, engineered NST enzymes of the present invention can comprise a single N-sulfotransferase domain that is mutated relative to the N-sulfotransferase domain of any of the natural NDST enzymes within EC 2.8.2.8, including enzymes having the amino acid sequences illustrated in  FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C . In other embodiments, engineered NST enzymes of the present invention can further comprise an N-deacetylase domain that has an identical or mutated amino acid sequence of the N-deacetylase domain of any of the natural NDST enzymes within EC 2.8.2.8. 
     In another embodiment, mutations engineered into the amino acid sequences of the engineered NST enzymes facilitate a biological activity in which aryl sulfate compounds can both bind and react with the enzyme as sulfo group donors. In another embodiment, although the engineered NST enzymes can bind and react with an aryl sulfate compound as a sulfo group donor, they retain the natural NDSTs&#39; biological activity with heparosan-based polysaccharides comprising disaccharide units having the structure of Formula II, including but not limited to N-deacetylated heparosan, as a sulfo group acceptor. Without being limited by a particular theory, it is believed that because of the mutations inserted into the amino acid sequences of the engineered NST enzymes, their sulfotransferase activity may comprise the direct transfer of a sulfo group from an aryl sulfate compound to the sulfo acceptor polysaccharide, using a similar mechanism as described in  FIGS.  7 A- 7 C  above, except that the PAPS is substituted with the aryl sulfate compound. Otherwise, it is believed that the mutations may cause the sulfotransferase activity to comprise a two-step process including the hydrolysis of an aryl sulfate compound and formation of a sulfohistidine intermediate, followed by the nucleophilic attack of the sulfohistidine intermediate by an N-unsubstituted glucosamine within N-deacetylated heparosan to form the N-sulfated product. By either mechanism, the engineered NST enzymes are able to achieve sulfo transfer from an aryl sulfate compound to a heparosan-based polysaccharide, as described in the examples, below. 
     In another embodiment, an engineered NST enzyme can comprise one or more mutated amino acid sequence motifs relative to the conserved amino acid sequence motifs, corresponding to SEQ ID NOs 221-225, which are found in the N-sulfotransferase domains of natural NDSTs, as described above and indicated in the multiple sequence alignment in  FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C . In another embodiment, each mutated amino acid sequence motif that is present in the amino acid sequence of the engineered NST enzyme comprises at least one amino acid mutation relative to the corresponding conserved amino acid sequence motif within the N-sulfotransferase domains of natural NDST enzymes within EC 2.8.2.8. In another embodiment, an engineered NST enzyme comprises one mutated amino acid sequence motif. In another embodiment, an engineered NST enzyme comprises two mutated amino acid sequence motifs. In another embodiment, an engineered NST enzyme comprises three mutated amino acid sequence motifs. In another embodiment, an engineered NST enzyme comprises four mutated amino acid sequence motifs. In another embodiment, an engineered NST enzyme comprises five mutated amino acid sequence motifs. In another embodiment, an engineered NST enzyme that includes at least one mutated amino acid sequence motif can have an amino acid sequence selected from the group consisting of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, and SEQ ID NO: 25. 
     In another embodiment, upon viewing the crystal structure of the N-sulfotransferase domain of the human NDST1 (PDB code: 1NST) within a 3D molecular visualization system (including, as a non-limiting example, the open-source software, PyMOL), the structure of related sequences, such as those of engineered NST enzymes that contain one or more amino acid sequence motifs that are mutated relative to the human NDST1 N-sulfotransferase domain (SEQ ID NO: 164), can be modeled for comparison as illustrated in  FIGS.  8 - 11   . In one non-limiting example,  FIG.  8    shows a magnified view of the active site of the human NDST1 N-sulfotransferase domain that is overlaid with an engineered NST enzyme comprising the amino acid sequence of SEQ ID NO: 13, in which the structure of the engineered enzyme is calculated upon making mutations relative to the human N-sulfotransferase domain amino acid sequence. Adenosine 3′,5′-diphosphate, which is the product of a sulfotransfer reaction in which PAPS is the sulfo donor, and which was co-crystallized with the NDST1 N-sulfotransferase domain, is also illustrated within the active site. PNS is also modeled into the engineered enzyme active site, using the consensus solutions of molecular dynamics (MID) simulations that designed to calculate the optimized position and orientation of a ligand within an enzyme active site adjacent to the polysaccharide binding site (not shown), if such solutions are possible. 
     As illustrated in  FIG.  8   , although there are several mutations within SEQ ID NO: 13 made relative to sequence of the human NDST1 N-sulfotransferase domain (SEQ ID NO: 164, UniProtKB Accession No. P52848) indicated in  FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C , the respective protein backbones are in a nearly identical location to one another, enabling a one-to-one comparison of the active sites. Within the structure of the engineered enzyme comprising the sequence of SEQ ID NO: 13, the consensus solutions from MD simulations indicate that the sulfate moiety within PNS is favored to bind adjacent to a histidine residue, His-45, that has been mutated relative to the natural threonine residue at that position, which is universally conserved within EC 2.8.2.8. On the other hand, within the human NDST1 N-sulfotransferase domain, the adenosine 3′,5′-diphosphate is located near to the conserved His-143, described above. Although the sulfo group that would be comprised within the PAPS substrate is not shown, those skilled in the art would appreciate that if PAPS were present, the sulfate group would be oriented in a position immediately adjacent to His-143 and partially overlapping with the sulfate group within PNS. Without being limited by a particular theory, it is believed that the nearly overlapping location of the sulfate groups accounts for the engineered enzyme&#39;s ability to facilitate sulfo group transfer by using His-143 as a base to remove the proton from the glucosaminyl residue within the polysaccharide. 
     However, even though the sulfate groups appear to bind in a nearly identical location within the active site, aryl sulfate compounds cannot be utilized with natural NDST enzymes to facilitate sulfo group transfer to a polysaccharide. As described above, the amino acid residues within the active site of the natural sulfotransferases are evolved to have strong binding affinity for PAPS, and without being limited by a particular theory, it is believed that the enzymes likely do not have enough affinity for aryl sulfate compounds to drive binding and sulfotransferase activity. Consequently, it is believed that other mutations can assist to drive binding of aryl sulfate compounds within the active site.  FIG.  9    illustrates other mutations that surround PNS within the engineered enzyme comprising the amino acid sequence of SEQ ID NO: 13, including Trp-106, His-69, and His-40. PNS carbon atoms are positioned between Trp-106 and His-69, and appear to provide π-π stacking binding contacts with both amino acid side chains. Additionally, the ε2 nitrogen atoms within His-69 and His-40 appear to coordinate with the sulfuryl group of PNS directly. Lysine residues retained from the natural enzyme sequence, Lys-41 (not shown, for clarity) and Lys-103 appear to be in position to coordinate with the sulfate group during transfer in order to stabilize the transition state. Of note, the natural amino acid residue, Lys-260, which also coordinates with the sulfate group in PAPS, is mutated to a valine residue within the engineered enzyme sequence. Without being limited by a particular theory, it is believed that His-45, which is necessary for the reaction with PNS, would exhibit charge repulsion with a lysine residue at position 260, and that the mutation to a valine residue retains some steric bulk within the binding site while eliminating the charge repulsion. Lys-103 is nonetheless positioned to coordinate with the sulfuryl group, particularly when the sulfuryl group is associated or bound to His-45, as shown in  FIG.  9   . 
     In another non-limiting example,  FIG.  10    shows a magnified view of the active site of the N-sulfotransferase domain of human NDST1 (SEQ ID NO: 164,_UniProtKB Accession No. P52848) overlaid with a different engineered NST enzyme, comprising the amino acid sequence of SEQ ID NO: 5. PNS is modeled into the engineered enzyme active site, as described above. As with the engineered enzyme comprising the amino acid sequence SEQ ID NO: 13, the protein backbone of the engineered enzyme comprising the amino acid sequence of SEQ ID NO: 5 also has a nearly identical structure to the N-sulfotransferase domain of the human enzyme. However, the consensus solutions from MD simulations indicate that the sulfate moiety within PNS is favored to bind adjacent to a different histidine mutation (His-49), which is mutated from a leucine residue that is conserved within the active site of the natural NDST enzymes. Consequently, mutations within SEQ ID NO: 13 that formed binding contacts with PNS are not necessarily present in SEQ ID NO: 5. As illustrated in  FIG.  11    and similar to SEQ ID NO: 13, there are two mutations present within SEQ ID NO: 5 that appear to form π-π stacking binding contacts surrounding the aromatic moiety of PNS, Trp-45 and His-67. Other mutations that comprise side chains that appear to coordinate with PNS include Ser-69 (coordinating with the nitro functional group of PNS) and His-260 (coordinating with the sulfate moiety). Similar to SEQ ID NO: 13, because the natural lysine residue at position 260 is mutated, the natural Lys-103 residue is utilized within SEQ ID NO: 5 to coordinate with the sulfate moiety within PNS. 
     Those skilled in the art would appreciate that engineered NST enzymes of any other amino acid sequence, including, but not limited to, those described by SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 15, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, and SEQ ID NO: 25, would likely exhibit a similar structure to the N-sulfotransferase domain of human NDST1 and engineered NST enzymes having the amino acid sequence of SEQ ID NO: 5 and SEQ ID NO: 13. Without being limited by a particular theory, it is also believed that NCS would bind in a similar position as PNS within the active site of any of the engineered NST enzymes, since the structures of the two aryl sulfate compounds are very similar, except that the sulfate group is located ortho on the aromatic ring relative to the nitro group, rather than para to the nitro group. 
     Further, the engineered NST enzymes of the present invention can include mutated amino acid sequence motifs that comprise one or more of the above-described mutations as well as other mutations that facilitate binding of substrates, the sulfotransfer reaction, or the stability of the enzyme during protein expression. In another embodiment, an engineered NST enzyme can include the mutated amino acid sequence motif, X 1 -K-T-G-A-W/F-A/L-L-X 2 -H (SEQ ID NO: 278), mutated from the conserved amino acid sequence Q-K-T-G-T-T-A-L-Y-L (SEQ ID NO: 277) within natural NDST enzymes, wherein X 1  is selected from the group consisting of glutamine, serine, and alanine; and X 2  is selected from the group consisting of tyrosine, threonine, and histidine. Engineered NST enzymes that include the mutated amino acid sequence motif X 1 -K-T-G-A-W/F-A/L-L-X 2 -H (SEQ ID NO: 278) include, but are not limited to SEQ ID NO: 5 (described above), as well as SEQ ID NO: 7, SEQ ID NO: 15; SEQ ID NO: 18, SEQ ID NO: 20, SEQ ID NO: 21, and SEQ ID NO: 25. In further embodiments, engineered NST enzymes can further include the mutated amino acid sequence motif, T-X 3 -X 4 —S(SEQ ID NO: 279), mutated from the conserved amino acid sequence T-F-E-E (SEQ ID NO: 222), wherein X 3  is a mutation selected from the group consisting of histidine and glycine; X 4  is a mutation selected from the group consisting of glycine, histidine, and serine; and wherein at least one of X 3  and X 4  is a histidine residue. In some even further embodiments, X 1  is glutamine and X 2  is tyrosine (SEQ ID NO: 280), X 3  is histidine and X 4  is glycine (SEQ ID NO: 237), and the engineered NST enzyme further comprises the mutated amino acid sequence motif, C-L-G-K/R-S-H-G-R (SEQ ID NO: 281). In other even further embodiments, X 1  is serine and X 2  is threonine (SEQ ID NO: 282), X 3  is glycine and X 4  is histidine (SEQ ID NO: 238), and the engineered NST enzyme further comprises the mutated amino acid sequence motif, C-H-G-K/R-R-W-G-R (SEQ ID NO: 283). In sill other even further embodiments, X 1  is alanine and X 2  is histidine (SEQ ID NO: 284), X 3  is histidine and X 4  is serine (SEQ ID NO: 285), and the engineered NST enzyme further comprises the mutated amino acid sequence motif, C-A-H-K/R-G-L-G-R (SEQ ID NO: 286). 
     In another embodiment, engineered NST enzymes can include the mutated amino acid sequence motif, H-X 5 -T-G-X 6 -H-A (SEQ ID NO: 226), mutated from the conserved amino acid sequence Q-K-T-G-T-T-A (SEQ ID NO: 221), wherein X 5  is selected from the group consisting of lysine and glycine; and X 6  is a mutation selected from the group consisting of glycine and valine. Engineered NST enzymes that include the mutated amino acid sequence motif H-X 5 -T-G-X 6 -H-A (SEQ ID NO: 226) include, but are not limited to SEQ ID NO: 13 (described above), as well as SEQ ID NO: 9, SEQ ID NO: 11; SEQ ID NO: 19, SEQ ID NO: 22, SEQ ID NO: 23, and SEQ ID NO: 24. In further embodiments, X 5  is glycine and X 6  is glycine (SEQ ID NO: 227). In some even further embodiments, the engineered NST enzyme further comprises the mutated amino acid sequence motif, C-G-G-K/R-H-L-G-R (SEQ ID NO: 287). In other even further embodiments, the engineered NST enzyme further comprises the mutated amino acid sequence motif, F-E-H-S-G (SEQ ID NO: 288). 
     In another embodiment, within any of the engineered NST enzymes that include the mutated amino acid sequence motif, H-X 5 -T-G-X 6 -H-A (SEQ ID NO: 226), X 5  is selected to be lysine and X 6  is selected to be valine (SEQ ID NO: 228), and the engineered NST enzyme further comprises the mutated amino acid sequence motif, T-G-N-H (SEQ ID NO: 289). 
     Furthermore, the amino acid sequences (SEQ ID NO: 5, SEQ ID NO: 7 SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15) of six engineered NST enzymes, which have been experimentally determined to be active with aryl sulfate compounds as sulfo group donors (see Example 3 below) can be compared with the amino acid sequence of the N-sulfotransferase domain of the human NDST1 enzyme (SEQ ID NO: 164, entry sp|P52848|NDST1_HUMAN) in a multiple sequence alignment to determine if there are relationships between mutations among each of the enzymes. Within the multiple sequence alignment, a period within the amino acid sequence of an engineered enzyme indicates identity at a particular position with the N-sulfotransferase domain of human NDST1. As shown in  FIG.  12   , the sequence alignment demonstrates that while over 90% of the amino acid residues within the six sulfotransferase sequences are identical, there are several positions in which multiple amino acids can be chosen. Without being limited by a particular theory, these enzymes appear to have a similar relationship with each other as the N-sulfotransferase domains of the NDST enzymes that comprise EC 2.8.2.8. As a result, and in another embodiment, engineered NST enzymes comprising an amino acid sequence in which multiple amino acids can be chosen at defined positions are disclosed as SEQ ID NO: 18 and SEQ ID NO: 19. Positions at which the identity of an amino acid can be chosen from a selection of possible residues are denoted in terms “Xaa,” “Xn,” or “position n,” where n refers to the residue position. 
     In another embodiment, within an engineered NST enzyme comprising the amino acid sequence of SEQ ID NO: 18 or SEQ ID NO: 19, the amino acid residue at position 41 is lysine, the amino acid residue at position 44 is alanine, the amino acid residue at position 45 is an aromatic amino acid residue, preferably tyrosine or phenylalanine, and the amino acid residue at position 49 is histidine. In another embodiment, when the engineered NST enzyme comprises the above residues from positions 41-49, the amino acid residue at position 67 is glycine or histidine, the amino acid residue at position 68 is selected from the group consisting of glycine, histidine, and serine, and the amino acid residue at position 69 is serine. 
     In another embodiment, within an engineered NST enzyme comprising the amino acid sequence of SEQ ID NO: 18 or SEQ ID NO: 19, the amino acid residue at position 40 is histidine and the amino acid residue at position 45 is histidine. In further embodiments, the amino acid residue at position 41 is glycine and the amino acid residue at position 44 is glycine. In other further embodiments, the amino acid residue at position 41 is lysine and the amino acid residue at position 44 is valine. In even further embodiments, the amino acid residue at position 67 is glycine and the amino acid residue at position 69 is histidine. In still further embodiments, the amino acid residue at position 106 is tryptophan. In even still further embodiments, the amino acid residue at position 260 is valine. 
     In another embodiment, within an engineered NST enzyme comprising the amino acid sequence of SEQ ID NO: 18 or SEQ ID NO: 19, the amino acid sequence can optionally include one or more mutations at residue positions not specified by an “Xn” or “Xaa,” so long as any such mutations do not eliminate the NST and/or aryl sulfate-dependent activity of the enzyme. In another embodiment, such mutations not eliminating aryl sulfate-dependent activity at positions not specified by an “Xn” or “Xaa” can include substitutions, deletions, and/or additions. 
     Accordingly, in another embodiment, an engineered NST enzyme utilized in accordance with any of the methods of the present invention can comprise an amino acid sequence selected from the group consisting of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, and SEQ ID NO: 25. In another embodiment, engineered NST enzymes comprising the amino acid sequence of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, or SEQ ID NO: 25 can react with any aryl sulfate compound. In further embodiments, the aryl sulfate compound is selected from the group consisting of PNS, MUS, 7-hydroxycoumarin sulfate, phenyl sulfate, 4-acetylphenyl sulfate, indoxyl sulfate, 1-naphthyl sulfate, 2NapS, and NCS. In some even further embodiments, the aryl sulfate compound is PNS. In other even further embodiments, the aryl sulfate compound is NCS. 
     Engineered 2OSTs 
     In nature, 2OSTs recognize, bind, and react with N-sulfated heparosan polysaccharides as sulfo group acceptors. Within the N-sulfated heparosan, a majority of the glucosaminyl residues are generally N-sulfated, and the sulfo group is transferred to the 2-O position of a hexuronic acid residue, generally glucuronic acid or iduronic acid. As with the natural NDST enzymes described above, natural 2OSTs transfer the sulfo group to the polysaccharide upon reacting with PAPS as a sulfo group donor. However, natural 2OSTs are members of the EC 2.8.2.—enzyme class. N-sulfated heparosan that react with natural 2OST enzymes as sulfo group acceptors typically comprise at least one of two distinct structural motifs. In a first non-limiting example, natural 2OST enzymes can recognize, bind, and react with N-sulfated heparosan having the structure of Formula IV, below: 
     
       
         
         
             
             
         
       
     
     In another non-limiting example, natural 2OST enzymes can recognize, bind, and react with N-sulfated heparosan having the structure of Formula V, below: 
     
       
         
         
             
             
         
       
     
     In both instances, the hexuronic acid residue (glucuronic acid in Formula IV, iduronic acid in Formula V) is flanked on either side by N-sulfated glucosamine residues that are otherwise unsubstituted at the 3-O and 6-O positions. Natural 2OST enzymes, and their biological activity with polysaccharides comprising the structures of Formula IV or Formula V, have been described by Rong, J., et al., (2001)  Biochemistry  40 (18):5548-5555, the disclosure of which is incorporated by reference in its entirety. 
     As described above, although the portion of the N-sulfated heparosan comprising the structure of Formula IV or Formula V contains N-sulfated glucosamine residues, other glucosamine residues within the polysaccharide can be N-sulfated, N-acetylated, 3-O sulfated, and/or 6-O sulfated, and hexuronyl residues can be glucuronic acid or iduronic acid, either of which can be 2-O sulfated. Similarly, heparosan-based polysaccharides can comprise one or more structural motifs comprising the structure of Formula IV and/or the structure of Formula V within the same polysaccharide, any of which can be 2-O sulfated by the same enzyme. Typically, N-sulfated heparosan capable of reacting with 2OST comprises at least eight monosaccharide residues. In another embodiment, the engineered 2OSTs of the present invention have identical preference as natural 2OSTs for N-sulfated heparosan as a sulfo group acceptor, particularly N-sulfated heparosan comprising the structure(s) of Formula IV and/or Formula V. 
     The stereochemistry of the hexuronic acid residue in N-sulfated heparosan comprising the structure of Formula IV or Formula V can be controlled by the presence of a glucuronyl C 5 -epimerase, which reversibly inverts the stereochemistry of the C 5 -carbon of hexuronic acid residues. However, once the hexuronyl residue within a polysaccharide comprising the structure of Formula IV or Formula V is 2-O sulfated, the hexuronic acid residue can no longer be epimerized. Generally, N-sulfated heparosan that can react with a 2OST in vivo are almost exclusively synthesized as disaccharide units of N-sulfoglucosamine and glucuronic acid. One or more of these glucuronic acid residues are often epimerized to an iduronic acid residue prior to reacting with the 2OST enzyme to form 2-O sulfated iduronic acid residues. However, and without being limited by a particular theory, it is believed that natural 2OST enzymes generally have preference for binding and reacting with N-sulfated heparosan comprising the structure of Formula V, and that most N,2O-HS polysaccharides produced in vivo generally comprise 2-O sulfated iduronic acid. 
     Upon successfully binding PAPS and N-sulfated heparosan comprising the structure of Formula IV, natural 2OST enzymes can catalyze transfer of the sulfo group to the 2-O position of a glucuronic acid residue, forming an N,2O-HS product comprising the structure of Formula VI, below: 
     
       
         
         
             
             
         
       
     
     Upon successfully binding PAPS and N-sulfated heparosan comprising the structure of Formula V, natural 2OST can catalyze transfer of the sulfo group to the 2-O position of an iduronic acid residue, forming an N,2O-HS product comprising the structure of Formula VII, below: 
     
       
         
         
             
             
         
       
     
     In another embodiment, in order to be 2-O sulfated, a glucuronic acid or iduronic acid residue must be adjacent to two N-sulfated glucosamine residues, as shown in Formula IV and Formula V. A non-limiting example of one such polysaccharide is illustrated in  FIG.  13   . In  FIG.  13   , hexuronyl residues 10 within polysaccharide 40 are flanked by glucosaminyl residues 20, 21, and 22, that are either N-sulfated, N-acetylated, or unsubstituted, respectively. In another embodiment, upon reacting the polysaccharide 40 with an engineered 2OST, only the hexuronyl residue 10 flanked by two N-sulfated glucosamine residues 20 can be 2-O sulfated, ultimately forming a 2-O sulfated hexuronyl residue 110 within the product polysaccharide 41. 
     In another non-limiting example, portions of N-sulfated heparosan comprising the structures of Formula IV and Formula V are illustrated by polysaccharide 50 in each of  FIG.  14   ,  FIG.  15   , and  FIG.  16   . In  FIG.  14   ,  FIG.  15   , and  FIG.  16   , a hexuronyl residue 10 and an epimerized hexuronyl residue 30 are alternated between three N-sulfoglucosaminyl residues 20 within polysaccharide 50. Although hexuronyl residues 10 and 30 are represented in a chair conformation, those skilled in the art can appreciate that such monosaccharide residues within a longer oligo- or polysaccharide chain can adopt several different conformations, including chair, half-chair, boat, skew, and skew boat conformations, and that those additional conformations are omitted for clarity. 
     In another embodiment, upon reacting polysaccharide 50 with an engineered aryl sulfate-dependent 2OST enzyme, the enzyme can catalyze sulfo group transfer to hexuronyl residue 10 to form a sulfated hexuronyl residue 110 within product polysaccharide 51 ( FIG.  14   ), to epimerized hexuronyl residue 30 to form a sulfated epimerized hexuronyl residue 130 within product polysaccharide 52 ( FIG.  15   ), or to both hexuronyl residue 10 and epimerized hexuronyl residue 30 to form a sulfated hexuronyl residue 110 and a sulfated epimerized hexuronyl residue 130, respectively, within product polysaccharide 53 ( FIG.  16   ). 
     Natural 2OSTs generally comprise approximately 325-375 amino acid residues that in some cases vary greatly in their sequence, yet ultimately have the exact same function, namely, to catalyze the transfer of a sulfo group from PAPS to the 2-O position of hexuronyl residues within N-sulfated heparosan. Without being limited by a particular theory, it is believed that each of the natural 2OSTs can catalyze the same chemical reaction because there are multiple amino acid sequence motifs and secondary structures, particularly in region(s) that define their active sites, that are either identical or highly conserved across all species. 
     Further, it is believed that several of the conserved amino acid sequence motifs are directly involved in binding of either PAPS and/or the polysaccharide, or participate in the chemical reaction itself. The identity between the natural 2OST enzymes can be demonstrated by comparing the amino acid sequence of the chicken 2OST (SEQ ID NO: 179), which has known crystal structures (PDB codes: 3F5F and 4NDZ) in which amino acid residues within the active site have been identified, alongside the amino acid sequences of other natural 2OSTs within EC 2.8.2.—. A multiple sequence alignment of twelve enzymes, including the chicken, human, and other eukaryotic 2OST enzymes (SEQ ID NOs 179-190), is shown in  FIG.  17 A ,  FIG.  17 B ,  FIG.  17 C , and  FIG.  17 D , along with percent identity relative to the chicken 2OST reference sequence (SEQ ID NO: 179, UniProtKB Accession No. Q76KB1). As illustrated in  FIG.  17 A ,  FIG.  17 B ,  FIG.  17 C , and  FIG.  17 D , sequences range from having 94.9% sequence identity with the Q76KB1 reference sequence (SEQ ID NO: 188, entry tr|T1DMV2|T1DMV2_CROHD) for the timber rattlesnake 2OST, down to 56.3% sequence identity (SEQ ID NO: 180, entry tr|A0A131Z2T4|A0A131Z2T4_RHIAP) for the brown ear tick 2OST. The human enzyme (SEQ ID NO: 186, entry sp|Q7LGA3|HS2ST_HUMAN) has 94.1% sequence identity with the Q76KB1 reference sequence. Those skilled in the art would appreciate that the multiple sequence alignment was limited to twelve sequences for clarity, and that there are hundreds of amino acid sequences encoding for natural 2OST enzymes that have been identified and that have highly conserved active site and/or binding regions as well. 
     Within  FIG.  17 A ,  FIG.  17 B ,  FIG.  17 C , and  FIG.  17 D , amino acids that are depicted in white with a black background at a particular position, are 100% identical across all sequences. Amino acids that are highly conserved, meaning that the amino acids are either identical, or chemically or structurally similar, at a particular position are enclosed with a black outline. Within highly conserved regions, consensus amino acids that are present in a majority of the sequences are in bold. Amino acids at a particular position that are not identical or highly conserved are typically variable. A period within a sequence indicates a gap that has been inserted into the sequence in order to facilitate the sequence alignment with other sequence(s) that have additional residues between highly conserved or identical region. Finally, above each block of sequences are a series of arrows and coils that indicate secondary structure that is conserved across all sequences, based on the identity of the amino acids within the alignment and using the structure of the natural chicken HS 2OST enzyme as a reference. The β symbol adjacent to an arrow refers to a β-sheet, whereas a coil adjacent to an a symbol or a η symbol refers to a helix secondary structure. 
     Within the twelve aligned sequences in  FIG.  17 A ,  FIG.  17 B ,  FIG.  17 C , and  FIG.  17 D , there are several conserved amino acid motifs that include one or more amino acids that comprise the active site, based on the crystal structures of the chicken 2OST enzyme described above. Based on the numbering of the amino acid residues within  FIG.  17 A ,  FIG.  17 B ,  FIG.  17 C , and  FIG.  17 D , these motifs include residues 12-19 (R-V-P-K-T-A/G-S-T), residues 40-44 (N-T-S/T-K-N), residues 71-74 (Y-H-G-H), residues 108-115 (F-L-R-F/H-G-D-D/N-F/Y), residues 121-125 (R-R-K/R-Q-G), and residues 217-222 (S-H-L-R-K/R-T), which correspond to SEQ ID NO: 244, SEQ ID NO: 273, SEQ ID NO: 274, SEQ ID NO: 245, SEQ ID NO: 246, and SEQ ID NO: 247 in the sequence listing, respectively. Without being limited by a particular theory, it is believed that these residues either facilitate or participate in the chemical reaction, or enable binding of PAPS or the polysaccharide within the active site. In particular and as illustrated in  FIG.  18 A ,  FIG.  18 B , and  FIG.  18 C , the histidine residue at position 74 abstracts the proton from the 2-O position of the iduronic acid residue within the polysaccharide, enabling nucleophilic attack and removal of the sulfo group from PAPS, whereas the lysine residue at position 15 coordinates with the phosphate moiety of PAPS to stabilize the transition state of the enzyme before the N,2O-HS product is released from the active site. 
     However, as described above, the natural 2OST enzymes within EC 2.8.2.—are unable to catalyze the transfer of the sulfate group from an aryl sulfate compound to the polysaccharide. As with the natural NDST enzymes, it is believed that the binding pocket for PAPS within the active site of the natural sulfotransferase either does not have a high enough affinity for aryl sulfate compounds to facilitate binding and/or that the aryl sulfate compounds are sterically hindered from entering the active site altogether. Consequently, and in another embodiment, any natural 2OST enzyme can be selected and mutated in several locations within its amino acid sequence to enable binding of the aryl sulfate compound within the active site and/or to optimally position the aryl sulfate compound so transfer of the sulfate group to the polysaccharide can occur. 
     Accordingly, and in another embodiment, the engineered 2OST enzymes of the present invention can be mutants of natural 2OST enzymes within EC 2.8.2.—, including enzymes having the amino acid sequences illustrated in  FIG.  17 A ,  FIG.  17 B ,  FIG.  17 C , and  FIG.  17 D  (SEQ ID NOs 179-190). In another embodiment, mutations engineered into the amino acid sequences of the engineered 2OSTs facilitate a biological activity in which aryl sulfate compounds can both bind and react with the enzyme as sulfo group donors. In another embodiment, although the engineered 2OSTs can bind and react with an aryl sulfate compound as a sulfo group donor, they can retain the natural 2OST enzymes&#39; biological activity with N-sulfated heparosan as a sulfo group acceptor. Without being limited by a particular theory, it is believed that because of the mutations inserted into the amino acid sequences of the engineered 2OST enzymes, their sulfotransferase activity may comprise the direct transfer of a sulfuryl group from an aryl sulfate compound to the heparosan-based polysaccharide, using a similar mechanism as described in Figured  18 A- 18 C above, except that the PAPS is substituted with the aryl sulfate compound. Otherwise, it is believed that the mutations may cause the sulfotransferase activity to comprise a two-step process including the hydrolysis of an aryl sulfate compound and formation of a sulfohistidine intermediate, followed by the nucleophilic attack of the sulfohistidine intermediate by the oxygen atom at the 2-O position of a hexuronic acid residue, to form the N,2O-HS product. By either mechanism, engineered 2OST enzymes are able to achieve sulfo transfer from an aryl sulfate compound to a heparosan-based polysaccharide, as described in the examples, below. 
     In another embodiment, an engineered 2OST enzyme can comprise one or more mutated amino acid sequence motifs relative to the conserved amino acid sequence motifs that are found in the natural 2OST enzymes within EC 2.8.2.—, as described above and indicated in the multiple sequence alignment in  FIG.  17 A ,  FIG.  17 B ,  FIG.  17 C , and  FIG.  17 D . In another embodiment, each mutated amino acid sequence motif that is present in the amino acid sequence of the engineered enzyme comprises at least one amino acid mutation relative to the corresponding conserved amino acid sequence motif within the natural 2OST enzymes. In another embodiment, an engineered 2OST enzyme can comprise one mutated amino acid sequence motif. In another embodiment, an engineered 2OST enzyme can comprise two mutated amino acid sequence motifs. In another embodiment, an engineered 2OST enzyme can comprise three mutated amino acid sequence motifs. In another embodiment, an engineered 2OST enzyme can comprise four mutated amino acid sequence motifs. In another embodiment, an engineered 2OST enzyme can comprise five mutated amino acid sequence motifs. In another embodiment, an engineered 2OST enzyme can comprise six mutated amino acid sequence motifs. In another embodiment, an engineered 2OST enzyme that includes at least one mutated amino acid sequence motif relative to any of the natural enzymes within EC 2.8.2.—can have an amino acid sequence selected from the group consisting of SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 68, and SEQ ID NO: 69. 
     In another embodiment, upon viewing a crystal structure of the chicken 2OST (PDB code: 3F5F) within a 3D molecular visualization system (including, as a non-limiting example, the open-source software, PyMOL), the structure of related sequences, such as those of engineered 2OST enzymes that contain one or more mutated amino acid sequence motifs relative to the chicken 2OST amino acid sequence (SEQ ID NO: 179), can be modeled for comparison as illustrated in  FIG.  19   .  FIG.  19    shows a magnified view of the active site of the chicken 2OST enzyme overlaid with the modeled active sites of two engineered 2OST enzymes, comprising the amino acid sequences of SEQ ID NO: 63 and SEQ ID NO: 65, in which the structure of the engineered enzyme is calculated upon making mutations relative to the chicken 2OST amino acid sequence. Adenosine 3′,5′-diphosphate, which is the product of a sulfotransfer reaction in which PAPS is the sulfo donor, and which was co-crystallized with the chicken 2OST, is also illustrated within the active site. The sulfate group that would be present in the natural substrate, PAPS, is modeled onto the 5′-phosphate functional group to illustrate its approximate position within the active site prior to initiating the reaction. NCS is also modeled into the active site of the engineered enzymes, using the consensus solutions of molecular dynamics (MD) simulations that designed to calculate the optimized position and orientation of a ligand within an enzyme active site adjacent to the polysaccharide binding site (not shown), if such solutions are possible. Hydrogen atoms are not shown. 
     As illustrated in  FIG.  19   , although there are several mutations made to SEQ ID NO: 63 and SEQ ID NO: 65, relative to the chicken 2OST, the respective protein backbones appear to be in a nearly identical location to one another, enabling a one-to-one comparison of the active sites. When comparing the models of the two active sites, PAPS is located in the background and adjacent to a lysine residue (position 15 of SEQ ID NO: 179), whereas the convergent solutions from the above MD simulations indicate that binding of NCS appears to be favored on the opposite side of the active site. However, binding of NCS would be sterically hindered in the natural 2OST enzyme in part by the lysine residue as well as the phenylalanine residue located on the nearby a-helix (position 108 of SEQ ID NO: 179). Without being limited by a particular theory, it is believed that binding of NCS in the active site of the engineered enzyme comprising the amino acid sequence of SEQ ID NO: 63 is facilitated by the mutation of the lys-15 residue to a histidine residue, which creates additional space within the active site and provides a π-π stacking partner for the aromatic ring within NCS. Also without being limited by a particular theory, it is believed that binding of NCS in the active site of the engineered enzyme comprising the amino acid sequence of SEQ ID NO: 65 is facilitated by the mutation of the lys-15 to an arginine residue in concert with the adjacent mutation of the proline residue (position 14 of SEQ ID NO: 179) to a histidine residue. The increased number of conformational degrees of freedom of the arginine side chain appears to facilitate entry of the NCS while still being in a position to provide a polar contact to stabilize the transition state during the transfer reaction, while the adjacent histidine appears to provide additional binding contacts for NCS. 
     Another mutation of note includes the mutation from an arginine residue (position 220 of SEQ ID NO: 179) to a histidine residue, a mutation that is found at position 221 in both SEQ ID NO: 63 and SEQ ID NO: 65. Without being limited by a particular theory, it is believed that the mutated histidine residue appears to be in a favorable position to facilitate removal of the sulfate group from NCS. Other illustrated mutations from the chicken 2OST enzyme amino acid sequence (SEQ ID NO: 179), particularly mutations present in SEQ ID NO: 65 (His-20, Ser-114, Lys-116, Met-122) may similarly drive binding of NCS within the active site, either by providing a direct binding contact with the sulfate moiety within NCS (His-20), coordinating with other mutated residues (Ser-114 coordinating with His-221), or by increasing the hydrophobic environment near NCS (Met-122). 
     Those skilled in the art would appreciate that engineered 2OST enzymes of any other amino acid sequence, including, but not limited to, those disclosed by SEQ ID NO: 68 and SEQ ID NO: 69, would likely exhibit a similar structure to the chicken 2OST, as well as engineered 2OSTs having the amino acid sequence of SEQ ID NO: 63 and SEQ ID NO: 65. Without being limited by a particular theory, it is believed that PNS would bind in a similar position as NCS within the active site of any of the engineered 2OST enzymes, since the structures of the two aryl sulfate compounds are very similar, except that the sulfate group is located ortho on the aromatic ring relative to the nitro group in NCS, rather than para to the nitro group in PNS. 
     Accordingly, in another embodiment, an engineered 2OST enzyme of the present invention can comprise an amino acid sequence selected from the group consisting of SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 68, and SEQ ID NO: 69. In another embodiment, engineered 2OST enzymes comprising the amino acid sequence of SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 68, or SEQ ID NO: 69 can react with any aryl sulfate compound. In further embodiments, the aryl sulfate compound is selected from the group consisting of PNS, MUS, 7-hydroxycoumarin sulfate, phenyl sulfate, 4-acetylphenyl sulfate, indoxyl sulfate, 1-naphthyl sulfate, 2-naphthyl sulfate, and NCS. In some even further embodiments, the aryl sulfate compound is PNS. In other even further embodiments, the aryl sulfate compound is NCS. 
     In another embodiment, within reaction mixtures that comprise any natural or engineered 2OST enzyme, particularly an engineered 2OST enzyme comprising the amino acid sequence of SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 68, or SEQ ID NO: 69, the reaction mixture can further comprise a glucuronyl C 5 -epimerase to catalyze formation of an N,2O-HS product. In some embodiments, the N,2O-HS product can comprise the structure of Formula VI. In other embodiments, the N,2O-HS product can comprise the structure of Formula VII. In another embodiment, the glucuronyl C 5 -epimerase can comprise the amino acid sequence of SEQ ID NO: 67. In another embodiment, the glucuronyl C 5 -epimerase can comprise residues 34-617 of SEQ ID NO: 67. 
     Engineered 6OSTs 
     In nature, 6OSTs generally recognize, bind, and react with N-, 2-O sulfated heparosan-based polysaccharides (N,2O-HS) as sulfo group acceptors. Additionally, either adjacent hexuronic acid residue can be either glucuronic acid or iduronic acid, and can optionally be 2-O sulfated. Typically, the hexuronic acid at the non-reducing end of the glucosamine residue receiving the 6-O sulfo group is 2-O sulfated iduronic acid, and in many instances, the glucosamine residue itself is also N-sulfated. Similar to the natural NDST and 2OST enzymes, natural 6OST enzymes transfer the sulfo group to the polysaccharide upon reacting with PAPS as a sulfo group donor. As with wild-type 2OSTs, natural 6OST enzymes are also members of the EC 2.8.2.—enzyme class. In a non-limiting example, natural 6OST enzymes can recognize, bind, and react with N,2O-HS polysaccharides comprising the structure of Formula VIII, below: 
     
       
         
         
             
             
         
       
     
     wherein the glucosamine residue receiving the 6-O sulfo group is N-sulfated and is adjacent to a 2-O sulfated iduronic acid residue at its non-reducing end, and X comprises any of the hexuronyl residues depicted in Formula VIII, above. Natural 6OST enzymes having biological activity with N,2O-HS, including but not limited to those comprising the structure of Formula VIII, have been described by Xu, Y., et al., (2017)  ACS Chem. Biol.  12 (1):73-82 and Holmborn, K., et al., (2004)  J. Biol. Chem.  279, (41):42355-42358, the disclosures of which are incorporated by reference in their entireties. 
     As described above, although the portion of the heparosan-based polysaccharide that reacts with the 6OST enzyme can comprise the structure of Formula VIII, other glucosamine residues within the polysaccharide can be N-sulfated, N-acetylated, 3-O sulfated, and/or 6-O sulfated, and hexuronyl residues can be glucuronic acid or iduronic acid, either of which can be 2-O sulfated. Similar to the other engineered sulfotransferase enzymes above, engineered 6OST enzymes can transfer a sulfo group to multiple glucosamine residues within the same polysaccharide molecule, and multiple glucosamine residues within the same polysaccharide molecule can be 6-O sulfated by the same polypeptide. Typically, heparosan-based polysaccharides that can react with the engineered 6OST enzymes, including N,2O-HS polysaccharides comprising the structure of Formula VIII, can comprise at least three monosaccharide residues. In another embodiment, engineered 6OSTs of the present invention can have the same preference as natural 6OST enzymes for N,2O-HS, particularly with N,2O-HS comprising the structure of Formula VIII, as a sulfo group acceptor. 
     Upon successfully binding PAPS and an N,2O-HS comprising the structure of Formula VIII, natural 6OST enzymes can catalyze transfer of the sulfo group to the 6-O position of the glucosamine residue, forming an N,2O,6O-HS product comprising the structure of Formula IX, below: 
     
       
         
         
             
             
         
       
     
     wherein X comprises any of the hexuronyl residues depicted in Formula IX, above. 
     In another embodiment, engineered 6OSTs of the present invention can bind and react with any of the heparosan-based polysaccharides described herein, including heparosan-based polysaccharides that are recognized as sulfo group acceptors by the engineered NSTs, engineered 2OSTs, and engineered 3OSTs (described in further detail below). In another embodiment, engineered 6OSTs of the present invention can bind and react with N,2O-HS comprising the structure of Formula VIII, in order to form N,2O,6O-HS products comprising the structure of Formula IX. A non-limiting example of one such heparosan-based polysaccharide that can react with an engineered 6OST enzyme as a sulfo group acceptor is illustrated in  FIG.  20   .  FIG.  20    shows a polysaccharide 240 that includes three N-substituted glucosamine residues 210 that can be N-substituted with either an acetyl group  211  or a sulfate group  212 . Within the polysaccharide 240, N-substituted glucosamine residues 210 that are capable of acting as a sulfo acceptor are flanked by two hexuronyl residues. Hexuronyl residues can include any residue represented by the functional group “X” in Formula VIII, particularly glucuronyl residue 220 and iduronyl residue 230. Either the glucuronyl residue 220 or iduronyl residue 230 can further be substituted by a sulfate group  231  at the 2-O position. Upon reacting the polysaccharide 240 with an engineered 6OST enzyme and a sulfo group donor, the 6-O position 213 of any of the glucosamine residues 210 can be sulfated, ultimately forming 6-O sulfated glucosamine residues 310 within the product polysaccharide 241. 
     Natural 6OST enzymes generally comprise approximately 300-700 amino acid residues that can in some cases vary greatly in their sequence, yet ultimately have the exact same function, namely, to catalyze the transfer of a sulfo group from PAPS to the 6-O position of glucosamine residues within N,2O-HS, particularly those comprising the structure of Formula VIII. Without being limited by a particular theory, it is believed that each of the natural 6OSTs can catalyze the same chemical reaction because there are multiple amino acid sequence motifs and secondary structures that are either identical or highly conserved across all species. 
     Further, it is believed that several of the conserved amino acid sequence motifs are directly involved in binding of either PAPS and/or the polysaccharide, or participate in the chemical reaction itself. The identity between the natural 6OST enzymes can be demonstrated by comparing the amino acid sequence of the zebrafish 6OST isoform 3-B enzyme (SEQ ID NO: 204), which has known crystal structures (PDB codes 5T03, 5T05 and 5T0A) in which amino acid residues within the active site have been identified, alongside the amino acid sequences of other natural 6OSTs. A multiple sequence alignment of fifteen enzymes (SEQ ID NOs 191-205) is shown in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C , along with the percent identity of each sequence relative to the mouse 6OST (isoform 1) reference sequence (SEQ ID NO: 191, UniProtKB Accession No. Q9QYK5). As illustrated in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C , sequences range from having 97.3% identity with the Q9QYK5 reference sequence (SEQ ID NO: 192, entry 060243|H6ST1_HUMAN) down to 53.7% identity (SEQ ID NO: 205, entry A0A3P8W3M9|A0A3P8W3M9_CYSNE). For comparison, the zebrafish 6OST3-B enzyme (SEQ ID NO: 204, entry A0MGZ7|H6S3B_DANRE) has 60.4% sequence identity with SEQ ID NO: 191. Those skilled in the art would appreciate that the multiple sequence alignment was limited to fifteen sequences for clarity, and that there are hundreds of amino acid sequences encoding for natural 6OST enzymes that have been identified and that have highly conserved active site and/or binding regions as well. 
     Within  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C , amino acids that are depicted in white with a black background at a particular position, are 100% identical across all sequences. Amino acids that are highly conserved, meaning that the amino acids are either identical or chemically or structurally similar, at a particular position are enclosed with a black outline. Within highly conserved regions, consensus amino acids that are present in a majority of the sequences, are in bold. Amino acids at a particular position that are not identical or highly conserved are typically variable. A period within a sequence indicates a gap that has been inserted into the sequence in order to facilitate the sequence alignment with other sequence(s) that have additional residues between highly conserved or identical region. Finally, above each block of sequences are a series of arrows and coils that indicate secondary structure that is conserved across all sequences, based on the identity of the amino acids within the alignment and using the structure of the natural zebrafish 6OST enzyme (SEQ ID NO: 204) as a reference. The β symbol adjacent to an arrow refers to a β-sheet, whereas a coil adjacent to an α symbol refers to a helix secondary structure. Each of the fifteen aligned sequences in illustrated  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C  (SEQ ID NOs 191-205) have been truncated relative to their natural full-length sequences to coincide with the engineered enzymes of the present invention, particularly those having the amino acid sequences SEQ ID NO: 104, SEQ ID NO: 106, and SEQ ID NO: 108. In particular, the residues illustrated in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C  are aligned with residues 67-377 of SEQ ID NO: 191. 
     Within the fifteen aligned sequences in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C , there are several conserved amino acid sequence motifs that include one or more amino acids that comprise the active site, based on the crystal structure of the zebrafish 6OST3-B enzyme (SEQ ID NO: 204, entry A0MGZ7|H6S3B_DANRE) described above. Based on the numbering of the amino acid residues within  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C , these conserved amino acid sequence motifs include amino acid residues 29 through 34 (Q-K-T-G-G-T); 81 through 86 (C-G-L-H-A-D); 127 through 139 (S-E-W-R/K-H-V-Q-R-G-A-T-W-K); 178 through 184 (N-L-A-N-N-R-Q); and 227 through 231 (L-T-E-F/Y-Q), which correspond to SEQ ID NO: 254, SEQ ID NO: 255, SEQ ID NO: 256, SEQ ID NO: 290, and SEQ ID NO: 276 in the sequence listing, respectively. In particular, and as illustrated in  FIG.  22 A ,  FIG.  22 B , and  FIG.  22 C , the histidine residue within the C-G-L-H-A-D conserved amino acid sequence motif (SEQ ID NO: 255) appears to be in position to abstract the hydrogen atom from the 6′-hydroxyl group of an N-sulfoglucosamine residue, enabling the negatively-charged oxygen atom to then initiate the nucleophilic attack of PAPS and remove the sulfate group. Additionally, the universally conserved lysine residue within the Q-K-T-G-G-T conserved amino acid sequence motif (SEQ ID NO: 254) appears to coordinate with the 5′-phosphate in PAPS, while the universally conserved histidine and tryptophan residues at positions 131 and 138 coordinate with the N-sulfoglucosamine residue (see Xu, Y., et al., above). 
     However, as described above, natural 6OST enzymes are unable to catalyze the transfer of the sulfate group from an aryl sulfate compound to a polysaccharide. Without being limited by a particular theory, and as with the natural NDST and 2OST enzymes described above, it is believed that the binding pocket for PAPS within the active site of the natural 6OST either does not have a high enough affinity for aryl sulfate compounds to facilitate binding and/or that the aryl sulfate compounds are sterically hindered from entering the active site. Consequently, and in another embodiment, a natural 6OST enzyme can be mutated in several locations to enable binding of the aryl sulfate compound within the active site and/or to optimally position the aryl sulfate compound so transfer of the sulfate group to the polysaccharide can occur. 
     Accordingly, and in another embodiment, engineered 6OST enzymes of the present invention can be mutants of natural 6OST enzymes within EC 2.8.2.—, including enzymes having the amino acid sequences illustrated in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C  (SEQ ID NOs 191-205). In another embodiment, mutations engineered into the amino acid sequences of the engineered 6OST enzymes facilitate a biological activity in which aryl sulfate compounds can both bind and react with the enzyme as sulfo group donors. In another embodiment, although the engineered 6OST enzymes can bind and react with an aryl sulfate compound as a sulfo group donor, they can retain the natural 6OST enzymes&#39; biological activity with N,2O-HS polysaccharides, including but not limited to those comprising the structure of Formula VIII, as sulfo group acceptors. Without being limited by a particular theory, it is believed that because of the mutations selected for the amino acid sequences of the engineered 6OST enzymes, their sulfotransferase activity may comprise the direct transfer of a sulfuryl group from an aryl sulfate compound to the heparosan-based polysaccharide, using a similar mechanism as described in  FIGS.  22 A- 22 C , above, except that the PAPS is substituted with the aryl sulfate compound. Otherwise, it is believed that the mutations may cause the sulfotransferase activity to comprise a two-step process including the hydrolysis of an aryl sulfate compound and formation of a sulfohistidine intermediate, followed by the nucleophilic attack of the sulfohistidine intermediate by the oxygen atom at the 6-O position of a glucosamine residue, to form a 6-O sulfated HS product. In another embodiment, the 6-O sulfated HS product of either sulfotransfer mechanism is an N,2O,6O-HS product. Engineered 6OST enzymes of the present invention are able to achieve sulfo group transfer from an aryl sulfate compound to N,2O-HS, as described in the examples below. 
     In another embodiment, an engineered 6OST enzyme can comprise one or more mutated amino acid sequence motifs relative to the conserved amino acid sequence motifs (SEQ ID NO: 254, SEQ ID NO: 255, SEQ ID NO: 256, SEQ ID NO: 290, and SEQ ID NO: 276) found in natural 6OST enzymes, as described above and indicated in the multiple sequence alignment of SEQ ID NOs 191-205 in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C . In another embodiment, each mutated amino acid sequence motif that is present in the amino acid sequence of the engineered 6OST enzyme comprises at least one amino acid mutation relative to the corresponding conserved amino acid sequence motif within the natural 6OST enzymes. In another embodiment, an engineered 6OST enzyme can comprise one mutated amino acid sequence motif. In another embodiment, an engineered 6OST enzyme can comprise two mutated amino acid sequence motifs. In another embodiment, an engineered 6OST enzyme can comprise three mutated amino acid sequence motifs. In another embodiment, an engineered 6OST enzyme can comprise four mutated amino acid sequence motifs. In another embodiment, an engineered 6OST enzyme can comprise five mutated amino acid sequence motifs. In another embodiment, an engineered 6OST enzyme that includes at least one mutated amino acid sequence motif relative to any of the natural 6OST enzymes within EC 2.8.2.—can have an amino acid sequence selected from the group consisting of SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122. 
     In another embodiment, upon viewing any of the crystal structures of the zebrafish 6OST3-B (SEQ ID NO: 204, UniProtKB Accession No. A0MGZ7) within a 3D molecular visualization system (including, as a non-limiting example, the open-source software, PyMOL), the structure of related sequences, such as those of engineered 6OST enzymes that contain one or more mutated amino acid sequence motifs relative to any of the zebrafish 6OST structures, can be modeled for comparison as illustrated in  FIG.  23   .  FIG.  23    shows a magnified view of the active site of the zebrafish 6OST3-B enzyme (PDB code: 5T03) overlaid with one of the engineered enzymes of the present invention, comprising the amino acid sequence of SEQ ID NO: 108, in which the structure of the engineered 6OST enzyme is calculated upon making mutations relative to the zebrafish 6OST amino acid sequence. Adenosine 3′,5′-diphosphate, which is the product of a sulfotransfer reaction in which PAPS is the sulfo donor, and which was co-crystallized with the zebrafish 6OST3-B, is also illustrated within the active site. PNS is also modeled into the active site of the engineered enzymes, using the consensus solutions of molecular dynamics (MD) simulations that designed to calculate the optimized position and orientation of a ligand within an enzyme active site adjacent to the polysaccharide binding site (not shown), if such solutions are possible. Hydrogen atoms are not shown for clarity. 
     As illustrated in  FIG.  23   , although there are several mutations made SEQ ID NO: 108, relative to the zebrafish 6OST enzyme, the respective protein backbones appear to be in a nearly identical location to one another, enabling a one-to-one comparison of the active sites. However, when comparing the two active sites, the adenosine 3′,5′-diphosphate product appears to be located on the opposite side of the central a-helix as the PNS molecule, as determined by the convergent solutions from the above MD simulations. Without being limited by a particular theory, it is believed that the convergent MD simulation solutions place PNS on the opposite side of the a-helix because there is not enough of an affinity toward PNS in the same or similar position as PAPS within the zebrafish enzyme. As described by Xu, Y., et al., above, the conserved histidine abstracts the proton from the 6′ hydroxyl group of N-sulfoglucosamine, which is then subsequently able to react with PAPS to initiate sulfo group transfer. Yet, despite the apparent differences in the binding pocket for PAPS and PNS, engineered 6OST enzymes comprising the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, and SEQ ID NO: 108 all achieved sulfo group transfer from an aryl sulfate compound to the 6-O position of one or more glucosamine residues within a heparosan-based polysaccharide, as described in the examples below. 
     As a result, and without being limited by a particular theory, one or more of the mutations present within the active site of engineered 6OST enzymes may assist binding of the sulfate moiety of the aryl sulfate compound in a position in which it can be transferred to the sulfo acceptor HS polysaccharide. As illustrated in  FIG.  23   , the engineered enzyme has the amino acid sequence SEQ ID NO: 108, and the aryl sulfate compound is PNS. However, a heparosan-based polysaccharide is not illustrated. In a non-limiting example, the histidine residue engineered into position 31 of SEQ ID NO: 108 may be in position to facilitate removal of the sulfate group from PNS using a ping-pong mechanism, similar to the mechanism described in Malojcic, et al, above. Additionally, the histidine residue engineered into position 133 of SEQ ID NO: 108 may further coordinate with the sulfate moiety along with the conserved histidine at position 132 of SEQ ID NO: 108 (corresponding to position 131 in each of SEQ ID NOs 190-205). Mutation to G-A-N at positions 137-139 of SEQ ID NO: 22 (corresponding to the conserved A-T-W motif at positions 136-138 of SEQ ID NOs 190-205) removes steric bulk that may prevent binding of PNS in a position where the sulfate can be abstracted by the engineered histidine at position 31 of SEQ ID NO: 108. The mutations to G-A-N within the loop containing A-T-W also appears to cause the loop to move away from PNS, which may further assist PNS to reach its binding pocket. Finally, a serine residue engineered into position 84 of SEQ ID NO: 108 may create an additional hydrogen-binding contact to assist the engineered enzyme in retaining the zebrafish enzyme&#39;s natural activity with the sulfo acceptor polysaccharide. 
     Those skilled in the art would appreciate that engineered 6OST enzymes of any other amino acid sequence, including, but not limited to, those disclosed by SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122, would likely exhibit similar structural motifs, particularly within the active site. Without being limited by a particular theory, it is believed that NCS would bind in a similar position as PNS within any of the engineered enzymes, since the structures of the two aryl sulfate compounds are very similar, except that the sulfate group is located ortho on the aromatic ring relative to the nitro group, rather than para to the nitro group. 
     In another embodiment, engineered 6OST enzymes that can be utilized in accordance with methods of the present invention can comprise one or more mutated amino acid sequence motifs, which can be determined in-part by comparing conserved amino acid sequence motifs indicated in the multiple sequence alignment of SEQ ID NOs 191-205 in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C  with the known structure(s) of natural enzymes and/or modeled engineered enzymes, including but not limited to, as a non-limiting example, enzymes illustrated in  FIG.  23   . In another embodiment, mutated amino acid sequence motifs that can be comprised within an engineered 6OST enzyme can be selected from the group consisting of (a) G-H-T-G-G-T (SEQ ID NO: 257); (b) C-G-X 1 -X 2 -A-D (SEQ ID NO: 291), wherein X 1  is selected from the group consisting of threonine and serine, and X 2  is selected from the group consisting of asparagine, arginine, and histidine; (c) X 3 -X 4 -W-R-H-X 5 -Q-R-G-G-X 6 -N-K (SEQ ID NO: 260), wherein X 3  is selected from the group consisting of serine and glycine, X 4  is selected from the group consisting of glycine and histidine, X 5  is selected from the group consisting of histidine and threonine, and X 6  is selected from the group consisting of alanine and threonine; and (d) N-L-X 7 -N-N-R-Q (SEQ ID NO: 292), wherein X 7  is selected from the group consisting of alanine and glycine; including any combination thereof. Each of the mutated amino acid sequence motifs corresponds with a conserved amino acid motif indicated in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C  above: SEQ ID NO: 257 corresponds to the conserved amino acid sequence motif, Q-K-T-G-G-T (SEQ ID NO: 254); mutated amino acid sequence motif SEQ ID NO: 291 corresponds to the conserved amino acid sequence motif, C-G-L-H-A-D (SEQ ID NO: 255); mutated amino acid sequence motif SEQ ID NO: 260 corresponds to the conserved amino acid sequence motif, S-E-W-(R/K)-H-V-Q-R-G-A-T-W-K (SEQ ID NO: 256); and mutated amino acid sequence motif SEQ ID NO: 292 corresponds to the conserved amino acid sequence motif, N-L-A-N-N-R-Q (SEQ ID NO: 290). In another embodiment, engineered 6OST enzymes comprising at least one mutated amino acid sequence motif described above can be selected from the group consisting of: SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122. 
     In another embodiment and in one non-limiting example, engineered 6OST enzymes can comprise the mutated amino acid sequence motifs SEQ ID NO: 291 and SEQ ID NO: 260 within the same amino acid sequence. Engineered enzymes comprising the mutated amino acid sequence motifs SEQ ID NO: 291 and SEQ ID NO: 260 include, but are not limited to, enzymes comprising the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, or SEQ ID NO: 122. In another embodiment, each of the engineered 6OST enzymes comprising the mutated amino acid sequence motifs SEQ ID NO: 291 and SEQ ID NO: 260 have a similar active site as SEQ ID NO: 108, as illustrated in  FIG.  23   . Without being limited to another theory, it is believed that several of the mutations comprised within mutated amino acid sequence motifs SEQ ID NO: 291 and SEQ ID NO: 260 have one or more functions during sulfotransferase activity, including not limited to: increasing the affinity of aryl sulfate compounds to the active site by reducing the size of the binding pocket, increasing the hydrophobicity of the pocket, removing or creating polar or hydrogen bonding contacts, and/or creating π-π interactions with the aromatic moieties of the aryl sulfate compounds; stabilizing the transition state of the enzyme during the chemical reaction; and/or participating in the chemical reaction itself. 
     In another embodiment, within engineered 6OST enzymes that comprise the mutated amino acid sequence motifs SEQ ID NO: 291 and SEQ ID NO: 260, X 4  is glycine and X 5  is histidine (as illustrated in SEQ ID NO: 263). In other embodiments, X 4  is histidine and X 5  is threonine (as illustrated in SEQ ID NO: 264). 
     In another embodiment, within engineered 6OST enzymes comprising the mutated amino acid sequence motifs SEQ ID NO: 291 and SEQ ID NO: 260, X 3  is serine and X 6  is alanine (as illustrated in SEQ ID NO: 262), and X 7  is glycine (as illustrated in SEQ ID NO: 293). In other embodiments, X 3  is glycine and X 6  is threonine (as illustrated in SEQ ID NO: 261), and X 7  is alanine (as illustrated in SEQ ID NO: 294). 
     Furthermore, the amino acid sequences (SEQ ID NO: 104, SEQ ID NO: 106, and SEQ ID NO: 108) of three engineered 6OST enzymes, which have been experimentally determined to be active sulfotransferases with aryl sulfate compounds as sulfo group donors (see Example 5 below) can be compared with the amino acid sequence of the mouse 6OST1 enzyme (SEQ ID NO: 191, entry Q9QYK5|H6ST1_MOUSE) in a multiple sequence alignment to determine if there are relationships between mutations among each of the enzymes. A period within the amino acid sequence of an engineered enzyme indicates identity at a particular position with the mouse 6OST enzyme. As shown in  FIG.  24   , the sequence alignment demonstrates that while over 90% of the amino acid residues within the three sulfotransferase sequences are identical, there are several positions in which multiple amino acids can be chosen. Without being limited by a particular theory, these enzymes have a similar relationship with each other as the natural 6OST enzymes within EC 2.8.2.—. As a result, and in another embodiment, engineered 6OST enzymes comprising an amino acid sequence in which multiple amino acids can be chosen at defined positions are disclosed as SEQ ID NO: 112 and SEQ ID NO: 113. Positions at which the identity of an amino acid can be chosen from a selection of possible residues are denoted in terms “Xaa,” “Xn,” or “position n,” where n refers to the residue position. 
     In another embodiment, within SEQ ID NO: 112, residues having the designation, “Xaa,” illustrate known instances in which there is a lack of identity at a particular position within the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, and SEQ ID NO: 108. In another embodiment, the amino acid sequence, SEQ ID NO: 113, also illustrates known instances in which there is a lack of identity at a particular position within the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, and SEQ ID NO: 108, but SEQ ID NO: 113 further comprises N-terminal residues 1-66, and C-terminal residues 378-411, of several natural full-length 6OST enzymes within EC 2.8.2.—, including, as non-limiting examples, the mouse, human, and pig 6OST1 enzymes (SEQ ID NOs 295-297). In contrast, amino acid residues in SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, and SEQ ID NO: 112 correspond with residues 67-377 of several full-length 6OST enzymes within EC 2.8.2.—, including, as non-limiting examples, the mouse, human, and pig 6OST enzymes (SEQ ID NOs 191-193). To facilitate protein expression, an N-terminal methionine residue was added to each of the SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, and SEQ ID NO: 112 amino acid sequences, relative to residues 67-377 of the mouse, human, and pig 6OST1 enzymes (SEQ ID NOs 191-193). 
     In another embodiment, any selection can be made for an Xaa residue, defined by the amino acid sequence SEQ ID NO: 112 or SEQ ID NO: 113, so long as the resulting enzyme maintains its 6OST activity upon reacting with an aryl sulfate compound as a sulfo group donor. 
     In another embodiment, within an engineered 6OST enzyme comprising the amino acid sequence of SEQ ID NO: 112, the amino acid residue at position 129 is glycine and the amino acid residue at position 133 is histidine. In another embodiment, within an engineered 6OST enzyme comprising the amino acid sequence of SEQ ID NO: 112, the amino acid residue at position 129 is histidine and the amino acid residue at position 133 is threonine. In another embodiment, within an engineered 6OST enzyme comprising the amino acid sequence of SEQ ID NO: 113, the amino acid residue at position 194 is glycine and the amino acid residue at position 198 is histidine. In another embodiment, within an engineered 6OST enzyme comprising the amino acid sequence of SEQ ID NO: 113, the amino acid residue at position 194 is histidine and the amino acid residue at position 198 is threonine. 
     In another embodiment, within an engineered 6OST enzyme comprising the amino acid sequence of SEQ ID NO: 112, the amino acid residue at position 128 is serine, the amino acid residue at position 138 is alanine, and the amino acid residue at position 181 is glycine. In another embodiment, within an engineered 6OST enzyme comprising the amino acid sequence of SEQ ID NO: 112, the amino acid residue at position 128 is glycine, the amino acid residue at position 138 is threonine, and the amino acid residue at position 181 is alanine. In another embodiment, within an engineered 6OST enzyme comprising the amino acid sequence of SEQ ID NO: 113, the amino acid residue at position 193 is serine, the amino acid residue at position 203 is alanine, and the amino acid residue at position 246 is glycine. In another embodiment, within an engineered 6OST enzyme comprising the amino acid sequence of SEQ ID NO: 113, the amino acid residue at position 193 is glycine, the amino acid residue at position 203 is threonine, and the amino acid residue at position 246 is alanine. 
     In another embodiment, within an engineered 6OST enzyme comprising the amino acid sequence of SEQ ID NO: 112 or SEQ ID NO: 113, the amino acid sequence can optionally include one or more mutations at residue positions not specified by an “Xn” or “Xaa,” so long as any such mutations do not eliminate the 6OST and/or aryl sulfate-dependent activity of the enzyme. In another embodiment, such mutations not eliminating aryl sulfate-dependent activity at positions not specified by an “Xn” or “Xaa” can include substitutions, deletions, and/or additions. 
     Accordingly, in another embodiment, an engineered 6OST enzyme utilized in accordance with any of the methods of the present invention can comprise an amino acid sequence selected from the group consisting of SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122. In another embodiment, engineered 6OST enzymes comprising the amino acid sequence of SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122 can react with any aryl sulfate compound. In further embodiments, the aryl sulfate compound is selected from the group consisting of PNS, 4-methylumbelliferyl sulfate, 7-hydroxycoumarin sulfate, phenyl sulfate, 4-acetylphenyl sulfate, indoxyl sulfate, 1-naphthyl sulfate, 2NapS, and NCS. In some even further embodiments, the aryl sulfate compound is PNS. In other even further embodiments, the aryl sulfate compound is NCS. 
     Engineered 3OSTs 
     In nature, HS 3OSTs generally recognize, bind, and react with N,2O-HS and N,2O,6O-HS heparosan-based polysaccharides as sulfo group acceptors. Generally, the glucosamine residue that receives the sulfo group at the 3-O position is N-sulfated, and is optionally also 6-O sulfated. Additionally, either adjacent hexuronic acid residue can be glucuronic acid or iduronic acid, either of which can optionally be 2-O sulfated. Often, the glucosamine residue being 3-O sulfated is adjacent to a glucuronic acid on its non-reducing end and a 2-O sulfated iduronic acid on its reducing end. Similar to each of the natural sulfotransferases described above, naturally-occurring 3OSTs transfer a sulfo group to the heparosan-based polysaccharide upon reacting with PAPS as a sulfo group donor. Natural 3OST enzymes that utilize PAPS as the sulfo group donor are members of the EC 2.8.2.23 enzyme class. In a non-limiting example, natural 3OST enzymes can recognize, bind, and react with N,2O,6O-HS polysaccharides comprising the structure of Formula X, below: 
     
       
         
         
             
             
         
       
     
     wherein the central glucosamine residue is N-sulfated and is adjacent to glucuronic acid at its non-reducing end and a 2-O sulfated iduronic acid residue at its reducing end, X can optionally be a sulfate group or an acetyl group, and Y can optionally be a sulfate group or a hydroxyl group. 
     As described above, although the portion of the heparosan-based polysaccharide that reacts with the 3OST enzyme can comprise the structure of Formula X, other glucosamine residues within the polysaccharide can be N-sulfated, N-acetylated, 3-O sulfated, and/or 6-O sulfated, and hexuronyl residues can be glucuronic acid or iduronic acid, either of which can be 2-O sulfated. Similar to the other engineered sulfotransferase enzymes above, engineered 3OST enzymes can transfer a sulfo group to multiple glucosamine residues within the same polysaccharide molecule, and multiple glucosamine residues within a polysaccharide molecule can be 3-O sulfated by the same polypeptide. Typically, N,2O,6O-HS polysaccharides that can react with natural 3OSTs as sulfo group acceptors typically comprise at least five monosaccharide residues, as shown in Formula X. In another embodiment, N,2O,6O-HS polysaccharides comprising the structure of Formula X and can react with natural 3OSTs as sulfo group acceptors can comprise at least thirty-two monosaccharide residues. In another embodiment, engineered 3OSTs of the present invention can have the same preference as natural 3OST enzymes for N,2O,6O-HS, particularly with N,2O,6O-HS comprising the structure of Formula X, as sulfo group acceptors. 
     Upon successfully binding PAPS and an N,2O,6O-HS polysaccharide comprising the structure of Formula X, natural 3OST enzymes can catalyze transfer of the sulfo group to the 3-O position of the central glucosamine residue, forming an N,2O,3O,6O-HS product comprising the structure of Formula I, below: 
     
       
         
         
             
             
         
       
     
     wherein X is either a sulfo group or an acetate group and Y is either a sulfo group or a hydroxyl group. Natural 3OST enzymes, which have biological activity with N,2O,6O-HS polysaccharides comprising the structure of Formula X as sulfo group acceptors and form N,2O,3O,6O-HS products comprising the structure of Formula I, have been described by Xu, D., et al., (2008)  Nat. Chem. Biol.  4(3): 200-202 and Edavettal, S. C., et al., (2004)  J. Biol. Chem.  24(11): 25789-25797, the disclosures of which are incorporated by reference in their entireties. Further, N,2O,3O,6O-HS products comprising the structure of Formula I can be found within unfractionated heparin (UFH), as well as low molecular weight heparins (LMWH) that are derived from UFH. Methods for forming anticoagulant N,2O,3O,6O-HS, including UFH, using engineered 3OSTs are described in further detail, below. 
     A non-limiting example of N,2O,6O-HS that can react as a sulfo group acceptor with engineered 3OST enzymes of the present invention is illustrated in  FIG.  25   .  FIG.  25    shows a polysaccharide 440 that includes three glucosamine residues 410 comprising an N-sulfo group  411  at each N-position and an O-sulfo group  412  at each 6-O position. Within the polysaccharide 440, glucosamine residues 410 that are capable of acting as a sulfo acceptor must be flanked by two hexuronic acid residues. Hexuronic acid residues can include any residue represented by the functional group “X” in Formula X, and are shown in  FIG.  25    as glucuronic acid residue 420 and iduronic acid residue 430. Either hexuronic acid residue can further be substituted by a sulfo group  431  at the 2-O position. Upon reacting the polysaccharide 440 with an 3OST enzyme and a sulfo group donor, the 3-O position 413 of any of the glucosaminyl residues 410 can be sulfated. As shown in  FIG.  25   , the central glucosamine residue 410 receives a sulfo group, ultimately forming a 3-O sulfated glucosaminyl residue 510 within the sulfated product polysaccharide 441. Also as shown, sulfated product polysaccharide 441 comprises the structure of Formula I. 
     Natural 3OST enzymes within EC 2.8.2.23 generally comprise approximately 300-325 amino acid residues that can in some cases vary greatly in their sequence, yet ultimately have the exact same function, namely, to catalyze the transfer of a sulfuryl group from PAPS to the 3-O position of N-sulfoglucosamine residues within N,2O-HS or N,2O,6O-HS polysaccharides, particularly those comprising the structure of Formula X. Without being limited by a particular theory, it is believed that each of the natural 3OSTs within the EC 2.8.2.23 enzyme class can catalyze the same chemical reaction because there are multiple amino acid sequence motifs and secondary structures that are either identical or highly conserved across all species. 
     Further, it is believed that several of the conserved amino acid sequence motifs are directly involved in binding of either PAPS and/or the polysaccharide, or participate in the chemical reaction itself. The identity between the natural 3OST enzymes can be demonstrated by comparing the amino acid sequences of the mouse or human 3OST1 enzyme (SEQ ID NO: 213 and SEQ ID NO: 206, respectively), which have known crystal structures (PDB codes 3UAN and 1ZRH, respectively) in which amino acid residues within the active site have been identified, alongside the amino acid sequences of other natural 3OSTs within EC 2.8.2.23. Further, a direct comparison of the mouse and human 3OST structures indicate that both enzymes have nearly identical active sites and overall folds, even though the two enzymes have only an 83% sequence identity with one another. 
     A multiple sequence alignment of the amino acid sequences of fifteen enzymes within EC 2.8.2.23 (SEQ ID NOs 206-220), including the mouse (SEQ ID NO: 213) and human 3OST1 (SEQ ID NO: 206) enzymes, is shown in  FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C , along with the percent identity of each sequence relative to the human 3OST1 reference sequence (SEQ ID NO: 206, UniProtKB Accession No. 014792). As illustrated in  FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C , sequences range from having 98% identity with SEQ ID NO: 206 (SEQ ID NO: 207, entry tr|H9ZG39|H9ZG39_MACMU) for the rhesus monkey 3OST1, down to 53% identity (SEQ ID NO: 220,_entry sp|Q8IZT8|HS3S5_HUMAN) for human 3OST5. Those skilled in the art would appreciate that the multiple sequence alignment was limited to fifteen sequences for clarity, and that there are hundreds of amino acid sequences encoding for natural 3OST enzymes that have been identified and that have highly conserved active site and/or binding regions as well. 
     Within  FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C , amino acids that are depicted in white with a black background at a particular position, are 100% identical across all sequences. Amino acids that are highly conserved, meaning that the amino acids are either identical or chemically or structurally similar, at a particular position are enclosed with a black outline. Within highly conserved regions, consensus amino acids that are present in a majority of the sequences, are in bold. Amino acids at a particular position that are not identical or highly conserved are typically variable. A period within a sequence indicates a gap that has been inserted into the sequence in order to facilitate the sequence alignment with other sequence(s) that have additional residues between highly conserved or identical region. Finally, above each block of sequences are a series of arrows and coils that indicate secondary structure that is conserved across all sequences, based on the identity of the amino acids within the alignment and using the structure of the natural human sulfotransferase enzyme as a reference. The β symbol adjacent to an arrow refers to a β-sheet, whereas a coil adjacent to an α symbol or a η symbol refers to a helix secondary structure. 
     Within the fifteen aligned sequences in  FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C  (SEQ ID NOs 206-220), there are several conserved amino acid sequence motifs that include one or more amino acids that comprise the active site, based on the crystal structures of the mouse (SEQ ID NO: 213, entry sp|O35310|HS3S1_MOUSE) and human 3OST1 (SEQ ID NO: 206, entry sp|O14792|HS3S1_HUMAN) enzymes described above. Based on the numbering of the amino acid residues within  FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C , these motifs include residues 16-27 (including G-V-R-K-G-G from residues 18-23), residues 43-48 (E-V/I-H-F-F-D), residues 78-81 (P-A/G-Y-F), residues 112-117 (including S-D-Y-T-Q-V), and residues 145-147 (Y-K-A). The conserved amino acid sequence motifs G-V-R-K-G-G, E-V/I-H-F-F-D, P-A/G-Y-F, and S-D-Y-T-Q-V correspond to SEQ ID NO: 265, SEQ ID NO: 298, SEQ ID NO: 266, and SEQ ID NO: 267 in the sequence listing, respectively. It is believed that these residues either facilitate or participate in the chemical reaction, or enable binding of PAPS or the polysaccharide within the active site. In particular, within residues 43-48, as described above and as illustrated in  FIG.  4 A ,  FIG.  4 B , and  FIG.  4 C , the glutamic acid residue at position 43 abstracts the proton from the 3-O position of the N-sulfoglucosamine residue within the polysaccharide, enabling the nucleophilic attack and removal of the sulfo group from PAPS, whereas His-45 and Asp-48 coordinate to stabilize the transition state of the enzyme before the sulfurylated polysaccharide product is released from the active site. 
     However, as described above, the natural 3OST enzymes are unable to catalyze the transfer of the sulfate group from an aryl sulfate compound to a polysaccharide. Without being limited by a particular theory, and as with the natural NDST, 2OST, and 6OST enzymes described above, it is believed that the binding pocket for PAPS within the active site of the natural sulfotransferase either does not have a high enough affinity for aryl sulfate compounds to facilitate binding and/or that the aryl sulfate compounds are sterically hindered from entering the active site. Consequently, and in another embodiment, a natural 3OST enzyme can be mutated in several locations within its amino acid sequence to enable binding of the aryl sulfate compound within the active site and/or to optimally position the aryl sulfate compound so transfer of the sulfate group to the polysaccharide can occur. 
     Accordingly, and in another embodiment, engineered 3OST enzymes of the present invention can be mutants of natural 3OST enzymes within EC 2.8.2.23, including enzymes having the amino acid sequences of SEQ ID NOs 206-220. In another embodiment, mutations engineered into the amino acid sequences of the engineered 3OST enzymes facilitate a biological activity in which aryl sulfate compounds can both bind and react with the enzyme as sulfo group donors. In another embodiment, although the engineered 3OST enzymes can bind and react with an aryl sulfate compound as a sulfo group donor, they can retain the natural 3OST enzymes&#39; biological activity with N,2O,6O-HS, including but not limited to those comprising the structure of Formula X, as sulfo group acceptors. Without being limited by a particular theory, it is believed that because of the mutations inserted into the amino acid sequences of the engineered 3OST enzymes, their sulfotransferase activity may comprise the direct transfer of a sulfuryl group from an aryl sulfate compound to the heparosan-based polysaccharide, using a similar mechanism as described in  FIGS.  4 A- 4 C , above, except that the PAPS is substituted with the aryl sulfate compound. Otherwise, it is believed that the mutations may cause the sulfotransferase activity to comprise a two-step process including the hydrolysis of an aryl sulfate compound and formation of a sulfohistidine intermediate, followed by the nucleophilic attack of the sulfohistidine intermediate by the oxygen atom at the 3-O position of a glucosamine residue, to form a 3-O sulfated HS product. In another embodiment, the 3-O sulfated product of either sulfotransfer mechanism is an N,2O,3O,6O-HS product. 
     In another embodiment, an engineered 3OST enzyme can comprise one or more mutated amino acid sequence motifs relative to the conserved amino acid sequence motifs (SEQ ID NO: 265, SEQ ID NO: 298, SEQ ID NO: 266, and SEQ ID NO: 267) found in natural 3OST enzymes, as described above and indicated in the multiple sequence alignment in  FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C  and SEQ ID NOs 206-220. In another embodiment, each mutated amino acid sequence motif that is present in the amino acid sequence of the engineered enzyme comprises at least one amino acid mutation relative to the corresponding conserved amino acid sequence motif within the natural 3OST enzymes. In another embodiment, an engineered 3OST enzyme can comprise one mutated amino acid sequence motif. In another embodiment, an engineered 3OST enzyme can comprise two mutated amino acid sequence motifs. In another embodiment, an engineered 3OST enzyme can comprise three mutated amino acid sequence motifs. In another embodiment, an engineered 3OST enzyme can comprise four mutated amino acid sequence motifs. In another embodiment, an engineered 3OST enzyme can comprise five mutated amino acid sequence motifs. In another embodiment, an engineered 3OST enzyme that includes at least one mutated amino acid sequence motif relative to any of the wild-type 3OST enzymes within EC 2.8.2.23 can have an amino acid sequence selected from the group consisting of SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160. 
     In another embodiment, upon viewing the crystal structure of the mouse 3OST within a 3D molecular visualization system (including, as a non-limiting example, the open-source software, PyMOL), the structure of related sequences, such as those of engineered 3OST enzymes that contain one or more mutated amino acid sequence motifs relative to the mouse 3OST1 (SEQ ID NO: 213, UniProtKB Accession No. 035310) structure, can be modeled for comparison as illustrated in  FIG.  27   .  FIG.  27    shows a magnified view of the active site of the mouse 3OST1 enzyme (PDB code: 3UAN) with three engineered 3OST enzymes, comprising the amino acid sequences of SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151. Adenosine 3′,5′-diphosphate, which is the product of a sulfotransfer reaction in which PAPS is the sulfo donor, and which was co-crystallized with the mouse 3OST1, is also illustrated within the active site. PNS is also modeled into the active site of the engineered enzymes, using the consensus solutions of molecular dynamics (MD) simulations that designed to calculate the optimized position and orientation of a ligand within an enzyme active site adjacent to the polysaccharide binding site (not shown), if such solutions are possible. Hydrogen atoms are not shown for clarity. 
     As illustrated in  FIG.  27   , although there are several mutations made to SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151 relative to the amino acid sequence of the natural mouse 3OST1 enzyme (SEQ ID NO: 213), the respective protein backbones are in a nearly identical location to one another, enabling a one-to-one comparison of the active sites. However, when comparing the two active sites, the adenosine 3′,5′-diphosphate product from the natural sulfotransfer reaction is adjacent to the lysine residue (shown in  FIG.  27    as Lys68), whereas the convergent solutions from the above MD simulations indicate that PNS binding within the engineered enzymes is favored on the opposite side of the active site. Without being limited by a particular theory, it is believed that the convergent MD simulation solutions place PNS on the opposite side of the active site because there is not enough of an affinity toward PNS in the same or similar position as PAPS. Yet, despite the apparent differences in the binding pocket for PAPS and PNS, engineered 3OST enzymes comprising the amino acid sequences of SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151 all achieved sulfo transfer from an aryl sulfate compound to the 3-O position of one or more positions within a heparosan-based polysaccharide, as described in the examples below. 
     Further, the arginine residue corresponding to position 20 of the mouse 3OST1 (SEQ ID NO: 213) and which is conserved in all of the other 3OST enzymes in SEQ ID NOs 206-220, would appear to block PNS from binding in the position indicated in  FIG.  27   . Accordingly, and in another embodiment, engineered 3OST enzymes that bind PNS can comprise a mutation of the active site arginine residue to a glycine residue, which removes all steric hindrance for PNS to bind within the binding pocket. As indicated in the amino acid sequences for SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, and SEQ ID NO: 157, the arginine to glycine mutation is at position 21. As indicated in the amino acid sequences for SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160, the arginine to glycine mutation is at position 99. 
     Similarly, the next amino acid residue in each of the engineered enzymes, corresponding to position 22 in the amino acid sequences SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, and SEQ ID NO: 157, is mutated to a histidine residue. Without being limited by a particular theory, it is believed that the mutation to a histidine residue from the conserved lysine residue (corresponding to position 21 in each of the amino acid sequences in  FIG.  26 A ) facilitates removal of the sulfate group from PNS, using a similar mechanism as described by Malojcic, et al., above. As indicated in the amino acid sequences for SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160, the lysine to histidine residue is at position 100. 
     Those skilled in the art would appreciate that engineered 3OST enzymes of any other amino acid sequence, including, but not limited to, those disclosed by SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160, would likely exhibit a similar structure would exhibit similar structural motifs as engineered enzymes having the amino acid sequences of SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151, particularly within the active site. Without being limited by a particular theory, it is also believed that NCS would bind in a similar position as PNS within the active site of any of the engineered enzymes, since the structures of the two aryl sulfate compounds are very similar, except that the sulfate group is located ortho on the aromatic ring relative to the nitro group, rather than para to the nitro group. 
     In another embodiment, engineered 3OST enzymes of the present invention can comprise one or more mutated amino acid sequence motifs, which can be determined in-part by comparing conserved amino acid sequence motifs (SEQ ID NO: 265, SEQ ID NO: 298, SEQ ID NO: 266, and SEQ ID NO: 267) indicated in the multiple sequence alignment of SEQ ID NOs 206-220 in  FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C  with the known structure(s) of native 3OST enzymes and/or modeled engineered enzymes, including but not limited to the engineered 3OST enzymes illustrated in  FIG.  27   . In another embodiment, mutated amino acid sequence motifs that can be comprised within an engineered 3OST enzyme can be selected from the group consisting of (a) G-V-G-H-G-G (SEQ ID NO: 268); (b) H-S-Y-F (SEQ ID NO: 269); (c) S-X 1 -X 2 -T-H-X 3  (SEQ ID NO: 299), wherein X 1  is selected from the group consisting of alanine and leucine; X 2  is selected from the group consisting of tyrosine and glycine, and X 3  is selected from the group consisting of methionine and leucine; and (d) Y-X 4 -G, wherein X 4  is selected from the group consisting of valine and threonine; including any combination thereof. Each of the mutated amino acid sequence motifs corresponds with a conserved amino acid motif indicated in  FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C  above: SEQ ID NO: 268 corresponds to the conserved amino acid sequence motif G-V-R-K-G-G (SEQ ID NO: 265); SEQ ID NO: 269 corresponds to the conserved amino acid sequence motif P-A/G-Y-F (SEQ ID NO: 266); SEQ ID NO: 299 corresponds to the conserved amino acid sequence motif S-D-Y-T-Q-V (SEQ ID NO: 267); and the mutated amino acid sequence motif Y-X 4 -G corresponds to the conserved amino acid sequence motif Y-K-A. In another embodiment, an engineered 3OST enzyme comprising each of the mutated amino acid sequence motifs above can be selected from the group consisting of: SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160. 
     In another embodiment, each of the mutated amino acid sequence motifs can comprise at least one mutation that is made relative to the conserved amino acids found in the natural 3OST enzymes within EC 2.8.2.23. In another embodiment, SEQ ID NO: 268 contains an R-K to G-H mutation, relative to the conserved amino acid sequence motif, G-V-R-K-G-G (SEQ ID NO: 265). In another embodiment, SEQ ID NO: 269 contains a P-A/G to an H-S mutation relative to the conserved amino acid sequence motif, P-A/G-Y-F (SEQ ID NO: 266). In another embodiment, in addition to potential mutations made at the X 1 , X 2 , and X 3  positions, SEQ ID NO: 299 comprises a Q to H mutation, relative to the conserved amino acid sequence motif, S-D-Y-T-Q-V (SEQ ID NO: 267). In another embodiment, in addition to a mutation at the X 4  position, mutated amino acid sequence motif Y-X 4 -G comprises an A to G mutation, relative to the conserved amino acid sequence motif, Y-K-A. 
     In another embodiment, X 1  is alanine, X 2  is tyrosine and X 3  is methionine (SEQ ID NO: 270), and X 4  is valine or threonine. In other embodiments, X 1  is leucine, X 2  is glycine, and X 3  is leucine (SEQ ID NO: 300), and X 4  is threonine. Without being limited to another theory, it is believed that one or more of the mutations comprised within mutated amino acid sequence motifs SEQ ID NO: 269, SEQ ID NO: 299, and Y-X 4 -G play a role in stabilizing the transition state of the enzyme during the chemical reaction, or in increasing the affinity of aryl sulfate compounds to the active site, including by reducing the size of the binding pocket, increasing the hydrophobicity of the pocket, and/or creating π-π interactions with the aromatic moieties of the aryl sulfate compounds. 
     Furthermore, the amino acid sequences (SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151) of three engineered 3OST enzymes, which have been experimentally determined to be active with aryl sulfate compounds as sulfo group donors (see Example 6 below) can be compared with the amino acid sequence of the human 3OST1 enzyme (SEQ ID NO: 206, entry sp|O14792|HS3S1_HUMAN) in a multiple sequence alignment to determine if there are relationships between mutations among each of the enzymes. A period within the amino acid sequence of an engineered enzyme indicates identity at a particular position with the human 3OST enzyme. As shown in  FIG.  28   , the sequence alignment demonstrates that while over 90% of the amino acid residues within the three sulfotransferase sequences are identical, there are several positions in which multiple amino acids can be chosen. As a result, and in another embodiment, an engineered 3OST enzyme comprising an amino acid sequence in which multiple amino acids can be chosen at defined positions is disclosed as SEQ ID NO: 154. Positions at which the identity of an amino acid can be chosen from a selection of possible residues are denoted in terms “Xaa,” “Xn,” or “position n,” where n refers to the residue position. 
     In another embodiment, within an engineered 3OST enzyme comprising the amino acid sequence of SEQ ID NO: 154, the amino acid residue at position 114 is alanine and the amino acid residue at position 118 is methionine. In further embodiments, the amino acid residue at position 147 is selected from the group consisting of valine and threonine. 
     In another embodiment, within an engineered 3OST enzyme comprising the amino acid sequence of SEQ ID NO: 154, the amino acid residue at position 114 is leucine, the amino acid residue at position 118 is leucine, and the amino acid residue at position 121 is valine. In further embodiments, the amino acid residue at position 115 is glycine. In even further embodiments, the amino acid residue at position 147 is threonine. 
     In another embodiment, within an engineered 3OST enzyme comprising the amino acid sequence of SEQ ID NO: 154, the amino acid sequence can optionally include one or more mutations at residue positions not specified by an “Xn” or “Xaa,” so long as any such mutations do not eliminate the 3OST and/or aryl sulfate-dependent activity of the enzyme. In another embodiment, such mutations not eliminating aryl sulfate-dependent activity at positions not specified by an “Xn” or “Xaa” can include substitutions, deletions, and/or additions. 
     Accordingly, in another embodiment, an engineered 3OST enzyme utilized in accordance with any of the methods of the present invention can comprise an amino acid sequence selected from the group consisting of SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160. In another embodiment, engineered 3OST enzymes comprising the amino acid sequence of SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160 can react with any aryl sulfate compound. In further embodiments, the aryl sulfate compound is selected from the group consisting of PNS, 4-methylumbelliferyl sulfate, 7-hydroxycoumarin sulfate, phenyl sulfate, 4-acetylphenyl sulfate, indoxyl sulfate, 1-naphthyl sulfate, 2NapS, and NCS. In some even further embodiments, the aryl sulfate compound is PNS. In other even further embodiments, the aryl sulfate compound is NCS. 
     In Vitro Synthesis of Sulfated Polysaccharides 
     In an embodiment of the invention, any of the engineered sulfotransferase enzymes described above can be utilized to synthesize HS polysaccharide products. Generally, sulfation can be accomplished by treating a heparosan-based polysaccharide and an aryl sulfate compound with an engineered sulfotransferase enzyme to form the sulfated product. As described above and without being limited by a particular theory, it is believed that sulfotransferase enzymes that recognize heparosan-based polysaccharides as sulfo group acceptors, but also bind and react with aryl sulfate compounds as sulfo donors, have neither been observed in nature nor described previously. 
     HS polysaccharide compositions that are utilized for industrial, commercial, or pharmaceutical uses can be obtained in large quantities by isolating them from animal sources, particularly pigs and cattle, within which the polysaccharides are produced in vivo. (see Xu, Y., et al., (2011)  Science  334 (6055): 498-501). A worldwide contamination crisis in 2007 and 2008 of heparin obtained from pigs shone a spotlight on the fragility of solely relying on obtaining them from animal sources. Consequently, there has been a push to develop synthetic routes to synthesizing heparin, LMWH, and other anticoagulant HS polysaccharides in vitro in large enough quantities to compliment or replace animal-sourced products. That push has only been strengthened even further by the African swine flu epidemic that decimated the worldwide pig population, especially in China, in  2019 . 
     In order to synthesize HS polysaccharides in vitro, there have historically been two reaction schemes: total chemical synthesis and chemoenzymatic synthesis. While both types of reaction schemes have led to purified products that in some instances are homogeneous, synthetic routes as a whole have been inadequate to produce specific HS polysaccharide compositions, particularly heparin, on an industrial scale. For example, the production of such polysaccharides using total chemical synthesis has historically required as many as 60 steps and resulted in very low yields (see Balagurunathan, K., et al., (eds.) (2015)  Glycosaminoglycans: Chemistry and Biology , Methods in Molecular Biology, vol. 1229, DOI 10.1007/978-1-4939-1714-3_2, © Springer Science+Business Media New York). 
     Chemoenzymatic synthesis routes, on the other hand, generally utilize far fewer steps and increase the scale of the generated anticoagulant products into multi-milligram amounts (See U.S. Pat. Nos. 8,771,995 and 9,951,149, the disclosures of which are incorporated by reference in its entirety). The improvements in the quantity of obtainable product can be attributed to the ability to combine recombinant versions of natural HS sulfotransferases with PAPS in a reaction vessel in order to catalyze the transfer of sulfo groups to heparosan-based polysaccharides. Yet, chemoenzymatic methods to this point are still not suitable to synthesize gram- or larger-scale amounts of anticoagulant HS polysaccharides because of the wild-type sulfotransferases&#39; reliance on PAPS for their activity, as described in U.S. Pat. Nos. 5,541,095, 5,817,487, 5,834,282, 6,861,254, 8,771,995, 9,951,149, and U.S. Pat. Pubs. 2009/0035787, 2013/0296540, and 2016/0122446, the disclosures of which are incorporated by reference in their entireties. PAPS is a highly expensive and unstable molecule that has been an obstacle to the large-scale production of enzymatically sulfated products, including heparin, because the half-life of PAPS at pH 8.0 is only about 20 hours. 
     Furthermore, product inhibition by adenosine 3′,5′-diphosphate has also been a limiting factor to large-scale synthesis of sulfated products. The highly negative impact of the product inhibition by adenosine 3′,5′-diphosphate can be somewhat reduced by employing a PAPS regeneration system (see U.S. Pat. No. 6,255,088, above, and Burkhart, et al. (2000) J. Org. Chem. 65: 5565-5574) that converts adenosine 3′,5′-diphosphate into PAPS. Despite the PAPS regeneration system, however, the absolute necessity to supply PAPS to initiate the chemical reaction with PAPS-dependent sulfotransferases nonetheless creates an insurmountably high-cost barrier to synthesize sulfated products, including heparin, on an industrial, production-grade scale. 
     In contrast to the known syntheses of heparin that require PAPS as sulfo donors in order to drive enzyme activity, the methods of the present invention obviate the need to use PAPS altogether, because each of the sulfotransferases of the present invention have been engineered to recognize, bind, and react with aryl sulfate compounds, which do not react with natural HS sulfotransferases, as sulfo donors. Without being limited by a particular theory, it is believed that the engineered sulfotransferases of the present invention are the only known sulfotransferases that are capable of reacting with aryl sulfate compounds as sulfo group donors, while also reacting with polysaccharides, particularly heparosan-based polysaccharides, as sulfo group acceptors. Generally, any of the methods described herein for synthesizing sulfated products such as heparin and ODSH can be performed using one or more engineered sulfotransferases, and such engineered sulfotransferases can comprise any amino acid sequence so long as its biological activity is dependent on transferring a sulfo group from an aryl sulfate compound to heparosan-based polysaccharide. Non-limiting examples of engineered enzymes, aryl sulfate compounds, and heparosan-based polysaccharides are described in further detail, below. 
     Thus, in another embodiment, the invention provides methods and kits for synthesizing HS polysaccharides. Generally, a method for sulfating a heparosan-based polysaccharide using the engineered sulfotransferases of the present invention comprises the following steps: (a) providing an aryl sulfate compound; (b) providing any of the engineered sulfotransferase enzymes described above, wherein the engineered sulfotransferase enzyme has biological activity with an aryl sulfate compound as a sulfo group donor; (c) providing a heparosan-based polysaccharide; (d) combining the aryl sulfate compound, the sulfotransferase enzyme, and the heparosan-based polysaccharide into a reaction mixture; and (e) transferring the sulfo group from the aryl sulfate compound to the heparosan-based polysaccharide, using the sulfotransferase enzyme, thereby forming the sulfated polysaccharide product. In another embodiment, the aryl sulfate compound can be selected from the consisting of PNS, 4-methylumbelliferyl sulfate, 7-hydroxycoumarin sulfate, phenyl sulfate, 4-acetylphenyl sulfate, indoxyl sulfate, 1-naphthyl sulfate, 2NapS, and NCS. According to the present invention, the aryl sulfate compound is PNS. According to the present invention, the aryl sulfate compound is NCS. 
     In any of the methods of the present invention described herein, one or more, and preferably all, of the N-, 2-O-, 3-O-, and 6-O sulfation steps, when performed, are catalyzed using sulfotransferase enzymes that are engineered to react with aryl sulfate compounds in the absence of PAPS. Such product compositions that can be synthesized comprise, as non-limiting examples, N-, 2-O sulfated heparan sulfate (N,2O-HS), N-, 6-O sulfated heparan sulfate (N,6O-HS), N-, 2-O, 6-O sulfated heparan sulfate (N,2O,6O-HS), and N-, 3-O, 6-O sulfated heparan sulfate (N,3O,6O-HS). In various embodiments, the N,2O-HS, N,6O-HS, N,2O,6O-HS, and N,3O,6O-HS product composition(s) synthesized by any of the methods described herein can have substantially the same structure(s) and pharmaceutical activities as any ODSH composition in the art produced by O-desulfating heparin, while also not possessing anticoagulant activity. 
     In a non-limiting example, N,6O-HS can be synthesized using a method comprising the following steps: (a) providing a starting polysaccharide composition comprising N-deacetylated heparosan; (b) reacting the starting polysaccharide composition within a reaction mixture comprising an N-sulfation agent, to form an N-sulfated heparan sulfate (NS-HS) product; and (c) reacting the NS-HS product within a reaction mixture comprising an aryl sulfate compound and an engineered 6OST enzyme, thereby forming the N,6O-HS product. In further embodiments, the method can further comprise the step of reacting either NS-HS or N,6O-HS with a 2OST and a sulfo group donor, to form either an N,2O-HS or N,2O,6O-HS product, respectively. In another embodiment, the reaction mixture that comprises the 2OST enzyme further comprises a glucuronyl C 5 -epimerase enzyme. 
     In an embodiment of the invention, methods are provided for chemoenzymatically synthesizing N-, 2-O-, 3-O-, 6-O-sulfated-HS (N,2,3,6-HS) products, particularly heparin. By controlling the molecular weight and N-acetyl glucosamine content of heparosan-based polysaccharides utilized as starting materials, an N,2,3,6-HS product composition can be formed that has a comparable molecular weight, sulfation, and anticoagulant activity to the United States Pharmacopeia (USP) reference standard (CAS No: 9041-08-1) for API heparin. In various embodiments, once the N,2O,6O,3O-HS product is formed according to any of the methods of the present invention, it can subsequently be O-desulfated according to any method known in the art to form an ODSH composition in vitro. Such ODSH compositions can be completely free of dermatan sulfate and chondroitin sulfate contaminants that can be found in ODSHs produced from animal-sourced heparin. Once the N,2O,6O,3O-HS product is formed, an ODSH can be formed according to any of the desulfation methods described in above in U.S. Pat. Nos. 5,990,097, 5,912,237, 5,808,021, 5,668,118, and 5,296,471, and in further detail below. 
     In another embodiment, when the engineered sulfotransferase enzyme is a NST enzyme, the heparosan-based polysaccharide can be an N-deacetylated heparosan polysaccharide comprising one or more disaccharide units comprising the structure of Formula II, and the engineered sulfotransferase can have an amino acid sequence selected from the group consisting of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, and SEQ ID NO: 25. In another embodiment, the N-sulfated HS polysaccharide comprises one or more disaccharide units having the structure of Formula III. 
     In another embodiment, N-deacetylated heparosan and/or other heparosan-based polysaccharides comprising disaccharide units having the structure of Formula II can be obtained commercially. In another embodiment, heparosan can be isolated from natural sources and chemically modified to N-deacetylate glucosamine residues and also control the molecular weight of the polysaccharides within the composition. In particular, heparosan can be found within bacteria as capsules that regulate cell entry by metabolites and other exogenous materials. Such bacteria, include, but are not limited to,  Pasteurella multocida  and  Escherichia coli  ( E. coli ). In some embodiments, heparosan can be extracted and purified from  E. coli , particularly the K5 strain of  E. coli , as a polydisperse mixture of polysaccharide molecules having varying molecular weights. Procedures for isolating heparosan from the K5 strain of  E. coli  are discussed and provided in Wang, Z., et al., (2010)  Biotechnol. Bioeng.  107 (6):964-973, the disclosure of which is incorporated by reference in its entirety; see also DeAngelis, P. L. (2015)  Expert Opinion on Drug Delivery  12 (3):349-352; Ly, M., et al., (2010)  Anal. Bioanal. Chem.  399:737-745; and Zhang, C., et al., (2012)  Metabolic Engineering  14:521-527, the disclosures of which are also incorporated in their entireties. 
     In another embodiment, a portion or all of the heparosan composition can be N-deacetylated by treating it with a base, particularly lithium hydroxide or sodium hydroxide (see Wang, Z., et al., (2011)  Appl. Microbiol. Biotechnol.  91 (1):91-99, the disclosure of which is incorporated by reference in its entirety; see also PCT publication PCT/US2012/026081, the disclosure of which is incorporated by reference in its entirety). In another embodiment, the base is sodium hydroxide. Depending on the degree of N-deacetylation desired, the concentration of the heparosan, and the concentration of the base, one skilled in the art can determine how long to incubate heparosan with the base according to the procedures described in Wang, et al., (2011), above. 
     In another embodiment, N-deacetylated heparosan can be obtained with molecular weight and N-acetyl glucosamine contents useful for synthesizing UFH that meets one or more of the benchmarks set forth by the United States Pharmacopeia (USP), described in further detail below. In another embodiment, heparosan can be incubated with a base, preferably sodium hydroxide, until a desired amount of N-acetylated glucosamine residues remains within the N-deacetylated product. In another embodiment, N-acetyl glucosamine residues can comprise less than 60%, including less than 30%, 20%, 18%, 16%, 14%, 12%, or 10%, down to less than 5%, and preferably in a range from 12% and up to 18%, of the glucosamine residues within the N-deacetylated heparosan. In another embodiment, the N-acetyl glucosamine can comprise about 15% of the glucosamine residues within the N-deacetylated heparosan. 
     Additionally, and without being limited by a particular theory, it is believed that in addition to N-deacetylating glucosamine residues, the reaction between heparosan and a base can simultaneously depolymerize the heparosan polysaccharides and reduce their molecular weight, which can in turn reduce the weight-average molecular weight ( M   w ) of the N-deacetylated heparosan. Typically, heparosan polysaccharides isolated from bacteria, including but not limited to  E. coli , have a molecular weight ranging from about 3,000 Da to about 150,000 Da, and compositions of isolated heparosan can have a  M   w  in the range of about 25,000 Da up to about 50,000 Da (see Ly, M., et al. and Wang, et al., (2011), above). In another embodiment, a heparosan composition either obtained from commercial sources or isolated from bacteria, including but not limited to  E. coli , can be treated with a base, preferably sodium hydroxide, for a time sufficient to reduce the  M   w  of the N-deacetylated heparosan to a target or desired level. In another embodiment, the N-deacetylated heparosan can have an  M   w  of at least 1,000 Da, including at least 2,000 Da, 4,000 Da, 6,000 Da, 7,000 Da, 8,000 Da, 8,500 Da, 9,000 Da, 9,500 Da, 10,000 Da, 10,500 Da, 11,000 Da, 11,500 Da, 12,000 Da, 12,500 Da, 13,000 Da, 13,500 Da, 14,000 Da, 15,000 Da, 16,000 Da, or 18,000 Da, up to at least 20,000 Da. In another embodiment, the N-deacetylated heparosan can have an  M   w  of less than 20,000 Da, including less than 18,000 Da, 16,000 Da, 15,000 Da, 14,000 Da, 13,500 Da, 13,000 Da, 12,500 Da, 12,000 Da, 11,500 Da, 11,000 Da, 10,500 Da, 10,000 Da, 9,500 Da, 9,000 Da, 8,500 Da, 8,000 Da, 7,000 Da, 6,000 Da, or 4,000 Da, down to less than 2,000 Da. In another embodiment, the N-deacetylated heparosan can have an  M   w  in any range listed above between and inclusive of 1,000 Da and 20,000 Da, and preferably in any range listed above between and inclusive of 9,000 Da and 12,500 Da. 
     The preparation of N-deacetylated heparosan having such molecular weight properties and N-acetyl glucosamine content is described in detail in Wang, et al., (2011), above. In another embodiment, the time sufficient to react a heparosan with a base, preferably sodium hydroxide, to form an N-deacetylated heparosan product having an  M   w  in a range between 9,000 Da and 12,500 Da, as well as an N-acetyl glucosamine content in a range from 12% and up to 18%, can be at least 1 hour, including at least 2, 4, 6, 8, 10, 12, or 18 hours, and up to at least 24 hours, depending on the molecular weight properties and concentration of the heparosan starting material, and the identity and concentration of the base used to carry out the reaction. 
     In another embodiment, the N-sulfated HS can be obtained by chemically N-sulfating N-deacetylated heparosan. In another embodiment, the N-deacetylated heparosan can be chemically sulfated by adding a composition comprising sulfur trioxide and/or one or more sulfur-trioxide containing compounds or adducts. Chemical N-sulfation of glucosamine residues within polysaccharides using sulfur trioxide is commonly known in the art (see Lloyd, A. G., et al., (1971)  Biochem. Pharmacol.  20 (3):637-648; Nadkarni, V. D., et al., (1996)  Carbohydrate Research  290:87-96; Kuberan, B., et al., (2003)  J. Biol. Chem.  278 (52):52613-52621; Zhang, Z., et al., (2008)  J. Am. Chem. Soc.  130 (39):12998-13007; and Wang, et al., (2011), above; see also U.S. Pat. No. 6,991,183 and U.S. Pat. Pub. 2008/020789, the disclosures of which are incorporated by reference in their entireties). Sulfur trioxide complexes are generally mild enough bases to enable the selected N-sulfation of polysaccharides without causing depolymerization, unlike sodium hydroxide (see Gilbert, E. E., (1962)  Chem. Rev.  62 (6):549-589). Non-limiting examples of sulfur trioxide-containing complexes include sulfur trioxide-pyridine, sulfur trioxide-dioxane, sulfur trioxide-trimethylamine, sulfur trioxide-triethylamine, sulfur trioxide-dimethylaniline, sulfur trioxide-thioxane, sulfur trioxide-Bis(2-chloroethyl) ether, sulfur trioxide-2-methylpyridine, sulfur trioxide-quinoline, or sulfur trioxide-dimethylformamide. 
     In another embodiment, when the engineered sulfotransferase enzyme is a 2OST enzyme, the heparosan-based polysaccharide can be an N-sulfated HS polysaccharide comprising one or more structural motifs comprising the structure of Formula IV and/or Formula V, and the engineered sulfotransferase can have an amino acid sequence selected from the group consisting of SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 67, and SEQ ID NO: 69. In another embodiment, the method can further comprise the step of providing a glucuronyl C 5 -epimerase, preferably a glucuronyl C 5 -epimerase comprising the amino acid sequence of SEQ ID NO: 67, and more preferably residues 34-617 of SEQ ID NO: 67, and combining the glucuronyl C 5 -epimerase with the reaction mixture. In another embodiment, the N-sulfated HS can be commercially obtained. In another embodiment, the N-sulfated HS can be the sulfated product of an engineered NST or natural NDST enzyme. In another embodiment, the sulfated polysaccharide product of the engineered 2OST enzyme is an N,2O-HS polysaccharide comprising the structure of Formula VI and/or Formula VII. 
     In another embodiment, when the engineered sulfotransferase enzyme is a 6OST enzyme, the heparosan-based polysaccharide is an N,2O-HS polysaccharide comprising one or more structural motifs comprising the structure of Formula VIII. In another embodiment, the engineered 6OST enzyme can have an amino acid sequence selected from the group consisting of SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122. In another embodiment, the heparosan-based polysaccharide for reacting with the engineered 6OST enzyme can be commercially obtained. In another embodiment, the heparosan-based polysaccharide for the engineered 6OST enzyme can be the sulfated N,2O-HS polysaccharide product of an engineered or natural 2OST enzyme. In another embodiment, the sulfated polysaccharide product of the engineered 6OST enzyme is an N,2O,6O-HS polysaccharide comprising the structure of Formula IX. 
     In another embodiment, when the engineered sulfotransferase enzyme is a 3OST enzyme, the heparosan-based polysaccharide can be an N,2O,6O-HS polysaccharide comprising one or more structural motifs comprising the structure of Formula X. In another embodiment, the engineered 3OST can have an amino acid sequence selected from the group consisting of SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160. In another embodiment, the heparosan-based polysaccharide for reacting with the engineered 3OST enzyme can be commercially obtained. In another embodiment, the heparosan-based polysaccharide for the engineered 3OST enzyme can be the sulfated N,2O,6O-HS polysaccharide product of an engineered or natural 6OST enzyme. In another embodiment, the sulfated polysaccharide product is an N,2O,3O,6O-HS polysaccharide comprising the structure of Formula I. In another embodiment, the N,2O,3O,6O-HS is obtained as a polydisperse composition having one or more molecular weight properties and/or anticoagulant activities as UFH. 
     As described above, UFH, LMWH, and other heparin compositions that have anticoagulant activity are comprised of N,2O,3O,6O-HS polysaccharides that include the structure of Formula I. (see Desai, U. R., et al., (1998)  J. Biol. Chem.  273 (13):7478-7487). The medical use of UFH, LMWH, and other heparins has been well documented for decades. The anticoagulant activity of heparins can include, but are not limited to, inactivation of Factor IIa (thrombin) and/or Factor Xa, two proteins that are vital in the blood-clotting cascade. In particular, when a N,2O,3O,6O-HS polysaccharide binds to antithrombin (AT), it causes a conformational change in the enzyme that enables the formation of a ternary complex between the polysaccharide, AT, and either thrombin or Factor Xa (see Li, W., et al., (2004)  Nat. Struct. Mol. Biol.  11 (9):857-862, the disclosure of which is incorporated by reference in its entirety). In order to bind with AT and induce its conformational change, an N,2O,3O,6O-HS polysaccharide comprises a specific five-residue AT-recognition sequence, which is equivalent to the structure of Formula I. 
     While anticoagulation can be induced by binding antithrombin with an oligosaccharide consisting only of the AT-recognition sequence, there is typically enhanced anticoagulant activity when the composition comprises N,2O,3O,6O-HS polysaccharides having more than five sugar residues (see Grey, E., et al., (2008)  Thromb. Haemost.  99:807-818, the disclosure of which is incorporated by reference in its entirety). As reported by Grey, et al, a secondary binding interaction can be formed between the polysaccharide and thrombin when the N,2O,3O,6O-HS polysaccharide comprises at least thirteen sugar residues on either side of the AT-recognition sequence to act as a “bridge” that allows the polysaccharide to bind to thrombin while also bound to AT. As a result, N,2O,3O,6O-HS polysaccharides typically require a minimum of eighteen sugar residues in order to potentially form the ternary complex between the N,2O,3O,6O-HS polysaccharide, AT, and thrombin. However, and without being limited by a particular theory, it is believed that because the distribution of the AT-recognition sequence within a particular polysaccharide molecule is random, some N,2O,3O,6O-HS polysaccharides between eighteen and thirty-one sugar residues can theoretically comprise an AT-recognition sequence toward the center of the molecule that does not have thirteen adjacent sugar residues on either side. Consequently, the N,2O,3O,6O-HS polysaccharide must be at least thirty-two sugar residues long to guarantee that the thirteen residue “bridge” adjacent to the AT-recognition sequence can be formed, no matter where the AT-recognition sequence is within the molecule. As a result, in some embodiments, the N,2O,3O,6O-HS polysaccharide product of the engineered 3OST enzyme can be at least five sugar residues, preferably at least eighteen sugar residues, and more preferably at least thirty-two sugar residues. 
     Anticoagulant activity is often measured in International Units per milligram (IU mg −1 ) and less often as International Units per milliliter (IU mL −1 ). In either case, an International Unit is an amount approximately equivalent to the quantity required to keep 1-mL of cat&#39;s blood fluid for 24 hours at 0° C. In another embodiment, anticoagulant N,2O,6O,3O-HS polysaccharides produced by methods of the present invention can have an anti-Xa activity of at least about 1 IU mg −1 , including at least about 50 IU mg −1 , at least 75 IU mg −1 , 100 IU mg −1 , 150 IU mg −1 , 200 IU mg −1 , or 500 IU mg −1 , up to at least about 1,000 IU mg −1 . In another embodiment, anticoagulant N,2O,6O,3O-HS polysaccharides produced by methods of the present invention can have an anti-IIa activity of at least about 1 IU mg −1 , including at least about 10 IU mg −1 , 25 IU mg −1 , 50 IU mg −1 , 100 IU mg −1 , 150 IU mg −1 , or 180 IU mg −1 , up to at least about 200 IU mg −1 . In another embodiment, the ratio of anti-Xa activity to anti-IIa activity of the N,2O,6O,3O-HS product is at least 0.5:1, including at least 0.75:1, 0.9:1, 1:1, 1.1:1, 1.3:1, 1.5:1, 2.0:1, 3.0:1, 4.0:1, 5.0:1, 6.0:1, 7.0:1, 8.0:1, 9.0:1, 10.0:1, 20:1, 40:1, 60:1, or 80:1, up to at least 100:1. In another embodiment, the ratio of anti-Xa activity to anti-IIa activity of the N,2O,6O,3O-HS product is less than 100:1, including less than 80:1, 60:1. 40:1, 20:1, 10.0:1, 9.0:1, 8.0:1, 7.0:1, 6.0:1, 5.0:1, 4.0:1, 3.0:1, 2.0:1, 1.5:1, 1.3:1, 1.1:1, 0.9:1, or 0.75:1, down to less than 0.5:1. In another embodiment, the ratio of anti-Xa activity to anti-IIa activity of the N,2O,6O,3O-HS product is in a range from about 0.9 to about 1.1. In another embodiment, the ratio of anti-Xa activity to anti-IIa activity of an N,2O,6O,3O-HS product is in a range from 0.5:1 up to 0.75:1, or 0.9:1, or 1:1, or 1.1:1, or 1.3:1, or 1.5:1, or 2.0:1, or 3.0:1, or 4.0:1, or 5.0:1, or 6.0:1, or 7.0:1, or 8.0:1, or 9.0:1, or 10.0:1. 
     In various embodiments, N,2O-HS, N,6O-HS, N,2O,6O-HS, and N,3O,6O-HS products, particularly N,6O-HS products, can have zero USP, aPTT, Anti-Xa, and/or Anti-IIa anticoagulant activity, distinguishing them from ODSH heparinoid compositions, which retain some anticoagulant activity from the heparin or low molecular weight heparin (LMWH) compositions from which they are derived. 
     Generally, heparins are divided into multiple classes based on their average molecular weights, particularly their  M   w . Samples of low-molecular weight heparin (LMWH) typically have an  M   w  of less than 8,000 Da, in which more than 60% of all of the polysaccharide molecules within the sample have an actual molecular weight of less than 8,000 Da (see Linhardt, R. J. and Gunay, N. S., (1999)  Seminars in Thrombosis and Hemostasis  25 (Suppl. 3):5-16, the disclosure of which is incorporated by reference in its entirety). LMWH is typically prepared by chemically or enzymatically modifying animal-sourced unfractionated heparin or API heparin. Unfractionated heparin typically has an  M   w  of greater than 8,000 Da. 
     In some embodiments, heparan sulfate products prepared by any of the methods of the present invention described herein can have an  M   w  of at least 1,000 Da, including at least 2,000 Da, 3,000 Da, 4,000 Da, 5,000 Da, 6,000 Da, 7,000 Da, 8,000 Da, 9,000 Da, 10,000 Da, 11,000 Da, 12,000 Da, 13,000 Da, 14,000 Da, 15,000 Da, 16,000 Da, 17,000 Da, 18,000 Da, 19,000 Da, 20,000 Da, 21,000 Da, 22,000 Da, 23,000 Da, or 24,000 Da, up to at least 50,000 Da. In another embodiment, heparan sulfate products prepared by any of the methods of the present invention described herein can have an  M   w  of less than 50,000 Da, including less than 24,000 Da, 23,000 Da, 22,000 Da, 21,000 Da, 20,000 Da, 19,000 Da, 18,000 Da, 17,000 Da, 16,000 Da, 15,000 Da, 14,000 Da, 13,000 Da, 12,000 Da, 11,000 Da, 10,000 Da, 9,000 Da, 8,000 Da, 7,000 Da, 6,000 Da, 5,000 Da, 4,000 Da, or 3,000 Da, down to less than 2,000 Da. In another embodiment, heparan sulfate products prepared by any of the methods of the present invention described herein can have an  M   w  in any range listed above between and inclusive of 1,000 Da and 50,000 Da, and preferably in any range listed above between and inclusive of 15,000 Da and about 19,000 Da. 
     Similarly, and in some embodiments, ODSH prepared from an N,2O,6O,3O-HS product synthesized according to methods of the present invention can have an  M   w  of at least 1,000 Da, including at least 2,000 Da, 3,000 Da, 4,000 Da, 5,000 Da, 6,000 Da, 7,000 Da, 8,000 Da, 9,000 Da, 10,000 Da, 11,000 Da, 12,000 Da, 13,000 Da, 14,000 Da, 15,000 Da, 16,000 Da, 17,000 Da, 18,000 Da, 19,000 Da, 20,000 Da, 21,000 Da, 22,000 Da, 23,000 Da, or 24,000 Da, up to at least 50,000 Da. In another embodiment, ODSH prepared from an N,2O,6O,3O-HS product synthesized according to methods of the present invention can have an  M   w  of less than 50,000 Da, including less than 24,000 Da, 23,000 Da, 22,000 Da, 21,000 Da, 20,000 Da, 19,000 Da, 18,000 Da, 17,000 Da, 16,000 Da, 15,000 Da, 14,000 Da, 13,000 Da, 12,000 Da, 11,000 Da, 10,000 Da, 9,000 Da, 8,000 Da, 7,000 Da, 6,000 Da, 5,000 Da, 4,000 Da, or 3,000 Da, down to less than 2,000 Da. In another embodiment, ODSH prepared from an N,2O,6O,3O-HS product synthesized according to methods of the present invention can have an  M   w  of any value or range between and inclusive of about 1,000 Da and about 50,000 Da. 
     In another embodiment, ODSH can be prepared from a low molecular weight HS (LMW-HS) product, which itself is synthesized from an N,2O,6O,3O-HS product and described in further detail below. In another embodiment, the LMW-HS product has an  M   w  in a range from 2,000 Da up to 3,000 Da, or 4,000 Da, or 5,000 Da, or 6,000 Da, or 7,000 Da, or 8,000 Da. In another embodiment, the LMW-HS product has an  M   w  in any range listed above between and inclusive of 2,000 Da and about 8,000 Da. 
     In another embodiment, anticoagulant N,2O,3O,6O-HS products of the engineered 3OST enzyme can satisfy benchmark requirements determined by the USP for pharmaceutical UFH compositions with regard to product purity, particularly purity from other sulfated polysaccharides, including but not limited to chondroitin sulfate. In particular, over-sulfated chondroitin sulfate (OSCS) was determined to be the source of contamination within pharmaceutical UFH compositions that caused hundreds of deaths worldwide in 2007 and 2008. In another embodiment, and without being limited by a particular theory, anticoagulant N,2O,3O,6O-HS products prepared using an engineered 3OST enzyme can be formed from to be substantially free from chondroitin sulfate, particularly OSCS, because the heparosan-based polysaccharides using as starting material can be provided and/or prepared in vitro without the same polysaccharide contaminants that are inherently present in anticoagulant N,2O,3O,6O-HS polysaccharides isolated from animal sources. 
     The USP has defined a reference standard (Chemical Abstracts Service (CAS) No: 9041-08-1) for UFH by which all pharmaceutical compositions are measured. The molecular weight properties of USP-compliant UFH must satisfy all of the following benchmarks: (1) the proportion of polysaccharides within the composition having a molecular weight over 24,000 Da is not more than 20%; (2) the  M   w  of the composition itself is between 15,000 Da and 19,000 Da; and (3) the ratio of the number of polysaccharides within the composition having a molecular weight between 8,000 Da and 16,000 Da relative to the number of polysaccharides within the composition having a molecular weight between 16,000 Da and 24,000 Da is not less than 1.0:1 (see Mulloy, B., et al., (2014)  Anal. Bioanal. Chem.  406:4815-4823, the disclosure of which is incorporated by reference in its entirety). Further, the anticoagulant activity of USP-compliant UFH must satisfy all of the following benchmarks: an anti-IIa activity of not less than 180 International Units per milligram (IU mg −1 ); an anti-Xa activity of not less than 180 IU mg −1 ; and a ratio of anti-Xa to anti-IIa activity in a range of 0.9:1 up to 1.1:1. In another embodiment, anticoagulant N,2O,3O,6O-HS products prepared by an engineered 3OST enzyme can satisfy any or more of the above anticoagulant activity and molecular weight requirements determined by the United States Pharmacopeia (USP) for pharmaceutical UFH compositions. 
     With respect to the molecular weight properties of the N,2O,3O,6O-HS product of engineered 3OST in particular, these can be controlled in part based on the control of the molecular weight properties of the heparosan-based polysaccharide utilized as the sulfo group acceptor. The most controllable opportunity to control the molecular weight of a heparosan-based polysaccharide is by N-deacetylating and depolymerizing heparosan, as described above. Thus, in another embodiment, a series of sulfotransferase reactions can be performed in order to control the molecular weight of the anticoagulant N,2O,3O,6O-HS product. In another embodiment, a series of sulfotransferase reactions can be performed according to the following steps: (a) forming an N-sulfated heparosan product from N-deacetylated heparosan using a NST; (b) forming an N,2O-HS polysaccharide product using a 2OST and the N-sulfated heparosan product of step (a); (c) forming an N,2O,6O-HS polysaccharide product using a 6OST and the N,2O-HS polysaccharide product of step (b); and (d) forming an anticoagulant N,2O,3O,6O-HS polysaccharide product using a 3OST and the N,2O,6O-HS polysaccharide product of step (c). In another embodiment, all of the sulfotransferases are engineered sulfotransferases, and the sulfo donor in each reaction is an aryl sulfate compound, preferably PNS or NCS. In another embodiment, the N-deacetylated heparosan has an  M   w  in a range between 9,000 Da and 12,500 Da, as well as an N-acetyl glucosamine content in a range from 12% and up to 18%, as described in Wang, et al., (2011), above. Alternatively, and in another embodiment, the N-sulfated heparosan product utilized as the sulfo group acceptor for the 2OST can be chemically sulfated from N-deacetylated heparosan, as described above. 
     In another embodiment, an N,2O,3O,6O-HS product prepared by methods of the present invention can have a size distribution such that less than 50%, including less than 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, 3%, or 2%, down to less than 1% of the N,2O,3O,6O-HS polysaccharides within the N,2O,3O,6O-HS product have a molecular weight greater than 24,000 Da. In another embodiment, less than or equal to 20% of the N,2O,3O,6O-HS polysaccharides within the N,2O,3O,6O-HS product have a molecular weight greater than 24,000 Da. In another embodiment, when less than or equal to 20% of the N,2O,3O,6O-HS polysaccharides within the N,2O,3O,6O-HS product have a molecular weight greater than 24,000 Da, the N,2O,3O,6O-HS product can have an  M   w  in any range listed above between and inclusive of 1,000 Da and 24,000 Da, and preferably in any range listed above between and inclusive of 15,000 Da and about 19,000 Da. 
     In another embodiment, an N,2O,3O,6O-HS product prepared by methods of the present invention can have a size distribution such that the ratio of the number of polysaccharides within the composition having a molecular weight between 8,000 Da and 16,000 Da relative to the number of polysaccharides within the composition having a molecular weight between 16,000 Da and 24,000 Da is not less than 0.5:1, including not less than 0.75:1, 0.9:1, 1.0:1, 1.1:1, 1.3:1, or 1.5:1, up to not less than 2.0:1, and preferably not less than 1.0:1. In another embodiment, N,2O,3O,6O-HS products in which the ratio of the number of polysaccharides within the composition having a molecular weight between 8,000 Da and 16,000 Da relative to the number of polysaccharides within the composition having a molecular weight between 16,000 Da and 24,000 Da is not less than 1.0:1 can also have an  M   w  in any range listed above between and inclusive of 1,000 Da and 24,000 Da, and preferably in any range listed above between and inclusive of 15,000 Da and about 19,000 Da, in which less than or equal to 20% of the N,2O,3O,6O-HS polysaccharides within the N,2O,3O,6O-HS product have a molecular weight greater than 24,000 Da. 
     In another embodiment, an anticoagulant N,2O,3O,6O-HS product prepared by an engineered 3OST enzyme can have an anti-Xa activity of at least about 1 IU mg −1 , including at least about 50 IU mg −1 , at least 75 IU mg −1 , 100 IU mg −1 , 150 IU mg −1 , 200 IU mg −1 , or 500 IU mg −1 , up to at least about 1,000 IU mg −1 . In another embodiment, an anticoagulant N,2O,3O,6O-HS product prepared by an engineered 3OST enzyme can have an anti-IIa activity of at least about 1 IU mg −1 , including at least about 50 IU mg −1 , at least 75 IU mg −1 , 100 IU mg −1 , 150 IU mg −1 , 200 IU mg −1 , or 500 IU mg −1 , up to at least about 1,000 IU mg −1 . In another embodiment, an anticoagulant N,2O,3O,6O-HS product prepared by an engineered 3OST enzyme can have a ratio of anti-Xa activity to anti-of at least 0.5:1, including at least 0.75:1, 0.9:1, 1:1, 1.1:1, 1.3:1, 1.5:1, 2.0:1, 3.0:1, 4.0:1, 5.0:1, 6.0:1, 7.0:1, 8.0:1, 9.0:1, 10.0:1, 20:1, 40:1, 60:1, or 80:1, up to at least 100:1. However, anticoagulant N,2O,3O,6O-HS polysaccharides that are thirty-two sugar residues or longer and are able to form the tertiary complex with AT and thrombin typically have a ratio of anti-Xa activity to anti-IIa activity that is usually close to 1:1, approximately between 0.9:1 to 1.1:1 (see Keire, D. A., et al., (2011)  Anal. Bioanal. Chem.  399:581-591, the disclosure of which is incorporated by reference in its entirety). 
     Post-Synthesis Processing of HS Products 
     As described above, heparins that are prescribed to patients generally adhere to a tightly-regulated set of purity, molecular weight and activity requirements, whereas LWMH compositions typically have an average molecular weight of less than 8,000 Da, in which more than 60% of all of the polysaccharide molecules within the sample have an actual molecular weight of less than 8,000 Da (see Linhardt, R. J. and Gunay, N. S., above). Furthermore, pharmaceutical LMWH compositions have their own regulated set of molecular weight and activity requirements in their own right, and are generally prepared from heparin. Accordingly, and in another embodiment, NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS products produced by any of the methods described above can be utilized to produce LMW-HS products, using any well-known means in the art. In another embodiment, an N,2O,6O,3O-HS product synthesized by a method described above can be utilized to produce an LMW-HS product, which can then subsequently be O-desulfated to form an O-desulfated LMW-HS product. In a further embodiment, an N,2O,6O,3O-HS product synthesized by a method described above can have a purity, molecular weight, and/or anticoagulant activity equivalent to USP heparin, and the formed LMW-HS product can have a purity, molecular weight, and/or anticoagulant activity equivalent to a USP LMWH composition. In another embodiment, an N,2O,6O,3O-HS product synthesized by a method described above can first be O-desulfated, and then modified to form an to form an O-desulfated LMW-HS product. In another embodiment, NS-HS, N,6O-HS, N,2O-HS, or N,2O,6O-HS products can subsequently be reacted to form an LMH-NS-HS, —N,6O-HS, —N,2O-HS, or —N,2O,6O-HS product. Non-limiting exemplary methods for synthesizing LMW-HS products from NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS products are described in further detail below. 
     In one non-limiting example, and in another embodiment, polysaccharides within an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product mixture that have a low molecular weight, particularly a molecular weight less than 15,000 Da, including less than 14,000 Da, 13,000 Da, 12,000 Da, 11,000 Da, 10,000 Da, 9,000 Da, 8,000 Da, 7,000 Da, 6,000 Da, 5,000 Da, 4,000 Da, or 3,000 Da, down to less than 2,000 can be separated from other polysaccharides within the same mixture, such as by electrophoretic mobility using gel electrophoresis, size exclusion chromatography, and/or precipitation with salts of a divalent cation and a weak anion, including but not limited to barium, calcium, magnesium, strontium, copper, nickel, cadmium, zinc, mercury, beryllium, palladium, platinum, iron, and tin salts. In another embodiment, the polysaccharides can be separated from higher molecular-weight polysaccharides in bulk, by separating all such polysaccharides under 15,000 Da from those above 15,000 Da, as a non-limiting example. In another embodiment, the polysaccharides can be separated into one or more fractions, such as 10,000 Da to 15,000 Da, 5,000 Da to 10,000 Da, and all polysaccharides under 5,000 Da, as another non-limiting example. 
     In another embodiment, NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product mixtures synthesized according to any of the methods of the present invention can be further modified by one or more subsequent processes to depolymerize and/or modify the HS product to form an LMW-HS product, as described above. In further embodiments, an N,6O-HS product mixture is depolymerized and/or modified to form an LMW-N,6O-HS product. Generally, and in another embodiment, the process for forming an LMW-HS product from an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product mixture comprises the following steps: (a) synthesizing an HS product according to any of the above methods; (b) providing one or more depolymerization agents; and (c) treating the HS product with the one or more depolymerization agents for a time sufficient to depolymerize at least a portion of the polysaccharides within the HS product, thereby forming the LMW-HS product. Without being limited by a particular theory, it is believed that the choice in the depolymerization agent can determine the chemical mechanism for forming the LMW-HS product, as well as the product(s) structure, anticoagulant activity (if prepared from an N,2O,6O,3O-HS product), and pharmacological properties. Known chemical mechanisms for forming an LMW-HS product from an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product include, but are not limited to: chemical and/or enzymatic p-elimination reactions; deamination reactions; and oxidation reactions, including combinations thereof. 
     In another embodiment, an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product, synthesized according to any of the methods of the present invention, can be modified by an enzymatic β-elimination reaction to form an enzymatically-depolymerized LMW-HS product. Historically, enzymatically-depolymerized LMWH products have been prepared by incubating USP heparin with one or more heparinase enzymes until the LMW-HS product comprises a desired chemical structure, average molecular weight, anticoagulant activity, and degree of sulfation. (see, e.g., “Tinzaparin Sodium” (2010)  European Pharmacopoeia  7.0, 3098; see also Linhardt, R. J. and Gunay, N. S., above). In another embodiment, the at least one heparinase can be a heparinase from any species, so long as the enzyme catalyzes β-eliminative cleavage of HS polysaccharides. In another embodiment, the time sufficient to form the enzymatically-depolymerized LMW-HS product is the time sufficient to cause the product to have a desired average molecular weight. In another embodiment, the  M   w  of the enzymatically-depolymerized LMW-HS product can be in the range of 2,000 Da to 10,000 Da, and when the starting material is an N,2O,6O,3O-HS product, preferably 5,500 Da to 7,500 Da, and more preferably 6,500 Da. 
     In another embodiment, an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product, synthesized according to any of the methods of the present invention, can be modified by a chemical β-elimination reaction to form a chemically β-eliminative, LMW-HS product. Historically, chemically β-eliminative LMWH products have been prepared by treating USP heparin or its quaternary ammonium salt with a base. Under these conditions, chemical β-elimination takes place, forming a chemically β-eliminative LMW-HS product having polysaccharides containing a 4,5-unsaturated uronic acid residue at the non-reducing end, a feature observed in enzymatically-depolymerized LMW-HS products, described above (see Linhardt, R. J. and Gunay, N. S., above). 
     In some embodiments, Control of the reaction conditions has led to the production of chemically β-eliminative LMW-HS compositions that have either been approved for clinical use or been administered during clinical trials, and are described in more detail below. a chemically β-eliminative LMW-HS composition can be prepared from an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product by the following steps: (i) reacting the NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product with a benzethonium salt, preferably benzethonium chloride, to form a benzethonium HS salt; and (ii) combining the benzethonium HS salt with a reaction mixture comprising Triton® B and methanol for a time sufficient to form the chemically β-eliminative LMW-HS product. In another embodiment, the time sufficient to depolymerize the benzethonium HS salt is the time sufficient to form a chemically β-eliminative LMW-HS product to having an M, in a range of at least 3,000 Da, up to 4,200 Da, and preferably 3,600 Da, and having a size distribution such that: less than 35% of the polysaccharide chains have an M r  less than 2,000; a range of at least 50% and up to 75% of the polysaccharide chains have an M r  in a range of at least 2,000 and up to 6,000; and less than 15% of the polysaccharide chains have an M r  greater than 6,000. In another embodiment, the step of preparing the chemically β-eliminative LMW-HS product from the benzethonium HS salt comprises the procedure reported in any of the examples in U.S. Pat. No. 4,981,955, preferably Example 3. U.S. Pat. No. 4,981,955 is herein incorporated by reference in its entirety. 
     In another non-limiting example, a chemically β-eliminative LMW-HS composition can be prepared by reacting the benzyl ester of a benzethonium HS salt with the strong phosphazene base, BEMP (2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,2,3-diaza-phosphorine), with subsequent saponification of the benzyl esters and purification (see Viskov, C., et al., (2009)  J. Thromb. Haemost.  7:1143-1551). Accordingly, a chemically β-eliminative LMW-HS composition can be prepared from an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product by the following steps: (i) reacting the NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product with a benzethonium salt, preferably benzethonium chloride, to form a benzethonium HS salt; (ii) esterification of the benzethonium HS salt using benzyl chloride to form a benzyl ester HS; (iii) transalification of the benzyl ester HS with a benzethonium salt, preferably benzethonium chloride, to form a benzethonium benzyl ester HS; (iv) depolymerization of the benzethonium benzyl ester HS with BEMP to form a benzyl ester chemically β-eliminative LMW-HS product; and (v) saponification of the benzyl ester chemically β-eliminative LMW-HS product to form the chemically β-eliminative LMW-HS product. 
     In another non-limiting example, a chemically β-eliminative LMW-HS composition can be prepared similarly to the above illustrated example, in that a benzyl ester form of USP heparin is prepared, before being reacted with a base. The benzyl ester is formed in a chlorinated organic solvent, such as chloroform or methylene chloride, in the presence of a chlorine derivative, such as benzyl chloride, which controls the amount of esterification in the resulting heparin benzyl ester, with about 9-14% efficiency. Once the benzyl ester is formed, it is subsequently treated with a strong, non-sterically hindered base, such as sodium hydroxide, at high temperature (see U.S. Pat. No. 5,389,618 and U.S. Reissue Patent RE38,743, the disclosures of which are incorporated by reference in their entireties. However, some (about 15% to 25%) polysaccharides in such preparations have been shown to additionally comprise a terminal 1,6-anhydro sugar residue (either 1,6-anhydromannose or 1,6-anhydroglucosamine) at the reducing end, in addition to the characteristic 4,5-unsaturated uronic acid at the non-reducing end (see Guerrini, M., (2010)  J. Med. Chem.  53:8030-8040). Accordingly, a chemically β-eliminative LMW-HS composition can be prepared from an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product by the following steps: (i) reacting the unfractionated N,2O,6O,3O-HS product with a benzethonium salt, preferably benzethonium chloride, to form a benzethonium HS salt; (ii) esterification of the benzethonium HS salt using benzyl chloride in the presence of a chlorinated solvent, preferably methylene chloride or chloroform, to form a benzyl ester HS; and (iii) combining the benzyl ester HS with a reaction mixture comprising sodium hydroxide to form the chemically β-eliminative LMW-HS product. In another embodiment, the benzyl ester HS has a degree of esterification of at least 9%, and up to about 14%. In another embodiment, the reaction between the benzyl ester HS and sodium hydroxide is performed at a temperature selected within the range of at least 50° C., up to 70° C., and preferably within the range of at least 55° C., and up to 65° C. In another embodiment, the benzyl ester HS and chemically β-eliminative LMW-HS product are prepared according to the procedure of Example 3 within U.S. RE38,743. 
     In another embodiment, an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product, synthesized according to any of the methods of the present invention, can be modified by a deamination reaction to form a deaminated LMW-HS product. Historically, deaminated LMWH products have been prepared by treating USP heparin with nitrous acid. Under these conditions, a deaminated LMW-HS product is formed that contains polysaccharides having a 2-O-sulfo-α-L-idopyranosuronic acid residue at the non-reducing end, and a 6-O-sulfo-2,5-anhydro-D-mannitol residue at the reducing end (see Linhardt, R. J. and Gunay, N. S., above). 
     In a first non-limiting example, a deaminated LMW-HS composition can be prepared as a sodium salt by an acid depolymerization of USP heparin, particularly by reacting USP heparin with nitrous acid (see e.g. U.S. Pat. No. 5,019,649, the disclosure of which is herein incorporated by reference in its entirety; see also (see Linhardt, R. J. and Gunay, N. S., above). In another non-limiting example, a deaminated LMW-HS composition can be prepared as a sodium or calcium salt by an acid depolymerization of USP heparin, using sodium nitrite in the presence of hydrochloric acid to maintain a pH of about 2.5 (see e.g. U.S. Pat. Nos. 4,686,388 and 5,599,801, the disclosures of which are incorporated by reference in their entireties). In another non-limiting example, a deaminated LMW-HS composition can be prepared by reacting heparin with isoamyl nitrite in the presence of acetic or hydrochloric acid (see, e.g., Ahsan, A., et al., (2000)  Clin. Appl. Thrombosis Hemostasis  6 (3):169-174). Accordingly, a deaminated LMW-HS composition can be prepared from an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product by the following steps: (a) synthesizing an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product according to any of the above methods; (b) providing a deamination reaction mixture comprising a deamination agent, preferably a deamination agent selected from the group consisting of isoamyl nitrate and nitrous acid; and (c) treating the NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product with the deamination reaction mixture for a time sufficient to depolymerize at least a portion of the N,2O,6O,3O-HS product, thereby forming the deaminated LMW-HS product. In another embodiment, the deamination agent is nitrous acid, the deamination reaction mixture can comprise stoichiometric quantities of an acid, preferably acetic acid or hydrochloric acid, and an alkali or alkaline earth metal nitrite salt, preferably sodium nitrite, wherein the nitrous acid is formed within the deamination reaction mixture in situ. In another embodiment, the deamination agent is isoamyl nitrite. 
     In another embodiment, an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product, synthesized according to any of the methods of the present invention, can be modified by an oxidation reaction to form an oxidized LMW-HS product. Historically, oxidized LMW-HS products have been prepared by treating HS with an acid, and then reacting the acidified HS with an oxidizing agent, particularly a peroxide or a superoxide compound such as hydrogen peroxide, at an elevated temperature. In particular, the acidified HS has been formed by reacting the HS with a strong acid, such as hydrochloric acid, or a weak acid, such as ascorbic acid. Acidified HS has also been formed by binding USP heparin to a strong cationic exchange resin. Similarly, the depolymerization conditions can be controlled with respect to the pH and temperature at which the depolymerization takes place, and the oxidizing agent itself. 
     In a non-limiting example, an oxidized LMW-HS composition can be prepared by forming the acidified HS using ascorbic acid, and subsequently depolymerizing the acidified HS under slightly basic conditions in the presence of cupric acetate monohydrate and hydrogen peroxide with incubation at 50° C. (see, e.g., U.S. Pat. No. 4,791,195, the disclosure of which is herein incorporated by reference in its entirety). Accordingly, an oxidized LMW-HS composition can be prepared from an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product by the following steps: (a) synthesizing an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product according to any of the above methods; (b) providing an oxidation reaction mixture comprising an oxidation agent, preferably hydrogen peroxide; and (c) treating the NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product with the oxidation reaction mixture for a time sufficient to depolymerize at least a portion of the NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product, thereby forming the oxidized LMW-HS product. In another embodiment, the step of treating the NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product with the oxidation reaction mixture can comprise the following sub-steps: (i) acidifying the NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product to form an acidified HS product; (ii) combining the acidified HS product with the oxidation reaction mixture; and (c) incubating the acidified HS product within the oxidation reaction mixture at a temperature of at least 50° C. until an oxidized LMW-HS product is formed. In another embodiment, the step of treating the N,2O,6O,3O-HS product with the oxidation reaction mixture can comprise the procedure of Example 1 of U.S. Pat. No. 4,791,195. 
     Those skilled in the art would appreciate that the examples described above of LMW-HS compositions, and methods for forming them from an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product synthesized using one or more engineered aryl sulfate-dependent sulfotransferase enzymes, are non-exhaustive, and that such other examples are excluded for clarity and brevity. Once an NS-HS, N,6O-HS, N,2O-HS, N,2O,6O-HS, or N,2O,6O,3O-HS product is formed according to any of the methods described above, it can be modified and/or depolymerized by any known process to form a secondary product, particularly an LMW-HS product. Such processes include, but are not limited to: fractionation using solvents (French Patent No. 2,440,376, U.S. Pat. No. 4,692,435); fractionation using an anionic resin (French Patent No. 2,453,875); gel filtration; affinity chromatography (U.S. Pat. No. 4,401,758); controlled depolymerization by means of a chemical agent including, but not limited to, nitrous acid (European Patent EP 0014184, European Patent EP 0037319, European Patent EP 0076279, European Patent EP 0623629, French Patent No. 2,503,714, U.S. Pat. No. 4,804,652 and PCT Publication No. WO 81/03276), β-elimination from a heparin ester (European Patent EP 0040144, U.S. Pat. No. 5,389,618), periodate (European Patent EP 0287477), sodium borohydride (European Patent EP 0347588, European Patent EP 0380943), ascorbic acid (U.S. Pat. No. 4,533,549), hydrogen peroxide (U.S. Pat. Nos. 4,629,699, 4,791,195), quaternary ammonium hydroxide from a quaternary ammonium salt of heparin (U.S. Pat. No. 4,981,955), alkali metal hydroxide (European Patent EP 0380943, European Patent EP 0347588), using heparinase enzymes (European Patent EP 0064452, U.S. Pat. No. 4,396,762, European Patent EP 0244235, European Patent EP 0244236; U.S. Pat. Nos. 4,826,827; 3,766,167), by means of irradiation (European Patent EP 0269981), purification and modification of fast-moving HS fractions (U.S. Pat. Nos. 7,687,479, 8,609,632), and other methods or combinations of methods such as those described in U.S. Pat. Nos. 4,303,651, 4,757,057, U.S. Publication No. 2007/287683, PCT Publication No. WO 2009/059284 and PCT Publication No. WO 2009/059283, the disclosures of which are incorporated by reference in their entireties. Any of the LMW-HS products formed from N,2O,6O,3O-HS by any of the above process can subsequently O-desulfated, to form an LMW ODSH product. 
     Preparation of Engineered Aryl Sulfate-Dependent Enzymes 
     In general, the engineered enzymes encoded by the disclosed nucleic acid and amino acid sequences can be expressed and purified using any microbiological technique known in the art, including as described below. The aryl sulfate-dependent activity of each purified enzyme can be determined spectrophotometrically or fluorescently and/or using mass spectrometry (MS) or nuclear magnetic resonance (NMR) spectroscopy to characterize the starting materials and/or sulfated polysaccharide products. Such methods are described below in the Examples section. 
     The engineered gene products, proteins and polypeptides of the present invention can also include analogs that contain insertions, deletions, or mutations relative to the disclosed DNA or peptide sequences, and that also encode for enzymes that catalyze reactions in which aryl sulfate compounds are substrates. In another embodiment, each analog similarly catalyzes sulfotransfer reactions in which aryl sulfate compounds are utilized as sulfo donors. Analogs can be derived from nucleotide or amino acid sequences as disclosed herein, or they can be designed synthetically in silico or de novo using computer modeling techniques. Those skilled in the art will appreciate that other analogs, as yet undisclosed or undiscovered, can be used to design and/or construct different sulfate-dependent enzymes of the present invention. There is no need for a gene product, protein, or polypeptide to comprise all or substantially all of a nucleic acid or amino acid sequence of an engineered enzyme as disclosed herein. Such sequences are herein referred to as “segments.” Further, the gene products, proteins, and polypeptides discussed and disclosed herein can also include fusion or recombinant engineered enzymes comprising full-length sequences or biologically functional segments of sequences disclosed in the present invention. Methods of preparing such proteins are known in the art. 
     In addition to the nucleic acid and amino acid sequences disclosed herein, any of the methods of the present invention can be practiced by engineered enzymes comprising amino acid sequences that are substantially identical to a disclosed amino acid sequence (SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160), or expressed from nucleic acids comprising a nucleotide sequence that is substantially identical to a disclosed nucleotide sequence (SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56, SEQ ID NO: 58, SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 71, SEQ ID NO: 73, SEQ ID NO: 75, SEQ ID NO: 77, SEQ ID NO: 79, SEQ ID NO: 81, SEQ ID NO: 83, SEQ ID NO: 85, SEQ ID NO: 87, SEQ ID NO: 89, SEQ ID NO: 91, SEQ ID NO: 93, SEQ ID NO: 95, SEQ ID NO: 97, SEQ ID NO: 99, SEQ ID NO: 101, SEQ ID NO: 103, SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 109, SEQ ID NO: 124, SEQ ID NO: 126, SEQ ID NO: 128, SEQ ID NO: 130, SEQ ID NO: 132, SEQ ID NO: 134, SEQ ID NO: 136, SEQ ID NO: 138, SEQ ID NO: 140, SEQ ID NO: 142, SEQ ID NO: 144, SEQ ID NO: 146, SEQ ID NO: 148, SEQ ID NO: 150, or SEQ ID NO: 152). Those skilled in the art can determine appropriate nucleotide sequences that encode for polypeptides having the amino acid sequence of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 66, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160 based on the nucleotide sequences SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56, SEQ ID NO: 58, SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 71, SEQ ID NO: 73, SEQ ID NO: 75, SEQ ID NO: 77, SEQ ID NO: 79, SEQ ID NO: 81, SEQ ID NO: 83, SEQ ID NO: 85, SEQ ID NO: 87, SEQ ID NO: 89, SEQ ID NO: 91, SEQ ID NO: 93, SEQ ID NO: 95, SEQ ID NO: 97, SEQ ID NO: 99, SEQ ID NO: 101, SEQ ID NO: 103, SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 109, SEQ ID NO: 124, SEQ ID NO: 126, SEQ ID NO: 128, SEQ ID NO: 130, SEQ ID NO: 132, SEQ ID NO: 134, SEQ ID NO: 136, SEQ ID NO: 138, SEQ ID NO: 140, SEQ ID NO: 142, SEQ ID NO: 144, SEQ ID NO: 146, SEQ ID NO: 148, SEQ ID NO: 150, or SEQ ID NO: 152. 
     “Substantially identical” sequences, as used in the art, refer to sequences which differ from a particular reference sequence by one or more deletions, substitutions, or additions, the net effect of which is to retain at least some of the biological activity of the engineered polypeptide encoded by the reference sequence. Namely, the biological activity of the engineered sulfotransferase enzymes comprises the transfer of a sulfo group from an aryl sulfate compound to a polysaccharide acting as a sulfo group acceptor. In another embodiment, the polysaccharide is a heparosan-based and/or HS polysaccharide. Accordingly, as used to describe the engineered enzymes of the present invention, “substantial identity” can refer either to identity with a particular gene product, polypeptide or amino acid sequence of an engineered enzyme, or a gene or nucleic acid sequence encoding for an engineered enzyme. Such sequences can include mutations of the disclosed sequences or a sequence in which the biological activity is altered, enhanced, or diminished to some degree but retains at least some of the original biological activity of a disclosed reference amino acid sequence or polypeptide encoded by a disclosed reference nucleic acid sequence. 
     Alternatively, DNA analog sequences are substantially identical to the specific DNA sequences disclosed herein if: (a) the DNA analog sequence is derived from coding regions of the any of the disclosed nucleic acid sequences; or (b) the DNA analog sequence is capable of hybridization of DNA sequences of (a) under stringent conditions and which encode for a biologically-active gene product; or (c) the DNA sequences are degenerate as a result of alternative genetic code to the DNA analog sequences defined in (a) and/or (b). Substantially identical analog proteins will be greater than about 60% identical to the corresponding sequence of the native protein. Sequences having lesser degrees of identity but comparable biological activity, namely, transferring a sulfo group from an aryl sulfate compound to polysaccharides, particularly heparosan-based or HS polysaccharides, are also considered to be substantially identical. In determining the substantial identity of nucleic acid sequences, all subject nucleic acid sequences capable of encoding substantially identical amino acid sequences are considered to be substantially identical to a reference nucleic acid sequence, regardless of differences in codon sequences or amino acid substitutions to create biologically functional equivalents. 
     At a biological level, identity is just that, i.e. the same amino acid at the same relative position in a given family member of a gene family. Homology and similarity are generally viewed as broader terms. For example, biochemically similar amino acids, for example leucine and isoleucine or glutamic acid/aspartic acid, can be alternatively present at the same position—these are not identical per se, but are biochemically “similar.” As disclosed herein, these are referred to as conservative differences or conservative substitutions. This differs from a conservative mutation at the DNA level, which changes the nucleotide sequence without making a change in the encoded amino acid, e.g., TCC to TCA, both of which encode serine. 
     In some embodiments, the genes and gene products include within their respective sequences a sequence “essentially as that” of a gene encoding for an engineered enzyme or its corresponding protein. A sequence essentially as that of a gene encoding for an engineered enzyme refers to sequences that are substantially identical or substantially similar to a portion of a disclosed nucleic acid sequence and contains a minority of bases or amino acids (whether DNA or protein) that are not identical to those of a disclosed protein or a gene, or which are not a biologically functional equivalent. Biological functional equivalence is well understood in the art and is further discussed in detail below. Nucleotide sequences are “essentially the same” where they have between about 75% and about 85%, or particularly, between about 86% and about 90%, or more particularly greater than 90%, or even more particularly between about 91% and about 95%, or still more particularly, between about 96% and about 99%, of nucleic acid residues which are identical to the nucleotide sequence of a disclosed gene. Similarly, peptide sequences which have about 80%, or 90%, or particularly from 90-95%, or more particularly greater than 96%, or even more particularly 95-98%, or still more particularly 99% or greater amino acids which are identical or functionally equivalent or biologically functionally equivalent to the amino acids of a disclosed polypeptide sequence will be sequences which are “essentially the same.” 
     Additionally, alternate nucleic acid sequences that include functionally equivalent codons are also encompassed by this invention. Functionally equivalent codons refer to codons that encode the same amino acid, such as the ACG and AGU codons for serine. Thus, substitution of functionally equivalent codons of Table 1, below, into the sequence examples of any of the nucleotide sequences disclosed above ultimately encode for biologically functional equivalent enzymes that are dependent on binding and reacting with aryl sulfate compounds in order to catalyze sulfo transfer. Thus, the present invention includes amino acid and nucleic acid sequences comprising such substitutions but which are not set forth herein in their entirety for convenience. 
     Those skilled in the art would recognize that amino acid and nucleic acid sequences can include additional residues, such as additional N- or C-terminal amino acids or 5′ or 3′ nucleic acid sequences, and yet still be essentially as set forth in one of the sequences disclosed herein, so long as the sequence retains its biological activity with respect to binding and reacting with aryl sulfate compounds as sulfo donors. The addition of terminal sequences particularly applies to nucleic acid sequences which can, for example, include various non-coding sequences flanking either of the 5′ or 3′ portions of the coding region or can include various internal sequences, or introns, which are known to occur within genes. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Functionally Equivalent Codons 
               
            
           
           
               
               
            
               
                 Amino Acids 
                 Codons 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 Alanine 
                 Ala 
                 A 
                 GCA GCC GCG GCU 
               
               
                 Cysteine 
                 Cys 
                 C 
                 UGC UGU 
               
               
                 Aspartic Acid 
                 Asp 
                 D 
                 GAC GAU 
               
               
                 Glutamic Acid 
                 Glu 
                 E 
                 GAA GAG 
               
               
                 Phenylalanine 
                 Phe 
                 F 
                 UUC UUU 
               
               
                 Glycine 
                 Gly 
                 G 
                 GGA GGC GGG GGU 
               
               
                 Histidine 
                 His 
                 H 
                 CAC CAU 
               
               
                 Isoleucine 
                 Ile 
                 I 
                 AUA AUC AUU 
               
               
                 Lysine 
                 Lys 
                 K 
                 AAA AAG 
               
               
                 Leucine 
                 Leu 
                 L 
                 UUA UUG CUA CUC CUG CUU 
               
               
                 Methionine 
                 Met 
                 M 
                 AUG 
               
               
                 Asparagine 
                 Asn 
                 N 
                 AAC AAU 
               
               
                 Proline 
                 Pro 
                 P 
                 CCA CCC CCG CCU 
               
               
                 Glutamine 
                 Gln 
                 Q 
                 CAA CAG 
               
               
                 Arginine 
                 Arg 
                 R 
                 AGA AGG CGA CGC CGG CGU 
               
               
                 Serine 
                 Ser 
                 S 
                 ACG AGU UCA UCC UCG UCU 
               
               
                 Threonine 
                 Thr 
                 T 
                 ACA ACC ACG ACU 
               
               
                 Valine 
                 Val 
                 V 
                 GUA GUC GUG GUU 
               
               
                 Tryptophan 
                 Trp 
                 W 
                 UGG 
               
               
                 Tyrosine 
                 Tyr 
                 Y 
                 UAC UAU 
               
               
                   
               
            
           
         
       
     
     As discussed above, modifications and changes can be made in the sequence of any of the disclosed engineered enzymes, including conservative and non-conserved mutations, deletions, and additions while still constituting a molecule having like or otherwise desirable characteristics. For example, certain amino acids can be substituted for other amino acids in a protein structure without appreciable loss of interactive capacity with particular structures or compounds, particularly aryl sulfate compounds and/or sulfo acceptor polysaccharides. This can occur because the ability of a protein to recognize, bind, and react with other structures or compounds within its environment defines that protein&#39;s biological functional activity, not the sequence itself. Consequently, certain amino acid sequence substitutions can be made in that protein&#39;s sequence to obtain a protein with the equal, enhanced, or diminished properties. One non-limiting example of such amino acid substitutions that can occur without an appreciable loss of interactive activity include substitutions in external domains or surfaces of the protein that do not affect the folding and solubility of the protein. Similarly, amino acids can potentially be added to either terminus of the protein so long as the ability of the protein to fold or to recognize and bind its substrates is not deleteriously affected. One skilled in the art can appreciate that several other methods and/or strategies can be utilized to alter an enzyme&#39;s sequence without affecting its activity. 
     Consequently, mutations, deletions, additions, or other alterations to a parent enzyme&#39;s structure or sequence in which the modified enzyme retains the parent enzyme&#39;s biological activity can be defined to be biologically functionally equivalent to the parent enzyme. Thus, biologically functional equivalent enzymes, with respect to the engineered aryl sulfate-dependent enzymes, can include any substitution or modification of an amino acid sequence disclosed in SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160, in which the resultant modified enzyme is dependent on interacting with aryl sulfate compounds, particularly PNS or NCS, to catalyze sulfo transfer to polysaccharides, particularly heparosan-based and/or HS polysaccharides. In particular, such substitutions or modifications can result from conservative mutations in the amino acid sequence in any portion of the protein, as described below, although non-conservative mutations in non-catalytically active regions of the enzyme are also contemplated. Consequently, the engineered enzymes can be expressed from any nucleic acid having a nucleotide sequence that encodes for a biologically functional equivalent enzyme, although such nucleotide sequences are not set forth herein in their entirety for convenience. 
     Alternatively, recombinant DNA technology can be used to create biologically functionally equivalent proteins or peptides in which changes in the protein structure can be engineered, based on considerations of the properties of the amino acids being exchanged. Rationally-designed changes can be introduced through the application of site-directed mutagenesis techniques, for example, to test whether certain mutations affect positively or negatively affect the enzyme&#39;s aryl sulfate-dependent catalytic activity and/or binding of sulfo donors or acceptors within the enzyme&#39;s active site. 
     Amino acid substitutions, such as those which might be employed in modifying any of the engineered enzymes described herein, are generally based on the relative similarity of the amino acid side-chain substituents, for example, their hydrophobicity, hydrophilicity, charge, size, and the like. Those skilled in the art are familiar with the similarities between certain amino acids, such as the size, shape and type of the amino acid side-chain substituents. Non-limiting examples include relationships such as that arginine, lysine and histidine are all positively charged residues; that alanine, glycine and serine are all of similar size; and that phenylalanine, tryptophan and tyrosine all have a generally similar shape. Consequently, the amino acids that comprise the following groups—arginine, lysine and histidine; alanine, glycine and serine; and phenylalanine, tryptophan and tyrosine—are defined herein as biologically functional equivalents to the other amino acids in the same group. Other biologically functionally equivalent changes will be appreciated by those of skill in the art. 
     One such method to evaluate biologically functional equivalents is to evaluate and consider the hydropathic index of each of the amino acids. Each of the twenty common amino acids has been assigned a hydropathic index on the basis of their hydrophobicity and charge characteristics, these are: isoleucine (+4.5); valine (+4.2); leucine (+3.8); phenylalanine (+2.8); cysteine (+2.5); methionine (+1.9); alanine (+1.8); glycine (−0.4); threonine (−0.7); serine (−0.8); tryptophan (−0.9); tyrosine (−1.3); proline (−1.6); histidine (−3.2); glutamic acid (−3.5); glutamine (−3.5); aspartic acid (−3.5); asparagine (−3.5); lysine (−3.9); and arginine (−4.5). 
     The relationship between an amino acid residue&#39;s hydropathic index and the biological function of a protein is generally understood in the art. (Kyte, J., et al., (1982)  J. Mol. Biol.  157 (1):105-132.) It is known that certain amino acids can be substituted for other amino acids having a similar hydropathic index or score and still retain a similar biological activity. In making changes based upon the hydropathic index, the substitution of amino acids whose hydropathic indices are within ±2 of the original value is the preferred measure to determine whether the substitution is biologically functionally equivalent, though those substitutions which are within ±1 of the original value are particularly preferred, and those within ±0.5 of the original value are even more particularly preferred. 
     Similarly, it is also understood in the art that the substitution of like amino acids can be made effectively on the basis of hydrophilicity. U.S. Pat. No. 4,554,101, the disclosure of which is incorporated by reference in its entirety, states that the greatest local average hydrophilicity of a protein, as governed by the hydrophilicity of its adjacent amino acids, correlates with its immunogenic, antigenic, and other biological properties of the protein. It is understood that an amino acid can be substituted for another having a similar hydrophilicity value and still obtain a biologically equivalent protein. As reported in U.S. Pat. No. 4,554,101, the following hydrophilicity values have been assigned to amino acid residues: arginine (+3.0); lysine (+3.0); aspartic acid (+3.0±1); glutamic acid (+3.0±1); serine (+0.3); asparagine (+0.2); glutamine (+0.2); glycine (0); threonine (−0.4); proline (−0.5±1); alanine (−0.5); histidine (−0.5); cysteine (−1.0); methionine (−1.3); valine (−1.5); leucine (−1.8); isoleucine (−1.8); tyrosine (−2.3); phenylalanine (−2.5); tryptophan (−3.4). 
     As when making mutations based on the hydropathic index of an amino acid, similar changes can be made with regard to hydrophilicity. Thus, the substitution of amino acids whose hydrophilicity values are within +2 of the original value is the preferred measure to determine whether the substitution is biologically functionally equivalent, though those substitutions which are within +1 of the original value are particularly preferred, and those within +0.5 of the original value are even more particularly preferred. 
     In another embodiment, isolated nucleic acids, or functional fragments thereof, that encode for the engineered enzymes of the present invention are provided. In some embodiments, the engineered enzymes comprise an amino acid sequence selected from the group consisting of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160. In other embodiments, the present invention provides isolated nucleic acids encoding functional fragments of the engineered enzymes of the present invention, or mutants thereof in which conservative substitutions have been made for particular residues in the amino acid sequences of any of the engineered enzymes listed above. 
     Additionally, isolated nucleic acids used to express any of the engineered enzymes of the present invention may be joined to other nucleic acid sequences for use in various applications. Thus, for example, the isolated nucleic acids may be ligated into cloning or expression vectors, as are commonly known in the art and as described in the examples below. Additionally, nucleic acids may be joined in-frame to sequences encoding another polypeptide so as to form a fusion protein, as is commonly known in the art. Fusion proteins can comprise a coding region for the engineered enzyme that is aligned within the same expression unit with other proteins or peptides having desired functions, such as for solubility, purification, or immunodetection. Thus, in another embodiment, cloning, expression and fusion vectors comprising any of the above-described nucleic acids, that encode for an engineered enzyme of the present invention are also provided. 
     Furthermore, nucleic acid segments of the present invention, regardless of the length of the coding sequence itself, can be combined with other DNA sequences, such as promoters, enhancers, polyadenylation signals, additional restriction enzyme sites, multiple cloning sites, other coding segments, and the like, such that their overall length can vary considerably. Those skilled in the art would recognize that a nucleic acid fragment of almost any length can be employed, with the total length typically being limited by the ease of preparation and use in the intended recombinant DNA protocol. 
     In particular, recombinant vectors in which the coding portion of the gene or DNA segment is positioned under the control of a promoter are especially useful. In some embodiments, the coding DNA segment can be associated with promoters isolated from bacterial, viral, eukaryotic, or mammalian cells. Promoters specific to the cell type chosen for expression are often the most effective. The use of promoter and cell type combinations for protein expression is generally known to those of skill in the art of molecular biology (See, e.g., Sambrook et al. (2012) Molecular Cloning: A Laboratory Manual, Fourth Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., incorporated by reference in its entirety). The promoters employed can be constitutive or inducible and can be used under the appropriate conditions to direct high-level expression of the introduced DNA segment, such as is advantageous in the large-scale production of recombinant proteins or peptides. Appropriate promoter systems that are often effective for high-level expression include, but are not limited to, the vaccinia virus promoter, the baculovirus promoter, and the Ptac promoter. 
     Thus, in some embodiments, an expression vector can be utilized that comprises a nucleotide sequence encoding for a biologically-active, engineered enzyme suitable the present invention. In one example, an expression vector can comprise any nucleotide sequence that encodes for an aryl sulfate-dependent gene product. In further embodiments, an expression vector comprises a nucleic acid comprising the nucleotide sequence of SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56, SEQ ID NO: 58, SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 71, SEQ ID NO: 73, SEQ ID NO: 75, SEQ ID NO: 77, SEQ ID NO: 79, SEQ ID NO: 81, SEQ ID NO: 83, SEQ ID NO: 85, SEQ ID NO: 87, SEQ ID NO: 89, SEQ ID NO: 91, SEQ ID NO: 93, SEQ ID NO: 95, SEQ ID NO: 97, SEQ ID NO: 99, SEQ ID NO: 101, SEQ ID NO: 103, SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 109, SEQ ID NO: 124, SEQ ID NO: 126, SEQ ID NO: 128, SEQ ID NO: 130, SEQ ID NO: 132, SEQ ID NO: 134, SEQ ID NO: 136, SEQ ID NO: 138, SEQ ID NO: 140, SEQ ID NO: 142, SEQ ID NO: 144, SEQ ID NO: 146, SEQ ID NO: 148, SEQ ID NO: 150, or SEQ ID NO: 152. In other further embodiments, the expression vector comprises a nucleic acid comprising any nucleotide sequence that encodes for a polypeptide comprising the amino acid sequence of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160. In even further embodiments, any nucleic acid sequence encoding for an engineered enzyme of the present invention can be codon-optimized based on the expression host used to produce the enzyme. The preparation of recombinant vectors and codon optimization are well known to those of skill in the art and described in many references, such as, for example, Sambrook et al. (2012) Molecular Cloning: A Laboratory Manual, Fourth Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. 
     Those skilled in the art would recognize that the DNA coding sequences to be expressed, in this case those encoding the engineered gene products, are positioned in a vector adjacent to and under the control of a promoter. As is known in the art, a promoter is a region of a DNA molecule typically within about 100 nucleotide pairs upstream of (i.e., 5′ to) the point at which transcription begins (i.e., a transcription start site). That region typically contains several types of DNA sequence elements that are located in similar relative positions in different genes. It is understood in the art that to bring a coding sequence under the control of such a promoter, one generally positions the 5′ end of the transcription initiation site of the transcriptional reading frame of the gene product to be expressed between about 1 and about 50 nucleotides “downstream” of (i.e., 3′ of) the chosen promoter. 
     One can also desire to incorporate into the transcriptional unit of the vector an appropriate polyadenylation site (e.g., 5′-AATAAA-3′), if one was not contained within the original inserted DNA. Typically, poly-A addition sites are placed about 30 to 2000 nucleotides “downstream” of the coding sequence at a position prior to transcription termination. 
     Another type of discrete transcription regulatory sequence element is an enhancer. An enhancer imposes specificity of time, location and expression level on a particular coding region or gene. A major function of an enhancer is to increase the level of transcription of a coding sequence in a cell that contains one or more transcription factors that bind to that enhancer. An enhancer can function when located at variable distances from transcription start sites so long as a promoter is present. 
     Optionally, an expression vector of the invention comprises a polynucleotide operatively linked to an enhancer-promoter. As used herein, the phrase “enhancer-promoter” means a composite unit that contains both enhancer and promoter elements. For example, an expression vector can comprise a polynucleotide operatively linked to an enhancer-promoter that is a eukaryotic promoter and the expression vector further comprises a polyadenylation signal that is positioned 3′ of the carboxy-terminal amino acid and within a transcriptional unit of the encoded polypeptide. As used herein, the phrase “operatively linked” means that an enhancer-promoter is connected to a coding sequence in such a way that the transcription of that coding sequence is controlled and regulated by that enhancer-promoter. Techniques for operatively linking an enhancer-promoter to a coding sequence are well known in the art; the precise orientation and location relative to a coding sequence of interest is dependent, inter alia, upon the specific nature of the enhancer-promoter. 
     An enhancer-promoter used in a vector construct of the present invention can be any enhancer-promoter that drives expression in a cell to be transfected. By employing an enhancer-promoter with well-known properties, the level and pattern of gene product expression can be optimized. 
     Engineered enzymes of the present invention can be expressed within cells or cell lines, either prokaryotic or eukaryotic, into which have been introduced the nucleic acids of the present invention so as to cause clonal propagation of those nucleic acids and/or expression of the proteins or peptides encoded thereby. Such cells or cell lines are useful for propagating and producing nucleic acids, including those disclosed in sequences SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56, SEQ ID NO: 58, SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 71, SEQ ID NO: 73, SEQ ID NO: 75, SEQ ID NO: 77, SEQ ID NO: 79, SEQ ID NO: 81, SEQ ID NO: 83, SEQ ID NO: 85, SEQ ID NO: 87, SEQ ID NO: 89, SEQ ID NO: 91, SEQ ID NO: 93, SEQ ID NO: 95, SEQ ID NO: 97, SEQ ID NO: 99, SEQ ID NO: 101, SEQ ID NO: 103, SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 109, SEQ ID NO: 124, SEQ ID NO: 126, SEQ ID NO: 128, SEQ ID NO: 130, SEQ ID NO: 132, SEQ ID NO: 134, SEQ ID NO: 136, SEQ ID NO: 138, SEQ ID NO: 140, SEQ ID NO: 142, SEQ ID NO: 144, SEQ ID NO: 146, SEQ ID NO: 148, SEQ ID NO: 150, or SEQ ID NO: 152. Such cells or cell lines are also useful for producing the engineered enzymes themselves, including those described by sequences SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160. As used herein, the term “transformed cell” is intended to embrace any cell, or the descendant of any cell, into which has been introduced any of the nucleic acids of the invention, whether by transformation, transfection, transduction, infection, or other means. Methods of producing appropriate vectors, transforming cells with those vectors, and identifying transformants are well known in the art. (See, e.g., Sambrook et al. (2012) Molecular Cloning: A Laboratory Manual, Fourth Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.) 
     Prokaryotic cells useful for producing transformed cells include members of the bacterial genera  Escherichia  (e.g.,  E. coli ),  Pseudomonas  (e.g.,  P. aeruginosa ), and  Bacillus  (e.g., B. subtilus,  B. stearothermophilus ), as well as many others well known and frequently used in the art. Prokaryotic cells are particularly useful for the production of large quantities of the proteins or peptides (e.g., engineered enzymes comprising the amino acid sequences of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160, fragments of those sequences thereof, or fusion proteins including those sequences). Bacterial cells (e.g.,  E. coli ) may be used with a variety of expression vector systems including, for example, plasmids with the T7 RNA polymerase/promoter system, bacteriophage X regulatory sequences, or M13 Phage regulatory elements. Bacterial hosts may also be transformed with fusion protein vectors that create, for example, Protein A, lacZ, trpE, maltose-binding protein (MBP), small ubiquitin-related modifier (SUMO), poly-His tag, or glutathione-S-transferase (GST) fusion proteins. All of these, as well as many other prokaryotic expression systems, are well known in the art and widely available commercially (e.g., pGEX-27 (Amrad, USA) for GST fusions). 
     In some embodiments of the invention, expression vectors comprising nucleic acid sequences as set forth in SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56, SEQ ID NO: 58, SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 71, SEQ ID NO: 73, SEQ ID NO: 75, SEQ ID NO: 77, SEQ ID NO: 79, SEQ ID NO: 81, SEQ ID NO: 83, SEQ ID NO: 85, SEQ ID NO: 87, SEQ ID NO: 89, SEQ ID NO: 91, SEQ ID NO: 93, SEQ ID NO: 95, SEQ ID NO: 97, SEQ ID NO: 99, SEQ ID NO: 101, SEQ ID NO: 103, SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 109, SEQ ID NO: 124, SEQ ID NO: 126, SEQ ID NO: 128, SEQ ID NO: 130, SEQ ID NO: 132, SEQ ID NO: 134, SEQ ID NO: 136, SEQ ID NO: 138, SEQ ID NO: 140, SEQ ID NO: 142, SEQ ID NO: 144, SEQ ID NO: 146, SEQ ID NO: 148, SEQ ID NO: 150, or SEQ ID NO: 152 can also comprise genes or nucleic acid sequences encoding for fusion proteins with any engineered enzyme. In further embodiments, expression vectors can additionally include the malE gene, which encodes for the maltose binding protein. Upon inducing protein expression from such expression vectors, the expressed gene product comprises a fusion protein that includes maltose binding protein and an engineered enzyme comprising the amino acid sequence set forth in SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160. In other further embodiments, an expression vector that includes any of the above nucleic acids that encode for any of the above engineered enzymes can additionally include a gene encoding for a SUMO modifier, such as, in a non-limiting example, SUMO-1. 
     In other embodiments, expression vectors according to the present invention can additionally include a nucleic acid sequence encoding for a poly-His tag. Upon inducing protein expression from such expression vectors, the expressed gene product comprises a fusion protein that includes the poly-His tag and an engineered enzyme comprising the amino acid sequence set forth in SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160. In a further embodiment, expression vectors can include both a nucleic acid sequence encoding for a poly-His tag and the malE gene or a SUMO gene, from which a fusion protein can be expressed that includes a poly-His tag, MBP, or SUMO, along with any engineered enzyme. 
     Eukaryotic cells and cell lines useful for producing transformed cells include mammalian cells (e.g., endothelial cells, mast cells, COS cells, CHO cells, fibroblasts, hybridomas, oocytes, embryonic stem cells), insect cells lines (e.g.,  Drosophila  Schneider cells), yeast, and fungi. Non-limiting examples of such cells include, but are not limited to, COS-7 cells, CHO, cells, murine primary cardiac microvascular endothelial cells (CME), murine mast cell line C57.1, human primary endothelial cells of umbilical vein (HUVEC), F9 embryonal carcinoma cells, rat fat pad endothelial cells (RFPEC), and L cells (e.g., murine LTA tk-cells). 
     Vectors may be introduced into the recipient or “host” cells by various methods well known in the art including, but not limited to, calcium phosphate transfection, strontium phosphate transfection, DEAE dextran transfection, electroporation, lipofection, microinjection, ballistic insertion on micro-beads, protoplast fusion or, for viral or phage vectors, by infection with the recombinant virus or phage. 
     In some embodiments, the present invention provides substantially pure preparations of engineered enzymes dependent on reacting with aryl sulfate compounds for biological activity. In further embodiments, purified engineered enzymes can comprise the amino acid sequence disclosed as SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160. 
     In another embodiment, the present invention provides engineered enzyme variants in which conservative or non-conservative substitutions have been made for certain residues within the amino acid sequence disclosed as SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160. Conservative or non-conservative substitutions can be made at any point in the amino acid sequence, including residues that surround the active site or are involved in catalysis, provided that the enzyme retains measurable catalytic activity; namely, the transfer of a sulfo group from an aryl sulfate compound to a polysaccharide, particularly a heparosan-based and/or HS polysaccharide. In other embodiments, the aryl sulfate compound is PNS. In still other embodiments, the aryl sulfate compound is NCS. 
     In another embodiment, the engineered sulfotransferase enzymes have at least 50%, including at least 60%, 70%, 80%, 85%, 90% or 95% up to at least 99% amino acid sequence identity to an amino acid sequence disclosed as SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160, while retaining its catalytic activity of transfer of a sulfo group from an aryl sulfate compound to a polysaccharide, particularly a heparosan-based and/or HS polysaccharide. Such sequences may be routinely produced by those of ordinary skill in the art, and sulfotransferase activity may be tested by routine methods such as those disclosed herein. 
     Further, and in another embodiment, the amino acid sequence(s) of any of the engineered sulfotransferases utilized in accordance with any of the methods described herein can be characterized as a percent identity relative to a natural sulfotransferase that catalyzes the same reaction using PAPS as the sulfo donor, so long as the sulfotransferase has aryl sulfate-dependent activity. For example, and in another embodiment, an engineered aryl sulfate-dependent NST that can be utilized in accordance with any of the methods of the present invention can comprise an amino acid sequence that has at least 50%, including at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, up to at least 97% sequence identity with the amino acid sequence of the N-sulfotransferase domain of any of the natural NDST enzymes within EC 2.8.2.8, including biological functional fragments thereof. In a further embodiment, the engineered NST can comprise at least 50%, including at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, up to at least 97% sequence identity with the amino acid sequence of the N-sulfotransferase domain of the human NDST1 enzyme (entry sp|P52848NDST_1_HUMAN, in  FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C , above). 
     In another embodiment, an engineered aryl sulfate-dependent 2OST that can be utilized in accordance with any of the methods of the present invention can comprise an amino acid sequence that has at least 50%, including at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, up to at least 97% sequence identity with the amino acid sequence of any of the natural 2OST enzymes within EC 2.8.2.—, including biological functional fragments thereof. In a further embodiment, the engineered 2OST can comprise at least 50%, including at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, up to at least 97% sequence identity with the amino acid sequence of the natural chicken 2OST enzyme (entry sp|Q76KB1HS2ST_CHICK, in  FIG.  17 A ,  FIG.  17 B ,  FIG.  17 C , and  FIG.  17 D , above). 
     In another embodiment, an engineered aryl sulfate-dependent 6OST that can be utilized in accordance with any of the methods of the present invention can comprise an amino acid sequence that has at least 50%, including at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, up to at least 97% sequence identity with the amino acid sequence of any of the natural 6OST enzymes within EC 2.8.2.—, including biological functional fragments thereof. In a further embodiment, the engineered 6OST can comprise at least 50%, including at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, up to at least 97% sequence identity with the amino acid sequence of the mouse 6OST1 enzyme (UniProtKB Accession No. Q9QYK5). In a further embodiment, the engineered 6OST can comprise at least 50%, including at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, up to at least 97% sequence identity with residues 67-377 of the amino acid sequence of the mouse 6OST1 enzyme (entry Q9QYK5|H6ST1_MOUSE, in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C , above). 
     In another embodiment, an engineered aryl sulfate-dependent 3OST that can be utilized in accordance with any of the methods of the present invention can comprise an amino acid sequence that has at least 50%, including at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, up to at least 97% sequence identity with the amino acid sequence of any of the natural enzymes within EC 2.8.2.23, including biological functional fragments thereof. In a further embodiment, the engineered 3OST can comprise at least 50%, including at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, up to at least 97% sequence identity with residues 48-311 of the amino acid sequence of the natural human 3OST1 enzyme (entry O14792|HS3S1_HUMAN, in  FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C , above). 
     Substantially pure engineered enzymes may be joined to other polypeptide sequences for use in various applications. Thus, for example, engineered enzymes may be joined to one or more additional polypeptides so as to form a fusion protein, as is commonly known in the art. The additional polypeptides may be joined to the N-terminus, C-terminus or both termini of the engineered enzyme. Such fusion proteins may be particularly useful if the additional polypeptide sequences are easily identified (e.g., by providing an antigenic determinant), are easily purified (e.g., by providing a ligand for affinity purification), or enhance the solubility of the engineered enzyme in solution. 
     In another embodiment, substantially pure proteins may comprise only a portion or fragment of the amino acid sequence of an engineered enzyme. In some instances, it may be preferable to employ a minimal fragment retaining aryl sulfate-dependent activity, particularly if the minimal fragment enhances the solubility or reactivity of the enzyme. Thus, in some embodiments, methods of the present invention can be practiced using substantially pure engineered sulfotransferases of any length, including full-length forms described by the amino acid sequences of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 110, SEQ ID NO: 111, SEQ ID NO: 112, SEQ ID NO: 113, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, SEQ ID NO: 122, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, SEQ ID NO: 151, SEQ ID NO: 153, SEQ ID NO: 154, SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160, including minimal functional fragments thereof. Additionally, these proteins may also comprise conservative or non-conservative substitution variants as described above. 
     The engineered enzymes may be substantially purified by any of a variety of methods selected on the basis of the properties revealed by their protein sequences. Typically, the engineered enzymes, fusion proteins, or fragments thereof, can be purified from cells transformed or transfected with expression vectors, as described above. Insect, yeast, eukaryotic, or prokaryotic expression systems can be used, and are well known in the art. In the event that the protein or fragment localizes within microsomes derived from the Golgi apparatus, endoplasmic reticulum, or other membrane-containing structures of such cells, the protein may be purified from the appropriate cell fraction. Alternatively, if the protein does not localize within these structures, or aggregates in inclusion bodies within the recombinant cells (e.g., prokaryotic cells), the protein may be purified from whole lysed cells or from solubilized inclusion bodies by standard means. 
     Purification can be achieved using standard protein purification procedures including, but not limited to, affinity chromatography, gel-filtration chromatography, ion-exchange chromatography, high-performance liquid chromatography (RP-HPLC, ion-exchange HPLC, size-exclusion HPLC), high-performance chromatofocusing chromatography, hydrophobic interaction chromatography, immunoprecipitation, or immunoaffinity purification. Gel electrophoresis (e.g., PAGE, SDS-PAGE) can also be used to isolate a protein or peptide based on its molecular weight, charge properties and hydrophobicity. 
     An engineered enzyme, or a fragment thereof, may also be conveniently purified by creating a fusion protein including the desired sequence fused to another peptide such as an antigenic determinant, a poly-histidine tag (e.g., QIAexpress vectors, QIAGEN Corp., Chatsworth, Calif.), or a larger protein (e.g., GST using the pGEX-27 vector (Amrad, USA), green fluorescent protein using the Green Lantern vector (GlBCO/BRL. Gaithersburg, Md.), maltose binding protein using the pMAL vector (New England Biolabs, Ipswich, Mass.), or a SUMO protein. The fusion protein may be expressed and recovered from prokaryotic or eukaryotic cells and purified by any standard method based upon the fusion vector sequence. For example, the fusion protein may be purified by immunoaffinity or immunoprecipitation with an antibody to the non-aryl sulfate-dependent enzyme portion of the fusion or, in the case of a poly-His tag, by affinity binding to a nickel column. The desired engineered enzyme protein or fragment can then be further purified from the fusion protein by enzymatic cleavage of the fusion protein. Methods for preparing and using such fusion constructs for the purification of proteins are well known in the art and numerous kits are now commercially available for this purpose. 
     Furthermore, in some embodiments, isolated nucleic acids encoding for any engineered enzyme may be used to transform host cells. The resulting proteins may then be substantially purified by well-known methods including, but not limited to, those described in the examples below. Alternatively, isolated nucleic acids may be utilized in cell-free in vitro translation systems. Such systems are also well known in the art. 
     While particular embodiments of the invention have been described, the invention can be further modified within the spirit and scope of this disclosure. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures, embodiments, claims, and examples described herein. As such, such equivalents are considered to be within the scope of the invention, and this application is therefore intended to cover any variations, uses or adaptations of the invention using its general principles. Further, the invention is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the appended claims. 
     It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements. 
     The contents of all references, patents, and patent applications mentioned in this specification are hereby incorporated by reference, and shall not be construed as an admission that such reference is available as prior art to the present invention. Additionally, the disclosures of U.S. Pat. Nos. 11,473,068 and 11,542,534; U.S. Patent Pub. Nos. 2021/0363503, 2021/0363504, and 2022/0042062; U.S. patent application Ser. Nos. 17/894,924, 17/894,929, 17/894,932, 17/894,933, and 17/949,489; U.S. Provisional Application No. 63/051,764; and International Application No. PCT/US2021/041537 are all herein incorporated by reference in their entireties. All of the incorporated publications and patent applications in this specification are indicative of the level of ordinary skill in the art to which this invention pertains, and are incorporated to the same extent as if each individual publication or patent application was specifically indicated and individually indicated by reference. 
     The invention is further illustrated by the following working and prophetic examples, neither of which should be construed as limiting the invention. Additionally, to the extent that section headings are used, they should not be construed as necessarily limiting. Any use of the past tense to describe an example otherwise indicated as constructive or prophetic is not intended to reflect that the constructive or prophetic example has actually been carried out. 
     EXAMPLES 
     The following working and prophetic examples illustrate the embodiments of the invention that are presently best known. However, it is to be understood that the following are only exemplary or illustrative of the application of the principles of the present invention. Numerous modifications and alternative compositions, methods, and systems may be devised by those skilled in the art without departing from the spirit and scope of the present invention. Thus, while the present invention has been described above with particularity, the following examples provide further detail in connection with what are presently deemed to be the most practical and preferred embodiments of the invention. 
     Example 1: Cloning, Expression, and Purification of the Engineered Aryl Sulfate-Dependent Enzymes 
     A study was conducted in accordance with embodiments of the present disclosure to determine whether genes according to the present invention could be transformed into host cells capable of overexpressing engineered aryl sulfate-dependent enzymes, particularly enzymes having sulfotransferase activity. After expression, each aryl sulfate-dependent enzyme was isolated and purified from the host cell. 
     Generally, DNA coding for genes of any sequence can be synthesized de novo by methods commonly known in the art, including but not limited to oligonucleotide synthesis and annealing. Alternatively, DNA can be synthesized commercially and purchased from any one of several laboratories that regularly synthesize genes of a given sequence, including but not limited to ThermoFisher Scientific, GenScript, DNA 2.0, or OriGene. Persons skilled in the art would appreciate that there are several companies that provide the same services, and that the list provided above is merely a small sample of them. Genes of interest can be synthesized independently and subsequently inserted into a bacterial or other expression vector using conventional molecular biology techniques, or the genes can be synthesized concurrently with the DNA comprising the expression vector itself. Similar to genes of interest, suitable expression vectors can also be synthesized or obtained commercially. Often, bacterial expression vectors include genes that confer selective antibiotic resistance to the host cell, as well as genes that permit the cell to overproduce the protein of interest in response to the addition of isopropyl β-D-1-thiogalactopyranoside (IPTG). Bacterial production of proteins of interest using IPTG to induce protein expression is widely known in the art. 
     As described above, expression vectors can also include genes that enable production of fusion proteins that include the desired protein that is co-expressed with an additional, known protein to aid in protein folding and solubility. Non-limiting examples of fusion proteins that are commonly produced and are well-known in the art include fusions with MBP, SUMO, or green fluorescent protein. In particular, MBP fusion proteins facilitate easier purification because MBP possesses high affinity for amylose-based resins used in some affinity chromatography columns, while SUMO fusion proteins can include a poly-histidine tag that enables affinity purification on columns with Ni 2+ -based resins as a stationary phase. Often, fusion proteins between the protein of interest and MBP and/or SUMO can optionally include an amino acid linking sequence that connects the two proteins. Non-limiting examples of commercial expression vectors that can be purchased to produce MBP fusion proteins include the pMAL-c5E™ and pMAL-c5X™ vectors, which can be obtained from New England Biolabs. Similarly, and in another non-limiting example, commercial expression vectors can also be purchased to produce SUMO fusion proteins, such as the pE-SUMOpro AMP vector, available from LifeSensors, Inc. Once the fusion proteins are produced and purified, proteases can be utilized to cleave the fused protein and any associated linker sequences from the enzyme, if cleavage is necessary for activity. 
     Additionally, expression vectors can also include DNA coding for a poly-histidine tag that can be synthesized at either the N- or C-terminus of the protein of interest. As with MBP fusions, proteins that include a poly-histidine tag simplify the enzyme purification because the tag has a high affinity for Ni 2+  resins that are utilized in many purification columns. Additionally, poly-histidine tags can optionally be cleaved after purification if it is necessary for optimal activity of the enzyme. A non-limiting example of an expression vector encoding for a C-terminal poly-histidine tag is the pET21b vector, available from Novagen. Another non-limiting example of an expression vector encoding for a poly-histidine tag is the pE-SUMO vector, which encodes for a poly-histidine tag at the N-terminus of the SUMO protein. 
     In the present example, double-stranded DNA fragments comprising the nucleotide sequences of SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56, SEQ ID NO: 58, SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 71, SEQ ID NO: 73, SEQ ID NO: 75, SEQ ID NO: 77, SEQ ID NO: 79, SEQ ID NO: 81, SEQ ID NO: 83, SEQ ID NO: 85, SEQ ID NO: 87, SEQ ID NO: 89, SEQ ID NO: 91, SEQ ID NO: 93, SEQ ID NO: 95, SEQ ID NO: 97, SEQ ID NO: 99, SEQ ID NO: 101, SEQ ID NO: 103, SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 109, SEQ ID NO: 124, SEQ ID NO: 126, SEQ ID NO: 128, SEQ ID NO: 130, SEQ ID NO: 132, SEQ ID NO: 134, SEQ ID NO: 136, SEQ ID NO: 138, SEQ ID NO: 140, SEQ ID NO: 142, SEQ ID NO: 144, SEQ ID NO: 146, SEQ ID NO: 148, SEQ ID NO: 150, or SEQ ID NO: 152, encoding for engineered aryl sulfate-dependent enzymes comprising the amino acid sequences of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, or SEQ ID NO: 151, respectively, were synthesized using Integrated DNA Technologies&#39; (IDT) gBlocks® Gene Fragments synthesis service. Polymerase chain reactions (PCR) were initiated to generate copies of each double-stranded DNA fragment, using forward and reverse primers comprising appropriate restriction enzyme recognition sequences to facilitate insertion into an expression vector. Genes comprising the nucleotide sequences SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 124, SEQ ID NO: 126, SEQ ID NO: 128, SEQ ID NO: 130, SEQ ID NO: 132, SEQ ID NO: 134, SEQ ID NO: 136, SEQ ID NO: 138, SEQ ID NO: 140, SEQ ID NO: 142, SEQ ID NO: 144, SEQ ID NO: 146, SEQ ID NO: 148, SEQ ID NO: 150, or SEQ ID NO: 152, encoding for engineered enzymes comprising the amino acid sequences SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, or SEQ ID NO: 151, respectively, contained NdeI and BamHI restriction enzyme recognition sequences, and were ligated into the pMAL-c5x expression vector using quick ligation kits provided by NEB. Expression vectors were then transformed into competent DH5-α  E. coli  cells. Single clones were incubated in LB medium with 100 μL/mL ampicillin. Nucleotide sequences of each gene and expression vector within the transformed host cells were confirmed by commercial DNA sequencing (GeneWiz). 
     Protein expression of engineered enzymes comprising the amino acid sequences SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, or SEQ ID NO: 151 was achieved by transforming confirmed DNA constructs into competent SHuffle® T7 Express lysY  E. coli  cells, although protein expression has also been achieved by transforming confirmed DNA constructs into competent BL21 (DE3)  E. coli  cells. From either construct, resultant colonies were used to inoculate 250 mL cultures in LB medium, which were allowed to shake and incubate at 32° C. until an optical density at 600 nM (OD 600) of approximately 0.4 to 0.6 was observed. Expression was induced by the addition of 100 μM IPTG to each culture at 18° C. 
     Upon incubation at 18° C. overnight, expressed cells were harvested by centrifuging at 3,620 g and resuspending the pellet in 10 mL of resuspension buffer (25 mM Tris-HCl, pH 7.5; 0.15 M NaCl; 0.2 mg/mL lysozyme; 10 μg/ml DNase I; 5 mM MgCl 2 ; and 0.1% (w/v) Triton-X 100). Resuspended cells were lysed upon sonication on ice for three pulses of 10 seconds each, and subsequently passed through a 0.45-μm syringe filter. The resulting supernatant was loaded into a 5-mL spin column (G-biosciences) comprising Dextrin Sepharose® resin (GE Biosciences) suspended in a binding buffer comprising 25 mM Tris-HCl, pH 7.5 and 0.15 M NaCl. Enzymes of interest were eluted from the column upon adding an elution buffer comprising 25 mM Tris-HCl, pH 7.5; 0.15 M NaCl; and 40 mM maltose. 
     On the other hand, genes comprising the nucleotide sequences SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56, SEQ ID NO: 58, SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 71, SEQ ID NO: 73, SEQ ID NO: 75, SEQ ID NO: 77, SEQ ID NO: 79, SEQ ID NO: 81, SEQ ID NO: 83, SEQ ID NO: 85, SEQ ID NO: 87, SEQ ID NO: 89, SEQ ID NO: 91, SEQ ID NO: 93, SEQ ID NO: 95, SEQ ID NO: 97, SEQ ID NO: 99, SEQ ID NO: 101, SEQ ID NO: 103, SEQ ID NO: 105, SEQ ID NO: 107, or SEQ ID NO: 109, encoding for engineered enzymes comprising the amino acid sequences SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, or SEQ ID NO: 108, respectively, contained BsaI and XbaI restriction enzyme recognition sequences, and were ligated into the pE-SUMO vector (LifeSensors, Inc.). Expression vectors were then transformed into competent BL21-DE3  E. coli  cells. Single clones were incubated in Terrific Broth with 100 μL/mL ampicillin. Nucleotide sequences of each gene and expression vector within the transformed host cells were confirmed by commercial DNA sequencing (GeneWiz). 
     Protein expression of engineered enzymes comprising the amino sequences SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, or SEQ ID NO: 108 was achieved by inoculating 500 mL cultures in Terrific Broth with ampicillin and allowing the cultures to incubate with shaking at 35° C. until an OD 600 of approximately 0.6-0.8 was reached. Protein expression was induced by the addition of 0.2 mM IPTG at 18° C. Cultures were then allowed to incubate at 18° C. overnight, and were subsequently lysed and filtered using an identical procedure as described above. The engineered enzymes were subsequently purified in a 5-mL spin column (G-biosciences) comprising HisPur Ni-NTA resin (Thermofisher) suspended in a binding buffer comprising 25 mM Tris-HCl, pH 7.5, 0.15 M NaCl, 5 mM MgCl 2 , and 30 mM imidazole. Enzymes of interest were eluted from the column upon adding an elution buffer comprising 25 mM Tris-HCl, pH 7.5, 0.15 M NaCl, 5 mM MgCl 2 , and 300 mM imidazole. 
     Example 2: Confirmation of Aryl Sulfate-Dependent Sulfatase Activity 
     Generally, the sulfatase activity of the aryl sulfate-dependent enzymes can be readily determined because the desulfurylated aromatic products of many aryl sulfate compounds, including but not limited to, PNS, MUS, 7-hydroxycoumarin sulfate, phenyl sulfate, 4-acetylphenyl sulfate, indoxyl sulfate, 1 naphthyl sulfate, 2NapS, and NCS each have the ability to absorb light or fluoresce in the near ultraviolet or visible spectrum. The absorbance or fluorescence by the desulfurylated aromatic product can be detected using a spectrophotometer or a fluorimeter, respectively. Those skilled in the art would readily be able to determine which instrument to use to monitor the progress of a reaction based on the spectral properties of the particular aryl sulfate compound and its desulfurylated aromatic product(s). 
     In one non-limiting example, reactions in which PNS is utilized as a substrate produce p-nitrophenol as a product upon hydrolysis of the sulfate ester linkage. Reaction mixtures having a pH greater than the pKa of p-nitrophenol (about 7.15) turn yellow because the negatively-charged p-nitrophenolate ion is prevalent over the neutrally-charged p-nitrophenol. Typically, the maximum absorbance of visible light by a solution containing the p-nitrophenolate ion can be observed at a wavelength of about 405 nm. Consequently, an absorbance value under reaction conditions that is greater than a negative control containing only PNS in identical buffer conditions indicates that the enzyme is active. Similarly, as more p-nitrophenolate ion is produced as a result of catalysis by a particular aryl sulfate-dependent enzyme, the absorbance of the reaction mixture as a function of time can be measured at about 405 nm to determine reaction rate and other kinetic information. As another non-limiting example, the production of the desulfurylated product of NCS, 4-nitrocatechol, upon hydrolysis of the sulfate ester linkage can be measured in reactions having a pH greater than the pKa of 4-nitrocatechol (about 7.17), by observing the absorbance of visible light at a wavelength of about 515 nm. 
     As another limiting example, the desulfurylated products of 2NapS can fluoresce in solution in response to being excited by radiation at a lower wavelength. Depending on the pH of the solution, the desulfurylated product is either 2-naphthol or the 2-naphtholate ion (pKa=9.5). To ensure the presence of a single 2-naphthyl species in solution, compositions with completed reactions are typically quenched with either an acid or a base in order to drive equilibrium to either the complete formation of 2-naphthol, which has an emission maximum of around 355 nM, or the 2-naphtholate ion, which has an emission maximum of about 410 nm. In either instance, the desulfurylated product can be excited at a wavelength of around 320 nm. 
     Thus, a study was conducted in accordance with embodiments of the present disclosure to determine the sulfatase activity of purified enzymes comprising the amino acid sequences of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO: 102, SEQ ID NO: 104, SEQ ID NO: 106, SEQ ID NO: 108, SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, or SEQ ID NO: 151. Non-steady state sulfatase activity with PNS, NCS, and 2NapS was monitored in 100-μL reactions containing 50 μM enzyme and 5 mM of substrate in elution buffer. In reactions containing PNS, the absorbance of the reaction mixture as a result of the production of p-nitrophenolate was measured at 401 nm. In reactions containing NCS, the absorbance of the reaction mixture as a result of the production of 4-nitrocatechol was measured at 515 nm. Reaction mixtures containing 2NapS were quenched by adding 0.1M NaOH to convert all of the 2-naphthol produced as a result of the reaction to the 2-naphtholate ion. All of the sets of activity experiments were conducted using a Spectramax M2 Microplate Reader (Molecular Dynamics). Additionally, a negative control reaction condition was set up for each experiment, which contained the aryl sulfate compound in the elution buffer (see above), but with no enzyme present. Activity experiments for the engineered enzymes were conducted in several data sets. All raw data were normalized and evaluated as a percentage of the increase in signal over a control in which all other components but enzyme was added, with results reported below in Tables 2-10. In particular, the results of enzymes that are mutants of natural NDST enzymes are reported in Table 2, Table 3, and Table 4, the results of enzymes that are mutants of natural 2OSTs are reported in Table 5 and Table 6, the results of enzymes that are mutants of natural 6OSTs are reported in Table 7 and Table 8, and the results of enzymes that are mutants of natural 3OSTs are reported in Table 9 and Table 10. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 PNS (Abs 401 ) 
                 (−) control 
                 % increase 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 SEQ ID NO: 1 
                 0.078 
                 0.055 
                 42% 
               
               
                   
                 SEQ ID NO: 3 
                 0.1095 
                 0.055 
                 99% 
               
               
                   
                 SEQ ID NO: 5 
                 0.0965 
                 0.055 
                 75% 
               
               
                   
                 SEQ ID NO: 7 
                 0.0925 
                 0.055 
                 68% 
               
               
                   
                 SEQ ID NO: 9 
                 0.107 
                 0.079 
                 35% 
               
               
                   
                 SEQ ID NO: 11 
                 0.128 
                 0.079 
                 62% 
               
               
                   
                 SEQ ID NO: 15 
                 0.083 
                 0.059 
                 42% 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 NCS (Abs 515 ) 
                 (−) control 
                 % increase 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 SEQ ID NO: 3 
                 0.0545 
                 0.041 
                  33% 
               
               
                   
                 SEQ ID NO: 5 
                 0.0545 
                 0.041 
                  33% 
               
               
                   
                 SEQ ID NO: 7 
                 0.057 
                 0.041 
                  39% 
               
               
                   
                 SEQ ID NO: 9 
                 0.168 
                 0.083 
                 102% 
               
               
                   
                 SEQ ID NO: 11 
                 0.213 
                 0.083 
                 157% 
               
               
                   
                 SEQ ID NO: 13 
                 0.201 
                 0.083 
                 143% 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 2NapS (λ em, 410 ) 
                 (−) control 
                 % increase 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 SEQ ID NO: 3 
                 2.974 × 10 6   
                 1.804 × 10 6   
                 65% 
               
               
                 SEQ ID NO: 5 
                 3.188 × 10 6   
                 1.804 × 10 6   
                 76% 
               
               
                 SEQ ID NO: 9 
                 2.972 × 10 6   
                 1.804 × 10 6   
                 65% 
               
               
                 SEQ ID NO: 11 
                 2.965 × 10 6   
                 1.804 × 10 6   
                 64% 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 NCS (Abs 515 ) 
                 (−) control 
                 % increase 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 SEQ ID NO: 27 
                 0.064 
                 0.046 
                 39% 
               
               
                   
                 SEQ ID NO: 29 
                 0.063 
                 0.046 
                 37% 
               
               
                   
                 SEQ ID NO: 33 
                 0.072 
                 0.046 
                 56% 
               
               
                   
                 SEQ ID NO: 45 
                 0.085 
                 0.046 
                 85% 
               
               
                   
                 SEQ ID NO: 53 
                 0.082 
                 0.046 
                 78% 
               
               
                   
                 SEQ ID NO: 63 
                 0.069 
                 0.046 
                 50% 
               
               
                   
                 SEQ ID NO: 65 
                 0.065 
                 0.046 
                 41% 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 PNS (Abs 401 ) 
                 (−) control 
                 % increase 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 SEQ ID NO: 27 
                 0.103 
                 0.073 
                 41% 
               
               
                   
                 SEQ ID NO: 33 
                 0.077 
                 0.046 
                 67% 
               
               
                   
                 SEQ ID NO: 35 
                 0.076 
                 0.046 
                 65% 
               
               
                   
                 SEQ ID NO: 37 
                 0.089 
                 0.046 
                 93% 
               
               
                   
                 SEQ ID NO: 39 
                 0.076 
                 0.046 
                 65% 
               
               
                   
                 SEQ ID NO: 41 
                 0.084 
                 0.046 
                 82% 
               
               
                   
                 SEQ ID NO: 45 
                 0.124 
                 0.080 
                 55% 
               
               
                   
                 SEQ ID NO: 47 
                 0.194 
                 0.095 
                 105%  
               
               
                   
                 SEQ ID NO: 51 
                 0.210 
                 0.095 
                 121%  
               
               
                   
                 SEQ ID NO: 53 
                 0.120 
                 0.080 
                 50% 
               
               
                   
                 SEQ ID NO: 55 
                 0.067 
                 0.046 
                 45% 
               
               
                   
                 SEQ ID NO: 57 
                 0.072 
                 0.046 
                 57% 
               
               
                   
                 SEQ ID NO: 59 
                 0.073 
                 0.046 
                 59% 
               
               
                   
                 SEQ ID NO: 61 
                 0.068 
                 0.046 
                 48% 
               
               
                   
                 SEQ ID NO: 63 
                 0.105 
                 0.073 
                 44% 
               
               
                   
                 SEQ ID NO: 65 
                 0.105 
                 0.080 
                 31% 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 PNS (Abs 401 ) 
                 (−) control 
                 % increase 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 SEQ ID NO: 70 
                 0.1340 
                 0.114 
                 18% 
               
               
                   
                 SEQ ID NO: 72 
                 0.0740 
                 0.065 
                 14% 
               
               
                   
                 SEQ ID NO: 74 
                 0.1150 
                 0.103 
                 12% 
               
               
                   
                 SEQ ID NO: 76 
                 0.0990 
                 0.075 
                 32% 
               
               
                   
                 SEQ ID NO: 78 
                 0.1020 
                 0.075 
                 36% 
               
               
                   
                 SEQ ID NO: 80 
                 0.1010 
                 0.075 
                 35% 
               
               
                   
                 SEQ ID NO: 82 
                 0.1160 
                 0.103 
                 13% 
               
               
                   
                 SEQ ID NO: 86 
                 0.0950 
                 0.075 
                 27% 
               
               
                   
                 SEQ ID NO: 88 
                 0.1070 
                 0.075 
                 43% 
               
               
                   
                 SEQ ID NO: 90 
                 0.1290 
                 0.106 
                 22% 
               
               
                   
                 SEQ ID NO: 92 
                 0.0910 
                 0.08 
                 14% 
               
               
                   
                 SEQ ID NO: 94 
                 0.0980 
                 0.08 
                 23% 
               
               
                   
                 SEQ ID NO: 106 
                 0.0810 
                 0.068 
                 19% 
               
               
                   
                 SEQ ID NO: 108 
                 0.0840 
                 0.068 
                 23% 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                 NCS (Abs 515 ) 
                 (−) control 
                 % increase 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 SEQ ID NO: 70 
                 0.097 
                 0.077 
                 27% 
               
               
                   
                 SEQ ID NO: 74 
                 0.079 
                 0.072 
                  9% 
               
               
                   
                 SEQ ID NO: 76 
                 0.06 
                 0.044 
                 36% 
               
               
                   
                 SEQ ID NO: 78 
                 0.056 
                 0.044 
                 27% 
               
               
                   
                 SEQ ID NO: 80 
                 0.057 
                 0.044 
                 30% 
               
               
                   
                 SEQ ID NO: 82 
                 0.08 
                 0.072 
                 10% 
               
               
                   
                 SEQ ID NO: 84 
                 0.064 
                 0.056 
                 14% 
               
               
                   
                 SEQ ID NO: 86 
                 0.06 
                 0.049 
                 22% 
               
               
                   
                 SEQ ID NO: 88 
                 0.067 
                 0.049 
                 37% 
               
               
                   
                 SEQ ID NO: 90 
                 0.087 
                 0.072 
                 20% 
               
               
                   
                 SEQ ID NO: 92 
                 0.058 
                 0.05 
                 16% 
               
               
                   
                 SEQ ID NO: 94 
                 0.061 
                 0.05 
                 22% 
               
               
                   
                 SEQ ID NO: 96 
                 0.093 
                 0.077 
                 22% 
               
               
                   
                 SEQ ID NO: 98 
                 0.092 
                 0.077 
                 20% 
               
               
                   
                 SEQ ID NO: 100 
                 0.049 
                 0.044 
                 11% 
               
               
                   
                 SEQ ID NO: 102 
                 0.053 
                 0.047 
                 12% 
               
               
                   
                 SEQ ID NO: 104 
                 0.054 
                 0.044 
                 23% 
               
               
                   
                 SEQ ID NO: 106 
                 0.064 
                 0.056 
                 15% 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 9 
               
               
                   
                   
               
               
                   
                 PNS (Abs 401 ) 
                 (−) control 
                 % increase 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 SEQ ID NO: 123 
                 0.0730 +/− .00283 
                 0.0545 
                 34% 
               
               
                 SEQ ID NO: 127 
                 0.0745 +/− .00354 
                 0.0544 
                 37% 
               
               
                 SEQ ID NO: 129 
                 0.0730 +/− .00141 
                 0.0545 
                 34% 
               
               
                 SEQ ID NO: 133 
                 0.0730 +/− 0.0   
                 0.0544 
                 34% 
               
               
                 SEQ ID NO: 135 
                 0.1000 +/− .00566 
                 0.0658 
                 52% 
               
               
                 SEQ ID NO: 137 
                 0.1060 +/− .00141 
                 0.0658 
                 61% 
               
               
                 SEQ ID NO: 141 
                 0.0860 +/− .00283 
                 0.0589 
                 46% 
               
               
                 SEQ ID NO: 143 
                 0.1030 +/− 0.0   
                 0.0792 
                 30% 
               
               
                 SEQ ID NO: 147 
                 0.0865 +/− .00071 
                 0.0588 
                 47% 
               
               
                 SEQ ID NO: 149 
                 0.0890 +/− 0.0   
                 0.0589 
                 51% 
               
               
                 SEQ ID NO: 151 
                 0.0900 +/− 0.0   
                 0.0588 
                 53% 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 10 
               
               
                   
                   
               
               
                   
                 NCS (Abs 515 ) 
                 (−) control 
                 % increase 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 SEQ ID NO: 123 
                 0.0505 +/− .00354 
                 0.0391 
                 29% 
               
               
                 SEQ ID NO: 125 
                 0.0505 +/− .00495 
                 0.0391 
                 29% 
               
               
                 SEQ ID NO: 131 
                 0.0560 +/− .00141 
                 0.0409 
                 37% 
               
               
                 SEQ ID NO: 135 
                 0.0735 +/− .01768 
                 0.0420 
                 75% 
               
               
                 SEQ ID NO: 137 
                 0.0560 +/− .00283 
                 0.0421 
                 61% 
               
               
                 SEQ ID NO: 139 
                 0.1550 +/− .00265 
                 0.0829 
                 87% 
               
               
                 SEQ ID NO: 141 
                 0.0560 +/− .00141 
                 0.0409 
                 37% 
               
               
                 SEQ ID NO: 143 
                 0.1520 +/− .00954 
                 0.0831 
                 83% 
               
               
                 SEQ ID NO: 145 
                 0.1850 +/− .001  
                 0.0830 
                 123%  
               
               
                 SEQ ID NO: 149 
                 0.0565 +/− .00212 
                 0.0409 
                 38% 
               
               
                 SEQ ID NO: 151 
                 0.0585 +/− .00212 
                 0.0409 
                 43% 
               
               
                   
               
            
           
         
       
     
     As can be observed in the Tables above, some of the enzymes are active with PNS, some are active with NCS, and many are active with both PNS and NCS. Generally, reaction mixtures containing enzymes active with either aryl sulfate compound demonstrated an absorbance that was approximately 1.1 to 2.5 times greater than the negative control. 
     Example 3: Mass Spectrometric Characterization of the N-Sulfated Polysaccharide Products of Engineered Aryl Sulfate-Dependent NST Enzymes 
     A study was conducted in accordance with embodiments of the present disclosure to confirm glucosaminyl N-sulfotransferase activity of enzymes comprising the amino acid sequence of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, or SEQ ID NO: 15 by detecting the presence of N-sulfated polysaccharide products formed as a result of their sulfotransfer reaction, using mass spectrometry (MS). Each engineered enzyme was purified according to the procedure of Example 1. Sulfotransferase activity was monitored in 100 μL reactions containing 50 μM of enzyme. To each purified protein solution, 20 mg of an aryl sulfate compound (either PNS or NCS) was dissolved in 2 mL of reaction buffer (50 mM MES pH 7.0, 2 mM CaCl 2 ), added to the protein solution, and incubated at 37° C. for 10 min. 2.5 mL of 2 mg/mL solution of N-deacetylated heparosan was added to protein/donor solution and incubated overnight at 37° C. The N-deacetylated heparosan was synthesized according to the protocol described in Balagurunathan, K. et al (eds.) (2015),  Glycosaminoglycans: Chemistry and Biology , Methods in Molecular Biology, vol. 1229, DOI 10.1007/978-1-4939-1714-3_2, © Springer Science+Business Media, New York, pp. 11-19 (section 3.1). To purify the N-sulfated product, the incubated reaction mixture was centrifuged the following day at 5,000×g for 10 min. The filter was washed once with 2 mL water, and centrifuged again. The filtrate was added to a 1K MWCO Dialysis membrane, dialyzed for 2 days in Milli-Q water, with water changes at 1 h, 2 h, 8 h, 16 h, 32 h, and then lyophilized. 
     The lyophilized N-sulfated products from each reaction were subsequently digested with a mixture of three carbon-oxygen lyases comprising the amino acid sequences of SEQ ID NO: 161, SEQ ID NO: 162, and SEQ ID NO: 163, which catalyze the β-eliminative cleavage of heparosan-based polysaccharides. Such lyases are available from New England Biolabs, among other chemical and biological commercial entities. 1 μL of each lyase was incubated with 50 μg of the lyophilized sulfated polysaccharide product and the provided digestion buffer, and incubated over 24 hours according to the packaged instructions provided by New England Biolabs with each lyase. After digestion, the lyase enzymes were inactivated by heating to 100° C. for 5 minutes. Samples were centrifuged at 14,000 rpm for 30 minutes before introduction to a strong anion exchange, high performance liquid chromatography (SAX) analysis. SAX analysis was performed on a Dionex Ultimate 3000 LC system interface. Separation was carried out on a 4.6×250 mm Waters Spherisorb analytical column with 5.0 μm particle size at 45° C. Mobile phase solution A was 2.5 mM sodium phosphate, pH 3.5, while mobile phase solution B was 2.5 mM sodium phosphate, pH 3.5, and 1.2 M Sodium perchlorate. After each sample was loaded onto the column, mobile phase solutions were applied to the column at a ratio of 98% mobile phase solution A and 2% mobile phase solution B for five minutes at a flow rate of 1.4 mL/min. After five minutes, a linear gradient of increasing mobile phase solution B was applied until the ratio of mobile phase solution A to mobile phase solution B was 50:50. 
     Using the SAX analysis, it was determined that six of the eight tested enzymes were active as sulfotransferases. However, each of the sulfotransferases were not necessarily active with both PNS and NCS. Enzymes having the amino acid sequences of SEQ ID NO: 5, SEQ ID NO: 7, and SEQ ID NO: 13 had activity with NCS only, and the enzyme having the amino acid sequence of SEQ ID NO: 15 had activity with PNS only. Enzymes having the amino acid sequences of SEQ ID NO: 9 and SEQ ID NO: 11 had activity with both aryl sulfate compounds. 
     Representative chromatograms from SAX analysis illustrating the presence of N-sulfated products produced as a result of the reaction are shown in  FIG.  29   . Both the N-deacetylated heparosan starting material and the N-sulfated product produced by SEQ ID NO: 13 were digested with the lyases having the amino acid sequence of SEQ ID NO: 161, SEQ ID NO: 162, and SEQ ID NO: 163 according the digestion procedure described above. Two disaccharide standards (HD005 and HD013) that are commercially available from Iduron, Ltd were also analyzed using SAX. The HD013 disaccharide comprises an unsubstituted glucosamine residue and a reduced hexuronic acid. The HD005 disaccharide is the same as HD013 except that the glucosamine residue is N-sulfated. All of the overlaid chromatograms are normalized so the most prominent peak in each chromatogram is assigned a normalized relative fluorescence value of 1.0. 
     As shown in  FIG.  29   , the most prominent peak for HD013 disaccharide (illustrated with a * symbol) elutes almost immediately, whereas the most prominent peak for the HD005 disaccharide (illustrated with a ** symbol) elutes after approximately 17 minutes. This is expected under SAX conditions because positively-charged species (like HD013) typically do not bind to the column, whereas negatively-charged species (like HD005) do bind to the column. The N-deacetylated heparosan, which is similarly non-sulfated, most prominently elutes at a nearly identical time as HD013. Similarly, the lyophilized sample produced during the reaction shows a peak at a nearly identical time as HD005, indicating that the sample contains an N-sulfated product. Other peaks within each of the chromatograms, particularly within the synthesized starting materials and products, indicate a lack of sample purity based on the use of spin-filtration columns as the sole basis of purifying the polysaccharides in each instance. Those skilled in the art would appreciate that there are several other separations techniques that can be utilized if a more purified product is desired. Additionally, the drifting upward of the baseline of the fluorescent signal in the chromatograms is a known phenomenon when increasing amounts of salt are introduced onto the column via the mobile phase. 
     Example 4: Mass Spectrometric Characterization of the 2-O Sulfated Polysaccharide Products of Engineered Aryl Sulfate-Dependent 2OST Enzymes 
     A study was conducted in accordance with embodiments of the present disclosure to confirm hexuronyl 2-O sulfotransferase activity of enzymes comprising the amino acid sequence of SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 61, SEQ ID NO: 63, or SEQ ID NO: 65 by detecting the presence of 2-O sulfated polysaccharide products formed as a result of their sulfotransfer reaction, using a similar procedure as in Example 3, except that the sulfo acceptor polysaccharide was commercial heparan sulfate in which the 2-O sulfate groups had been selectively removed by chemical means (product DSH001/2, available from Galen Laboratory Supplies) and analysis of each of the digested samples containing sulfated products was conducted using mass spectrometry, coupled with SAX-based high performance liquid chromatography (LCMS). 
     Disaccharides obtained by digesting the 2-O sulfated products using the carbon-oxygen lyases having the amino acid sequence of SEQ ID NO: 161, SEQ ID NO: 162, and SEQ ID NO: 163 and according to the procedure described above in Example 3 were quantified on a Shimadzu LCMS-8050 Triple Quadrupole Liquid Chromatograph Mass Spectrometer. 100 ng of each of the digested samples, diluted in 10 mM ammonium bicarbonate (pH 10). The disaccharides were separated on a Thermo Hypercarb HPLC column (100×2.1 mm, 5 μm). The mobile phase consisted of 10 mM ammonium bicarbonate (pH 10), and the disaccharides were eluted with an acetonitrile gradient of 0% to 20% for 2.5 min, held at 20% for the next 2.5 min, with 2 min of equilibration at 0% before the next injection; the flow rate was 0.2 mL/min, and the total run time was 7.1 min. 
     The extracted ion chromatograms from the LCMS are shown in  FIG.  30 A  and  FIG.  3 B , corresponding to 2-O sulfated products obtained from reactions with engineered enzymes having the amino acid sequences of SEQ ID NO: 63 or SEQ ID NO: 65, respectively. Peaks were compared with chromatograms of a series of eight disaccharide standards, as well as a chromatogram from 100 ng of a commercial UFH polysaccharide (CAS code: 9041-08-1, available from Millipore Sigma), which was also digested using the lyase mixture. The eight reference disaccharide standards (D0A0, D0S0, D0A6, D2A0, D0S6, D2S0, D2A6, D2S6) represent disaccharides that are variably sulfated at the N-, 2-O and 6-O positions. In particular, the disaccharide D2S0 represents a disaccharide having a hexuronyl residue sulfated at the 2-O position and an N-sulfated glucosamine residue. The retention time and peak areas from the spectra from all of the disaccharide standards (not shown), the digested commercial sulfated polysaccharide (not shown), and the sulfated polysaccharide products of the engineered enzymes having the amino acid sequence of SEQ ID NO: 63 or SEQ ID NO: 65 are collected in Table 11, below. Since the ionization of each individual disaccharide is different, the present percent in EIC chromatograms may not represent their actual abundance. However, the ionization efficiency is identical for each disaccharide from sample to sample. Therefore, it is believed that comparing the peak area percent of the same saccharides from sample to sample can still be achieved. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 11 
               
             
            
               
                   
                   
               
               
                   
                 Peak Area % 
                   
               
            
           
           
               
               
               
               
               
            
               
                 Peak 
                   
                 Commercial 
                 SEQ ID 
                 SEQ ID 
               
               
                 No. 
                 Disaccharides 
                 standard 
                 NO: 63 
                 NO: 65 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 D0A0 
                 3.9 
                 5.9 
                 9.1 
               
               
                 2 
                 D0S0 
                 3.9 
                 87.1  
                 85.5  
               
               
                 3 
                 D0A6 
                 3.4 
                 ND 
                 ND 
               
               
                 4 
                 D2A0 
                 1.8 
                 ND 
                 ND 
               
               
                 5 
                 D0S6 
                 11.8 
                 4.1 
                 3.1 
               
               
                 6 
                 D2S0 
                 6.6 
                 2.9 
                 2.3 
               
               
                 7 
                 D2A6 
                 1.6 
                 ND 
                 ND 
               
               
                 8 
                 D2S6 
                 67.0 
                 ND 
                 ND 
               
               
                   
               
            
           
         
       
     
     Sulfotransferase activity of the engineered enzymes was confirmed by the re-sulfation at the 2-O position of hexuronic acid residues within the sulfo acceptor polysaccharide that had previously been desulfated prior to the reaction. This is illustrated by the presence of D2S0 disaccharides within the products isolated from reactions of both engineered enzymes and NCS. Without being limited by a particular theory, it is also believed that the activity of the engineered enzyme is dependent on reacting with a portion of the polysaccharide in which the hexuronic acid residue is adjacent to a glucosamine residue that is N-sulfated, but not 6-O sulfated. This is illustrated by the lack of D2S6 (2-O sulfated hexuronic acid residue and an N,6-sulfated glucosamine residue) and D2A6 (2-O sulfated hexuronic acid residue and a 6-O sulfated N-acetyl glucosamine residue) disaccharides detected within the isolated sulfated polysaccharide product. This is a similar sulfo acceptor reactivity to natural 2OST enzymes EC 2.8.2.—, which react with N-sulfated heparosan comprising either the structure of Formula IV or Formula V. 
     Example 5: Mass Spectrometric Characterization of the 6-O Sulfated Polysaccharide Products of Engineered Aryl Sulfate-Dependent 6OST Enzymes 
     A study was conducted in accordance with embodiments of the present disclosure to confirm glucosaminyl 6-O sulfotransferase activity of enzymes comprising the amino acid sequence of SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78, SEQ ID NO: 80, SEQ ID NO: 82, SEQ ID NO: 84, SEQ ID NO: 86, SEQ ID NO: 88, SEQ ID NO: 90, SEQ ID NO: 92, SEQ ID NO: 94, SEQ ID NO: 96, SEQ ID NO: 98, SEQ ID NO: 100, SEQ ID NO 102, SEQ ID NO: 104, SEQ ID NO: 106, or SEQ ID NO: 108 by detecting the presence of 6-O sulfated polysaccharide products as a result of their sulfotransfer reaction, using a similar LCMS procedure as in Example 4, except that the sulfo acceptor polysaccharide was prepared by chemically 6-O desulfating commercially available UFH (CAS code: 9041-08-1, available from Millipore Sigma), according to the procedure provided by Kariya, Y., et al., (2000)  J. Biol. Chem.  275 (34):25949-25958). 
     The extracted ion chromatograms corresponding to 6-O sulfated products obtained from reactions with engineered enzymes having the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, or SEQ ID NO: 108 are shown in  FIG.  31 A ,  FIG.  31 B , and  FIG.  31 C , respectively. Enzymes having the sequence of SEQ ID NO: 104 and SEQ ID NO: 106 were active when NCS was the sulfo group donor, while the enzyme having the sequence of SEQ ID NO: 108 was active when PNS was the sulfo group donor. Assigned peaks were based on the determined retention times of eight reference disaccharide standards. The eight reference disaccharide standards (D0A0, D0S0, D0A6, D2A0, D0S6, D2S0, D2A6, and D2S6) represent disaccharides that are variably sulfated at the N-, 2-O, and 6-O positions. D0A6, D0S6, D2A6, and D2S6 comprise 6-O sulfated glucosamine residues. S6 indicates an N,6-sulfated glucosamine residue, while A6 indicates a 6-O sulfated N-acetyl glucosamine residue. Each chromatogram indicates two integrable peaks, D0S6 and D2S6, correlating to the synthesis of N,6-sulfated glucosamine residues, adjacent to a hexuronic acid residue that is either non sulfated or sulfated at the 2-O position, respectively. The peak area % of all the labelled disaccharides is in Table 12, below. Since the ionization of each individual disaccharide is different, especially for D0A0 and D2S6, the present percent in EIC chromatograms may not represent their actual abundance. However, the ionization efficiency is identical for each disaccharide from sample to sample. Therefore, it is believed that comparing the peak area percent of the same saccharides from sample to sample can still be achieved. 
     
       
         
           
               
               
             
               
                   
                 TABLE 12 
               
             
            
               
                   
                   
               
               
                   
                 Peak Area % 
               
            
           
           
               
               
               
               
               
               
            
               
                 Peak 
                   
                 RT 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
               
               
                 No. 
                 Disaccharides 
                 (min) 
                 NO: 104 
                 NO: 106 
                 NO: 108 
               
               
                   
               
               
                 1 
                 D0A0 
                  7.7 
                 4.6 
                 6.0 
                 5.4 
               
               
                 2 
                 D0S0 
                 16.4 
                 14.2  
                 18.4  
                 13.0  
               
               
                 3 
                 D0A6 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 4 
                 D2A0 
                 20.0 
                 1.1 
                 1.8 
                 1.3 
               
               
                 5 
                 D0S6 
                 23.7 
                 4.0 
                 3.7 
                 5.6 
               
               
                 6 
                 D2S0 
                 25.6 
                 73.5  
                 68.4  
                 72.4  
               
               
                 7 
                 D2A6 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 8 
                 D2S6 
                 32.7 
                 2.5 
                 1.7 
                 2.3 
               
               
                   
               
            
           
         
       
     
     Sulfotransferase activity of the engineered enzymes was confirmed by the re-sulfation at the 6-O position of glucosamine residues that had been desulfated by the procedure according to Kariya, Y., et al, above. This is illustrated by the presence of D0S6 and D2S6 disaccharides within the products isolated from the reactions with each enzyme. Among each of the engineered enzymes, it appears that the 6OST having the amino acid sequence of SEQ ID NO: 108 was the most active, based on comparing the peak area percentages of the D0S6 and D2S6 disaccharides. However, while D0A6 and D2A6 polysaccharides were not observed in any of the 6-O sulfated products produced by the engineered enzymes, without being limited by any particular theory, it is believed that these enzymes may nonetheless be able to transfer a sulfo group to N-acetyl glucosamine residues in different reaction conditions, particularly by increasing the concentration of the enzyme and/or polysaccharide where the presence of N-acetyl glucosamine residues is confirmed prior to the reaction, based on the reactivity of natural 6OST enzymes. 
     Example 6: Mass Spectrometric Characterization of the 3-O Sulfated Polysaccharide Products of Engineered Aryl Sulfate-Dependent 3OST Enzymes 
     A study was conducted in accordance with embodiments of the present disclosure to confirm glucosaminyl 3-O sulfotransferase activity of enzymes comprising the amino acid sequence of SEQ ID NO: 123, SEQ ID NO: 125, SEQ ID NO: 127, SEQ ID NO: 129, SEQ ID NO: 131, SEQ ID NO: 133, SEQ ID NO: 135, SEQ ID NO: 137, SEQ ID NO: 139, SEQ ID NO: 141, SEQ ID NO: 143, SEQ ID NO: 145, SEQ ID NO: 147, SEQ ID NO: 149, or SEQ ID NO: 151 by detecting the presence of 3-O sulfated polysaccharide products as a result of their sulfotransfer reaction, using a reaction, using a similar LCMS procedure as in Example 4, except that the sulfo acceptor polysaccharide was commercially-available UFH (CAS code: 9041-08-1, available from Millipore Sigma). Even though the unmodified UFH contains ˜3.5% (w/w) of 3-O sulfated glucosamine residues, about ˜60% of the glucosamine residues are N,6-sulfated and are adjacent to a 2-O sulfated hexuronic acid residue, as in Formula X. Consequently, these N,6-sulfated glucosamine residues can still be 3-O sulfated. 
     The extracted ion chromatograms are shown in  FIG.  32 A  and  FIG.  32 B , along with chromatograms of a series of ten reference standards and 100 ng of the commercial polysaccharide, which was also digested using the lyase mixture. The ten reference standards (D0A0, D0S0, D0A6, D2A0, D0S6, D2S0, D2A6, D2S6, D0A6G0S3, and D0A6G0S9) represent di- or tetrasaccharides that are variably sulfated at the N-, 2-O, 3-O, and 6-O positions ( FIG.  32 A , top). For clarity, reference peaks that include 3-O sulfated glucosamine residues (D0A6G0S3) and (D0A6G0S9) are indicated in the digested commercial polysaccharide spectrum ( FIG.  32 A , center). Four mass spectra representing the digested sulfated polysaccharide products from reactions with enzymes comprising the amino acid sequence of SEQ ID NO: 147 (PNS,  FIG.  32 B , center), SEQ ID NO: 149 (PNS,  FIG.  32 B , bottom) (NCS,  FIG.  32 A , bottom), and SEQ ID NO: 151 (NCS,  FIG.  32 A , top) are shown below the digested commercial polysaccharide spectrum. The peak area % of all the labelled disaccharides and tetrasaccharides is in Table 13, below. Since the ionization of each individual disaccharide is different, especially for D0A0 and D2S6, the present percent in EIC chromatograms may not represent their actual abundance. However, the ionization efficiency is identical for each disaccharide or tetrasaccharide from sample to sample. Therefore, it is believed that comparing the peak area percent of the same saccharides from sample to sample can still be achieved. 
     
       
         
           
               
               
             
               
                   
                 TABLE 13 
               
             
            
               
                   
                   
               
               
                   
                 Peak Area % 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                 SEQ ID 
                   
                 SEQ ID 
               
               
                 peak 
                   
                 RT 
                 Commercial 
                 SEQ ID 
                 NO: 149 
                 SEQ ID 
                 NO: 149 
               
               
                 No. 
                 Disaccharides 
                 (min) 
                 standard 
                 NO: 147 
                 (NCS) 
                 NO: 151 
                 (PNS) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 1 
                 D0A0 
                 4.5 
                 1.9 
                 0.6 
                 0.8 
                 1.4 
                 N.D. 
               
               
                 2 
                 D0S0 
                 22.5 
                 3.7 
                 1.4 
                 1.7 
                 2.3 
                 N.D. 
               
               
                 3 
                 D0A6 
                 24.6 
                 4.2 
                 2.8 
                 3.1 
                 4.5 
                 N.D. 
               
               
                 4 
                 D2A0 
                 26.2 
                 2.2 
                 0.5 
                 0.8 
                 0.5 
                 N.D. 
               
               
                 5 
                 D0S6 
                 37.5 
                 16.0 
                 10.9 
                 10.6 
                 13.1 
                 N.D. 
               
               
                 6 
                 D2S0 
                 38.5 
                 6.5 
                 4.9 
                 5.4 
                 5.4 
                 N.D. 
               
               
                 7 
                 D2A6 
                 40.3 
                 1.6 
                 0.8 
                 0.8 
                 0.9 
                 N.D. 
               
               
                 8 
                 D2S6 
                 48.4 
                 60.3 
                 73.4 
                 71.6 
                 64.0 
                 100.0 
               
               
                 9 
                 D0A6G0S3 
                 52.9 
                 0.6 
                 0.8 
                 0.9 
                 1.4 
                 N.D. 
               
               
                 10 
                 D0A6G0S9 
                 58.2 
                 3.0 
                 4.0 
                 4.1 
                 6.5 
                 N.D. 
               
               
                   
               
            
           
         
       
     
     Sulfotransferase activity of each of the engineered enzymes was confirmed by the increase in the abundance of the D0A6G0S3 (hexuronic acid-6-O-sulfated N-acetyl glucosamine-glucuronic acid-N,3,6-sulfated glucosamine) and D0A6G0S9 (hexuronic acid-6-O-sulfated N-acetyl glucosamine-glucuronic acid-N,3-sulfated glucosamine) tetrasaccharides relative to the commercial UFH sample. However, the total abundance of disaccharides in the SEQ ID NO: 149 PNS sample was much lower than other samples. Subsequent trials included re-running the experiment with 10 times more injection volume, and a re-digestion of the sample with the lyase mixture. Nonetheless, only the D2S6 disaccharide could ever be found, indicating that the abundance of the SEQ ID NO: 149 PNS sulfated polysaccharide sample isolated initially was extremely low, and/or that the polysaccharide resists lyase digestion, causing the product to potentially elute from the column with a retention time longer than one hour. 
     Nonetheless, NMR studies (indicated below in Example 7) indicated 3-O sulfotransferase activity with the enzyme comprising the amino acid sequence SEQ ID NO: 149 when PNS is the aryl sulfate compound. Further, the enzyme having the amino acid sequence of SEQ ID NO: 149 was determined to be active as a sulfotransferase when NCS is the aryl sulfate compound. Therefore, it is believed that the observed results for the SEQ ID NO: 149 PNS sulfated polysaccharide sample during the LCMS experiment result from the sample produced for the purpose of the experiment, and not the activity of the enzyme itself. Otherwise, a higher abundance of 3-O sulfation was found in all of the other sulfated polysaccharide products from SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151, relative to the commercial UFH standard. 
     Example 7: Confirmation of Sulfotransferase Activity of the Engineered 3OSTs Using Nuclear Magnetic Resonance 
     A study was conducted in accordance with embodiments of the present disclosure to confirm the 3-O sulfotransferase activity of the engineered enzymes having the amino acid sequence of SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151, particularly the activity of the enzyme having the amino acid sequence SEQ ID NO: 149 with PNS as the sulfo group donor. Each enzyme was purified according to the procedure of Example 1. To each purified protein solution, 20 mg of an aryl sulfate compound (PNS or NCS) dissolved in 2 mL of reaction buffer (50 mM MES pH 7.0, 2 mM CaCl 2 )) was added to the protein solution and incubated at 37° C. for 10 min. 2.5 mL of 2 mg/mL solution of the commercial UFH polysaccharide utilized in Example 6 was added to protein/donor solution and incubated overnight at 37° C. 
     Each reaction was centrifuged at 5,000×g for 10 min, applied to a pre-wetted 30K MWCO Amicon-15 filter and centrifuged at 5,000×g for 10 min. The filter was washed once with 2 mL water, and centrifuged again. The filtrate was added to a 1K MWCO Dialysis membrane, dialyzed for 2 days in Milli-Q water, with water changes at 1 h, 2 h, 8 h, 16 h, 32 h, and then lyophilized. The dry, white powder was resuspended in 400 μL D 2 O, lyophilized to remove exchangeable protons, then resuspended in 600 μL D 2 O and transferred to NMR tubes (Wilmad, 0.38 mm×7″). To determine if sulfotransfer took place,  1 H-NMR spectra were obtained on a Bruker 600 MHz NMR, 32 scans, with water suppression. The overall reaction scheme is shown in  FIG.  33   . Within  FIG.  33   , the 3-O positions of any of the glucosamine residues can be sulfated by the 3OST enzyme. The sulfated 3-O position is circled in the central polysaccharide. Exchangeable protons having the ability to exhibit resonance upon deuterium exchange are shown in bold, in the bottom polysaccharide. Crude mixture peaks were integrated to literature-referenced spectra for the sulfo acceptor polysaccharide and associated 3-O sulfated product. 
     As shown in the overlain spectra in  FIG.  34   , a sharp peak at 5.15 ppm that correlates to the proton at the C2 carbon of the 2-O sulfated iduronic acid present in the commercial UFH disappears upon reacting with enzymes comprising the amino acid sequence of SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151. The proton of interest is circled in the polysaccharide shown above the spectra. The  1 H NMR spectra for a 3-O sulfated product synthesized by enzymes comprising the amino acid sequence of SEQ ID NO: 147, SEQ ID NO: 149, or SEQ ID NO: 151 in reaction with either PNS and/or NCS are all illustrated. In each of the product spectra, the IdoA 2S  peak shifts to between approximately 5.0 and 5.05 ppm. A similar transition is shown when incubating the natural human sulfotransferase enzyme with the same polysaccharide substrate and PAPS (data not shown). 
     As shown in  FIG.  35   , the region between 4.5 and 3.5 shows several peaks that similarly shift in response to the addition of the sulfate group to the 3-O position of a glucosamine residue, all of which correlate to the same shifts observed upon incubating the human 3OST1 enzyme with the same commercial UFH substrate and PAPS. Peaks that shift are indicated in curved arrows, and positions of the peaks from 3-O sulfated polysaccharides produced by enzymes having the amino acid sequence of SEQ ID NO: 147, SEQ ID NO: 149, or SEQ ID NO: 151, are shown with straight arrows. The largest shift occurs for H3 of Glc NS3S6S , from 3.7 ppm to 4.2 ppm. This results from being closest to the newly added 3-O sulfate group. Additionally, the H3 proton of Ido 2S  and H5 of Glc NS3S6S  both converge toward a peak at 4.07 ppm, which shows two overlapping peaks. H4 of Glc NS3S6S  shifts moderately downfield from the 3.7 ppm region to the 3.8 ppm region, and according to references, many peaks such as H3 &amp; H4 from Glc NS6S  and H3, H4, and H5 from GlcA shift from the 3.7 ppm region to the 3.6 ppm region. 
     Example 8: Chemical Synthesis of N-Sulfated Heparosan for Use with Engineered Sulfotransferases of the Present Invention 
     A study was conducted in accordance with embodiments of the present disclosure to chemically synthesize N-sulfated heparosan for use as sulfo acceptor polysaccharides with any of the engineered aryl sulfate-dependent sulfotransferases of the present invention, particularly the engineered 2OST enzymes. N-deacetylated heparosan was prepared according to the protocol described in Balagurunathan, K. et al., above. Particularly, the heparosan that eluted from the DEAE resin was precipitated overnight in ethanol saturated with sodium acetate, at −30° C., before being resuspended in water and dialyzed within a cellulose dialysis membrane having a 1,000 Da molecular weight cut-off (MWCO). 
     To N-deacetylate the heparosan, enough sodium hydroxide pellets (−4.0 g) were dissolved to make a 2.5 M solution in a 40 mL aliquot of the dialyzed heparosan in water. The solution was incubated at 55° C. for 16 hours, with shaking at 100 rpm. The sodium hydroxide within the sample was then neutralized with acetic acid until the solution reached a pH of ˜7.0, and then dialyzed in water overnight within a 1,000 MWCO dialysis membrane. 
     Subsequent N-sulfation of the N-deacetylated heparosan was accomplished by adding 100 mg of sodium carbonate and 100 mg of sulfur trioxide-triethylamine complex, and allowing the composition to incubate at 48° C. until all of the solid was dissolved. The pH of the solution was then readjusted to ˜9.5, using acetic acid. After incubation at 48° C. overnight with shaking at 100 rpm, an additional 100 mg of sodium carbonate and 100 mg of sulfur trioxide-triethylamine complex was added, before subsequent readjustment of the pH to ˜9.5 using acetic acid. The solution was incubated at 48° C. for an additional 24 hours. The sulfated polysaccharide solution was neutralized with acetic acid to a pH of ˜7.0, and dialyzed in water overnight within a 1,000 MWCO dialysis membrane. The dialyzed N-sulfated heparosan was then lyophilized prior to further use. The N-sulfated heparosan was then further purified by loading it onto a Zenix SEC-100 column and eluting it isocratically with 0.1 M ammonium acetate, pH 9.0. 
     The functionalization of the purified heparosan-based polysaccharide was characterized by digesting it with a mixture of three carbon-oxygen lyases comprising the amino acid sequences of SEQ ID NO: 161, SEQ ID NO: 162, and SEQ ID NO: 163, and analyzing the digested samples using SAX, using a similar procedure described above. As a positive control, the commercial HD005 disaccharide of Example 3, containing N-sulfated glucosamine residues, was also analyzed. Representative chromatograms of both samples are shown in  FIG.  36   . In both chromatograms, a strong peak is present at about 16.5 minutes, indicating that the synthesized sample contains N-sulfated glucosamine residues. 
     Example 9: Preparation of an N,2O-HS Polysaccharide Product 
     A study was conducted in accordance with embodiments of the present disclosure to synthesize an N,2O-HS polysaccharide product comprising the structure of either Formula VI or Formula VII, using an engineered 2OST and the N-sulfated heparosan synthesized in Example 8 as the sulfo acceptor. In a conical-bottom centrifuge tube, 80 mM aliquots of NCS were dissolved in 50 mM MES pH 7.0, 2 mM CaCl 2 . To each solution, 2 mg of the enzyme having the sequence of SEQ ID NO: 63, based on the absorbance of the enzyme sample at 280 nm, was added (about 4 mL). 5 mg of the lyophilized N-sulfated heparosan synthesized in Example 8 was resuspended in 1 mL of water and added to the reaction mixture containing the enzyme and NCS. The entire reaction mixture was then incubated at 34° C. with shaking at 30 rpm, for 48 hours. A second set of reactions were prepared using the same procedure, except that 2 mg of a C 5 -hexuronyl epimerase comprising the amino acid sequence of SEQ ID NO: 67 was also added to the reaction mixture, prior to incubation. 
     The polysaccharide products from both sets of reactions were purified by first precipitating out the proteins from the reaction mixtures by placing the reaction vessels in boiling water for 10 minutes and centrifuging at high speed to form a pellet. The supernatant containing the polysaccharide products was decanted from the pellet and dialyzed in water overnight within a 1,000 MWCO dialysis membrane. The dialyzed products were then lyophilized for future use. 
     To characterize the polysaccharide products, lyophilized samples were resuspended in 400 μL of water, and purified using a Q-Sepharose Fast Flow Column (GE Biosciences). Samples were eluted from the column using a gradient ranging from 0 to 2M NaCl, in 20 mM sodium acetate buffer, pH 5.0. Purified polysaccharides were then digested and analyzed by SAX according to the procedures in Example 3 above, along with a commercial polysaccharide, HD002 (Iduron), which contains disaccharides of 2-O sulfated uronic acid and N-sulfated glucosamine. Representative chromatograms of reactions either without or including the epimerase enzyme are shown in  FIG.  37    and  FIG.  38   , respectively. In  FIG.  37   , the chromatogram for the HD002 disaccharide has a single, sharp peak at about 21.1 minutes, which correlates to a sharp peak at a nearly identical time in the reaction product, indicating the time that an N,2O-HS product comprising the structure of Formula VI was formed as a result of the reaction. In  FIG.  38   , the HD002 disaccharide was provided within a mixture containing other disaccharide standards, with the disaccharide corresponding to HD002 eluting at 20.5 minutes, corresponding with the elution time of the HD002 standard in  FIG.  37   . The epimerized reaction product has a sharp peak at a nearly identical elution time to the HD002 standard, indicating that an N,2O-HS product comprising the structure of Formula VII was formed as a result of the reaction. 
     Example 10: Preparation of an N,2O,6O-HS Product 
     A study was conducted in accordance with embodiments of the present disclosure to synthesize an N,2O,6O-HS product comprising the structure of Formula IX, using the procedure of Example 9, except that the epimerized N,2O-HS product of Example 9 was used as the sulfo acceptor polysaccharide, and the engineered 6OST having the amino acid sequence of SEQ ID NO: 104 was used as the enzyme. 
     Representative chromatograms of the sulfated polysaccharide product and a mixture of commercial disaccharides are shown in  FIG.  39   . The chromatogram of the commercial mixture exhibits a peak at about 23.7 minutes, correlates to disaccharide HD001 (Iduron), which consists of disaccharides of 2-O sulfated uronic acid and N-, 6-O sulfated glucosamine, while the reaction product exhibits a similar peak at 23.4 minutes, indicating that an N,2O,6O-HS product was formed as a result of the reaction. Other peaks present within the N,2O,6O-HS product include undigested polysaccharide (2.5 min), unsubstituted uronic acid and N-acetylated glucosamine (5.5 min), and unsubstituted uronic acid and N-, 6-O sulfated glucosamine. 
     Example 11: Preparation of an N,2O,3O,6O-HS Product 
     A study is conducted in accordance with embodiments of the present disclosure to synthesize a sulfated polysaccharide product comprising the structure of Formula I and having N-, 6-O, 3-O sulfated glucosamine and 2-O sulfated hexuronic acid residues, using the procedure of Example 9 except that the chemically synthesized N-, 2-O, 6-O sulfated polysaccharide of Example 10 is used as the sulfo acceptor polysaccharide, and an engineered 3-O sulfotransferase enzyme having the amino acid sequence of SEQ ID NO: 147, SEQ ID NO: 149, or SEQ ID NO: 151 is used as the sulfotransferase. Sulfated polysaccharide products are digested and analyzed according to the procedure of Example 9, using SAX. It is expected that upon comparison to a digested commercial tetrasaccharide comprising a N-, 6-O, 3-O sulfated glucosamine residue, that it will be determined that the sulfated polysaccharide product is 3-O sulfated as a result of the reaction. 
     Example 12: Confirmation of Anticoagulant Activity of the N,2O,3O,6O-HS Product 
     A study is conducted in accordance with embodiments of the present disclosure to determine whether N,2O,3O,6O-HS products produced according to procedures of Example 6 or Example 7, using any of the 3OST enzymes described herein, which are expected to have a binding affinity to antithrombin (See Meneghetti, G., et al. (2017) Org. Biomol. Chem. 15:6792-6799). A control reaction containing a commercial N,2O,3O,6O-HS product known to have activity with antithrombin, such as the USP reference standard (CAS No: 9041-08-1). Human antithrombin (AT) (1 mg/mL) is incubated with different substrates in the presence of a dye, such as the SyproOrange™ dye (Invitrogen). The dye is diluted in water (1 unit Sypro:50 units water (v/v)) and 3.5 μL of the diluted dye is added to the mixture reaction in PBS buffer. The SyproOrange™ dye has an excitation wavelength of 300 nm or 470 nm and emits at 570 nm when bound to hydrophobic residues. 25 μg of a N,2O,3O,6O-HS product is included in each reaction mixture. Reactions are incubated at 31° C. for 2 min, before being subjected to a step-wise temperature gradient from 32 to 85° C. in a 0.5° C. steps. Between each temperature step, a 5-second incubation period can be taken to ensure sample equilibrations. Reactions can be developed using a real-time PCR System. It is expected that the melting curves of the control reaction with the USP reference standard, as well as the synthesized N,2O,3O,6O-HS products, will each be shifted to a higher temperature than a standard with the dye and AT alone, indicating that the AT can bind to the N,2O,3O,6O-HS products because the N,2O,3O,6O-HS products contain at least one AT-recognition sequence comprising the structure of Formula I. 
     Example 13: Determination of Engineered Aryl Sulfate-Dependent Mutants of Other EC 2.8.2.8 Enzymes 
     A study is conducted in accordance with embodiments of the present disclosure to engineer additional aryl sulfate-dependent NST enzymes. As described above, the aryl sulfate-dependent NST enzymes having the amino acid sequences of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, or SEQ ID NO: 15 have been engineered to be mutants of the N-sulfotransferase domain of the human NDST1 enzyme (see entry sp|P52848|NDST_1_HUMAN, in  FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C  above), which is a member of enzyme class EC 2.8.2.8. By generating and analyzing a multiple sequence alignment that includes the amino acid sequences of the N-sulfotransferase domain of one or more of the other NDST enzymes as well as the amino acid sequences of aryl sulfate-dependent NST enzymes having the amino acid sequences of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, and/or SEQ ID NO: 15, mutations in the amino acid sequences in the engineered NST enzymes can be observed relative to the amino acid sequences of the native EC 2.8.2.8 enzymes within the same alignment. Upon selecting the amino acid sequence of the N-sulfotransferase domain of a natural 2.8.2.8 enzyme that is not the human NDST1, mutations that are present within the amino acid sequences of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, and/or SEQ ID NO: 15 can be engineered into the native sequence in order to form additional mutants that can have aryl sulfate-dependent sulfotransferase activity. 
     As a non-limiting example, the amino acid sequence encoding for the N-sulfotransferase domain of the pig NDST1 (entry tr|M3V841|M3V841_PIG, as illustrated in the sequence alignment in  FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C , above), is aligned with the amino acid sequences of SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, and SEQ ID NO: 15. Amino acid mutations that are present in SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, and SEQ ID NO: 15 are engineered into their equivalent positions within the amino acid sequence of the N-sulfotransferase domain of the pig NDST1 enzyme, in order to generate the mutant amino acid sequences SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, or SEQ ID NO: 25, respectively. Enzymes comprising the amino acid sequences of SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, or SEQ ID NO: 25, respectively, will be utilized in Example 14 and Example 15, below. However, a person skilled in the art would appreciate that the same procedure can be applied to generate mutants of the N-sulfotransferase domain, or the entire enzyme, with respect to any of the other glucosaminyl natural NDST enzymes, and that those are omitted for clarity. 
     Example 14: Expression and Purification of Engineered Aryl Sulfate-Dependent EC 2.8.2.8 Mutants 
     A study is conducted in accordance with embodiments of the present disclosure to determine whether genes encoding for engineered NST enzymes having the amino acid sequences SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, or SEQ ID NO: 25, respectively, can be transformed into host cells, and that enzymes comprising each of those amino acid sequences can be subsequently expressed, isolated, and purified according to the procedure of Example 1, above. Codon-optimized nucleotide sequences are determined that encode for enzymes having the amino acid sequences of SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, or SEQ ID NO: 25, respectively, based on the desired expression host. Upon synthesizing or inserting those genes within a suitable expression vector, it is expected that genes encoding for each of the amino acid sequences SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, and SEQ ID NO: 25, respectively, will be transformed into host cells, and that enzymes containing those sequences will be subsequently expressed, isolated, and purified in a sufficient quantity and purity to determine aryl sulfate-dependent NST activity. 
     Example 15: Sulfotransferase Activity of EC 2.8.2.8 Mutants 
     A study is conducted in accordance with embodiments of the present disclosure to determine whether mutant enzymes comprising the sequences of SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, or SEQ ID NO: 25, respectively, are active sulfotransferases, using the procedures of Example 3. It is expected that SAX studies will confirm the presence of N-sulfated polysaccharide products formed as a result of reacting N-deacetylated heparosan and an aryl sulfate compound with each of the engineered enzymes comprising the sequences of SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, or SEQ ID NO: 25, respectively. 
     Example 16: Determination of Engineered Aryl Sulfate-Dependent Mutants of Other 2OST Enzymes within EC 2.8.2.— 
     A study is conducted in accordance with embodiments of the present disclosure to engineer additional aryl sulfate-dependent 2OST enzymes. As described above, the aryl sulfate-dependent 2OST enzymes having the amino acid sequences of SEQ ID NO: 63 and SEQ ID NO: 65 have been engineered to be mutants of the chicken HS 2OST enzyme (see entry sp|Q76KB1|HS2ST_CHICK, in  FIG.  17 A ,  FIG.  17 B ,  FIG.  17 C , and  FIG.  17 D , above), which is a member of enzyme class EC 2.8.2.—. By generating and analyzing a multiple sequence alignment that includes the amino acid sequences of one or more of the other 2OST enzymes within EC 2.8.2.—, as well as the amino acid sequences of aryl sulfate-dependent 2OST enzymes having the amino acid sequences of SEQ ID NO: 63 and/or SEQ ID NO: 65, mutations in the amino acid sequences in the engineered 2OST enzymes can be observed relative to the amino acid sequences of the wild-type 2OST enzymes within the same alignment. Upon selecting the amino acid sequence of a wild-type 2OST enzyme that is not the chicken 2OST enzyme, mutations that are present within the amino acid sequences of SEQ ID NO: 63 and/or SEQ ID NO: 65 can be engineered into the wild-type sequence in order to form additional mutants that can have aryl sulfate-dependent sulfotransferase activity. 
     As a non-limiting example, the amino acid sequence encoding for the human 2OST enzyme (entry sp|Q7LGA3|HS2ST_HUMAN, as illustrated in the sequence alignment in  FIG.  17 A ,  FIG.  17 B ,  FIG.  17 C , and  FIG.  17 D , above), is aligned with the amino acid sequences of SEQ ID NO: 63 and SEQ ID NO 65. Amino acid mutations that are present in SEQ ID NO 63 and SEQ ID NO: 65 are engineered into their equivalent positions within the amino acid sequence of the human 2OST enzyme, in order to generate the mutant amino acid sequences SEQ ID NO: 68 or SEQ ID NO: 69, respectively. Enzymes comprising the amino acid sequences of SEQ ID NO: 68 or SEQ ID NO: 69, respectively, will be utilized in Example 17 and Example 18, below. However, a person skilled in the art would appreciate that the same procedure can be applied to generate aryl sulfate-dependent mutants with respect to any of the other 2OST enzymes within the EC 2.8.2.—enzyme class, and that those are omitted for clarity. 
     Example 17: Expression and Purification of EC 2.8.2.—Mutants Having Hexuronyl 2-O Sulfotransferase Activity 
     A study is conducted in accordance with embodiments of the present disclosure to determine whether genes encoding for engineered 2OST enzymes having the amino acid sequences SEQ ID NO: 68 or SEQ ID NO: 69, respectively, can be transformed into host cells, and that enzymes comprising each of those amino acid sequences can be subsequently expressed, isolated, and purified according to the procedure of Example 1, above. Codon-optimized nucleotide sequences are determined that encode for enzymes having the amino acid sequences of SEQ ID NO: 68 or SEQ ID NO: 69, respectively, based on the desired expression host. Upon synthesizing or inserting those genes within a suitable expression vector, it is expected that genes encoding for each of the amino acid sequences SEQ ID NO: 68 and SEQ ID NO: 69, respectively, will be transformed into host cells, and that enzymes containing those sequences will be subsequently expressed, isolated, and purified in a sufficient quantity and purity to determine aryl sulfate-dependent hexuronyl 2-O sulfotransferase activity. 
     Example 18: Hexuronyl 2-O Sulfotransferase Activity of EC 2.8.2.—Mutants 
     A study is conducted in accordance with embodiments of the present disclosure to determine whether mutant enzymes comprising the sequences of SEQ ID NO: 68 or SEQ ID NO: 69, respectively, are active sulfotransferases, using the procedures of Example 4. It is expected that MS studies will confirm the presence of N,2O-HS products formed as a result of reacting an N-sulfated heparosan-based polysaccharide and an aryl sulfate compound with each of the engineered enzymes comprising the sequences of SEQ ID NO: 68 and SEQ ID NO: 69, respectively. It is also expected that both enzymes will be active with heparosan-based polysaccharides comprising either or both of Formula IV or Formula V. 
     Example 19: Determination of Engineered Aryl Sulfate-Dependent Mutants of Other 6OST Enzymes within EC 2.8.2.— 
     A study is conducted in accordance with embodiments of the present disclosure to engineer additional aryl sulfate-dependent 6OST enzymes. As described above, the aryl sulfate-dependent 6OST enzymes having the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, or SEQ ID NO: 108 have been engineered to be mutants of the mouse 6OST1 enzyme (see entry Q9QYK5|H6ST1_MOUSE, in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C , above), which is a member of enzyme class EC 2.8.2.—. By generating and analyzing a multiple sequence alignment that includes both the amino acid sequences of one or more of the other 6OST enzymes within EC 2.8.2.—, as well as the amino acid sequences of aryl sulfate-dependent 6OST enzymes having the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, and/or SEQ ID NO: 108, mutations in the amino acid sequences in the engineered 6OST enzymes can be observed relative to the amino acid sequences of the wild-type 6OST enzymes within the same alignment. Upon selecting the amino acid sequence of a wild-type 6OST enzyme that is not the mouse 6OST1 enzyme, mutations that are present within the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, and/or SEQ ID NO: 108 can be engineered into the wild-type sequence in order to form additional mutants that can have aryl sulfate-dependent sulfotransferase activity. 
     As a non-limiting example, the amino acid sequence encoding for the pig 6OST1 enzyme (entry I3LAM6|I3LAM6_PIG, as illustrated in the sequence alignment in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C , above), is aligned with the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, and SEQ ID NO: 108. Amino acid mutations that are present in SEQ ID NO: 104, SEQ ID NO: 106, and SEQ ID NO: 108 are engineered into their equivalent positions within the amino acid sequence of the pig 6OST enzyme, in order to generate mutant amino acid sequences. Generated mutant amino acid sequences corresponding to residues 67-377 of the pig 6OST1 enzyme, as illustrated in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C , above, are disclosed as SEQ ID NO: 114, SEQ ID NO: 115, and SEQ ID NO: 116, respectively. Generated mutant amino acid sequences corresponding to the full-length amino acid sequence for the pig 6OST1 enzyme (not shown in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C , above) are disclosed as SEQ ID NO: 117, SEQ ID NO: 118, and SEQ ID NO: 119, respectively. 
     In another non-limiting example, the full-length amino acid sequence encoding for the encoding for the mouse 6OST3 enzyme (entry Q9QYK4|H6HS3_MOUSE, a truncated sequence for which is illustrated in the sequence alignment in  FIG.  21 A ,  FIG.  21 B , and  FIG.  21 C , above) is aligned with the amino acid sequences of SEQ ID NO: 104, SEQ ID NO: 106, and SEQ ID NO: 108. Amino acid mutations that are present in SEQ ID NO: 104, SEQ ID NO: 106, and SEQ ID NO: 108 are engineered into their equivalent positions within the amino acid sequence of the mouse 6OST3 enzyme, in order to generate mutant amino acid sequences. The generated full-length amino acid sequences are disclosed as SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122, respectively. Enzymes comprising the amino acid sequences of SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, or SEQ ID NO: 122, respectively, will be utilized in Example 20 and Example 21, below. However, a person skilled in the art would appreciate that the same procedure can be applied to generate aryl sulfate-dependent mutants with respect to any of the other natural 6OST enzymes within the EC 2.8.2.—enzyme class, and that those are omitted for clarity. 
     Example 20: Expression and Purification of EC 2.8.2.—Mutants Having Glucosaminyl 6-O Sulfotransferase Activity 
     A study is conducted in accordance with embodiments of the present disclosure to determine whether genes encoding for engineered 6OST enzymes having the amino acid sequences SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, or SEQ ID NO: 122, respectively, can be transformed into host cells, and that enzymes comprising each of those amino acid sequences can be subsequently expressed, isolated, and purified according to the procedure of Example 1, above. Codon-optimized nucleotide sequences are determined that encode for enzymes having the amino acid sequences of SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, or SEQ ID NO: 122, respectively, based on the desired expression host. Upon synthesizing or inserting those genes within a suitable expression vector, it is expected that genes encoding for each of the amino acid sequences SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122, respectively, will be transformed into host cells, and that enzymes containing those sequences will be subsequently expressed, isolated, and purified in a sufficient quantity and purity to determine aryl sulfate-dependent glucosaminyl 6-O sulfotransferase activity. 
     Example 21: Glucosaminyl 6-O Sulfotransferase Activity of EC 2.8.2.—Mutants 
     A study is conducted in accordance with embodiments of the present disclosure to determine whether mutant enzymes comprising the sequences of SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, or SEQ ID NO: 122, respectively, are active sulfotransferases, using the procedures of Example 5. It is expected that MS studies will confirm the presence of N,2O,6O-HS products formed as a result of reacting an N,2O-HS polysaccharide and an aryl sulfate compound with each of the engineered enzymes comprising the sequences of SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122, respectively. 
     Example 22: Determination of Engineered Aryl Sulfate-Dependent Mutants of Other 3OST Enzymes within EC 2.8.2.23 
     A study is conducted in accordance with embodiments of the present disclosure to engineer additional aryl sulfate-dependent 3OST enzymes. As described above, the aryl sulfate-dependent 3OST enzymes having the amino acid sequences of SEQ ID NO: 147, SEQ ID NO: 149, or SEQ ID NO: 151 have been engineered to be mutants of the human 3OST1 enzyme (see entry sp|O14792|HS3S1_HUMAN, in  FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C , above), which is a member of enzyme class EC 2.8.2.23. By generating and analyzing a multiple sequence alignment that includes both the amino acid sequences of one or more of the other 3OST enzymes within EC 2.8.2.23, as well as the amino acid sequences of aryl sulfate-dependent 3OST enzymes having the amino acid sequences of SEQ ID NO: 147, SEQ ID NO: 149, and/or SEQ ID NO: 151, mutations in the amino acid sequences in the engineered 3OST enzymes can be observed relative to the amino acid sequences of the wild-type 3OST enzymes within the same alignment. Upon selecting the amino acid sequence of a wild-type 3OST enzyme that is not the human 3OST1 enzyme, mutations that are present within the amino acid sequences of SEQ ID NO: 147, SEQ ID NO: 149, and/or SEQ ID NO: 151 can be engineered into the wild-type sequence in order to form additional mutants that can have aryl sulfate-dependent sulfotransferase activity. 
     As a non-limiting example, the amino acid sequence encoding for the pig 3OST1 enzyme (entry tr|I3LHH5|I3LHH5_PIG, as illustrated in the sequence alignment in  FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C , above), is aligned with the amino acid sequences of SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151. Amino acid mutations that are present in SEQ ID NO: 147, SEQ ID NO: 149, or SEQ ID NO: 151 are engineered into their equivalent positions within the amino acid sequence of the pig 3OST1 enzyme, in order to the generate mutant amino acid sequences SEQ ID NO: 155, SEQ ID NO: 156, or SEQ ID NO: 157, respectively. 
     In another non-limiting example, the full-length amino acid sequence encoding for the encoding for the mouse 3OST5 enzyme (not shown in  FIG.  26 A ,  FIG.  26 B , and  FIG.  26 C , above) is aligned with the amino acid sequences of SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151. Amino acid mutations that are present in SEQ ID NO: 147, SEQ ID NO: 149, and SEQ ID NO: 151 are engineered into their equivalent positions within the amino acid sequence of the mouse 3OST5 enzyme, in order to generate mutant amino acid sequences. The generated full-length amino acid sequences are disclosed as SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160, respectively. 
     Enzymes comprising the amino acid sequences of SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160 respectively, will be utilized in Example 23 and Example 24, below. However, a person skilled in the art would appreciate that the same procedure can be applied to generate aryl sulfate-dependent mutants with respect to any of the other 3OST enzymes within the EC 2.8.2.23 enzyme class, and that those are omitted for clarity. 
     Example 23: Expression and Purification of EC 2.8.2.23 Mutants Having Glucosaminyl 3-O Sulfotransferase Activity 
     A study is conducted in accordance with embodiments of the present disclosure to determine whether genes encoding for engineered 3OST enzymes having the amino acid sequences SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160, respectively, can be transformed into host cells, and that enzymes comprising each of those amino acid sequences can be subsequently expressed, isolated, and purified according to the procedure of Example 1, above. Codon-optimized nucleotide sequences are determined that encode for enzymes having the amino acid sequences of SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160, respectively, based on the desired expression host. Upon synthesizing or inserting those genes within a suitable expression vector, it is expected that genes encoding for each of the amino acid sequences SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160, respectively, will be transformed into host cells, and that enzymes containing those sequences will be subsequently expressed, isolated, and purified in a sufficient quantity and purity to determine aryl sulfate-dependent glucosaminyl 3-O sulfotransferase activity. 
     Example 24: Glucosaminyl 3-O Sulfotransferase Activity of EC 2.8.2.23 Mutants 
     A study is conducted in accordance with embodiments of the present disclosure to determine whether mutant enzymes comprising the sequences of SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, or SEQ ID NO: 160, respectively, are active sulfotransferases, using the procedures of Example 6 and/or Example 7. It is expected that MS and/or NMR studies will confirm the presence of N,2O,3O,6O-HS products formed as a result of reacting an N,2O,6O-HS polysaccharide and an aryl sulfate compound with each of the engineered enzymes comprising the sequences of SEQ ID NO: 155, SEQ ID NO: 156, SEQ ID NO: 157, SEQ ID NO: 158, SEQ ID NO: 159, and SEQ ID NO: 160, respectively.