Patent Publication Number: US-11643450-B2

Title: Chemoenzymatic glycoengineering of antibodies and Fc fragments thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional application claiming priority to U.S. patent application Ser. No. 16/431,907 filed on Jun. 5, 2019, now U.S. Pat. No. 10,836,805, which is a divisional application claiming priority to U.S. patent application Ser. No. 15/843,160 filed on Dec. 15, 2017, now U.S. Pat. No. 10,344,063, which is a continuation application claiming priority to U.S. patent application Ser. No. 15/256,854 filed on Sep. 6, 2016, now U.S. Pat. No. 9,845,360, which is a divisional application of U.S. patent application Ser. No. 14/376,248, filed on Aug. 1, 2014, now U.S. Pat. No. 9,434,786, which in turn was filed under the provisions of U.S.C. § 371 and claimed priority to International Patent Application No. PCT/US2013/025553 filed on Feb. 11, 2013, which in turn claimed priority of U.S. Provisional Application No. 61/597,468 filed on Feb. 10, 2012, the contents of which are incorporated by reference herein for all purposes. 
    
    
     GOVERNMENT RIGHTS IN INVENTION 
     This invention was made with government support under Grant Numbers GM080374 and GM096973 awarded by the National Institutes of Health. The government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to glycoprotein synthesis, and more particularly, to the use of a recombinant and mutant Endo S, an Endo-β-N-acetylglucosaminidase from  Streptococcus pyogenes , that possesses transglycosylation activity and limited hydrolyzing activity thereby providing for efficient glycosylation remodeling of antibody-Fc domain. 
     Description of the Related Art 
     Monoclonal antibodies (mAbs) of the IgG type are an important class of therapeutic proteins used for the treatment of cancer, autoimmune, and infectious diseases.(1-3) IgG antibodies are composed of two heavy chains and two light chains that are associated to form three distinct protein domains, including two variable Fab domains and a constant (crystallizable) Fc domain linked by a flexible hinge region. The Fab domains are responsible for antigen binding, while the Fc domain is engaged in Fc receptor-mediated effector functions, such as antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC).(2, 4) The Fc domain is a homodimer bearing two N-glycans at the conserved N-glycosylation sites (N297). The attached oligosaccharides are biantennary complex type with considerable structural heterogeneity, in which the N-linked heptasaccharide core can be differentially decorated with core fucose (Fuc), bisecting N-acetylglucosamine (GlcNAc), terminal galactose (Gal), and terminal sialic acid (Sia) as shown in  FIG.  1   .(5-7) X-ray crystallographic and NMR structural studies indicate that the Fc glycans are sandwiched between the two CH2/CH3 subdomains and have multiple noncovalent interactions with the Fc domains.(8-14) These studies have shown that the attachment of different Fc glycans can have distinct impact on the Fc domain conformations, implicating an important role of glycosylation in maintaining an appropriate Fc domain structures for interactions with respective Fc receptors associated with antibody&#39;s effector functions.(8-14) 
     It has been further demonstrated that the fine structures of Fc N-glycans are important determinants of the pro- and anti-inflammatory activities of antibodies.(2, 15) For example, the lack of the core fucose, as well as the attachment of a bisecting GlcNAc moiety, dramatically enhances the affinity of antibody for the FcγIIIa receptor (FcγRIIIa), which is responsible for the antibody-dependent cellular cytotoxicity (ADCC).(11, 16-18) Thus, low-fucose content mAbs are sought out for improved in vivo anticancer efficacy.(19, 20) On the other hand, the terminal α-2,6-sialylated Fc glycoform, a minor component of the intravenous immunoglobulin (IVIG) pooled from the sera of thousands of healthy blood donors, was recently identified as the active species for the anti-inflammatory activity of IVIG in a mouse model of rheumatoid arthritis (RA).(21-23) However, commercially available IgGs, including monoclonal antibodies and IVIG, typically exist as mixtures of glycoforms that are not optimal for their respective therapeutic activities. For instance, the major Fc glycoforms of monoclonal antibodies currently used for cancer treatment are core-fucosylated that possess relatively low affinity for the activation receptor FcγRIIIa, demonstrating low efficacy particularly for those patients with the low-affinity FcγRIIIa-F158 allelic polymorphism.(2, 19, 20) 
     The impact of glycosylation on the biological functions and therapeutic outcome of IgG antibodies has stimulated tremendous interest in developing methods to control antibody&#39;s glycosylation. One approach is to control the glycosylation profiles during production through glycan biosynthetic pathway engineering in various expression systems, including mammalian, plant, and yeast host cells.(24-30) This control of glycosylation has resulted in the production of low-fucose or nonfucosylated monoclonal antibodies with improved ADCC activities. But, the glycoforms that can be generated by this approach have been limited, and in most cases, a complete control to a defined homogeneous glycoform is difficult. 
     A recent analysis of several therapeutic glycoprotein drugs on the market, including monoclonal antibody rituximab, has indicated significant changes of the glycosylation profiles from different batches produced in different periods.(31) This analysis implicates the challenge in maintaining consistent production of glycoprotein-based drugs and also raises regulatory concerns, as changes of the Fc glycosylation would most likely impact the therapeutic efficacy. 
     An alternative approach to addressing the inconsistence and heterogeneity in glycosylation of glycoproteins is to perform glycosylation remodeling through trimming off the heterogeneous N-glycans and extending the sugar chains by enzymatic glycosylation.(32, 33) Such enzymatic glycosylation has been recently described by using a chemoenzymatic method for Fc glycosylation remodeling that takes advantage of the transglycosylation activity of several endoglycosidases and their glycosynthase mutants using glycan oxazolines as their substrates.(34-36) This remodeling approach consists of two steps: trimming off all the heterogeneous N-glycans by an endoglycosidase to leave only the first GlcNAc at the glycosylation site(s) and then adding back a well-defined N-glycan en bloc via an endoglycosidase-catalyzed transglycosylation reaction. (32) 
     Recent work has demonstrated that IgG-Fc domain glycosylation engineering can be achieved by a combination of yeast or CHO cell expression of the Fc domain and its subsequent chemoenzymatic remodeling through an enzymatic deglycosylation/reglycosylation approach.(34-36) It has been shown that the endo-β-N-acetylglucosaminidase from  Arthrobacter protophormiae , EndoA, is highly efficient to glycosylate the GlcNAc-containing Fc domain by using various synthetic N-glycan core oxazolines as substrates.(34, 35) Nevertheless, the limitations of the current status of the method are apparent: (a) neither EndoA nor EndoM (another endoglycosidase from  Mucor hiemalis ) was able to transform core-fucosylated IgG-Fc domain,(35) the major glycoforms of recombinant mAbs and IVIG; (b) EndoD mutants were able to attach a Man3GlcNAc core to a fucosylated GlcNAc-Fc domain,(36) but none of EndoD, EndoA, EndoM, and their mutants(36-39) were capable of transferring intact complex type N-glycan to either fucosylated or nonfucosylated GlcNAc-Fc domain; and (c) glycosylation remodeling of intact full-length IgG antibodies with complex type N-glycans is yet to be achieved. 
     In an attempt to develop efficient enzymatic deglycosylation/glycosylation system for glycoprotein glycosylation remodeling, attention has been turned to EndoS, an endo-β-N-acetylglucosaminidase (ENGase) from  Streptococcus pyogenes  that is capable of hydrolyzing the Fc N-glycans of intact IgG antibodies by cleaving the β-1,4-glycosidic bond in the chitobiose core of the N-glycans.(40-42). Endo-S possesses transglycosylation activity, such as that capable of using Man 3 GlcNAc oxazoline as donor substrate to glycosylate a GlcNAc acceptor. However, wild type Endo-S also possesses highly active hydrolytic activity, so the glycosylated IgG product is also subject to rapid hydrolysis if wild type Endo-S is used for synthesis and glycosylation remodeling. 
     In light of the above known activities of Endo S, it would be advantageous to provide a mutant Endo-S that exhibits transglycosylating activity with reduced hydrolyzing activity. 
     SUMMARY OF THE INVENTION 
     The present invention provides for recombinant Endo-S and selected mutants thereof that exhibit reduced hydrolysis activity and increased transglycosylation activity for the synthesis of IgG antibodies and Fc fragments thereof, wherein a desired sugar chain is added to a core fucosylated or nonfucosylated GlcNAc-IgG acceptor. As such, the present invention allows for the synthesis and remodeling of therapeutic antibodies and Fc fragments thereof to provide for certain biological activities, such as, prolonged half-life time in vivo, less immunogenicity, enhanced in vivo activity, increased targeting ability, and/or ability to deliver a therapeutic agent. 
     In one aspect, the present invention provides for transglycosylation activity of an endo-β-N-acetylglucosamindase of  Streptococcus pyogenes  (SEQ ID NO: 1) and mutants thereof, wherein the mutants have at least 95% homology thereto and exhibit transglycosylation activity on both core fucosylated and nonfucosylated GlcNAc-IgG acceptors, wherein the endoglycosidases enable the transfer of an oligosaccharide (in the form of an activated sugar oxazoline) en bloc to a fucosylated or nonfucosylated GlcNAc-IgG (or an Fc fragment thereof) to form a new glycoform of IgG (or an Fc fragment thereof). 
     In another aspect, the present invention provides for Endo-S mutants that show remarkably enhanced transglycosylation efficiency and diminished or abrogated product hydrolytic activity. Mutants preferably include site-specific mutations including a mutation at Asp-233. The mutants include, but are not limited to, D233Q (SEQ ID NO: 2) and D233A (SEQ ID NO: 3). 
     In a further aspect, the present invention provides for a chemoenzymatic method for the preparation of a homogeneous core fucosylated or nonfucosylated glycoforms of IgG antibodies, comprising: 
     a. providing an acceptor selected from the group consisting of a core fucosylated GlcNAc-IgG, nonfucosylated GlcNAc-IgG or corresponding IgG-Fc fragments; and 
     b. reacting the acceptor with a donor substrate including an activated oligosaccharide moiety, in the presence of  Streptococcus pyogenes  Endo-S Asp-233 mutants to transfer the activated oligosaccharide moiety to the acceptor and yield the homogeneous fucosylated or nonfucosylated glycoprotein. 
     In a still further aspect, the present invention provides a method for preparing a core-fucosylated IgG or IgG-Fc fragment having a predetermined oligosaccharide moiety, comprising: 
     a. providing a core-fucosylated IgG acceptor comprising an asparagine-linked core-fucosylated N-acetylglucosamine (GlcNAc) residue; and 
     b. enzymatically reacting the core-fucosylated IgG acceptor with an activated oligosaccharide donor in the presence of Endoglycosidase-S D233Q (SEQ ID NO: 2) and D233A (SEQ ID NO: 3) mutant, wherein the activated oligosaccharide donor carries an oligosaccharide moiety comprising a predetermined number and type of sugar residues, wherein the oligosaccharide moiety is covalently linked to the core-fucosylated IgG acceptor, thereby preparing the core-fucosylated IgG or IgG-Fc fragment having the predetermined oligosaccharide moiety. 
     In yet another aspect, the present invention provides for an activated oligosaccharide moiety, such as glycan or oligosaccharide oxazoline, glycosyl fluoride, glycosyl azide or an aryl glycoside, as a donor substrate for the synthesis of homogeneous core-fucosylated glycoproteins or nonfucosylated glycoproteins. Preferably the activated oligosaccharide moiety is an oligosaccharide oxazoline. 
     In a further aspect, the present invention relates to a chemoenzymatic method for the preparation of a homogeneous fucosylated or nonfucosylated monomer antibody or Fc fragment thereof, said method comprising:
         providing an acceptor selected from core fucosylated or nonfucosylated GlcNAc-antibody or Fc fragment thereof; and   reacting the acceptor with a donor substrate in the presence a  Streptococcus pyogenes  Endo-S Asp-233 mutant, wherein the donor substrate comprises a predetermined oligosaccharide component with a defined number and type of sugar residues and specific linkage types, thereby providing the homogeneous fucosylated or nonfucosylated monomer antibody or Fc fragment thereof. In one embodiment, a fucosylated GlcNAc containing protein is an alpha-1-6-fucosyl-GlcNAc-protein.       

     In another aspect, the present invention relates to a method of remodeling an antibody or Fc fragment thereof with an oligosaccharide having a predetermined oligosaccharide component with a defined number and type of sugar residues and with specific linkage types, the method comprising: 
     a. providing a core fucosylated antibody or Fc fragment thereof comprising Fc N-glycans; 
     b. treating the core fucosylated antibody or Fc fragment with a hydrolyzing endo-enzyme to yield a Asn-linked GlcNAc moiety; and 
     c. attaching the oligosaccharide to the Asn-linked GlcNAc moiety in the presence of an Endo-S mutant having an amino acid sequence selected from the group consisting of SEQ ID NO: 2 and SEQ ID NO: 3, thereby adding the predetermined oligosaccharide component. 
     In a further aspect, the present invention relates to a remodeling method of a core fucosylated or nonfucosylated IgG or IgG-Fc fragment with an oligosaccharide having a predetermined oligosaccharide component with a defined number and type of sugar residues and with specific linkage types, the method comprising: 
     a. providing a core fucosylated or nonfucosylated IgG or IgG-Fc fragment obtained from natural or recombinant sources carrying heterogeneous N-glycans; 
     b. treating the natural or recombinant IgG or IgG-Fc fragment with an endo-enzyme (a wild type endoglycosidase or a mutant endoglycosidase with efficient hydrolytic activity) to hydrolyze the bond between the two GlcNAc residues positioned closest to the peptide domain thereby forming a deglycosylated protein carrying a core fucosylated or nonfucosylated GlcNAc-acceptor; and
 
c. attaching the predetermined oligosaccharide component to the GlcNAc-acceptor to reconstitute the natural beta-1,4-glycosidic bond through transglycosylation with a  Streptococcus pyogenes  Endo-S Asp-233 mutant, thereby adding the predetermined the oligosaccharide component to remodel the core fucosylated or nonfucosylated IgG ro IgG-Fc fragment.
 
     Applicable oligosaccharide oxazolines include, but not limited to, high-mannose type, hybrid type, sialoglycan oxazoline and complex type N-glycan, as well as their selectively modified derivatives such as those with specific tags. Preferably, di-, tri-, tetra-, penta-, hexyl-, hepta-, octyl-, nona-, deca-, or undeca-saccharide oxazolines are utilized as donor substrates for a highly efficient chemoenzymatic synthesis of homogeneous core fucosylated or nonfucosylated IgG antibodies and IgG-Fc fragments. 
     In yet another aspect, the present invention relates to a method to synthesize a modified antibody or fragment thereof, the method comprising; 
     a. providing a naturally existing IgG antibody, a recombinant antibody or a Fc domain carrying Fc N-glycans as precursors; 
     b. Fc deglycosylating using an endoglycosidase such as a wild Endo-S to deglycosylate the Fc domain to form a GlcNAc-acceptor; wherein the GlcNAc-acceptor is positioned on the Fc region of the antibody and the GlcNAc-acceptor is either core fucosylated or nonfucosylated; and
 
c. transglycosylating the GlcNAc-acceptor in the naturally existing IgG antibody, the recombinant antibody or the Fc domain with an oligosaccharide oxazoline or a sialoglycan oxazoline having a predetermined number of sugar residues under the catalysis of an enzyme selected from the group consisting of Endo-S mutants including SEQ ID NO: 2, and SEQ ID NO: 3 to form the modified antibody with the predetermined number of sugar residues.
 
     In yet another aspect, the present invention provides a method of remodeling an intravenous immunoglobulin (IVIG) exhibiting Fc-sialylated glycoforms, the method comprising: 
     a. providing an IVIG carrying Fc N-glycans; 
     b. Fc deglycosylating the Fc N-glycans using an endoglycosidase including wild Endo-S to form GlcNAc-acceptors; wherein the GlcNAc-acceptors are positioned on the Fc region of the IVIG and the GlcNAc-acceptors are either fucosylated or nonfucosylated; and 
     c. transglycosylating the GlcNAc-acceptors with a sialoglycan oxazoline having a predetermined number of sugar residues under the catalysis of an enzyme selected from the group consisting of Endo-S mutants including SEQ ID NO: 2 and SEQ ID NO: 3 to form a sialylated IVIG. 
     Another aspect of the present invention provides for an IVIG preparation containing composition comprising at least 90% of homogeneous sialylated Fc glycoforms to increase anti-inflammatory activity, wherein the sialylated Fc glycoforms are synthesized using a  Streptococcus pyogenes  Endo-S Asp-233 mutant in combination with a GlcNAc moiety positioned on the Fc region of a deglycosylated IVIG and a sialoglycan oxazoline having a predetermined number of sugar residues. 
     In a still further aspect, the present invention relates to a method of synthesizing homogeneous core fucosylated or nonfucosylated IgG antibodies or IgG-Fc fragments, the method comprising: 
     a. providing a natural or recombinant IgG antibody or IgG-Fc fragment, wherein the recombinant IgG or IgG-Fc is produced from a typical protein expression system, including but not limited to yeast, insect, plant, and any mammalian expression system; 
     b. removing the N-glycans by an enzyme selected from the group consisting of Endo-H, Endo-A, Endo-S, and/or Endo-F3 to form a core fucosylated or nonfucosylated GlcNAc-containing protein; 
     c. providing a sugar oxazoline or sialoglycan oxazoline with a desired oligosaccharide component comprising a defined number and type of sugar residues in the chain; and 
     d. enzymatically transglycosylating the fucosylated or nonfucosylated GlcNAc-containing protein with a sugar oxazoline having a desired number of sugar residues or sialoglycan oxazoline having a desired number of sugar and sialic acid residues with an endoglycosidase selected from the group consisting of a  Streptococcus pyogenes  Endo-S Asp-233 mutants, thereby forming a homogeneous core fucosylated or nonfucosylated IgG antibody or IgG-Fc fragment having an extension of desired number of sugar residues and/or sialic acid. 
     It is envisioned that the oligosaccharide oxazoline or sialoglycan oxazoline having a predetermined oligosaccharide component with a defined number and type of sugar residues may further comprises an additional moiety or tag including, a therapeutic agent or drug such as for treating cancer, HIV or other viruses, substances that activates receptors on the cell plasma membrane, agents that affects intracellular chemistry, agents that affects cellular physics, genes, gene analogs, RNA, RNA analogs, DNA, DNA analogs, amino acid sequences of surface receptors such as CCR5 or CD4, antigenic structure having affinity for a specific antibody; amino acid sequences of receptor ligands such as gp120, gp41 or gp160, receptor antagonists, receptor blockers, enzymes, enzyme substrates, enzyme inhibitors, enzyme modulators, therapeutic proteins, protein analogs, metabolites, metabolite analogs, oligonucleotides, oligonucleotide analogs, antigens, antigen analogs, antibodies or fragments thereof, antibody analogs, an antibody different from the modified antibody which is reactive to another receptor bacteria, viruses, inorganic ions, metal ions, metal clusters, polymers, fluorescent compounds and any combinations thereof. 
     As such, the present invention further provides a delivery device for delivering a drug or therapeutic agent having biological activity to treat a condition, the delivery device comprising: a remodeled IgG or IgG-Fc fragment having a predetermined sugar chain or sialoglycan and a therapeutic agent or drug attached to the terminal sugar residue or sialic acid. 
     The present invention envisions modifying monoclonal antibodies related to HIV including, but not limited to 17b, 48d, A32, C11, 2G12, F240, IgG1b12, 19e, X5, TNX-355 and F91, all of which are commercially available. 
     Further antibodies related to cancer or other diseases may also be remodeled for individual fit to certain receptors thereby increasing biological activity, the monoclonal antibodies may include, but are not limited to, cetuximab, rituximab, muromonab-CD3, abciximab, daclizumab, basiliximab, palivizumab, infliximab, trastuzumab, gemtuzumab ozogamicin, alemtuzumab, ibritumomab tiuxetan, adalimumab, omalizumab, tositumomab, I-131 tositumomab, efalizumab, bevacizumab, panitumumab, pertuzumab, natalizumab, etanercept, IGN101 (Aphton), volociximab (Biogen Idec and PDL BioPharm), Anti-CD80 mAb (Biogen Idec), Anti-CD23 mAb (Biogen Idel), CAT-3888 (Cambridge Antibody Technology), CDP-791 (Imclone), eraptuzumab (Immunomedics), MDX-010 (Medarex and BMS), MDX-060 (Medarex), MDX-070 (Medarex), matuzumab (Merck), CP-675,206 (Pfizer), CAL (Roche), SGN-30 (Seattle Genetics), zanolimumab (Serono and Genmab), adecatumumab (Sereno), oregovomab (United Therapeutics), nimotuzumab (YM Bioscience), ABT-874 (Abbott Laboratories), denosumab (Amgen), AM 108 (Amgen), AMG 714 (Amgen), fontolizumab (Biogen Idec and PDL BioPharm), daclizumab (Biogent Idec and PDL BioPharm), golimumab (Centocor and Schering-Plough), CNTO 1275 (Centocor), ocrelizumab (Genetech and Roche), HuMax-CD20 (Genmab), belimumab (HGS and GSK), epratuzumab (Immunomedics), MLN1202 (Millennium Pharmaceuticals), visilizumab (PDL BioPharm), tocilizumab (Roche), ocrerlizumab (Roche), certolizumab pegol (UCB, formerly Celltech), eculizumab (Alexion Pharmaceuticals), pexelizumab (Alexion Pharmaceuticals and Procter &amp; Gamble), abciximab (Centocor), ranibizimumab (Genetech), mepolizumab (GSK), TNX-355 (Tanox), or MYO-029 (Wyeth). 
     A still further aspect of the invention relates to a method of remodeling an antibody which initially includes a heterogeneous sugar chain, the method comprising: 
     a. removing the heterogeneous sugar chain from the antibody with an endoglycosidase to leave a single fucosylated- or nonfucosylated-GlcNAc moiety attached to an original glycosylation site; and 
     b. transferring a core oligosaccharide or sialoglycan oxazoline with at least one tag to the fucosylated- or -nonfucosylated GlcNAc moiety by an endoglycosidase catalyzed transglycosylation to yield a tagged antibody, wherein the endoglycosidase is selected from the group consisting of Endo-S mutants including SEQ ID NO: 2 and SEQ ID NO: 3. 
     The tag moiety may include, but is not limited to, antigens, therapeutic drugs such as for cancer or HIV, toxins, fluorescent probes, biotin, PEG species, lipids, or nucleotides. 
     In another aspect, the present invention provides for a composition comprising at least one  Streptococcus pyogenes  Endo-S Asp-233 mutant selected from the group consisting of D233Q (SEQ ID NO:2) and D233A (SEQ ID No: 3). 
     In yet another aspect, the present invention provides a substantially homogeneous preparation of core fucosylate or nonfucosylated antibody or Fc fragment thereof having a predetermined oligosaccharide moiety, wherein the substantially homogeneous preparation is produced by any of the aforementioned methods. Also provided are compositions comprising such homogeneous preparations. 
     In a still further aspect, the present invention provides for a method of treatment using a remodeled antibody having a desired glycosylation state and/or sialylated form in an amount sufficient to modulate biological activity in the treated subject. 
     Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1   a    shows the alpha backbone structure of human IgG showing functional regions (modeled on the basis of PDB code 1HZH). (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  1   b    shows the structure of a full-length bi-antennary complex type N-glycan attached to the Asn-297 in the Fc domain, (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  2    shows the sequence alignment of EndoS (SEQ ID NO: 4) and EndoF3 (SEQ ID NO: 5). 
         FIG.  3    A shows the scheme for glycosylation remodeling of rituximab to homogeneous natural glycoforms (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  3    B shows the scheme for glycosylation remodeling of rituximab to selectively modified glycoforms (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  4 A  shows the SDS-PAGE analysis of the glycosylation remodeling of rituximab: Lane 0, protein markers; Lane 1, commercial rituximab; Lane 2, EndoS de-glycosylated rituximab (1); Lane 3, transglycosylation product (3) from the EndoS-D233A catalyzed reaction between (1) and sialoglycan oxazoline (2); Lane 4, transglycosylation product from the EndoS-D233Q catalyzed reaction of (1) and (2); lane 5, the transglycosylation product (5) from the EndoS-D233Q catalyzed reaction between the deglycosylated rituximab (1) and Man3GlcNAc oxazoline (4); lane 6, the transglycosylation product (7) from the EndoS-D233Q catalyzed reaction between the deglycosylated rituximab (1) and N3Man3GlcNAc oxazoline (6). 
         FIG.  4 B  shows the ESI-MS (after deconvolution) analysis of the heavy chain of the commercial rituximab. 
         FIG.  4 C  shows the ESI-MS analysis of the de-glycosylated rituximab (1). 
         FIG.  4 D  shows the ESI-MS analysis of the transglycosylation product (3). 
         FIG.  4 E  shows the ESI-MS analysis of the transglycosylation product (5). 
         FIG.  4 F  shows the ESI-MS analysis of the transglycosylation product (7). 
         FIG.  5    A shows the enzymatic remodeling to non-fucosylated homogeneous glycoform of rituximab (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  5    B shows the enzymatic remodeling to non-fucosylated homogeneous glycoform of rituximab (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  6   a    shows SDS-PAGE analysis of glycoengineering of rituximab to the non-fucosylated G2 glycoform: Lane 0, protein markers; Lane 1, commercial rituximab; Lane 2, the EndoS de-glycosylated rituximab (1); Lane 3, the defucosylated product (8); Lane 4, the glycoengineered G2 glycoform. 
         FIG.  6   b    shows the ESI-MS (after deconvolution) analysis of the heavy chain of the defucosylated rituximab (8). 
         FIG.  6   c    shows the ESI-MS analysis of the heavy chain of the glycoengineered G2 rituximab (10). 
         FIG.  7    shows the Site-specific Fc glycoengineering of human IVIG. (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  8   a    shows the fluorescent HPLC profiles of 2AB-labeled N-glycans from Fab and Fc of IVIG from native IVIG Fc. The glycan structures include the following components: (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  8   b    shows the fluorescent HPLC profiles of 2AB-labeled N-glycans from Fab and Fc of IVIG from glycoengineered IVIG Fc. The glycan structures include the following components: (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  8   c    shows the fluorescent HPLC profiles of 2AB-labeled N-glycans from Fab and Fc of IVIG from native IVIG Fab. The glycan structures include the following components: (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  8   d    shows the fluorescent HPLC profiles of 2AB-labeled N-glycans from Fab and Fc of IVIG from glycoengineered IVIG Fab. The glycan structures include the following components: (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  8   e    shows the glycan structures corresponding to HPLC peaks 1-15 in  FIGS.  8   a   - 8   d.    
         FIG.  9    A shows typical SPR sensorgrams of the binding of G2-rituximab and commercial rituximab with FcγRIIIa-V158. The antibodies were immobilized by Protein A capture and the binding was analyzed by injecting the respective Fcγ receptors at a serial 2-fold dilutions starting at 40 μg/mL (1.33 uM). 
         FIG.  9    B shows typical SPR sensorgrams of the binding of G2-rituximab and commercial rituximab with FcγRIIIa-F158. The antibodies were immobilized by Protein A capture and the binding was analyzed by injecting the respective Fcγ receptors at a serial 2-fold dilutions starting at 40 μg/mL (1.33 uM). 
         FIG.  9    C shows typical SPR sensorgrams of the binding of G2-rituximab and commercial rituximab with FcγRIIb. The antibodies were immobilized by Protein A capture and the binding was analyzed by injecting the respective Fcγ receptors at a serial 2-fold dilutions starting at 40 μg/mL (1.33 uM). 
         FIG.  10    shows the MALDI-TOF MS of the Fc N-glycans released by PNGase F treatment with the same symbols as defined in  FIG.  1   . 
         FIG.  11    shows the MALDI-TOF MS of the Fc N-glycans released by EndoS treatment with the same symbols as defined in  FIG.  1   . 
         FIG.  12    A shows the LC-MS profile of reduced rituximab. 
         FIG.  12    B shows the ESI-MS of the light chain of rituximab. 
         FIG.  12    C shows the ESI-MS of the deconvoluted MS of the light chain of rituximab. 
         FIG.  12    D shows the ESI-MS of the heavy chain of rituximab. 
         FIG.  12    E shows the ESI-MS of the deconvoluted MS of the heavy chain of rituximab. 
         FIG.  13   a    shows the fluorescent HPLC profile of the 2-AB-labeled N-glycans released from commercial rituximab samples by PNGase F treatment. (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  13   b    shows the fluorescent HPLC profile of the 2-AB-labeled N-glycans released from sialylated rituximab (3) sample by PNGase F treatment. (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  13   c    shows the fluorescent HPLC profile of the 2-AB-labeled N-glycans released from non-fucosylated rituximab (10) sample by PNGase F treatment. (  GlcNAc;   Man;   Gal;   Glc;   Fuc;   Sia). 
         FIG.  14    shows the SDS-PAGE analysis of transglycosylation by wild type EndoS. Lane 0, protein markers; Lane 1, commercial rituximab; Lane 2, EndoS de-glycosylated rituximab (1); Lane 3 to Lane 7, monitoring of the transglycosylation reaction between de-glycosylated rituximab (1) and sialoglycan oxazoline (2): Lane 3, 15 mins; Lane 4, 30 mins; Lane 5, 1 h; Lane 6, 2 h; Lane 7, 4 h. 
         FIG.  15    A shows the LC-MS monitoring on defucosylation of Fuc(α2,6)GlcNAc-rituximab (1) with bovine kidney α-fucosidase. The deconvoluted ESI-MS profiles of the rituximab&#39;s heavy chain were shown (FG-Rx, heavy chain of Fuc(α2,6)GlcNAc-rituximab; G-Rx, heavy chain of GlcNAc-rituximab) following incubation with the α-fucosidase for 2 days. 
         FIG.  15    B shows the LC-MS monitoring on defucosylation of Fuc(α2,6)GlcNAc-rituximab (1) with bovine kidney α-fucosidase. The deconvoluted ESI-MS profiles of the rituximab&#39;s heavy chain were shown (FG-Rx, heavy chain of Fuc(α2,6)GlcNAc-rituximab; G-Rx, heavy chain of GlcNAc-rituximab) following incubation with the α-fucosidase for 7 days. 
         FIG.  15    C shows the LC-MS monitoring on defucosylation of Fuc(α2,6)GlcNAc-rituximab (1) with bovine kidney α-fucosidase. The deconvoluted ESI-MS profiles of the rituximab&#39;s heavy chain were shown (FG-Rx, heavy chain of Fuc(α2,6)GlcNAc-rituximab; G-Rx, heavy chain of GlcNAc-rituximab) following incubation with the α-fucosidase for 14 days. 
         FIG.  15    D shows the LC-MS monitoring on defucosylation of Fuc(α2,6)GlcNAc-rituximab (1) with bovine kidney α-fucosidase. The deconvoluted ESI-MS profiles of the rituximab&#39;s heavy chain were shown (FG-Rx, heavy chain of Fuc(α2,6)GlcNAc-rituximab; G-Rx, heavy chain of GlcNAc-rituximab) following incubation with the α-fucosidase for 20 days. 
         FIG.  16    shows the SDS-PAGE analysis of IVIG glycoengineering. Lane 0, protein marker; Lane 1, commercial IVIG; Lane 2, IVIG (11) after deglycosylation by EndoS; Lane 3, IVIG (12) after EndoS-D233Q catalyzed transglycosylation with sialoglycan oxazoline. 
         FIG.  17    A shows the amino acid residues of  Streptococcus pyogenes  Endo-S Asp-233 mutant D233Q (SEQ ID NO:2). 
         FIG.  17    B shows the amino acid residues of  Streptococcus pyogenes  Endo-S Asp-233 mutant D233A (SEQ ID No: 3). 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides for novel glycosynthase EndoS Asp 233 mutants that show remarkable transglycosylation efficiency capable of transferring complex type N-glycans from activated glycan oxazolines to deglycosylated intact antibodies without product hydrolysis. It has been found herein that the glycosynthase EndoS Asp 233 mutants acted efficiently on both core fucosylated and nonfucosylated GlcNAc-Fc domain of intact antibodies to provide various defined IgG glycoforms. Further, antibodies and intravenous immunoglobulins were transformed into Fc fully sialylated glycoforms having increased anti-inflammatory activity. Still further, the present invention provides for a homogeneous glycoform having increased ADCC activity with enhanced FcγIIIa receptor-binding activity and azido-tagged glycoforms that can be further transformed into other glycoforms. 
     The practice of the present invention will employ, unless otherwise indicated, conventional techniques of immunology, molecular biology, microbiology, cell biology and recombinant DNA, which are within the skill of the art. See, e.g., Sambrook, et al. MOLECULAR CLONING: A LABORATORY MANUAL, 2nd edition (1989); CURRENT PROTOCOLS IN MOLECULAR BIOLOGY (F. M. Ausubel, et al. eds., (1987)); the series METHODS IN ENZYMOLOGY (Academic Press, Inc.): PCR 2: A PRACTICAL APPROACH (M. J. MacPherson, B. D. Hames and G. R. Taylor eds. (1995)), Harlow and Lane, eds. (1988) ANTIBODIES, A LABORATORY MANUAL, and ANIMAL CELL CULTURE (R. I. Freshney, ed. (1987)). 
     It is understood that aspects of the present invention described herein include “consisting” and/or “consisting essentially of” aspects. 
     Definitions 
     As used in the specification herein, “a” or “an” may mean one or more. As used herein in the claim(s), when used in conjunction with the word “comprising”, the words “a” or “an” may mean one or more than one. As used herein “another” may mean at least a second or more. 
     As used herein, “biological activity” refers to pharmacodynamic and pharmacokinetic properties including, for example, molecular affinity or resultant biochemical or physiological effect, receptor affinity or resultant biochemical or physiological effect, non-receptor affinity or biochemical or physiological effect, efficacy, bioavailability, absorption, distribution, metabolism, or elimination. 
     As used herein, “sugar” refers to an oxidized or nonoxidized carbohydrate-containing molecule, including, but not limited to, a monosaccharide, disaccharide, trisaccharide, oligosaccharide, or polysaccharide, including, for example, N-acetylglucosamine, mannose, galactose, N-acetylneuraminic acid (sialic acid), glucose, fructose, fucose, sorbose, rhamnose, mannoheptulose, N-acetylgalactosamine, dihydroxyacetone, xylose, xylulose, arabinose, glyceraldehyde, sucrose, lactose, maltose, trehalose, cellobiose or any combination thereof of the L- or D-isomer. Sugar further refers to, such molecules produced naturally, recombinantly, synthetically, and/or semi-synthetically. 
     As used herein, “homogenous” refers to core fucosylated glycoproteins or nonfucosylated glycoproteins wherein the oligosaccharide component comprises at least 75%, more preferably at least 80%, at least 85% or at least 90%, and most preferably at least 95% of the same number and types of sugar residues. 
     As used herein, “protein” or “glycoprotein” is interchangeable with the terms peptide and glycopeptide. 
     As used herein, “homology” refers to amino acid sequence having substantial identity or similarity between two polypeptides and having at least 90%, and more preferably at least 95% similarity to a reference polypeptide. For polypeptides, the length of comparison to obtain the above-described percent homologies between sequences will generally be at least 25 amino acids, alternatively at least 50 amino acids, more likely at least 100 amino acids, and most likely 200 amino acids or more. Substantially identity or homologous polypeptides include additions, truncations, internal deletions or insertions, conservative and non-conservative substitutions, or other modifications located at positions of the amino acid sequence which do not destroy the function of the endoglycosidase. Those of skill in the art will recognize the numerous amino acids that can be modified or substituted with other chemically similar residues without substantially altering activity. 
     As used herein, “modulates” refers to an increase or decrease in “biological activity”, as defined above, when comparing to a glycosylation-engineered antibody of the present invention to a non-glycosylation-engineered antibody. 
     As used herein, “immunoglobulin molecule” or “antibodies,” refers to molecules that contain an antigen binding site which specifically binds an antigen or an Fc region that binds to cell receptors. Structurally, the simplest naturally occurring antibody (e.g., IgG) comprises four polypeptide chains, two heavy (H) chains and two light (L) chains inter-connected by disulfide bonds. The natural immunoglobulins represent a large family of molecules that include several types of molecules, such as IgD, IgG, IgA, IgM and IgE. The term also encompasses hybrid antibodies, or altered antibodies, and fragments thereof, including Fc fragment(s). 
     Antibodies can be fragmented using conventional techniques as described herein and the fragments screened for utility in the same manner as described for whole antibodies. A Fab fragment of an immunoglobulin molecule is a multimeric protein consisting of the portion of an immunoglobulin molecule containing the immunologically active portions of an immunoglobulin heavy chain and an immunoglobulin light chain covalently coupled together and capable of specifically combining with an antigen. Fab and Fc fragments can be prepared by proteolytic digestion of substantially intact immunoglobulin molecules with papain using methods that are well known in the art. However, a Fab or Fc fragment may also be prepared by expressing in a suitable host cell the desired portions of immunoglobulin heavy chain and immunoglobulin light chain using methods known in the art. 
     As used herein, with respect to antibodies, “substantially pure” means separated from those contaminants that accompany it in its natural state or those contaminants generated or used in the process of the obtaining the antibody. This term further includes the desired product having a single glycosylation state, whether or not this state includes glycosylation at a single site or multiple sites. Typically, the antibody is substantially pure when it constitutes at least 60%, by weight, of the antibody in the preparation. For example, the antibody in the preparation is at least about 75%, in certain embodiments at least about 80%, in certain embodiments at about 85%, in certain embodiments at least about 90%, in certain embodiments at least about 95%, and most preferably at least about 99%, by weight, of the desired antibody. A substantially pure antibody includes a naturally, recombinantly, or synthetically produced antibody. 
     As used herein, “therapeutically effective amount” refers to an amount that results in an improvement or remediation of the symptoms of the disease or condition. 
     Antigens useful for attachment as a tag to a modified core fucosylated or nonfucosylated glycoprotein of the present invention and more preferably an antibody or fragment thereof may be a foreign antigen, an endogenous antigen, fragments thereof, or variants having the same functional activity. 
     As used herein, “endogenous antigen” refers to a protein or part thereof that is naturally present in the recipient animal cell or tissue, such as a cellular protein, an immunoregulatory agent, or a therapeutic agent. 
     As used herein, “foreign antigen” refers to a protein or fragment thereof, which is foreign to the recipient animal cell or tissue including, but not limited to, a viral protein, a parasite protein, an immunoregulatory agent, or a therapeutic agent. 
     The foreign antigen may be a protein, an antigenic fragment or antigenic fragments thereof that originate from viral and parasitic pathogens. 
     Alternatively, the foreign antigen may be encoded by a synthetic gene and may be constructed using conventional recombinant DNA methods; the synthetic gene may express antigens or parts thereof that originate from viral and parasitic pathogens. These pathogens can be infectious in humans, domestic animals or wild animal hosts. 
     The foreign antigen can be any molecule that is expressed by any viral or parasitic pathogen prior to or during entry into, colonization of, or replication in their animal host. 
     The viral pathogens, from which the viral antigens are derived include, but are not limited to, Orthomyxoviruses, such as influenza virus (Taxonomy ID: 59771); Retroviruses, such as RSV, HTLV-1 (Taxonomy ID: 39015) and HTLV-II (Taxonomy ID: 11909); Herpes viruses, such as EBV (Taxonomy ID: 10295), CMV (Taxonomy ID: 10358) or herpes simplex virus (ATCC #: VR-1487); Lentiviruses, such as HIV-1 (Taxonomy ID: 12721) and HIV-2 Taxonomy ID: 11709); Rhabdoviruses, such as rabies; Picornoviruses, such as Poliovirus (Taxonomy ID: 12080); Poxviruses, such as vaccinia Taxonomy ID: 10245); Rotavirus Taxonomy ID: 10912); and Parvoviruses, such as adeno-associated virus 1 (Taxonomy ID: 85106). 
     Examples of viral antigens include, but are not limited to, the human immunodeficiency virus antigens Nef (National Institute of Allergy and Infectious Disease HIV Repository Cat. #183; GenBank accession #AF238278), Gag, Env (National Institute of Allergy and Infectious Disease HIV Repository Cat. #2433; GenBank accession #U39362), Tat (National Institute of Allergy and Infectious Disease HIV Repository Cat. #827; GenBank accession #M13137), Rev (National Institute of Allergy and Infectious Disease HIV Repository Cat. #2088; GenBank accession #L14572), Pol (National Institute of Allergy and Infectious Disease HIV Repository Cat. #238; GenBank accession #AJ237568) and T cell and B cell epitopes of gp120; the hepatitis B surface antigen (GenBank accession #AF043578); rotavirus antigens, such as VP4 (GenBank accession #AJ293721) and VP7 (GenBank accession #AY003871); influenza virus antigens, such as hemagglutinin (GenBank accession #AJ404627); nucleoprotein (GenBank accession #AJ289872); and herpes simplex virus antigens, such as thymidine kinase (GenBank accession #AB047378). 
     The bacterial pathogens, from which the bacterial antigens are derived, include but are not limited to,  Mycobacterium  spp.,  Helicobacter pylori, Salmonella  spp.,  Shigella  spp.,  E. coli, Rickettsia  spp.,  Listeria  spp.,  Legionella pneumoniae, Pseudomonas  spp.,  Vibrio  spp., and  Borellia burgdorferi.    
     Examples of protective antigens of bacterial pathogens include the somatic antigens of enterotoxigenic  E. coli , such as the CFA/I fimbrial antigen and the nontoxic B-subunit of the heat-labile toxin; pertactin of  Bordetella pertussis , adenylate cyclase-hemolysin of  B. pertussis , fragment C of tetanus toxin of  Clostridium tetani , OspA of  Borellia burgdorferi , protective paracrystalline-surface-layer proteins of  Rickettsia prowazekii  and  Rickettsia typhi , the listeriolysin (also known as “Llo” and “Hly”) and/or the superoxide dismutase (also know as “SOD” and “p60”) of  Listeria monocytogenes ; the urease of  Helicobacter pylori , and the receptor-binding domain of lethal toxin and/or the protective antigen of  Bacillus  anthrax. 
     Example of antigens from biological weapons or pathogens include, but are not limited to, smallpox, anthrax, tularemia, plague,  listeria , brucellosis, hepatitis, vaccinia, mycobacteria, coxsackievirus, tuberculosis, malaria, erhlichosis and bacterial meningitis. 
     The parasitic pathogens, from which the parasitic antigens are derived, include but are not limited to,  Plasmodium  spp., such as  Plasmodium falciparum  (ATCC #: 30145); Trypanosome spp., such as  Trypanosoma cruzi  (ATCC #: 50797); Giardia spp., such as Giardia intestinalis (ATCC #: 30888D);  Boophilus  spp.;  Babesia  spp., such as  Babesia microti  (ATCC #: 30221);  Entamoeba  spp., such as  Entamoeba histolytica  (ATCC #: 30015);  Eimeria  spp., such as  Eimeria maxima  (ATCC #40357);  Leishmania  spp., (Taxonomy ID: 38568);  Schistosome  spp., such as  Schistosoma mansoni  (GenBank accession #AZ301495);  Brugia  spp., such as  Brugia malayi  (GenBank accession #BE352806); Fascida spp., such as  Fasciola hepatica  (GenBank accession #AF286903);  Dirofilaria  spp., such as  Dirofilaria immitis  (GenBank accession #AF008300);  Wuchereria  spp., such as  Wuchereria bancrofti  (GenBank accession #AF250996); and  Onchocerea  spp; such as  Onchocerca volvulus  (GenBank accession #BE588251). 
     Examples of parasite antigens include, but are not limited to, the pre-erythrocytic stage antigens of  Plasmodium  spp. such as the circumsporozoite antigen of  P. falciparum  (GenBank accession #M22982)  P vivax  (GenBank accession #M20670); the liver stage antigens of  Plasmodium  spp, such as the liver stage antigen 1 (as referred to as LSA-1; GenBank accession #AF086802); the merozoite stage antigens of  Plasmodium  spp; such as the merozoite surface antigen-1 (also referred to as MSA-1 or MSP-1; GenBank accession #AF199410); the surface antigens of  Entamoeba histolytica , such as the galactose specific lectin (GenBank accession #M59850) or the serine rich  Entamoeba histolytica  protein; the surface proteins of  Leishmania  spp, such as 63 kDa glycoprotein (gp63) of  Leishmania major  (GenBank accession #Y00647 or the 46 kDa glycoprotein (gp46) of  Leishmania major ; paramyosin of  Brugia malayi  (GenBank accession #U77590; the triose-phosphate isomerase of  Schistosoma mansoni  (GenBank accession #W06781; the secreted globin-like protein of  Trichostrongylus colubriformis  (GenBank accession #M63263; the glutathione-S-transferases of  Fasciola hepatica  (GenBank accession #M77682;  Schistosoma bovis  (GenBank accession #M77682);  S. japonicum  (GenBank accession #U58012; and KLH of  Schistosoma bovis  and  S. japonicum  (Bashir, et al., supra). 
     Examples of tumor specific antigens include prostate specific antigen (PSA), TAG-72 and CEA; human tyrosinase (GenBank accession #M27160); tyrosinase-related protein (also referred to as TRP; GenBank accession #AJ132933); and tumor-specific peptide antigens. 
     Examples of transplant antigens include the CD3 molecule on T cells and histocompatibility antigens such as HLA A, HLA B, HLA C, HLA DR and HLA. 
     Examples of autoimmune antigens include IAS 13 chain, which is useful in therapeutic vaccines against autoimmune encephalomyelitis (GenBank accession #D88762); glatamic acid decarboxylase, which is useful in therapeutic vaccines against insulin-dependent type 1 diabetes (GenBank accession #NM013445); thyrotropin receptor (TSHr), which is useful in therapeutic vaccines against Grave&#39;s disease (GenBank accession #NM000369) and tyrosinase-related protein 1, which is useful in therapeutic vaccines against vitiligo (GenBank accession #NM000550). 
     HIV drugs that may be used in the construction of the tagged antibodies or fragments thereof include, but are not limited to antiviral agents such as nucleoside RT inhibitors, CCR5 inhibitors/antagonists, viral entry inhibitors and their functional analogs. Specifically, an antiviral agent may nucleoside RT inhibitors, such as Zidovudine (ZDV, AZT), Lamivudine (3TC), Stavudine (d4T), Didanosine (ddl), Zalcitabine (ddC), Abacavir (ABC), Emirivine (FTC), Tenofovir (TDF), Delaviradine (DLV), Efavirenz (EFV), Nevirapine (NVP), Saquinavir (SQV), Ritonavir (RTV), Indinavir (IDV), Nelfinavir (NFV), Amprenavir (APV), Lopinavir (LPV), Atazanavir, Combivir (ZDV/3TC), Kaletra (RTV/LPV), Trizivir (ZDV/3TC/ABC); 
     CCR5 inhibitors/antagonists, such as SCH-C, SCH-D, PRO 140, TAK 779, TAK-220, RANTES analogs, AK602, UK-427, 857, monoclonal antibodies; and viral entry inhibitors, such as Fuzeon (T-20) (enfuvirtide), NB-2, NB-64, T-649, T-1249, SCH-C, SCH-D, PRO 140, TAK 779, TAK-220, RANTES analogs, AK602, UK-427, 857; and functional analogs or equivalents thereof. 
     It is envisioned that many different core fucosylated glycoproteins and nonfucosylated glycoproteins can be modified according to the methods of the present invention or used as a therapeutic agent for conjugation to a terminal sugar including but not limited to, adrenocorticotropic hormone (ACTH); adrenocorticotropic hormone derivatives (e.g., ebiratide); angiotensin; angiotensin II; asparaginase; atrial natriuretic peptides; atrial sodium diuretic peptides; bacitracin; beta-endorphins; blood coagulation factors VII, VIII and IX; blood thymic factor (FTS); blood thymic factor derivatives; bombesin; bone morphogenic factor (BMP); bone morphogenic protein; bradykinin; caerulein; calcitonin gene related polypeptide (CGRP); calcitonins; CCK-8; cell growth factors (e.g., EGF; TGF-alpha; TGF-beta; PDGF; acidic FGF; basic FGF); cerulein; chemokines; cholecystokinin; cholecystokinin-8; cholecystokinin-pancreozymin (CCK-PZ); colistin; colony-stimulating factors (e.g. CSF; GCSF; GMCSF; MCSF); corticotropin-releasing factor (CRF); cytokines; desmopressin; dinorphin; dipeptide; dismutase; dynorphin; eledoisin; endorphins; endothelin; endothelin-antagonistic peptides; endotherins; enkephalins; enkephalin derivatives; epidermal growth factor (EGF); erythropoietin (EPO); follicle-stimulating hormone (FSH); gallanin; gastric inhibitory polypeptide; gastrin-releasing polypeptide (GRP); gastrins; G-CSF; glucagon; glutathione peroxidase; glutathio-peroxidase; gonadotropins (e.g., human chorionic gonadotrophin and .alpha. and .beta. subunits thereof); gramicidin; gramicidines; growth factor (EGF); growth hormone-releasing factor (GRF); growth hormones; hormone releasing hormone (LHRH); human artrial natriuretic polypeptide (h-ANP); human placental lactogen; insulin; insulin-like growth factors (IGF-I; IGF-II); interferon; interferons (e.g., alpha-beta- and gamma-interferons); interleukins (e.g. 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11 and 12); intestinal polypeptide (VIP); kallikrein; kyotorphin; luliberin; luteinizing hormone (LH); luteinizing hormone-releasing hormone (LH-RH); lysozyme chloride; melanocyte-stimulating hormone (MSH); melanophore stimulating hormone; mellitin; motilin; muramyl; muramyldipeptide; nerve growth factor (NGF); nerve nutrition factors (e.g. NT-3; NT-4; CNTF; GDNF; BDNF); neuropeptide Y; neurotensin; oxytocin; pancreastatin; pancreatic polypeptide; pancreozymin; parathyroid hormone (PTH); pentagastrin; polypeptide YY; pituitary adenyl cyclase-activating polypeptides (PACAPs); platelet-derived growth factor; polymixin B; prolactin; protein synthesis stimulating polypeptide; PTH-related protein; relaxin; renin; secretin; serum thymic factor; somatomedins; somatostatins derivatives; superoxide dismutase; taftsin; tetragastrin; thrombopoietin (TPO); thymic humoral factor (THF); thymopoietin; thymosin; thymostimulin; thyroid hormone releasing hormone; thyroid-stimulating hormone (TSH); thyrotropin releasing hormone TRH); trypsin; tuftsin; tumor growth factor (TGF-alpha); tumor necrosis factor (TNF); tyrocidin; urogastrone; urokinase; vasoactive intestinal polypeptide; and vasopressin. 
     Core fucosylated and nonfucosylated glycoproteins are important classes of biomolecules that play crucial roles in many biological events such as cell adhesion, tumor metastasis, pathogen infection, and immune response. As indicated previously herein, a major problem in structural and functional studies of fucosylated or nonfucosylated glycoproteins is their structural microheterogeneity. Natural and recombinant fucosylated or nonfucosylated glycoproteins are typically produced as a mixture of glycoforms that differ only in the structure of the pendent oligosaccharides. 
     The remodeled glycoproteins, such as antibodies can be subjected to any further structural modifications that are necessary or desired, including, without limitation, glycosyl transfer, and selective ligation (e.g., click chemistry, Staudinger reaction, etc.) to introduce the additional functional groups or tags. The functional groups can be of any suitable type, including, without limitation, toxins, special antigens (such as alpha-Gal), radioactive species, photoactive species, PEGs, etc. The glycoprotein can be catalytically reacted in a “click chemistry” cycloaddition reaction of the azide functionality of the glycoprotein with an alkyne bearing the functional moiety of interest. The azido and alkyne functional groups can be switched in the respective ligation components, and the glycoprotein can be functionalized with an alkynyl functionality and reacted with an azide-functionalized compound including the moiety of interest. It will also be appreciated that other ligation pairs can be devised for the click chemistry reaction. 
     The core fucosylated and nonfucosylated antibodies or fragments thereof, produced according to the methods described herein, can be used for diagnosis and therapeutics. Approximately two-thirds of therapeutic proteins, such as monoclonal antibodies used on the market and/or currently in clinical trials are glycoproteins. However, the structural heterogeneity in different glycoforms of natural and recombinant glycoproteins presents a major barrier in developing glycoprotein-based drugs, as different glycoforms may have different biological activities and controlling glycosylation to a homogeneous glycoform is extremely difficult during expression. The previous discovery of the transglycosylation activity of a class of endoglycosidases represents a major advance in the field for glycosylation engineering to enhance glycoproteins&#39; therapeutic and diagnostic potentials and the Endo-S mutants of the present invention are able to transglycosylate core fucosylated and nonfucosylated natural and recombinant glycoproteins without the the negative aspects of hydrolysis. 
     The features and advantages of the present invention are more fully shown by the following non-limiting examples. 
     EXAMPLES 
     Generation of EndoS Glycosynthase Mutants and Their Use for Glycosylation Remodeling of Intact Monoclonal Antibody Rituximab 
     Glycosynthases have been previously made from several GH85 endoglycosidases (ENGases), including EndoA, EndoM, and EndoD, by site-directed mutagenesis of a key asparagine (Asn) residue responsible for promoting oxazolinium ion intermediate formation during hydrolysis.(36-39, 43) EndoS is an endoglycosidase belonging to the glycoside hydrolase family 18 (GH18),(40, 41) which is in the same GH family as EndoF1, EndoF2, and EndoF3 that were recently shown to have transglycosylation activity.(44) Based on the assumption that EndoS-catalyzed hydrolysis also proceeds by a substrate-assisted mechanism involving the formation of an oxazolinium ion intermediate, as demonstrated by other GH18 endoglycosidases such as EndoF3,(45) potential glycosynthases from EndoS were created by identifying and mutating the residue responsible for promoting oxazolinium ion formation. Previous structural and mutagenesis studies on EndoF3 have shown that an aspartic acid residue at position 165 (D165), instead of an asparagine residue as in the family GH85 enzymes, is responsible for promoting oxazoline formation and that the E167 residue is the general acid/base for catalytic hydrolysis.(45) Sequence alignment of EndoS with EndoF3 ( FIG.  2   ) led to the identification of two key residues in EndoS for catalysis: the D233 residue (corresponding to D165 in EndoF3) responsible for promoting oxazolinium ion formation and the E235 residue (equivalent to E167 of EndoF3) as the general acid/base residue in glycan hydrolysis as shown in  FIG.  2   . Functionally, the D233 residue should be also equivalent to the N171, N175, and N322 in the GH85 endoglycosidases, EndoA, EndoM, and EndoD, respectively. Thus, following the approach to creating glycosynthases from EndoA, EndoM, and EndoD that proceed in a substrate-assisted mechanism via an oxazolinium ion intermediate,(36-39) two specific mutants, D233A (SEQ ID NO: 2) and D233Q (SEQ ID NO: 3), as shown in  FIGS.  17 A- 17 B , were generated by site-directed mutagenesis of EndoS (SEQ ID NO:1). These mutants, as well as the wild-type EndoS, were expressed in  Escherichia coli  in high yield (30-40 mg/L) as a GST fusion protein and purified by glutathione affinity chromatography. 
     Rituximab, a therapeutic monoclonal antibody, was used as a model mAb to examine the deglycosylation activity and potential transglycosylation activity of the enzymes. The major Fc glycans of commercial rituximab are core-fucosylated biantennary complex type oligosaccharides carrying 0-2 galactose moieties named G0F, G1F, and G2F glycoforms, respectively, as revealed by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) analysis of the N-glycans released by PNGase F as shown in  FIG.  10   . Treatment of rituximab with the EndoS-GST fusion protein (here, referred as wild-type EndoS or EndoS) resulted in a rapid deglycosylation to give the corresponding Fc N-glycans (with only one GlcNAc at the reducing end), as shown in  FIG.  11   , and the deglycosylated rituximab that bears the fucosylated GlcNAc disaccharide moiety (Fucα1,6GlcNAc) at the glycosylation sites (N297). These results confirm the remarkable Fc glycan-hydrolyzing activity of the wild-type EndoS on intact IgG, implicating its usefulness in the first step for glycosylation remodeling of mAbs. The transglycosylation potential of EndoS and its mutants was then examined using the deglycosylated rituximab as the acceptor and several synthetic glycan oxazolines as the donor substrates, as depicted in  FIGS.  3    A and B. The glycosylation remodeling process was monitored by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) and liquid chromatography mass spectrometry (LC-MS) analysis, as shown in  FIG.  4 A . The heavy chain and light chain of rituximab appeared at approximately 50 KDa and approximately 25 KDa, respectively, under reducing conditions (a, lane 1, in  FIG.  4 A ). After deglycosylation with wild-type EndoS, the heavy chain appeared as a single band at approximately 48 KDa, suggesting the removal of the two N-glycans (each from a heavy chain) in rituximab (a, lane 2, in  FIG.  4 A ). Incubation of the deglycosylated rituximab (1) and the synthetic sialoglycan oxazoline (2) (see  FIG.  3 A  for structures) (donor/acceptor, 50:1, molar ratio) with mutant EndoS-D233A gave a transglycosylation product (3), the heavy chain of which appeared as a single band that was about 2 KDa larger than that of the deglycosylated rituximab (1) (a, lane 3,  FIG.  4 A ). This result suggests that a new N-glycan was attached to each of the Fc heavy chains. Incubation of (1) and (2) with EndoS-D233Q gave the same transglycosylation product (a, lane 4,  FIG.  4 A ). Interestingly, an essentially quantitative transglycosylation for the Fc domain of the intact antibody was achieved within 1 h incubation. It was found that a longer incubation (10 h) did not lead to hydrolysis of the transglycosylation product. These results indicate that the two EndoS mutants are new efficient glycosynthases that enable the glycosylation of deglycosylated intact IgG with complex type N-glycan without product hydrolysis. 
     The transglycosylation was further characterized by LC-MS analysis. The heavy chain and light chain of rituximab were separated under a LC-MS condition, as shown in  FIGS.  12 A- 12 E . Deconvolution of the light chain MS data gave a mass of 23 044, which was consistent with the calculated mass of rituximab light chain (M=23 042 Da).(47) Deconvolution of the MS data of the heavy chain gave three distinct m/z species, 50508, 50670, and 50834, as shown in  FIG.  4 B , which were in good agreement with the theoretical mass of heavy chain glycoforms: G0F, M=50 515 Da; G1F, M=50 677 Da; and G2F, M=50 839 Da; respectively.(47) The deconvoluted electron spray ionization mass spectrometry (ESI-MS) of the heavy chain of the deglycosylated rituximab (1) showed a single species at 49 420, as shown in  FIG.  4 C , which matched well with a heavy chain carrying a Fucα1,6GlcNAc disaccharide moiety (calculated, M=49 420 Da). After glycosylation remodeling, a single peak at 51 426 was observed from the heavy chain of the transglycosylation product (3), with an addition of 2006 Da to the deglycosylated heavy chain of the rituximab, as shown in  FIG.  4 D . This result indicates the attachment of a sialoglycan from the corresponding sugar oxazoline (2) to the heavy chain. The single band on SDS-PAGE and the neat MS spectra of the transglycosylation product clearly suggests that the transglycosylation was essentially quantitative on the two glycosylation sites of the Fc domain in rituximab (incomplete glycosylation of any of the two sites in the Fc homodimer would result in the observation of the Fucα1,6GlcNAc-heavy chain after reduction, M=49 420 Da). To further confirm that the N-glycan was specifically attached to the GlcNAc of the Fc domain, the whole N-glycan was released from the glyco-remodeled rituximab (3) by treatment with PNGase F, which specifically hydrolyzes the amide bond between the Asn-glycan linkage. The released N-glycans were labeled by fluorescent tag 2-aminobenzamide (2-AB) and were subjected to fluorescent high-performance liquid chromatography (HPLC) and MS analysis. The LC-MS analysis clearly revealed that the released N-glycan was the expected biantennary complex type N-glycan carrying core fucose and terminal sialic acids, which consisted of approximately 92% disialylated N-glycan and approximately 8% monosialylated N-glycan, as shown in  FIG.  13   b   . The N-glycan composition was well consistent with the ratio found in the corresponding N-glycan oxazoline (2) used for the transglycosylation. This result confirms that the transferred N-glycan was specifically attached to the GlcNAc primer in the deglycosylated rituximab. 
     The results set forth herein represents the first report of glycosylation remodeling of an intact IgG monoclonal antibody with an en bloc transfer of a full-size natural complex type N-glycan to the Fc domain through a highly efficient deglycosylation-reglycosylation protocol enabled by the combined use of EndoS and EndoS-based glycosynthase. After completion of the transglycosylation, the product was purified by a simple protein A affinity chromatography, giving the well-defined homogeneous glycoform. It should be pointed out that the commercial rituximab contains only trace amount of sialylated glycoform, as shown in  FIG.  13   a   . Since sialylated Fc and IgG were proposed to have anti-inflammatory activity, the glycoengineered rituximab carrying fully sialylated Fc N-glycans may gain an anti-inflammatory function, thus potentially expanding its therapeutic coverage from cancer treatment to the treatment of autoimmune diseases.(21, 22) 
     In addition to the sialylated complex type N-glycan oxazoline (2), the EndoS mutants were equally efficient to use the Man3GlcNAc core oxazoline (4)(48) and the azido-tagged N3Man3GlcNAc oxazoline (6)(49) for rituximab glycoengineering, leading to the formation of the corresponding homogeneous glycoforms, (5) and (7), respectively, as shown in  FIG.  3 A . The deconvoluted ESI-MS of the heavy chain of the transglycosylation product (5) showed a single species at 50 112, as shown in  FIG.  4 E , which matched well with the calculated molecular mass (M=50 109 Da) of the rituximab heavy chain carrying a Man3GlcNAc2 glycan. Similarly, the deconvoluted ESI-MS of the heavy chain of transglycosylation product (7) showed a single species at 50 143, as shown in  FIG.  4 F , which was in good agreement with the calculated molecular mass (M=50 134 Da) of the rituximab heavy chain carrying a N3Man3GlcNAc2 glycan. Again, these results indicate that the transglycosylation is essentially quantitative. It should be noted that decreasing the molar ratio of donor/acceptor to 25:1 still resulted in efficient transformation, implicating the remarkable transglycosylation efficiency of the EndoS glycosynthase mutants. In particular, the selective introduction of azide functionality on the core of the Fc N-glycan in intact monoclonal antibodies will allow further site-specific modifications of antibodies through click chemistry,(50, 51) which may be used for labeling and targeting purposes, or for expanding the diversity of antibody glycoforms for further structure-activity relationship studies. 
     Wild-type EndoS was also tested for transglycosylation of deglycosylate rituximab (1) with the glycan oxazolines (2 and 4) under the same conditions as with the EndoS mutants and it was observed that only transient formation of the corresponding transglycosylation products were found as monitored by LC-MS, probably due to quick in situ hydrolysis of the products by the wild-type enzyme. Recently, Scanlan, Davis, and co-workers reported an independent study on the substrate specificity of EndoS and demonstrated that wild-type EndoS could use Man3GlcNAc oxazoline for efficient transglycosylation of deglycosylated IgG.(42) To address this apparent discrepancy of observations, the transglycosylation efficiency of wild-type EndoS was re-evaluated at a lower temperature (4° C.) using a much less quantity of enzyme, following the recent report.(42) Using this modified condition, significant transglycosylation was observed of the deglycosylated rituximab (1) with the complex sugar oxazoline (2) by the wild-type EndoS at the initial incubation period, but the product was gradually hydrolyzed when the incubation continued, as shown in  FIG.  14   . Thus, the reaction condition should be carefully controlled in order to trap the transglycosylation product when wild-type EndoS is used. For practical application, the EndoS glycosynthase mutants should be the choice for efficient and complete transglycosylation, as they are devoid of product hydrolytic activity. 
     Glycoengineering of Rituximab to Provide Nonfucosylated and Galactosylated G2 Glycoform 
     For anticancer therapy, nonfucosylated IgG glycoforms are desirable as it has been previously demonstrated that mAbs with low-fucose contents of Fc N-glycans showed enhanced ADCC activity in vitro and enhanced anticancer efficacy in vivo, particularly for those patients carrying the low affinity F158 allele of the FcγIIIa receptor.(16-19, 52) No efficient method was available to efficiently transform an existing fucosylated mAb (the major glycoform of recombinant mAbs produced in mammalian cells) to a nonfucosylated mAb. To address this issue, a series of commercially available α-fucosidases were tested, but none could remove the α1,6-fucose in the intact rituximab, see scheme in  FIGS.  5    A and B. These results implicate that the α-1,6-fucose moiety might be shielded by the Fc domain and/or the complex N-glycan, making it inaccessible to α-fucosidases. It was theorized that, upon deglycosylation, the resulting Fuc(α1,6)GlcNAc glycoform of rituximab might be more accessible to α-fucosidases. Accordingly, the activity of several commercially available α-fucosidases was tested on the deglycosylated rituximab (1) that carries only the Fuc(α1,6)GlcNAc moiety. It was found that a nonspecific α-fucosidase from bovine kidney did have a moderate activity and was able to remove the fucose residue from the deglycosylated rituximab (1) to give the GlcNAc-containing rituximab (8) (See  FIGS.  15    A- 15  D). Although a relatively large amount of α-fucosidase and a prolonged reaction time were needed to achieve a complete defucosylation of the EndoS-deglycosylated rituximab due to the moderate activity of the α-fucosidase, the discovery of this α-fucosidase activity provides an alternative way to obtain the defucosylated rituximab precursor (8) for further glycoengineering. 
     Next, it was determined that the glycosynthases EndoS-D233A and EndoS-D233Q were also efficient to recognize the nonfucosylated GlcNAc in (8) for transglycosylation with a sialylated N-glycan oxazoline (9)(38) to provide the homogeneous, nonfucosylated G2 glycoform (10) in an essentially quantitative conversion,  FIGS.  5 A- 5 B . The product was purified by protein A affinity chromatography. The identity and purity of the glycoengineered product (10) were confirmed by SDS-PAGE and LC-MS analysis, as shown in  FIG.  6   a   . The defucosylated rituximab (8) showed a single species at 49 274 ( FIG.  6   b   ), confirming the removal of the fucose (calcd. for the heavy chain of GlcNAc-rituximab, M=49 274 Da). The deconvoluted ESI-MS of the heavy chain of the transglycosylation product (10) appeared as a single species at 50 695 ( FIG.  6   c   ), which matched well with the calculated molecular mass (M=50 693 Da) of the rituximab heavy chain carrying an asialylated biantennary complex type N-glycan, Gal2GlcNAc2Man3GlcNAc2. In a comparative study, it was also found that, while mutants D233A and D233Q recognized both the fucosylated GlcNAc-rituximab (1) and the nonfucosylated GlcNAc-rituximab (8) as acceptors for transglycosylation, the two glycosynthase mutants preferred the fucosylated GlcNAc-rituximab (1) as acceptor, with a faster transglycosylation reaction than the nonfucosylated acceptor (8) (data not shown). Taken together, these experimental results revealed a combined enzymatic approach to making the nonfucosylated and fully galactosylated homogeneous glycoform from commercially available monoclonal antibodies. The resulting nonfucosylated and galactosylated rituximab is expected to gain improved ADCC and CDC effector functions, as suggested by previously studies.(2, 16-20, 52) 
     Site-Selective Fc Glycoengineering of IVIG to Provide Fully Fc Sialylated IVIG Glycoforms 
     The successful glycosylation remodeling of rituximab prompted the examination of the chemoenzymatic method for glycoengineering of IVIG aiming to enhance its anti-inflammatory activity. IVIG is a pooled IgG fractions purified from the plasma of thousands of healthy donors. Recent studies have suggested that a minor, α2,6-sialylated Fc glycoform is the active species in IVIG that confers anti-inflammatory activity as demonstrated in a mouse model of rheumatoid arthritis.(21, 22, 53, 54) Since the sialylated Fc glycoforms are minor components in IVIG,(55) the dependence of IVIG&#39;s anti-inflammatory activity on terminal Fc sialylation may partially explain why a high dose (1-2 g/kg) of infusion of IVIG is required for conferring protection. Direct sialylation of Fc and IVIG was attempted using human α-1,6-sialyltransferase (ST6Gal-I) but the efficiency was low, and in most cases, only monosialylated glycoforms were obtained as the major products.(22, 56) Moreover, approximately 30% of the FAB domains in IVIG are N-glycosylated and lectin enrichment of Fc sialylated glycoforms of IVIG would be less efficient when the FAB glycans are sialylated.(2, 57) Therefore, it would be highly desirable if Fc-specific glycoengineering with sialylated N-glycans can be achieved without altering the FAB glycosylation. 
     It was found that EndoS was able to selectively deglycosylate the Fc domain of IVIG without hydrolyzing the N-glycans at the FAB domains under a mild condition. Moreover, the deglycosylated Fc domain of IVIG (11) could be selectively glycosylated with a sialoglycan oxazoline (2) by the EndoS-D233Q mutant to give the Fc fully sialylated IVIG (12), as shown in  FIG.  7   . The glycoengineering was first monitored by SDS-PAGE analysis. The deglycosylation and reglycosylation of IVIG were apparent as shown in the change of the band size of the heavy chain, as shown in  FIG.  16   . To further characterize the site-selectivity of the glycoengineering of IVIG, the FAB and Fc domains were disconnected by papain digestion.(58) The Fc domain was isolated by protein A affinity chromatography and the FAB domains left in the flow-through were isolated by size exclusion chromatography on a fast protein liquid chromatography (FPLC) system. Then, the Fc and FAB N-glycans were released separately by PNGase F treatment, labeled with 2-aminobenzamide (2-AB),(59) and analyzed by HPLC (fluorescent detection and quantitation) and MS characterization. The FAB and Fc N-glycan profiles before and after glycoengineering of IVIG were shown in  FIGS.  8   a - 8   d   . It was found that the Fc glycosylation patterns of IVIG were more complex than the Fc glycosylation of monoclonal antibody rituximab. In addition to G0F, G1F, and G2F glycoforms as the major components, there were a significant amount of monosialylated (peaks 2 and 7) glycoforms (approximately 10%) and bisecting GlcNAc-containing glycoforms (peaks 13-15) (5%) ( FIG.  8   a   ). The Fc glycosylation after glycoengineering (through EndoS-deglycosylation and subsequent transglycosylation with sialoglycan oxazoline (2) by EndoS-D233Q) showed the fully sialylated glycans (peaks 1 and 6) as the major glycoforms (&gt;90%) ( FIG.  8   b   ). Interestingly, the FAB glycosylation patterns were similar before and after the glycoengineering process (compare  FIGS.  8   c  and  8   d   ), except the generation of a small amount of the fully sialylated glycoform (peak 6). These results indicate that the EndoS-based glycosylation remodeling process is highly selective for the Fc N-glycans of intact IgG antibodies even in the presence of FAB glycosylation. The remarkable selectivity and high efficiency of the present Fc glycoengineering approach provide a novel avenue to transforming the commercial IVIG into fully Fc-sialylated IVIG preparation that is expected to exhibit enhanced anti-inflammatory activity, as demonstrated in previous studies using a mouse model.(21, 22, 53, 54). 
     Binding of the Glycoengineered Rituximab to the Stimulatory Fcγ Receptor (FcγRIIIa) and the Inhibitory Fcγ Receptor (FcγRIIb) 
     The affinity of the remodeled glycoforms of rituximab for respective Fcγ receptors (FcγRIIIa-F158, FcγRIIIa-V158, and FcγRIIb) was examined by surface plasmon resonance (SPR) analysis. The rituximab glycoforms were site-specifically immobilized on a protein A chips and the Fcγ receptors at various concentrations were injected as analytes, following our recently reported procedures.(35) As expected, the nonfucosylated G2 glycoform showed significantly enhanced affinity for both the low-affinity and high-affinity FcγIIIa receptors, FcγRIIIa-F158 and FcγRIIIa-V158, when compared with the commercially available rituximab, as shown in  FIGS.  9   a - 9   c   . The KD values for the binding of the G2 glycoform (10) to the FcγRIIIa-F158 and FcγRIIIa-V158 were 123±11 and 12±2 nM, respectively, which were obtained by fitting the binding data with a 1:1 steady-state model using the BIAcore T100 evaluation software. On the other hand, the KD values for the binding of the commercial rituximab to the FcγRIIIa-F158 and FcγRIIIa-V158 were estimated to be 1042±155 and 252±18 nM, respectively. Thus, the affinity of the glycoengineered G2 glycoform for the low-affinity and high-affinity Fcγ receptors (FcγRIIIa-F158 and FcγRIIIa-V158) was about 9-fold and 20-fold higher than the commercial rituximab, respectively. On the other hand, the G2 glycoform and the commercial rituximab demonstrated comparable affinity for the inhibitory Fcγ receptor FcγRIIb with the KD values of 2.3±0.5 and 2.0±0.7 μM, respectively. These results reveal a clear gain of beneficial functions for the glycoengineered rituximab. It should be pointed out that an efficient preparation of high-affinity FcγRIIIa-binding glycoforms is clinically significant to address the issue of Fcγ receptor polymorphism found in cancer patients who are less or not responsive to the treatment with common MAbs. In these patients, their FcγRIIIa-F158 allele has a low affinity to the therapeutic mAbs such as rituximab in comparison with the high-affinity receptor, FcγRIIIa-V158 allele.(52, 60, 61) Fcγ receptor-mediated effector functions were also suggested to be an important mechanism for achieving protective immunity for HIV-neutralizing antibodies.(62) Thus, the glycoengineering approach described here may find wide applications in producing various defined glycoforms of monoclonal antibodies valuable for functional studies as well as for biomedical applications. 
     An efficient chemoenzymatic approach to glycoengineering of intact IgG antibodies is described herein. The two new EndoS-based glycosynthases generated by site-directed mutagenesis demonstrate broad substrate specificity capable of transferring sialylated and asialylated and complex type N-glycans as well as selectively modified N-glycan core from the corresponding glycan oxazolines to Fc-deglycosylated intact antibodies. In addition, the deglycosylation/reglycosylation approach is efficient for both core-fucosylated and nonfucosylated IgG antibodies when an α-fucosidase is adequately combined. These new findings significantly expand the scope of the chemoenzymatic method and made possible an efficient transformation of intact monoclonal antibodies into various well-defined glycoforms that are hitherto difficult to obtain by existing methods. It is expected that this glycoengineering approach may facilitate the development of biosimilar and/or biobetter biologics that possess improved therapeutic efficacy and/or gain new functions. 
     Materials and Methods 
     Monoclonal antibody rituximab (rituxan, Genentech Inc., South San Francisco, Calif.) and IVIG were purchased through Premium Health Services Inc. (Columbia, Md.). Sialoglycan oxazoline (2) and asialo-complex-type glycan oxazoline (5) were synthesized following previously reported procedure.(38, 46) Bovine kidney α-1-fucosidase was purchased from Sigma (St. Louis, Mo.) and Prozyme (Hayward, Calif.). Endo-β-N-acetylglucosaminidase from  Arthrobacter protophormiae  (EndoA) and endo-β-N-acetylglucosaminidase from  Mucor hiemalis  (EndoM) and their mutants were overproduced in  E. coli  following the reported procedures.(38) PNGase F was purchased from New England Biolabs (Ipswich, Mass.). 
     Liquid Chromatography Mass Spectrometry (LC-MS) 
     The LC-MS was performed on a L×Q system (Thermo Scientific) with a Hypersil GOLD column (1.9 μm, 50×2.1 mm). The IgG samples were treated with 0.5% β-mercaptoethanol and heated at 60° C. for 15 min then subject to LC-MS measurement. The analysis was performed at 60° C. eluting with a linear gradient of 10-40% MeCN containing 0.1% formic acid within 10 min at a flow rate of 0.25 mL/min. 
     Electron Spray Ionization Mass Spectrometry (ESI-MS) and Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) 
     The ESI-MS spectra were measured on a Waters Micromass ZQ-4000 single quadruple mass spectrometer. The MALDI-TOF MS was performed on an Autoflex II MALDI-TOF mass spectrometer (Bruker Daltonics, Billerica, Mass.). The instrument was calibrated by using ProteoMass Peptide MALDI-MS calibration kit (MSCAL2, Sigma/Aldirich). The matrix of 2,5-dihydroxybenzoic acid (DHB) was used for the neutral glycans and 2′,4′,6′-trihydroxyacetophenone (THAP) was used for the acidic glycans. 
     Overexpression and Purification of EndoS and Mutants 
     Wild-type EndoS was overproduced in  E. coli  and purified according to the previously reported procedures,(40, 63) using the plasmid pGEX-EndoS that was kindly provided by Dr. M. Collin (Lund University, Sweden). The two EndoS mutants, D233A and D233Q, were generated using the GENEART site-directed mutagenesis kit (Invitrogen) per the manufacturer&#39;s directions. The pGEX-EndoS plasmid was used as the template, and LA Taq polymerase (Takara, Japan) was used for PCR. Mutations were confirmed by DNA sequencing and transformed into BL21(DE3). The transformants were cultured in Luria-Bertani medium containing 100 mg/L carbenicillin and induced with 0.1 mM isopropyl-β-d-thiogalactopyranoside for 16 h at 25° C. The cells were harvested by centrifugation at 1700 g for 15 min at 4° C. The cell pellet was suspended in phosphate-buffered saline (pH 7.4) with lysozyme and PMSF. The lysed mixture was centrifuged at 16 000 g for 20 min at 4° C. After centrifugation, the supernatant from the cell lysis was applied to 3 mL of 50% glutathione-Sepharose 4B resin (GE Healthcare). Samples were incubated at 25° C. for 60 min with gentle rocking. The resin was applied to a 10 mL column (PD-10 GE Healthcare) and washed five times with PBS. 500 μL of glutathione elution buffer (50 mM Tris-HCl, 10 mM glutathione, pH 8.0) was added to the column, incubated at room temperature for 5 min, collected, and then repeated three times. The eluted fractions were pooled and dialyzed against sodium phosphate buffer (50 mM, pH 7.0) overnight at 4° C. Protein samples were then concentrated using Amicon ultra centrifugal filters 10 kDa (Millipore). Concentrated protein samples were analyzed by SDS-PAGE, and protein concentration was quantified using a Nano-Drop 2000c spectrophotometer. The yield of overproduction of the wild-type EndoS was approximately 40 mg/L, and the yield for the mutants was approximately 30 mg/L. 
     Deglycosylation of Rituximab by Wild-Type EndoS to Give (Fucα1,6)GlcNAc-Rituximab (1) 
     Commercial rituximab (20 mg) in a Tris-Cl buffer (50 mM, pH 8.0, 2 mL) was incubated with EndoS (30 μg) at 37° C. for 1 h. LC-MS and SDS-PAGE analyses indicated the complete cleavage of the N-glycans on the heavy chain. The reaction mixture was subject to affinity chromatography on a column of protein A-agarose resin (5 mL) that was pre-equilibrated with a Tris-Cl buffer (20 mM, pH 8.0). The column was washed with Tris-Cl (20 mM, pH 8.0, 25 mL) and glycine-HCl (20 mM, pH 5.0, 20 mL) successively. The bound IgG was released with glycine-HCl (100 mM, pH 2.5, 20 mL), and the elution fractions were immediately neutralized with Tris-Cl buffer (1.0 M, pH 8.8). The fractions containing the Fc fragments were combined and concentrated by centrifugal filtration (Amicon Ultra centrifugal filter, Millipore, Billerica, Mass.) to give (Fucα1,6)GlcNAc-rituximab (1) (18 mg). LC-MS: calculated for the heavy chain of (Fucα1,6)GlcNAc-rituximab (1), M=49 420 Da;(47) found (m/z), 49 420 (deconvolution data). 
     Transglycosylation of (Fucα1,6)GlcNAc-Rituximab (1) with Sialoglycan Oxazoline (2) by EndoS Mutants D233A or D233Q 
     A solution of (Fucα1,6)GlcNAc-rituximab (1) (10 mg) and sialoglycan-oxazoline (2) (10 mg) in a Tris buffer (50 mM, pH 7.4, 2 mL) was incubated with the EndoS mutant D233A or D233Q (200 μg) at 30° C. Aliquots were taken at intervals and were analysis by LC-MS. After 2-3 h, LC-MS monitoring indicated the complete reaction of (Fucα1,6)GlcNAc-rituximab (1) to give the transglycosylation product (3) carrying the fully sialylated N-glycans. The reaction mixture was subject to an affinity chromatography on a protein A-agarose column following the procedure described above. Fractions containing the product were combined and concentrated by ultracentrifugation to give sialylated rituximab (3) (11 mg, quantitative). LC-MS: calculated for the heavy chain of (3) carrying the fully sialylated N-glycan, M=51 421 Da; found (m/z), 51 426 (deconvolution data). 
     Transglycosylation of (Fucα1,6)GlcNAc-Rituximab (1) with Man3GlcNAc Oxazoline (4) and the Azide-Tagged Man3GlcNAc Oxazoline (6) by EndoS-D233Q 
     The transglycosylation was performed as described for the preparation of (3) to give the corresponding products. LC-MS analysis of glycoengineered rituximab (5 and 7): calculated for the heavy chain of (5) carrying the fucosylated Man3GlcNAc2 N-glycan, M=50 109 Da; found (m/z), 50 112 (deconvolution data); calculated for the heavy chain of (7) carrying the fucosylated azido-Man3GlcNAc2 N-glycan, M=50 134 Da; found (m/z), 50 143 (deconvolution data). 
     Defucosylation of (Fucα1,6)GlcNAc-Rituximab (1) by Bovine Kidney α-Fucosidase 
     A solution of (Fucα1,6)GlcNAc-rituximab (1) (2 mg) in a phosphate buffer (50 mM, pH 5.5, 200 μL) containing 0.05 sodium azide was incubated with the fucosidase from bovine kidney (Prozyme, 5 U) at 37° C. Aliquots were taken at intervals and were analyzed by LC-MS. After 20 days, LC-MS monitoring indicated the complete defucosylation of (Fucα1,6)GlcNAc-rituximab (1) to give the product, GlcNAc-rituximab (2). The reaction mixture was subject to affinity chromatography on a column of protein A following the procedure described above. Fractions containing the product were combined and concentrated by ultracentrifugation to give GlcNAc-rituximab (2) (2 mg, quantitative). LC-MS: calculated for the heavy chain of GlcNAc-rituximab (2) carrying a GlcNAc moiety, M=49 274 Da; found (m/z), 49 274 (deconvolution data). 
     Transglycosylation of GlcNAc-Rituximab (4) with Asialylated Complex-Type Glycan Oxazoline (5) by D233Q Mutant 
     A solution of GlcNAc-rituximab (4) (2 mg) and oxazoline (5) (5 mg) in a Tris buffer (50 mM, pH 7.4, 0.5 mL) was incubated with the EndoS-D233Q (200 μg) at 37° C. Aliquots were taken at intervals and were analyzed by LC-MS. After 2 h, LC-MS monitoring indicated the complete reaction of 4 to give the corresponding transglycosylation product (6). The reaction mixture was subject to affinity chromatography on a column of protein A. Fractions containing the product were combined and concentrated by ultracentrifugation to give the nonfucosylated rituximab glycoform (6) (2 mg, quantitative). LC-MS: calculated for the heavy chain of (6) carrying the nonfucosylated N-glycan, M=50 693 Da; found (m/z), 50 695 (deconvolution data). 
     Site-Specific Deglycosylation at the Fc Domain of IVIG by EndoS 
     Commercial IVIG (20 mg) in a Tris-Cl buffer (50 mM, pH 8.0, 2 mL) was incubated with EndoS (SEQ ID NO: 1) (30 μg) at 37° C. for 1 h. The residue was subject to affinity chromatography on a column of protein A to give the (Fucα1,6)GlcNAc-IVIG (20 mg, quantitative), in which the Fc N-glycans were removed leaving the α1,6-fucosylated GlcNAc at the N297 sites. 
     Transglycosylation of (Fucα1,6)GlcNAc-IVIG with Sialoglycan Oxazoline (2) by D233Q Mutant 
     A solution of (Fucα1,6)GlcNAc-IVIG (3 mg) and sialoglycan-oxazoline (2) (3 mg) in a Tris buffer (50 mM, pH 7.4, 2 mL) was incubated with the D233Q mutant(SEQ ID NO: 2) (60 μg) at 30° C. After 2 h, SDS-PAGE analysis indicated the complete reaction of (Fucα1,6)GlcNAc-IVIG to give the transglycosylation product. The reaction mixture was subject to affinity chromatography on a column of protein A to provide the glyco-remodeled IVIG (3 mg, quantitative), in which the Fc N-glycans were remodeled to the fully sialylated complex type N-glycans. 
     Surface Plasmon Resonance (SPR) Binding Experiments 
     The binding between different glycoforms of IgG and Fcγ receptors was measured by surface plasmon resonance (SPR) using a Biacore T100 instrument (GE Healthcare, USA). Protein A of 5000 RU was immobilized on a CMS biosensor chip (GE Healthcare) using a standard primary amine coupling chemistry at pH 4.5 to capture the different glycoforms of IgG. A reference flow cell was prepared similarly without injecting protein A. Each individual glycoform of IgG in HBS-P buffer (10 mM HEPES pH 7.4, 0.15 M NaCl, 0.05% v/v surfactant P20) was injected at 10 μL/min onto the protein A surface and reached the capture level of 150 RU. A serial dilution of FcγIIIa and FcγIIb receptors was injected at 10 μL/min. After each cycle, the surface was regenerated by injecting 10 mM HCl at 10 μL/min for 30 s. Data were fitted into a 1:1 Langmuir binding model using BIAcore T100 evaluation software to obtain the equilibrium constant (KD) data. 
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