Patent Publication Number: US-2017369914-A1

Title: Methods of producing 6-carbon chemicals using 2,6-diaminopimelate as precursor to 2-aminopimelate

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 14/714,164, filed May 15, 2015, which claims priority to U.S. Application Ser. No. 61/993,532, filed on May 15, 2014, the disclosures of which are incorporated by reference in their entireties. 
    
    
     REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY 
     An official copy of the sequence listing is submitted electronically via EFS-Web as an ASCII formatted sequence listing with a file named “12444_0286-01000_SL.txt”, created on Jul. 6, 2017. Said ASCII copy is 153,047 bytes in size. The sequence listing contained in this ASCII formatted document is part of the specification and is herein incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     Disclosed herein are methods for biosynthesizing 2-aminopimelate in a recombinant host from 2,6-diaminopimelate using one or more of a polypeptide having 2-hydroxyacyl-CoA dehydratase activity, a polypeptide having mutase activity, a polypeptide having ammonia lyase activity, and a polypeptide having enoale reductase activity. The biosynthesized 2-aminopimelate can be enzymatically converted to a product selected from the group consisting of adipic acid, adipate semialdehyde, 6-aminohexanoic acid, 6-hydroxyhexanoic acid, caprolactam, hexamethylenediamine, and 1,6-hexanediol using, for example, one or more of a polypeptide having α-oxoacid decarboxylase activity classified under EC 4,1.1.-, a polypeptide having α-aminoacid decarboxylase activity classified under EC 4.1.1.-, a polypeptide having synthase activity, and a polypeptide having the activity of a dehydrogenase complex; and one or more optional polypeptides having an activity such as aldehyde dehydrogenase activity, alcohol dehydrogenase activity, CoA-transferase activity, carboxylate reductase activity, α-aminotransferase activity, thioesterase activity, hydrolase activity, ω-transaminase activity, N-acetyltransferase activity, or deacylase activity, and combinations thereof. 
     BACKGROUND 
     Nylons are polyamides which are sometimes synthesized by the condensation polymerisation of a diamine with a dicarboxylic acid. Similarly, nylons may be produced by the condensation polymerisation of lactams. A ubiquitous nylon is nylon 6,6, which is produced by reaction of hexamethylenediamine (HMD) and adipic acid. Nylon 6 is produced by a ring opening polymerisation of caprolactam. Therefore, adipic acid, hexamethylenediamine, and caprolactam are important intermediates in the production of nylons (Anton &amp; Baird, Polyamides Fibers, Encyclopedia of Polymer Science and Technology, 2001). 
     Industrially, adipic acid and caprolactam are produced via air oxidation of cyclohexane. The air oxidation of cyclohexane produces, in a series of steps, a mixture of cyclohexanone (K) and cyclohexanal (A), designated as KA oil, Nitric acid oxidation of KA oil produces adipic acid (Musser, Adipic acid, Ullmann&#39;s Encyclopedia of Industrial Chemistry, 2000). Caprolactam is produced from cyclohexanone via its oxime and subsequent acid rearrangement (Fuchs, Kieczka and Moran, Caprolactam, Ullmann&#39;s Encyclopedia of Industrial Chemistry, 2000). 
     Industrially, hexamethylenediamine (HMI)) is produced by hydrocyanation of C6 Building Block to adiponitrile, followed by hydrogenation to HMD (Herzog and Smiley, Hexamethylenediamine, Ullmann&#39;s Encyclopedia of Industrial Chemistry, 2012). 
     Given a reliance on petrochemical feedstocks; biotechnology offers an alternative approach via biocatalysis. Biocatalysis is the use of biological catalysts, such as enzymes, to perform biochemical transformations of organic compounds. 
     Both bioderived feedstocks and petrochemical feedstocks are via starting materials for the biocatalysis processes. 
     Accordingly, against this background, it is clear that there is a need for sustainable methods for producing adipic acid, caprolactam, 6-aminohexanoic acid, hexamethylenediamine and 1,6-hexanediol (hereafter “C6 building blocks”) wherein the methods are biocatalyst-based (Jang et al., Biotechnology &amp; Bioengineering, 2012, 109(10), 2437-2459). 
     However, no wild-type prokaryote or eukaryote naturally overproduces or excretes C6 building blocks to the extracellular environment. Nevertheless, the metabolism of adipic acid and caprolactam has been reported (Ramsay et al., Appl. Environ. Microbiol., 1986, 52(1), 152-156; Kulkarni and Kanekar,  Current Microbiology,  1998, 37, 191 194), 
     The dicarboxylic acid, adipic acid, is converted efficiently as a carbon source by a number of bacteria and yeasts via β-oxidation into central metabolites. β-oxidation of o adipate to 3-oxoadipate faciliates further catabolism via, for example, the ortho-cleavage pathway associated with aromatic substrate degradation. The catabolism of 3-oxoadipyl-CoA to acetyl-CoA and succinyl-CoA by several bacteria and fungi has been characterised comprehensively (Harwood and Parales,  Annual Review of Microbiology,  1996, 50, 553-590). Both adipate and 6-aminohexanoic acid are intermediates in the catabolism of caprolactam, finally degraded via 3-oxoadipyl-CoA to central metabolites. 
     Potential metabolic pathways have been suggested for producing adipic acid from biomass-sugar: (1) biochemically from glucose to cis,cis muconic acid via the ortho-cleavage aromatic degradation pathway, followed by chemical catalysis to adipic acid; (2) a reversible adipic acid degradation pathway via the condensation of succinyl-CoA and acetyl-CoA and (3) combining β-oxidation, fatty acid synthase, and ω-oxidation. However, no information using these strategies has been reported (Jang et al.,  Biotechnology  &amp;  Bioengineering,  2012, 109(10), 2437-2459). 
     An optimality principle states that microorganisms regulate their biochemical networks to support maximum biomass growth. Beyond the need for expressing heterologous pathways in a host organism, directing carbon flux towards C6 building blocks that serve as carbon sources rather than as biomass growth constituents, contradicts the optimality principle. For example, transferring the 1-butanol pathway from  Clostridium  species into other production strains has often fallen short by an order of magnitude compared to the production performance of native producers (Shen et al.,  Appl. Environ. Microbiol.,  2011, 77(9), 2905-2915). 
     The efficient synthesis of a six or seven carbon aliphatic backbone as central precursor is a key consideration in synthesizing C6 building blocks prior to forming terminal functional groups, such as carboxyl, amine or hydroxyl groups, on the C6 aliphatic backbone. 
     SUMMARY 
     This document is based, at least in part, on the discovery that it is possible to construct biochemical pathways for producing a seven carbon chain aliphatic backbone as a central precursor, which can be decarboxylated to a six carbon aliphatic backbone in which one or two functional groups, i.e., carboxyl, amine or hydroxyl, can be formed, leading to the synthesis of adipic acid, adipate semialdehyde, 6-aminohexanoic acid, 6-hydroxyhexanoate, hexamethylenediamine, caprolactam, or 1,6-hexanediol (hereafter “C6 building blocks). Adipic acid and adipate, 6-hydroxyhexanoic acid and 6-hydroxyhexanoate, and 6-aminohexanoic acid and 6-aminohexanoate are used interchangeably herein to refer to the compound in any of its neutral or ionized forms, including any salt forms thereof. It is understood by those skilled in the art that the specific form will depend on pH. These pathways, metabolic engineering, and cultivation strategies described herein use meso-2,6 diaminopimelate as a central metabolite, which can he enzymatically converted to (S) 2-aminopimelate or (R) 2-aminopimelate. 
     In the face of an optimality principle, surprisingly it has been discovered that appropriate non-natural pathways, feedstocks, host microorganisms, attenuation strategies to the host&#39;s biochemical network and cultivation strategies may be combined to efficiently produce one or more C6 building blocks. 
     In one aspect, this document features a method of biosynthesizing 2-aminopimelate in a recombinant host. The method includes enzymatically converting 2,6-diaminopimelate to 2-aminopimelate in the host using at least one polypeptide having an activity selected from the group consisting of 2-hydroxyacyl-CoA dehydratase activity, mutase activity, ammonia lyase activity, and enoate reductase activity. In some embodiments, the method can include enzymatically converting 2,6-diaminopimelate to (S) 2-aminopimelate. In some embodiments, the method can include enzymatically converting 2,6-diaminopimelate to (R) 2-aminopimelate. The method can include using a polypeptide having 2-hydroxyacyl-CoA dehydratase activity and a polypeptide having enoate reductase activity to enzymatically convert 2,6-diaminopimelate to 2-aminopimelate. The polypeptide having 2-hydroxyacyl-CoA dehydratase activity can have at least 70%, at least 80%, or at least 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 25 or SEQ ID NO: 28. The poly peptide having enoate reductase activity can have at least 70%, at least 80%, or at least 90% sequence identity to the amino acid sequence set forth in any one of SEQ ID NOs: 16-22. The method can o include using a polypeptide having mutase activity, a polypeptide having ammonia lyase activity, a said polypeptide having enoate reductase activity to enzymatically convert 2,6-diaminopimelate to 2-aminopimelate. The polypeptide having ammonia lyase activity can have at least 70%, at least 80%, or at least 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 23. The polypeptide having mutase activity has at least 70%, at least 80%, or at least 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 26. 
     The method disclosed can further include using at least one polypeptide having an activity selected from the group consisting of diaminopimelate dehydrogenase activity, 2-hydroxycarboxylate dehydrogenase activity, CoA-transferase activity, 2-hydroxyacid dehydratase activity, and carbaxylate reductase activity to enzymatically convert 2,6-diaminopimelate to 2-aminopimelate. The methods disclosed can further include using using at least one polypeptide having an activity selected from the group consisting of CoA ligase activity, CoA-transferase activity, carboxylate reductase activity, and aldehyde dehydrogenase activity to enzymatically convert 2,6-diaminopimelate to 2-aminopimelate. 
     In some embodiments, the central precursor comprises a C7 aliphatic backbone such as S)-2-aminopimelate or (R)-2-aminopimelate, for enzymatic conversion to one or more C6 building blocks. Such C7 aliphatic backbones can be formed from a lysine biosynthesis precursor such as meso-2,6 diaminopimelate. See  FIG. 1  and  FIG. 2 . 
     In some embodiments, a terminal carboxyl group can be enzymatically formed using a thioesterase, a CoA-transferase or CoA-ligase, or an aldehyde dehydrogenase. See  FIG. 3 . 
     In some embodiments, a terminal amine group can be enzymatically formed using an (R) alpha-aminodecarboxylase (classified, for example, under EC 4.1.1,—such as EC 4.1.1.20), (S) alpha-aminodecarboxylase (classified, for example, under EC 4.1.1.—such as EC 4.1.1.15, EC 4.1.1.17 or EC 4.1.1.18) or a transaminase (classified, for example, under EC 2.6.1.-). See  FIG. 4 ,  FIG. 5 ,  FIG. 6 , and  FIG. 7 . 
     In some embodiments, a terminal hydroxyl group can be enzymatically formed o using a NADPH-specific or NADH-specific alcohol dehydrogenase. See  FIG. 8 . 
     In some embodiments, the principal carbon source fed to the fermentation derived from a biological feedstock or a non-biological feedstock. 
     In some embodiments, the biological feedstock can be or can derive from, monosaccharides, disaccharides, lignocellulose, hemicellulose, cellulose, lignin, levulinic acid and formic acid, triglycerides, glycerol, fatty acids, agricultural waste, condensed distillers&#39; solubles, or municipal waste. 
     In some embodiments, the non-biological feedstock can be or can derive from natural gas, syngas, CO 2 H 2 , methanol, ethanol, benzoate, non-volatile residue (NVR) or a caustic wash waste stream from cyclohexane oxidation processes, or terephthalic acid/isophthalic acid mixture waste streams. 
     In some embodiments, the host microorganism is a prokaryote. For example, the prokaryote can be from the bacterial genus  Escherichia  such as  Escherichia coli ; from the bacterial genus  Clostridia  such as  Clostridium ljungdahlii, Clostridium autoethanogenum  or  Clostridium kluyveri ; from the bacterial genus  Corynebacteria  such as  Corynebacterium glutamicum , from the bacterial genus  Cupriavidus  such as  Cupriavidus necator  or  Cupriavidus metallidurans ; from the bacterial genus  Pseudomonas  such as  Pseudomonas fluorescens, Pseudomonas putida  or  Pseudomonas oleavorans;  from the bacterial genus  Delftia  such as  Delftia acidovorans;  from the bacterial genus  Bacillus  such as  Bacillus subtillis;  from the bacterial genus  Lactobacillus  such as  Lactobacillus delbrueckii,  or from the bacterial genus  Lactococcus  such as  Lactococcus lactis.  Such prokaryotes also can be a source of genes to construct recombinant host cells described herein that are capable of producing one or more C6 building blocks. 
     In some embodiments, the host microorganism is a eukaryote (e.g., a fungus such as a yeast). For example, the eukaryote can be from the fungus genus  Aspergillus  such as  Aspergillus niger;  from the yeast genus  Saccharomyces  such as  Saccharomyces cerevisiae;  from the yeast genus  Pichia  such as  Pichia pastoris;  from the yeast genus  Yarrowia  such as  Yarrowia lipolytica;  from the yeast genus  Issatchenkia  such as  Issathenkia orientalis ; from the yeast genus  Debaryomyces  such as  Debaryomyces hansenii;  from the yeast genus  Arxula  such as  Arxula adenoinivorans;  or from the yeast genus  Kluyveromyces  such as  Kluyveromyces lactis.  Such eukaryotes also can be a source of genes to construct recombinant host cells described herein that are capable of producing one or more C6 building blocks. 
     The reactions of the pathways described herein can be performed in one or more cell (e.g., host cell) strains (a) naturally expressing one or more relevant enzymes, (b) genetically engineered to express one or more relevant enzymes, or (c) naturally expressing one or more relevant enzymes and genetically engineered to express one or more relevant enzymes. Alternatively, relevant enzymes can be extracted from any of the above types of host cells and used in a purified or semi-purified form. Extracted enzymes can optionally be immobilized to a solid substrate such as the floors and/or walls of appropriate reaction vessels. Moreover, such extracts include lysates (e.g. cell lysates) that can be used as sources of relevant enzymes. In the methods provided by the document, all the steps can be performed in cells (e.g., host cells), all the steps can be performed using extracted enzymes, or some of the steps can be performed in cells and others can be performed using extracted enzymes. 
     Many of the enzymes described herein catalyze reversible reactions, and the reaction of interest may be the reverse of the described reaction. The schematic pathways shown in  FIGS. 1-8  illustrate the reaction of interest for each of the intermediates. 
     In some embodiments, the host microorganism&#39;s tolerance to high concentrations of a C6 building block is improved through continuous cultivation in a selective environment. 
     In some embodiments, the host microorganism&#39;s biochemical network is attenuated or augmented to (1) ensure the intracellular availability of oxaloacetate, (2) create an NADPH imbalance that may only be balanced via the formation of one or more C6 building blocks, (3) prevent degradation of central metabolites or central precursors leading to and including C6 building blocks and (4) ensure efficient efflux from the cell. 
     In some embodiments, the cultivation strategy entails either achieving an aerobic or micro-aerobic cultivation condition. 
     In some embodiments, the cultivation strategy entails nutrient limitation either via nitrogen, phosphate or oxygen limitation. 
     In some embodiments, the cultivation strategy entails preventing the incorporation of fatty acids into lipid bodies or other carbon storage units. 
     In some embodiments, one or more C6 building blocks are produced by a single type of microorganism, e.g., a recombinant host containing one or more exogenous nucleic acids, using, for example, a fermentation strategy. 
     In some aspects, the methods disclosed further comprising enzymatically converting 2-aminopimelate to a product selected from the group consisting of adipic acid, adipate semialdehyde, 6-aminohexanoic acid, 6-hydroxyhexanoic acid, caprolactam, hexamethylenediamine, and 1,6-hexanediol. The method includes enzymatically converting 2-aminopimelate to one or more of said products using (i) at least one polypeptide having an activity selected from the group consisting of α-oxoacid decarboxylase activity classified under EC 4.1.1.-, α-aminoacid decarboxylase activity classified under EC 4.1.1.-, synthase activity, and activity of a dehydrogenase complex; and (ii) one or more optional polypeptides having an activity selected from the group consisting of aldehyde dehydrogenase activity, alcohol dehydrogenase activity, CoA-transferase activity, carboxylate reductase activity, α-aminotransferase activity, thioesterase activity, hydrolase activity, ω-transaminase activity, N-acetyltransferase activity, and deacylase activity. The polypeptide having α-oxoacid decarboxylase activity can be classified under EC 4.1.1.43, EC 4.1.1.71, EC 4.1.1.72 or EC 4.1.1.74. The polypeptide having α-aminoacid decarboxylase activity can be classified under EC 4.1.1.15, EC 4.1.1.17, EC 4.1.1.18, EC 4.1.1.19. The polypeptide having synthase activity is classified under EC 2.2.1.6, or the polypeptide having the activity of a dehydrogenase complex comprises activities can be classified under EC 1.2.4.2, EC 1.8.1.4 and EC 2.3.1.61. 
     For example, the methods disclosed herein further can included enzymatically converting 2-aminopimelate to adipic acid using at least one polypeptide having an activity selected from the group consisting of α-aminotransferase activity, 2-exoacid decarboxylase activity, synthase activity, dehydrogenase complex activity, thioesterase activity, CoA-transferase activity, CoA-ligase activity, and aldehyde dehydrogenase activity. 
     For example, the methods disclosed herein further can included enzymatically converting 2-aminopimelate to adipate semialdehyde using at least one polypeptide having an activity selected from the group consisting of α-aminotransferase activity, 2-oxoacid decarboxylase activity, and synthase activity. 
     For example, the methods disclosed herein further can included enzymatically converting 2-aminopimelate to 6-aminohexanoic acid using a polypeptide having α-aminoacid decarboxylase activity. 
     For example, the methods disclosed herein further can included enzymatically converting adipate semialdehyde to 6-aminohexanoic from using a ω-transaminase. The methods can further include biosynthesizing caprolactam from 6-aminohexanoic acid using a polypeptide having the activity of a hydrolase. 
     For example, the methods disclosed herein further can included enzymatically converting 6-aminohexanoic acid to hexamethylenediamine from using at least one polypeptide having an activity selected from the group consisting of carboxylate reductase activity, N-acetyltransferase activity, ω-transaminase activity, and deacylase activity. 
     For example, the method further can include enzymatically converting adipate semialdehyde to hexamethylenediamine using at least one polypeptide having an selected from the group consisting of carboxylate reductase activity and ω-transaminase activity. 
     For example, the methods disclosed herein further can included enzymatically converting 2-aminopimelate to 6-hydroxyhexanoic acid using at least one polypeptide having an activity selected from the group consisting of α-aminotransferase activity, 2-oxoacid decarboxylase activity, synthase activity, and alcohol dehydrogenase activity. 
     For example, the methods disclosed herein further can included enzymatically converting 6-hydroxyhexanoic acid to hexamethylenediamine using at least one o polypeptide having an activity selected from the group consisting of carboxylate reductase activity, ω-transaminase activity, and alcohol dehydrogenase activity. 
     For example, the methods disclosed herein further can included enzymatically converting 6-hydroxyhexanoic acid to 1,6-hexanediol using a polypeptide having carboxylate reductase activity and a polypeptide having alcohol dehydrogenase activity. 
     The polypeptide having 2-oxoacid decarboxylase activity can have at least 70% sequence identity to the amino acid sequence set forth in SEQ ID NO:34, the polypeptide having α-aminoacid decarboxylase activity can have at least 70% sequence identity to the amino acid sequence set forth in any one of SEQ ID NOs: 29-34. 
     The polypeptide having carboxylate reductase activity can have at least 70% sequence identity to the amino acid sequence set forth in any one of SEQ ID NOs: 3-7. 
     The polypeptide having ω-transaminase activity can have at least 70% sequence identity to the amino acid sequence set forth in any one of SEQ ID NOs: 8-13. 
     The polypeptide having thioesterase activity can have at least 70% sequence identity to the amino acid sequence set forth in SEQ ID NO: 1 or SEQ ID NO: 2. 
     In some embodiments, the host comprises one or more of the following: the intracellular concentration of oxaloacetate for biosynthesis of a C6 building block is increased in the host by overexpressing recombinant genes forming oxaloacetate; wherein an imbalance in NADPH is generated that can be balanced via the formation of a C6 building block; wherein an exogenous lysine biosynthesis pathway synthesizing lysine from 2-oxoglutarate via 2-oxoadipate is introduced in a host using the meso 2,6 diaminopimelate pathway for lysine synthesis; wherein an exogenous lysine biosynthesis pathway synthesizing lysine from oxaloacetate to meso 2,6 diaminopimelate is introduced in a host using the 2-oxoadipate pathway for lysine synthesis; wherein endogenous degradation pathways of central metabolites and central precursors leading to and including C6 building blocks are attenuated in the host; or wherein the efflux of a C6 building block across the cell membrane to the extracellular media is enhanced or amplified by genetically engineering structural modifications to the cell membrane or increasing any associated transporter activity for a C6 building block. 
     This document also features a recombinant host that includes at least one o exogenous nucleic acid encoding at least one polypeptide having an activity selected from the group consisting of 2-hydroxyacyl-CoA dehydratase activity, mutase activity, ammonia lyase activity, and enoate reductase activity, said host producing 2-aminopimelate from 2,6-diaminopimelate. For example, the recombinant host can include a polypeptide having exogenous 2-hydroxyacyl-CoA dehydratase activity and a polypeptide having enoate reductase activity. For example, the recombinant host can include a polypeptide having mutase activity, a polypeptide having ammonia lyase activity, and a polypeptide having enoate reductase activity. The polypeptide having enoate reductase activity can have at least 70% sequence identity to the amino acid sequence set forth in any one of SEQ ID NOs: 16-22. The polypeptide having 2-hydroxyacyl-CoA dehydratase activity can have at least 70% sequence identity to the amino acid sequence set forth in SEQ ID NO: 25 or SEQ ID NO: 28. The polypeptide having mutase activity can have at least 70% sequence identity to the amino acid sequence set forth in SEQ ID NO: 26. The polypeptide having ammonia lyase activity can have at least 70% sequence identity to the amino acid sequence set forth in SEQ ID NO: 23. 
     The host can further include at least one or more exogenous polypeptides having an activity selected from the group consisting of a) diaminopimelate dehydrogenase activity, 2-hydroxycarboxylate dehydrogenase activity, CoA-transferase activity, 2-hydroxyacid dehydratase activity, and carboxylate reductase activity; or b) CoA ligase activity, CoA-transferase activity, carboxylate reductase activity, and aldehyde dehydrogenase activity. 
     The host can further include at least one or more exogenous polypeptides having an activity selected from the group consisting of α-oxoacid decarboxylase activity classified under EC 4.1.1.-, α-aminoacid decarboxylase activity classified under EC 4.1,1.-, synthase activity, and activity of a dehydrogenase complex. 
     The host can further include at least one or more exogenous polypeptides having an activity selected from the group consisting of aldehyde dehydrogenase activity, alcohol dehydrogenase activity, CoA-transferase activity, carboxylate reductase activity, α-aminotransferase activity, thioesterase activity, hydrolase activity, ω-transaminase activity, N-acetyltransferase activity, and deacylase activity, the host producing a product selected from the group consisting of adipic acid, adipate semialdehyde, 6-aminohexanoic acid, 6-hydroxyhexanoic acid, caprolactam, hexamethylenediamine, and 1,6-hexanediol. 
     The host can further include at least one or more exogenous polypeptides having an an activity selected from the group consisting of α-aminotransferase activity, 2-oxoacid decarboxylase activity, activity of a dehydrogenase complex, thioesterase activity, CoA-transferase activity, CoA-ligase activity, and aldehyde dehydrogenase activity, the host producing adipic acid. 
     The host can further include at least one or more exogenous polypeptides having an activity selected from the group consisting of α-aminotransferase activity, 2-oxoacid decarboxylase activity, synthase activity, the host producing adipate semialdehyde. 
     The host can further include at least one or more exogenous polypeptides having an α-aminoacid decarboxylase activity, the host producing 6-aminohexanoic acid. 
     A recombinant host producing 6-aminohexanoic acid can include an exogenous polypeptide having ω-transaminase activity. A recombinant host producing 6-aminohexanoic acid further can include an exogenous polypeptide having hydrolase activity, the host producing caprolactam. The host can further include one or more of an exogenous polypeptide having carboxylate reductase activity, N-acetyltransferase activity, ω-transaminase activity, or deacylase activity, the host producing hexamethylenediamine. 
     The host cell can further include at least one exogenous polypeptide having carboxylate reductase activity and/or at least one exogenous polypeptide having ω-transaminase activity, the host producing hexamethylenediamine. 
     The host cell can further include at at least one exogenous polypeptide having an activity selected from the group consisting of α-aminotransferase activity, α-oxoacid decarboxylase activity, alcohol dehydrogenase activity or synthase activity, the host producing 6-hydroxyhexanoic acid. 
     The host cell can further include at least one exogenous polypeptide having an activity selected from the group consisting of carboxy/ate reductase activity, ω-transaminase activity, and alcohol dehydrogenase activity, the host producing hexamethylenediamine. 
     The host cell can further include at an exogenous polypeptide having carboxylase reductase activity and/or an exogenous polypeptide having alcohol dehydrogenase activity, the host producing 1,6-hexanediol. 
     In one aspect, this document features a method for producing a bioderived 6-carbon compound. The method for producing a bioderived 6-carbon compound can include culturing or growing a recombinant host as described herein under conditions and for a sufficient period of time to produce the bioderived 6-carbon compound, wherein, optionally, the bioderived 6-carbon compound is selected from the group consisting of adipic acid, adipate semialdehyde, 6-aminohexanoic acid, 6-hydroxyhexanoic acid, caprolactam, hexamethylenediamine, 1,6-hexanediol, and combinations thereof. 
     In one aspect, this document features composition comprising a bioderived 6-carbon compound as described herein and a compound other than the bioderived 6-carbon compound, wherein the bioderived 6-carbon compound is selected from the group consisting of adipic acid, adipate semialdehyde, 6-aminohexanoic acid, 6-hydroxyhexanoic acid, caprolactam, hexamethylenediamine, 1,6-hexanediol, and combinations thereof. For example, the bioderived 6-carbon compound is a cellular portion of a host cell or an organism. 
     This document also features a biobased polymer comprising the bioderived adipic acid, adipate semialdehyde, 6-aminohexanoic acid, 6-hydroxyhexanoic add, caprolactam, hexamethylenediamine, 1,6-hexanediol, and combinations thereof. 
     This document also features a biobased resin comprising the bioderived adipic acid, adipate semi aldehyde, 6-aminohexanoic acid. 6-hydroxyhexanoic acid, caprolactam, hexamethylenediamine, 1,6-hexanediol, and combinations thereof, as well as a molded product obtained by molding a biobased resin. 
     In another aspect, this document features a process for producing a biobased polymer that includes chemically reacting the bioderived adipic acid, adipate o semialdehyde, 6-aminohexanoic acid, 6-hydroxyhexanoic acid, caprolactam, hexamethylenediamine, 1,6-hexanediol, with itself or another compound in a polymer producing reaction. 
     In another aspect, this document features a process for producing a biobased resin that includes chemically reacting the bioderived adipic acid, adipate semialdehyde, 6-aminohexanoic acid, 6-hydroxyhexanoic acid, caprolactam, hexamethylenediamine, 1,6-hexanediol, with itself or another compound in a resin producing reaction. 
     Any of the recombinant hosts described herein further can include attenuation of one or more of the following enzymes: a polyhydroxyalkanoate synthase, an acetyl-CoA thioesterase, a phosphotransacetylase forming acetate, an acetate kinase, a lactate dehydrogenase, a menaquinol-fumarate oxidoreductase, an alcohol dehydrogenase forming ethanol, a those phosphate isomerase, a pyruvate decarboxylase, a glucose-6-phosphate isomerase, NADH-consuming transhydrogenase, an NADH-specific glutamate dehydrogenase, a NADH/NADPH-utilizing glutamate dehydrogenase, a pimeloyl-CoA dehydrogenase; an acyl-CoA dehydrogenase accepting C6 building blocks and central precursors as substrates; a butyl-CoA dehydrogenase; or an adipyl-CoA synthetase. 
     Any of the recombinant hosts described herein further can overexpress one or more genes encoding: 2-hydroxyacyl-CoA dehydratase; a mutase; a CoA-ligase; an ammonia lyase; an acetyl-CoA synthetase; an enoate reductase; a 6-phosphogluconate dehydrogenase; a transketolase; a puridine nucleotide transhydrogenase; a glyceraldehyde-3P-dehydrogenase; a malic enzyme; a glucose-6-phosphate dehydrogenase; a glucose dehydrogenase; a fructose 1,6 diphosphatase; a L-alanine dehydrogenase; a L-glutamate dehydrogenase; a formate dehydrogenase; a L-glutamine synthetase; a diamine transporter; a dicarboxylate transporter; diaminopimelate dehydrogenase; 2-hydroxycarboxylate dehydrogenase, 2-hydroxyacid dehydratase, carboxylate reductase and/or a multidrug transporter. 
     Also, described herein is a biochemical network comprising a dehydrogenase, a CoA-transferase, a dehydratase, a reductase, a mutase, a CoA-ligase, an ammonia lyase, or a thioesterase and meso-2,6-diaminopimelate, wherein the dehydrogenase, the CoA-transferase, the dehydratase, the reductase, the mutase, the CoA-ligase, the ammonia lyase, or the thioesterase enzymatically converts the meso-2,6-diaminopimelate to 2-aminopimelate. The biochemical network can further include an α-aminotransferase, wherein the aminotransferase enzymatically converts 2-aminopimelate to 2-oxo-pimelate. The biochemical network can further include a decarboxylase, a synthase, or a dehydrogenase complex, wherein the decarboxylase, the synthase, or the dehydrogenase complex enzymatically converts 2-oxo-pimelate to adipyl-CoA or adipate semialdehyde. The biochemical network can further include a dehydrogenase, a CoA transferase, a CoA ligase or a thioesterase, wherein the dehydrogenase, the CoA transase, the CoA ligase, or the thioesterase enzymatically convert adipyl-CoA or adipate semialdehyde to adipic acid. 
     Also, described herein a biochemical network comprising dehydrogenase, a CoA-transferase, a dehydratase, a reductase, a mutase, a CoA-ligase, an ammonia lyase, or a thioesterase and meso-2,6-diaminopimelate, wherein the dehydrogenase, the CoA-transferase, the dehydratase, the reductase, the mutase, the CoA-ligase, the ammonia lyase, or the thioesterase enzymatically converts the meso-2,6-diaminopimelate to 2-aminopimelate. The biochemical network can further include a decarboxylase; wherein the decarboxylase enzymatically converts 2-aminopimelate to 6-aminohexanoic acid. The biochemical network can further include a hydrolase, a reductase (e.g., a carboxylate reductase), a transaminase, an N-acetyltransferase, or a deacylase, wherein the hydrolase, the reductase, the transaminase, the N-acetyltransferase, or the deacetylase enzymatically convert 6-aminohexanoic acid into at least one of caprolactam or hexamethylenediamine. 
     Also, described herein is a biochemical network comprising a dehydrogenase, a CoA-transferase, a dehydratase, a reductase, a mutase, a CoA-ligase, an ammonia lyase, or a thioesterase and meso-2,6-diaminopimelate, wherein the dehydrogenase, the CoA-transferase, the dehydratase, the reductase, the mutase, the CoA-ligase, the ammonia lyase, or the thioesterase enzymatically converts the meso-2,6-diaminopimelate to 2-aminopimelate. The biochemical network can further include an aminotransferase, a o synthase, a decarboxylase, or a dehydrogenase wherein the aminotransferase, the synthase, the decarboxylase, or the dehydrogenase enzymatically converts 2-aminopimelate to 6-hydroxyhexanoic acid. The biochemical network can further include a reductase (e.g., a carboxylate reductase), a transaminase, or an alcohol dehydrogenase, wherein the reductase, the transaminase, or the alcohol dehydrogenase enzymatically convert 6-hydroxyhexanoic acid into at least one of hexamethylenediamine and 1,6-hexanediol. 
     Also, described herein is a means for obtaining 2-aminopimelate using at least one of a dehydrogenase, a CoA-transferase, a dehydratase, a reductase, a mutase, a CoA-ligase, an ammonia lyase, or a thioesterase. The means can further include means for converting 2-aminopimelate to at least one of adipic acid, 6-aminohexanoic acid, caprolactam, hexamethylenediamine, 6-hydroxyhexanoic acid, and 1,6-hexanediol. The means can include a decarboxylase, a synthase, a dehydrogenase complex, a dehydrogenase, a CoA-transferase, a dehydratase, a reductase, a mutase, a CoA-ligase, a lyase, a thioesterase, an aminotransferase, a hydrolase, a transaminase, or an N-acetyltransferase. 
     Also described herein is (i) step for obtaining 2-aminopimelate using a dehydrogenase, a CoA-transferase, a dehydratase, a reductase, a mutase, a CoA-ligase, an ammonia lyase, or a thioesterase (ii) a step for obtaining adipic acid using a decarboxylase, a synthase, or a dehydrogenase complex; (iii) a step for obtaining 6-aminohexanoic acid using a decarboxylase; and (iv) a step for obtaining 6-hydroxyhexanoic acid using a at least one of a aminotransferase, a synthase, a decarboxylase, or a dehydrogenase. 
     In another aspect, this document features a composition comprising 2-aminopimelate and decarboxylase, a synthase, or a dehydrogenase complex. The composition can be cellular. The composition can further include a dehydrogenase, a CoA-transferase, a CoA-dehydratase, a dehydratase, a reductase, a mutase, a CoA-ligase, a lyase, a thioesterase, an aminotransferase, a hydrolase, a transaminase, or an N-acetyltransferase and at least one of adipic acid, 6-aminohexanoic acid, caprolactam, hexamethylenediamine, 6-hydroxyhexanoic acid, and 1,6-hexanediol. The composition can be cellular. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although methods and materials similar or equivalent to those described herein can be used to practice the invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. The word “comprising” in the claims may be replaced by “consisting essentially of” or with “consisting of,” according to standard practice in patent law. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic of an exemplary biochemical pathway leading to biosynthesis of (S) 2-aminopimelate using meso-2,6-diaminopimelate as a central metabolite. 
         FIG. 2  is a schematic of an exemplary biochemical pathway leading to the biosynthesis of (R) 2-aminopimelate using meso-2,6-diaminopimelate as a central metabolite. 
         FIG. 3  is a schematic of exemplary biochemical pathways leading to adipic acid using either (S) 2-aminopimelate or (R) 2-aminopimelate as a central precursor. 
         FIG. 4  is a schematic of exemplary biochemical pathways leading to 6-aminohexanoic acid using either (S) 2-aminopimelate, (R) 2-aminopimelate or adipate semialdehyde as a central precursor.  FIG. 4  also contains a schematic of an exemplary biochemical pathway to caprolactam from 6-aminohexanoic acid. 
         FIG. 5  is a schematic of exemplary biochemical pathways leading to hexamethylenediamine using 6-aminohexanoic acid or adipate semialdehyde as a central precursor. 
         FIG. 6  is a schematic of an exemplary biochemical pathway leading to hexamethylenediamine using 6-aminohexanoic acid as a central precursor. 
         FIG. 7  is a schematic of an exemplary biochemical pathway leading to hexamethylenediamine using 6-hydroxyhexanoic acid as a central precursor. 
         FIG. 8  is a schematic of (i) exemplary biochemical pathways leading to 6-hydroxyhexanoic acid using either (S) 2-aminopimelate or (R) 2-aminopimelate as a central precursor and (ii) exemplary biochemical pathways leading to 1,6-hexanediol using 6-hydroxyhexanoic acid as a central precursor. 
         FIG. 9  is a bar graph summarizing the change in absorbance at 340 nm after 20 minutes, which is a measure of the consumption of NADPH and activity of carboxylate reductases relative to the enzyme only controls (no substrate). 
         FIG. 10  is a bar graph of the change in absorbance at 340 nm after 20 minutes, which is a measure of the consumption of NADPH and the activity of carboxylate reductases for converting adipate to adipate semialdehyde relative to the empty vector control. 
         FIG. 11  is a bar graph of the change in absorbance at 340 nm after 20 minutes, which is a measure of the consumption of NADPH and the activity of carboxylate reductases for converting 6-hydroxhexanoate to 6-hydroxhexanal relative to the empty vector control. 
         FIG. 12  is a bar graph of the change in absorbance at 340 nm after 20 minutes, which is a measure of the consumption of NADPH and the activity of carboxylate reductases for converting N6-acetyl-6-aminohexanoate to N6-acetyl-6-aminohexanal relative to the empty vector control. 
         FIG. 13  is a bar graph of the change in absorbance at 340 nm after 20 minutes, which is a measure of the consumption of NADPH and activity of carboxylate reductases for converting adipate semialdehyde to hexanedial relative to the empty vector control. 
         FIG. 14  is a bar graph summarizing the percent conversion after 4 hours of pyruvate to L-alanine (mol/mol) as a measure of the ω-transaminase activity of the enzyme only controls (no substrate). 
         FIG. 15  is a bar graph of the percent conversion after 24 hours of pyruvate to L-alanine (mol/mol) as a measure of the ω-transaminase activity for converting 6-aminohexanoate to adipate semialdehyde relative to the empty vector control. 
         FIG. 16  is a bar graph of the percent conversion after 4 hours of L-alanine to pyruvate (mol/mol) as a measure of the ω-transaminase activity for converting adipate semialdehyde to 6-aminohexanoate relative to the empty vector control. 
         FIG. 17  is a bar graph of the percent conversion after 4 hours of pyruvate to L-alanine (mol/mol) as a measure of the ω-transaminase activity for converting hexamethylenediamine to 6-aminohexanal relative to the empty vector control. 
         FIG. 18  is a bar graph of the percent conversion after 4 hours of pyruvate to L-alanine (mol/mol) as a measure of the ω-transaminase activity for converting N6-acetyl-1,6-diaminohexane to N6-acetyl-6-aminohexanal relative to the empty vector control. 
         FIG. 19  is a bar graph of the percent conversion after 4 hours of pyruvate to L-alanine (mol/mol) as a measure of the o-transaminase activity for converting 6-aminohexanol to 6-oxohexanol relative to the empty vector control. 
         FIGS. 20A-20K  contains the amino acid sequences of a  Lactobacillus brevis thioesterase  (see GenBank Accession No. ABJ63754.1, SEQ ID NO: 1), an  Lactobacillus plantarum thioesterase  (see GenBank Accession No. CCC78182.1, SEQ ID NO: 2),  Mycobacterium marimum  carboxylate reductase (see Genbank Accession No. ACC40567.1, SEQ ID NO: 3), a  Mycobacterium smegmatis  carboxylate reductase (see Genbank Accession No. ABK71854.1, SEQ ID NO: 4), a  Segniliparus rugosus  carboxylate reductase (see Genbank Accession No. EFV11917.1, SEQ ID NO: 5), a  Mycobacterium massiliense  carboxylate reductase (see Genbank Accession No. EIV11143.1, SEQ ID NO: 6), a  Segniliparus rotundus  carboxylate reductase (see Genbank Accession No. ADG98140.1, SEQ ID NO: 7), a  Chromobacterium violaceum  ω-transaminase (see Genbank Accession No. AAQ59697.1, SEQ ID NO: 8), a  Pseudomonas aeruginosa  ω-transaminase (see Genbank Accession No. AAG08191.1, SEQ ID NO: 9), a  Pseudomonas syringae  ω-transaminase (see Genbank Accession No. AAY39893.1, SEQ ID NO: 10), a  Rhodobacter sphaeroides  ω-transaminase (see Genbank Accession No. ARA81135.1, SEQ ID NO: 11), an  Escherichia coli  ω-transaminase (see Genbank Accession No. AAA57874.1, SEQ ID NO: 12), a  Vibrio fluvialis  ω-transaminase (see Genbank Accession No. AEA39183.1, SEQ ID NO: 13), a  Bacillus subtilis  phosphopantetheinyl transferase (see Genbank Accession No. CAA44858.1, SEQ ID NO:14), a  Nocardia  sp. NRRL 5646 phosphopantetheinyl transferase (see Genbank Accession No. AB183656.1, SEQ ID NO:15), a  Bacillus subtilis  enoate reductase (see Genbank Accession No. BAA12619.1, SEQ ID NO: 16), a  Pseudomonas putida    
       enoate reductase (see Genbank Accession No. AAN66878.1., SEQ ID NO: 17), a  Kluyveromyces lactis  enoate reductase (see Genbank Accession No. AAA9881.5A, SEQ ID NO: 18), a  Lactobacillus casei  enoate reductase (see Genbank Accession No. AGP69310,1, SEQ ID NO: 19), a  Saccharomyces pastorianus  enoate reductase (see Genbank Accession No. CAA37666.1, SEQ ID NO: 20), a  Thermaanaerobacter pseudethanolicus  enoate reductase (see Genbank Accession No. ABY93685.1, SEQ ID NO: 21), an  Enterobacter cloacae  enoate reductase (see Genbank Accession No. AAB38683.1, SEQ ID NO: 22), a  Fusobacterium nucleatum  ammonia lyase (see Genbank Accession No. AAL93968.1, SEQ ID NO: 23), an  Acidaminococcus fermentans  2-hydroxyglutaryl-CoA dehydratase activator (see Genbank Accession No. CAA42196A, SEQ ID NO: 24), a  Clostridium symbiosum  2-hydroxyglutaryl-CoA dehydratase (see Genbank Accession No. AAD31677.1 &amp; AAD31675.1, SEQ ID NO: 25), a  Bacillus subtilis  aminomutase (see Genbank Accession No. AAB72069.1, SEQ ID NO: 26), a  Peptoclostridium difficile  2-Hydroxyisocaproyl-CoA dehydratase activator (see Genbank Accession No. AAV40818.1, SEQ ID NO: 27), a  Peptodostridium difficile  2-Hydroxyisocaproyl-CoA dehydratase (see Genbank Accession No. AAV40819.1 &amp; AAV40820.1, SEQ ID NO: 28), an  Escherichia coli  glutamate decarboxylase (see Genbank Accession No. AAA23833.1, SEQ ID NO: 29), an  Escherichia coli  lysine decarboxylase (see Genbank Accession No. AAA23536.1, SEQ ID NO: 30), an  Escherichia coli  ornithine decarboxylase (see Genbank Accession No. AAA62785.1, SEQ ID NO: 31), an  Escherichia coli  lysine decarboxylase (see Genbank Accession No. BAA21656.1, SEQ ID NO: 32), an  Escherichia coli  diaminopimelate decarboxylase (see Genbank Accession No. AAA83861.1., SEQ ID NO: 33), and a  Salmonella typhimurium  indole-3-pyruvate decarboxylase (see Genbank Accession NO. CAC48239.1, SEQ ID: 34). 
     
    
    
     DETAILED DESCRIPTION 
     Described herein are enzymes, non-natural pathways, cultivation strategies, feedstocks, host microorganisms and attenuations to the host&#39;s biochemical network, which generates a seven carbon chain aliphatic backbone from central metabolites which can be decarboxylated to a six carbon aliphatic backbone into which one or two terminal functional groups may be formed leading to the synthesis of adipic acid, adipate semialdehyde, caprolactam, 6-aminohexanoic acid, 6-hydroxyhexanoic acid, hexamethylenediamine or 1,6-hexanediol (referred to as “C6 building blocks” herein). As used herein, the term “central precursor” is used to denote any metabolite in any metabolic pathway shown herein leading to the synthesis of one or more C6 building blocks. The term “central metabolite” is used herein to denote a metabolite that is produced in all microorganisms to support growth. 
     Host microorganisms described herein can include endogenous pathways that can be manipulated such that one or more C6 building blocks can be produced. In an endogenous pathway, the host microorganism naturally expresses all of the enzymes catalyzing the reactions within the pathway. A host microorganism containing an engineered pathway does not naturally express all of the enzymes catalyzing the reactions within the pathway but has been engineered such that all of the enzymes within the pathway are expressed in the host. Within an engineered pathway, the enzymes can be from a single source, i.e., from one species, or can be from multiple sources, i.e., different species or genera. Nucleic acids encoding the enzymes described herein have been identified from various organisms and are readily available in publicly available databases such as GenBank or EMBL. Engineered hosts can naturally express none or some (e.g., one or more, two or more, three or more, four or more, five or more, or six or more) of the enzymes of the pathways described herein. Thus, a pathway within an o engineered host can include all exogenous enzymes, or can include both endogenous and exogenous enzymes. Endogenous genes of the engineered hosts also can be disrupted to prevent the formation of undesirable metabolites or prevent the loss of intermediates in the pathway through other enzymes acting on such intermediates. Engineered hosts can be referred to as recombinant hosts or recombinant host cells. Thus, as described herein recombinant hosts can include nucleic acids encoding one or more of a dehydrogenase, decarboxylase, reductase, dehydratase, CoA-transferase, thioesterase, hydrolase, ammonia lyase, mutase, synthase, aminotransferase, or transaminase as described in more detail below. 
     The term “exogenous” as used herein with reference to a nucleic acid (or a protein) and a host refers to a nucleic acid that does not occur in (and cannot be obtained from) a cell of that particular type as it is found in nature or a protein encoded by such a nucleic acid. Thus, a non-naturally-occurring nucleic acid is considered to be exogenous to a host once in the host. It is important to note that non-naturally-occurring nucleic acids can contain nucleic acid subsequences or fragments of nucleic acid sequences that are found in nature provided the nucleic acid as a whole does not exist in nature. For example, a nucleic acid molecule containing a genomic DNA sequence within an expression vector is non-naturally-occurring nucleic acid, and thus is exogenous to a host cell once introduced into the host, since that nucleic acid molecule as a whole (genomic DNA plus vector DNA) does not exist in nature. Thus, any vector, autonomously replicating plasmid, or virus (e.g., retrovirus, adenovirus, or herpes virus) that as a whole does not exist in nature is considered to be non-naturally-occurring nucleic acid. It follows that genomic DNA fragments produced by PCR or restriction endonuclease treatment as well as cDNAs are considered to he non-naturally-occurring nucleic acid since they exist as separate molecules not found in nature. It also follows that any nucleic acid containing a promoter sequence and polypeptide-encoding sequence (e.g., cDNA or genomic DNA) in an arrangement not found in nature is non-naturally-occurring nucleic acid. A nucleic acid that is naturally-occurring can be exogenous to a particular host microorganism. For example, an entire chromosome isolated from a cell of yeast x is an exogenous nucleic acid with respect to a cell of yeast y once that o chromosome is introduced into a cell of yeast y. 
     In contrast, the term “endogenous” as used herein with reference to a nucleic acid (e.g., a gene) (or a protein) and a host refers to a nucleic acid (or protein) that does occur in (and can be obtained from) that particular host as it is found in nature. Moreover, a cell “endogenously expressing” a nucleic acid (or protein) expresses that nucleic acid (or protein) as does a host of the same particular type as it is found in nature. Moreover, a host “endogenously producing” or that “endogenously produces” a nucleic acid, protein, or other compound produces that nucleic acid, protein, or compound as does a host of the same particular type as it is found in nature. 
     In some embodiments, depending on the host and the compounds produced by the host, one or more of the following polypeptides having 2-hydroxyacyl-CoA dehydratase activity, mutase activity, ammonia lyase activity, and enoate reductase activity may be expressed in the host in addition to one or more of: a polypeptide having α-oxoacid decarboxylase activity, a polypeptide having α-aminoacid decarboxylase activity, a polypeptide having synthase activity, a polypeptide having the activity of a dehydrogenase complex, a polypeptide having diaminopimelate dehydrogenase activity, a polypeptide having (R)-2-hydroxyisocaproate dehydrogenase activity, a polypeptide having (R)-2-hydroxyglutarate dehydrogenase activity, a polypeptide having glutaconate CoA-transferase activity, a polypeptide having 2-hydroxyisocaproyl-CoA dehydratase activity, a polypeptide having (R)-2-hydroxyglunyl-CoA dehydratase activity, a polypeptide having carboxylate reductase activity, a polypeptide having aldehyde dehydrogenase activity, a polypeptide having lysine 2,3-aminomutase activity, a polypeptide having succinate-CoA ligase activity, a polypeptide having 3-aminobutyryl-CoA ammonia lyase activity, a polypeptide having thioesterase activity, a polypeptide having CoA-transferase activity, a polypeptide having alpha-aminotransferase activity, a polypeptide having branch-chain-2-oxoacid decarboxylase activity, a polypeptide having acetolactate synthase activity, a polypeptide having aldehyde dehydrogenase activity, a polypeptide having hydrolase activity, a polypeptide having ω-transaminase activity, a polypeptide having N-acetyltransferase activity, a polypeptide having lysine N-acetyltransferase activity, or a polypeptide having alcohol dehydrogenase activity. In recombinant hosts expressing a carboxylate reductase, a phosphopantetheinyl transferase also can be expressed as it enhances activity of the carboxylase reductase. 
     For example, a recombinant host can include at least one exogenous polypeptide having an activity selected from the group consisting of 2-hydroxyacyl-CoA dehydratase activity, mutase activity, ammonia lyase activity, and enoate reductase activity and produce 2-aminopimelate from 2,6-diaminopimelate. 
     For example, a host can include an exogenous polypeptide having 2-hydroxyacyl-CoA dehydratase activity and an exogenous polypeptide having enoate reductase activity and produce 2-aminopimelate (e.g., (S)-aminopimelate). Such a host further can include at least one polypeptide having an activity selected from the group consisting of diaminopimelate dehydrogenase activity, 2-hydroxycarboxylate dehydrogenase activity, CoA-transferase activity, 2-hydroxyacid dehydratase activity, and carboxylate reductase activity. See, e.g.,  FIG. 1 . 
     For example, a recombinant host can include (i) an exogenous polypeptide having diaminopimelate dehydrogenase activity classified, for example, under EC 1.4.1.16, (ii) an exogenous polypeptide having 2-hydroxyisocaproate dehydrogenase activity or an exogenous polypeptide having (R)-2-hydroxyglutarate dehydrogenase activity classified, for example, under EC 1.1.1.- such as EC 1.1.1.337, (iii) an exogenous polypeptide having glutaconate CoA-transferase activity classified, for example, under EC 2.8.3.12, (iv) an exogenous polypeptide having 2-hydroxyisocaproyl-CoA dehydratase activity or a polypeptide having 2-hydroxyglutryl-CoA dehydratase activity classified, for example, under EC 4.2.1.-, (v) an exogenous polypeptide having carboxylase reductase activity classified, for example, under EC 1.2.99.6, (vi) an exogenous polypeptide having enoate reductase activity classified, for example, under EC 1.3.1.31 or EC 1.3.99.1, (vii) or an exogenous polypeptide having aldehyde dehydrogenase activity classified, for example, under EC 1.2.1.—such as EC 1.2.1.3 and produce (S) 2-aminopimelate. See,  FIG. 1 . 
     For example, a recombinant host can include an exogenous polypeptide having mutase activity, an exogenous polypeptide having ammonia lyase activity, and an exogenous polypeptide having enoate reductase activity and produce 2-aminopimelate (e.g., (R)-aminopimelate). Such a host further can include at least one polypeptide o having an activity selected from the group consisting of CoA ligase activity, CoA-transferase activity, carboxylate reductase activity, and aldehyde dehydrogenase activity. See,  FIG. 2 . 
     For example, a recombinant host can include (i) an exogenous polypeptide having lysine 2,3-aminomutase activity classified, for example, under EC 5.4.3.2, (ii) an exogenous polypeptide having succinate-CoA ligase activity classified, for example, under EC 6.2.1.5 or a polypeptide having CoA-transferase activity classified, for example, under EC 2.8.3.-, (iii) an exogenous polypeptide having 3-aminobutyryl-CoA ammonia lyase activity classified, for example, under EC 4.3.1.14, (iv) an exogenous polypeptide having thioesterase activity classified, for example, under EC 3.1.2.- or polypeptide having CoA-transferase activity classified, for example, under EC 2.8.3.-, (v) an exogenous polypeptide having carboxylate reductase activity classified, for example, under EC 1.2.99.6, (vi) an exogenous polypeptide having enoate reductase activity classified, for example, under EC 1.3.1.31 or EC 1.6.99.1 or (vii) a polypeptide having aldehyde dehydrogenase activity classified, for example, under EC 1.2.1.—such as EC 1.2.1.3 and produce (R) 2-aminopimelate. 
     A recombinant host producing 2-aminopimelate also can include at least one exogenous polypeptide having an activity selected from the group consisting of α-oxoacid decarboxylase activity classified under EC α-aminoacid decarboxylase activity classified under EC 4.1.1.-, synthase activity, and activity of a dehydrogenase complex. See, e.g.,  FIG. 3  and  FIG. 4 . 
     In some embodiments, a recombinant host producing 2-aminopimelate can include an exogenous polypeptide having 2-oxoacid decarboxylase activity classified, for example, under EC 4.1.1.—such as EC 4.1.1.43, EC 4.1.1.71, EC 4.1.1.72 or EC 4.1.1.74 or an exogenous polypeptide having acetolactate synthase activity classified, for example, under EC 2.2.1.6 and produce adipic acid. See,  FIG. 3 . 
     For example, a recombinant host producing 2-aminopimelate can include (i) an exogenous polypeptide having 2-oxoacid decarboxylase activity classified, for example, under EC 4.1.1.—such as EC 4.1.1.43, EC 4.1.1.71, EC 4.1.1.72 or EC 4.1174 or an exogenous polypeptide having acetolactate synthase activity classified, for example, under EC 2.2.1.6 and (ii) an exogenous polypeptide having α-aminotransferase activity classified, for example, under EC 2.6.1.—such as EC 2.6.1.39, EC 2.6.1.42 or EC 2.6.1.21 and produce adipate semialdehyde or adipic acid. See,  FIG. 3 . 
     For example, a recombinant host producing 2-aminopimelate can include (i) an exogenous polypeptide having 2-oxoacid decarboxylase activity classified, for example, under EC 4.1.1.—such as EC 4.1.1.43, EC 4.1.1.71, EC 4.1.1.72 or EC 4.1.1.74 or an exogenous polypeptide having acetolactate synthase activity classified, for example, under EC 2.2.1.6, (ii) an exogenous polypeptide having α-aminotransferase activity classified, for example, under EC 2.6.1.—such as EC 2.6.1.39, EC 2.6.1.42 or EC 2.6.1.21, and (iii) an exogenous polypeptide having aldehyde dehydrogenase activity classified, for example, under EC 1.2.1.—such as EC 1.2.1.3, EC 1.2.1.16, EC 1.2.1.20, EC 1.2.1.63 or EC 1.2.1.79 and produce adipic acid. See,  FIG. 3 . 
     In some embodiments, a recombinant host producing 2-aminopimelate can include an exogenous polypeptide having acetolactate synthase activity classified, for example, under EC 2.2.1.6 and produce adipic acid. See,  FIG. 3 . 
     For example, a recombinant host producing 2-aminopimelate can include (i) an exogenous polypeptide having acetolactate synthase activity classified, for example, under EC 2.2.1.6 and an exogenous polypeptide having α-aminotransferase activity classified, for example, under EC 2.6.1.—such as EC 2.6.1.39, EC 2.6.1.42 or EC 2.6.1.21, and produce adipic acid. See,  FIG. 3 . 
     For example, a recombinant host producing 2-aminopimelate can include an exogenous polypeptide having acetolactate synthase activity classified, for example, under EC 2.2.1.6, an exogenous polypeptide having alpha-aminotransferase activity classified, for example, under EC 2.6.1.—such as EC 2.6.1.39, EC 2.6.1.42 or EC 2.6.1.21, and an exogenous polypeptide having aldehyde dehydrogenase activity classified, for example, under EC 1.2.1.—such as EC 1.2.1.3, EC 1.2.1.16, EC 1.2.1.20, EC 1.2.1.63 or EC 1.2.1.79 and produce adipic acid. See,  FIG. 3 . 
     In some embodiments, a recombinant host producing 2-aminopimelate can include an exogenous dehydrogenase complex comprised of enzyme activities classified, for example, EC 1.2.4.2, EC 1.8.1.4 or EC 2.3.1.61 and produce adipic acid. See,  FIG. 3 . 
     For example, a recombinant host producing 2-aminopimelate can include (i) an exogenous dehydrogenase complex comprised of enzyme activities classified, for example, EC 1.2.4.2, EC 1.8.1.4 or EC 2.3.1.61 and (ii) an exogenous polypeptide having α-aminotransferase activity classified, for example, under EC 2.6.1.—such as EC 2,6.1.39, EC 2,6.1.42 or EC 2,6.1.21 and produce adipic acid. See,  FIG. 3 . 
     For example, a recombinant host producing 2-aminopimelate can include an exogenous dehydrogenase complex comprised of enzyme activities classified, for example, EC 1.2.4.2, EC 1.8.1.4 or EC 2.3.1.61 and an exogenous polypeptide having thioesterase activity classified, for example, under EC 3.1.2.—and produce adipic acid. See,  FIG. 3 . 
     For example, a recombinant host producing 2-aminopimelate can include an exogenous dehydrogenase complex and an exogenous polypeptide having glutaconate CoA-transferase activity classified, for example, under EC 2.8.3.12 or an exogenous polypeptide having succinate CoA-ligase activity classified, for example, under EC 6.2.1.5 and produce adipic acid. See,  FIG. 3 . 
     For example, a recombinant host producing 2-aminopimelate can include (i) an exogenous dehydrogenase complex comprised of enzyme activities classified, for example, EC 1.2.4.2, EC 1.8.1.4 or EC 2.3.1,61, (ii) an exogenous polypeptide having alpha-aminotransferase activity classified, for example, under EC 2.6.1.—such as EC 2.6.1.39, EC 2.6.1.42 or EC 2.6.1.21, and (iii) an exogenous polypeptide having thioesterase activity classified, for example, under EC 3.1.2.-, a polypeptide having CoA-ligase activity classified, for example, under EC 6.2.1.5 or a polypeptide having CoA-transferase activity classified, for example, under EC 2.8.3.12 and produce adipic acid. See,  FIG. 3 . 
     For example, a recombinant host producing 2-aminopimelate can include an exogenous dehydrogenase complex, an exogenous polypeptide having alpha-aminotransferase activity, and an exogenous polypeptide having gintaconate CoA-transferase activity or an exogenous polypeptide having succinelle CoA-ligase activity and produce adipic acid. See,  FIG. 3 . 
     In some embodiments, a recombinant host producing (S)-2-aminopimelate can include a polypeptide having decarboxylase activity classified, for example, under EC 4.1.1.—such as EC 4.1.1.15, EC 4.1.1.17, EC 4.1.1.18, EC 4.1.1.19 and produce 6-aminohexanoic acid, which can be converted to caprolactam using an exogenous polypeptide having amidohydrolase activity (classified, for example, under EC 3.5.2,-). See,  FIG. 4 . 
     In some embodiments, a recombinant host producing (R)-2-aminopimelate can include a polypeptide having decarboxylase activity classified, for example, under EC 4.1.1.- such as EC 4.1.1.20 and produce 6-aminohexanoic acid from (R)-2-aminopimelate, which can be converted to caprolactam using an exogenous polypeptide having hydrolase activity (classified, for example, under EC 3.5.2.4 See,  FIG. 4 . 
     A recombinant host producing 2-aminopimelate can include (i) an exogenous polypeptide having α-aminotransferase activity classified, for example, under EC 2.6.1—such as EC 2.6.1.21, EC 2.6.1.39 or EC 2.6.1.42 (ii) an exogenous polypeptide having decarboxylase activity classified, for example, under EC 4.1.1.—such as EC 4.1,1.43, EC 4.1.1.71, EC 4.1.1.71 or EC 4.1.1.74 or a polypeptide having acetolactate synthase activity classified, for example, under EC 2.2.1.6 and (iii) an exogenous polypeptide having ω-transaminase activity classified, for example, under EC 2.6.1.—such EC 2.6.1.18, EC 2.6.1.19, EC 2.6.1.48, EC 2.6.1.29, or EC 2.6.1.82 and produce 6-aminohexanoic acid. See,  FIG. 4 . 
     A recombinant host producing 6-aminohexanoic acid can further include (i) an exogenous polypeptide having carboxylate reductase activity classified, for example, under EC 1.2.99.6 (ii) an exogenous polypeptide having ω-transaminase activity classified, for example, under EC 2.6.1.—such as EC 2.6.1.18, EC 2.6.1.19, EC 2.6.1.48, EC 2.6.1.29, or EC 2.6.1.82 and produce hexamethylenediamine. See,  FIG. 5 . 
     A recombinant host producing 2-aminopimelate can include (i) an exogenous polypeptide having α-aminotransferase activity classified, for example, under EC 2.6.1.39 or EC 2.6.1.42, (ii) classified, for example, under EC 4.1.1.—such as EC 4.1.1.43, EC 4.1.1.71, EC 4.1.1.71 or EC 4.1.1.74 or a polypeptide having acetolactate synthase activity classified, for example, under EC 2.2.1.6, (iii) a polypeptide having carboxylate reductase activity classified, for example, under EC 1.2.99.6 and (iv) exogenous polypeptide having ω-transaminase activity classified, for example, under EC 2.6.1.—such EC 2.6.1.18, EC 2.6.1.19, EC 2.6.1.48, EC 2.6.1.29, or EC 2.6.1.82 and produce hexamethylenediamine. See,  FIG. 5 . 
     A recombinant host producing 6-aminohexanoic acid can further include (i) an exogenous polypeptide having N-acetyltransferase activity classified, for example, under EC 2.3.1.32 (ii) a polypeptide having carboxylate reductase activity classified, for example, under EC 1.2.99.6, (iii) a polypeptide having ω-transaminase activity classified, for example, under EC 2.6.1.—such as EC 2.6.1.18, EC 2.6.1.19, or EC 2.6.1.48, EC 2.6.1.29, or EC 2.6.1.82 and (iv) and a polypeptide having deacylase activity classified, for example, under EC 3.5.1.17 and produce hexamethylenediamine. See,  FIG. 6 . 
     In some embodiments, a recombinant host can include a polypeptide having α-aminotransferase activity classified, for example, under EC 2.6.1.—such as EC 2.6.1.39, EC 2.6.1.42 or EC 2.6.1.21 and produce 6-hydroxyhexanoic acid. See,  FIG. 7 . 
     For example, a recombinant host can include (i) a polypeptide having α-aminotransferase activity classified, for example, under EC 2.6.1.—such as EC 2.6.1.39, EC 2.6.1.42 or EC 2.6.1.21 and (ii) an exogenous polypeptide having 2-oxoacid decarboxylase activity classified, for example, under EC 4.1.1.—such as EC 4.1.1.43, EC 4.1.1.71, EC 4.1.1.72 or EC 4.1.1.74 or an exogenous polypeptide having acetolactate synthase activity classified, for example, under EC 2.2.1.6 and produce 6-hydroxyhexanoic acid, See,  FIG. 8 . 
     For example, a recombinant host can include (i) a polypeptide having α-aminotransferase activity classified, for example, under EC 2.6.1.—such as EC 2.6.1.39, EC 2.6.1.42 or EC 2.6.1.21 and (ii) an exogenous polypeptide having 2-oxoacid decarboxylase activity classified, for example, under EC 4.1.1.—such as EC 4.1.1.43, EC 4.1.1.71, EC 4.1.1.72 or EC 4.1.1.74 or an exogenous polypeptide having acetolactate synthase activity classified, for example, under EC 2.2.1.6, (iii) and a polypeptide having alcohol dehydrogenase activity classified, for example, under EC 1.1.1.—such as EC 1.1.1.2 or EC 1.1.1.258 and produce 6-hydroxyhexanoic acid. See,  FIG. 8 . 
     A recombinant host producing 6-hydroxyhexanoic acid can further include (i) a polypeptide having carboxylate reductase activity classified, for example, under EC 1.2.99.6, (ii) a polypeptide having ortransaminase activity classified, for example, under EC 2.6.1.—such as EC 2.6.1.18, EC 2.6.1.19, or EC 2.6.1.48, EC 2.6.1.29, or EC 2.6.1.82, and (iii) a polypeptide having alcohol dehydrogenase activity classified, for example, under EC 1.1.1.—such as EC 1.1.1.1 and produce hexamethylenediamine. See,  FIG. 7 . 
     A recombinant host producing 6-hydroxyhexanoic acid can further include (i) an exogenous polypeptide having carboxylate reductase activity classified, for example, under EC 1.2.99.6 and (ii) an exogenous polypeptide having alcohol dehydrogenase activity classified, for example, under EC 1.1.1.—such as EC 1.1.1.1, EC 1.1.1.2, EC 1.1.1.21 or EC 1.1.1.184 and produce 1,6 hexanediol. See,  FIG. 8 . 
     Any of the enzymes described herein that can be used for production of one or more C6 building blocks can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%) to the amino acid sequence of the corresponding wild-type enzyme. It will be appreciated that the sequence identity can be determined on the basis of the mature enzyme (e.g., with any signal sequence removed) or on the basis of the immature enzyme (e.g., with any signal sequence included). It also will be appreciated that the initial methionine residue may or may not be present on any of the enzyme sequences described herein. 
     Any of the enzymes described herein that can be used for production of one or more C6 building blocks can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of the corresponding wild-type enzyme. For example, a thioesterase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a  Lactobacillus brevis  thioesterase (see GenBank Accession No. ABJ63754.1, SEQ ID NO: 1) or to the amino acid sequence of a  Lactobacillus plantarum  thioesterase (see GenBank Accession No. CCC78182.1, SEQ ID NO: 2). See  FIG. 20A . 
     For example, a carboxylate reductase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a  Mycobacterium marimum  (see Genbank Accession No. ACC40567.1, SEQ ID NO: 3), a  Mycobacterium smegmatis  (see Genbank Accession No. ABK71854.1, SEQ ID NO: 4), a  Segniliparus rugosus  (see Genbank Accession No. EFV11917.1, SEQ ID NO: 5), a  Mycobacterium massiliense  (see Genbank Accession No. EIV11143.1, SEQ ID NO: 6), or a  Segniliparus rotundus  (see Genbank Accession No. ADG98140.1, SEQ ID NO: 7) carboxylate reductase. See,  FIGS. 20A-20E . 
     For example, a ω-transaminase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a  Chromobacterium violaceum  (see Genbank Accession No. AAQ59697.1, SEQ ID NO: 8), a  Pseudomonas aeruginosa  (see Genbank Accession No. AAG08191.1, SEQ ID NO: 9), a  Pseudomonas syringae  (see Genbank Accession No. AAY39893.1, SEQ ID NO: 10), a  Rhodobacter sphaeroides  (see Genbank Accession No. ABA81135.1, SEQ ID NO: 11), an  Escherichia coli  (see Genbank Accession No. AAA57874.1, SEQ ID NO: 12), or a  Vibrio fluvialis  (see Genbank Accession No. AEA39183.1, SEQ ID NO: 13) ω-transaminase. Some of these ω-transaminases are diamine ω-transaminases. See,  FIG. 20E  and  FIG. 20F . 
     For example, a phosphopantetheinyl transferase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a  Bacillus subtilis  phosphopantetheinyl transferase (see Genbank Accession No. CAA44858,1, SEQ ID NO: 14) or a  Nocardia  sp. NRRL 5646 phosphopantetheinyl transferase (see Genbank Accession No. ABI83656.1, SEQ ID NO:15), See,  FIG. 20F  and  FIG. 20G . 
     For example, an enoate reductase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 9.7%, 98%, 99%, or 100%) to the amino acid sequence of a  Bacillus subtilis  enoate reductase (see Genbank Accession No. BAA12619.1, SEQ ID NO: 16), a  Pseudomonas putida  enoate reductase (see Genbank Accession No. AAN66878,1, SEQ ID NO: 17), a  Kluyveromyces lactis  enoate reductase (see Genbank Accession No. AAA98815.1, SEQ ID NO: 18), a  Lactobacillus casei  enoate reductase (see Genbank Accession No. AGP69310.1, SEQ ID NO: 19), a  Saccharomyces pastoriamus  enoate reductase (see Genbank Accession No. CAA37666.1, SEQ ID NO: 20), a  Thermoanaerobacter pseudethanolicus  enoate reductase (see Genbank Accession No. ABY93685.1, SEQ ID NO: 21), a  Enterobacter cloacae  enoate reductase (see Genbank Accession No. AAB38683.1, SEQ ID NO: 22). 
     For example, an ammonia lyase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a  Fusobacterhun nucleatum  ammonia lyase (see Genbank Accession No. AAL93968.1, SEQ ID NO: 23). 
     For example, a dehydratase activator described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of an  Acidaminococcus fermentans  2-hydroxyglutaryl-CoA dehydratase activator (see Genbank Accession No. CAA.42196.1, SEQ ID NO: 24) or a  Peptoclostridium difficile  2-Hydroxyisocaproyl-CoA dehydratase activator (see Genbank Accession No. AAV40818.1, SEQ ID NO: 27). 
     For example, a 2-hydraryacyl-CoA dehydratase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a  Clostridium symbiosum  2-hydroxyglutaryl-CoA dehydratase (see Genbank Accession No. AAD31677.1 &amp; AAD31675.1, SEQ ID NO: 25), or a  Peptoclostrillum difficile  2-Hydroxyisocaproyl-CoA dehydratase (see Genbank Accession No. AAV40819.1 &amp; AAV40820.1, SEQ ID NO: 28). 
     For example, an aminomutase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a  Bacillus subtilis  aminomutase (see Genbank Accession No. AAB72069.1, SEQ ID NO: 26). 
     For example, a decarboxylase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of an  Escherichia coli  glutamate decarboxylase (see Genbank Accession No. AAA23833.1, SEQ ID NO: 29), an  Escherichia coli  lysine decarboxylase (see Genbank Accession No. AAA23536.1, SEQ ID NO: 30), an  Escherichia coli  ornithine decarboxylase (see Genbank Accession No. AAA62785.1, SEQ ID NO: 31), an  Escherichia coli  lysine decarboxylase (see Genbank Accession No. BAA21656,1, SEQ ID NO: 32), an  Escherichia coli  diaminopimelate decarboxylase (see Genbank Accession No. AAA83861.1, SEQ ID NO: 33), a  Salmonella typhimurium  indole-3-pyruvate decarboxylase (see Genbank Accession No. CAC48239,1, SEQ ID NO: 34). 
     The percent identity (homology) between two amino acid sequences can be determined as follows. First, the amino acid sequences are aligned using the BLAST 2 Sequences (Bl2seq) program from the stand-alone version of BLASTZ containing BLASTP version 2.0.14. This stand-alone version of BLASTZ can be obtained from Fish &amp; Richardson&#39;s web site (e.g., www.fr.com/blast/) or the U.S. government&#39;s National Center for Biotechnology Information web site (www.ncbi.nlm.nih.gov). Instructions explaining how to use the Bl2seq program can be found in the readme file accompanying BLASTZ. Bl2seq performs a comparison between two amino acid sequences using the BLASTP algorithm. To compare two amino acid sequences, the options of Bl2seq are set as follows: -i is set to a file containing the first amino acid sequence to be compared (e.g., C:\seq1.txt); -j is set to a file containing the second amino acid sequence to be compared (e.g., C:\seq2.txt); -p is set to blastp; -o is set to any desired file name (e.g., C:\output.txt); and all other options are left at their default setting. For example, the following command can be used to generate an output file containing a comparison between two amino acid sequences: C:\Bl2seq -i c:\seq1.txt -j c:\seq2.txt -p blastp -o c:\output.txt. if the two compared sequences share homology (identity), then the designated output file will present those regions of homology as aligned sequences. If the two compared sequences do not share homology (identity), then the designated output file will not present aligned sequences. Similar procedures can be following for nucleic acid sequences except that blastn is used. 
     Once aligned, the number of matches is determined by counting the number of positions where an identical amino acid residue is presented in both sequences. The o percent identity (homology) is determined by dividing the number of matches by the length of the full-length polypeptide amino acid sequence followed by multiplying the resulting value by 100. It is noted that the percent identity (homology) value is rounded to the nearest tenth. For example, 78.11, 78.12, 78.13, and 78.14 is rounded down to 78.1, while 78.15, 78.16, 78.17, 78.18, and 78.19 is rounded up to 78.2. It also is noted that the length value will always be an integer. 
     It will be appreciated that a number of nucleic acids can encode a polypeptide having a particular amino acid sequence. The degeneracy of the genetic code is well known to the art; i.e., for many amino acids, there is more than one nucleotide triplet that serves as the codon for the amino acid. For example, codons in the coding sequence for a given enzyme can be modified such that optimal expression in a particular species (e.g., bacteria or fungus) is obtained, using appropriate codon bias tables for that species. 
     Functional fragments of any of the enzymes described herein can also be used in the methods of the document. The term “functional fragment” as used herein refers to a peptide fragment of a protein that has at least 25% (e.g., at least: 30%; 40%; 50%; 60%; 70%; 75%; 80%; 85%; 90% 95%; 98%; 99%; 100%; or even greater than 100%) of the activity of the corresponding mature, full-length, wild-type protein. The functional fragment can generally, but not always, be comprised of a continuous region of the protein, wherein the region has functional activity. 
     This document also provides (i) functional variants of the enzymes used in the methods of the document and (ii) functional variants of the functional fragments described above. Functional variants of the enzymes and functional fragments can contain additions, deletions, or substitutions relative to the corresponding wild-type sequences. Enzymes with substitutions will generally have not more than 50 (e.g., not more than one, two, three, four, five, six, seven, eight, nine, ten, 12, 15, 20, 25, 30, 35, 40, or 50) amino acid substitutions (e.g., conservative substitutions). This applies to any of the enzymes described herein and functional fragments. A conservative substitution is a substitution of one amino acid for another with similar characteristics. Conservative substitutions include substitutions within the following groups: valine, alanine and glycine; leucine, valine, and isoleucine; aspartic acid and glutamic acid; asparagine and o glutamine; serine, cysteine, and threonine; lysine and arginine; and phenylalanine and tyrosine. The nonpolar hydrophobic amino acids include alanine, leucine, isoleucine, valine, proline, phenylalanine, tryptophan and methionine. The polar neutral amino acids include glycine, serine, threonine, cysteine, tyrosine, asparagine and glutamine. The positively charged (basic) amino acids include arginine, lysine and histidine. The negatively charged (acidic) amino acids include aspartic acid and glutamic acid. Any substitution of one member of the above-mentioned polar, basic or acidic groups by another member of the same group can be deemed a conservative substitution. By contrast, a nonconservative substitution is a substitution of one amino acid for another with dissimilar characteristics. 
     Deletion variants can lack one, two, three, four, five, six, seven, eight, nine, ten, 11, 12, 13, 14, 15. 16, 17, 18, 19, or 20 amino acid segments (of two or more amino acids) or non-contiguous single amino acids. Additions (addition variants) include fusion proteins containing: (a) any of the enzymes described herein or a fragment thereof; and (b) internal or terminal (C or N) irrelevant or heterologous amino acid sequences. In the context of such fusion proteins, the term “heterologous amino acid sequences” refers to an amino acid sequence other than (a). A heterologous sequence can be, for example a sequence used for purification of the recombinant protein (e.g., FLAG, polyhistidine (e.g., hexahistidine), hemagglutinin (HA), glutathione-S-transferase (GST), or maltosebinding protein (MBP)). Heterologous sequences also can be proteins useful as detectable markers, for example, luciferase, green fluorescent protein (GFP), or chloramphenicol acetyl transferase (CAT). In some embodiments, the fusion protein contains a signal sequence from another protein. In certain host cells (e.g., yeast host cells), expression and/or secretion of the target protein can be increased through use of a heterologous signal sequence. In some embodiments, the fusion protein can contain a carrier (e.g., KLH) useful, e.g., in eliciting an immune response for antibody generation) or ER or Golgi apparatus retention signals. Heterologous sequences can be of varying length and in some cases can be a longer sequences than the full-length target proteins to which the heterologous sequences are attached. 
     In addition, the production of one or more C6 building blocks can be performed in vitro using the isolated enzymes described herein, using a lysate (e.g., a cell lysate) from a host microorganism as a source of the enzymes, or using a plurality of lysates from different host microorganisms as the source of the enzymes. 
     The reactions of the pathways described herein can be performed in one or more host strains (a) naturally expressing one or more relevant enzymes, (b) genetically engineered to express one or more relevant enzymes, or (c) naturally expressing one or more relevant enzymes and genetically engineered to express one or more relevant enzymes. Alternatively, relevant enzymes can be extracted from of the above types of host cells and used in a purified or semi-purified form. Moreover, such extracts include lysates (e.g. cell lysates) that can be used as sources of relevant enzymes. In the methods provided by the document, all the steps can be performed in host cells, all the steps can be performed using extracted enzymes, or some of the steps can be performed in cells and others can be performed using extracted enzymes. 
     In addition, the production of one or more C6 building blocks can be performed in vitro using the isolated enzymes described herein, using a lysate (e.g., a cell lysate) from a host microorganism as a source of the enzymes, or using a plurality of lysates from different host microorganisms as the source of the enzymes. 
     Enzymes Generating the C7 Aliphatic Backbone for Conversion to C6 Building Blocks 
     In some embodiments, (S)-2-amino-6-oxopimelate in  FIG. 1  is substituted with the central precursor N-Acetyl-L-2-amino-6-oxopimelate. 
     In some embodiments, (S)-2-amino-6-oxopimelate in  FIG. 1  is substituted with the central precursor N-Succinyl-2-L-amino-6-oxoheptanedioate. 
     In some embodiments, the C7 aliphatic backbone can be enzymatically formed from meso-2,6-diaminopimelate using one or more of a dehydrogenase, a CoA-transferase, a dehydratase, a reductase, a mutase, a CoA-ligase, an ammonia lyase and a thioesterase. See,  FIGS. 1 and 2 . 
     In some embodiments, the dehydrogenase is a diaminopimelate dehydrogenase classified, for example, under EC 1.4.1.16. 
     In some embodiments, the dehydrogenase is a (R)-2-hydroxyisocaproate dehydrogenase such as the gene product of LdhA or a 2-hydroxyglutarate dehydrogenase such as the gene product of HgdH. 
     In some embodiments, the CoA-transferase is a glutaconate CoA-transferase, classified, for example, under EC 2.8.3.12, such as the gene product of GetAB or a pimelate CoA-transferase classified, for example, under EC 2.8.3.—such as the gene product of thnH. 
     In some embodiments, the CoA-ligase is a succinate CoA-ligase, for example, under EC 6.2.1.5. 
     In some embodiments, the dehydratase is a 2-hydroxyisocaproyl-CoA dehydratase such as SEQ ID NO: 28 or a 2-hydroxyglutaryl-CoA dehydratase such as SEQ ID NO: 25. 
     In some embodiments, the thioesterase is classified, for example, under EC 3.1.2.-, such as that encoded by YciA, tesB, acot13, SEQ ID NO: 1 or SEQ ID NO: 2. 
     In some embodiments, the reductase is a carboxylate reductase classified, for example, under EC 1.2.99.6 such as the gene products of car &amp; npt, GriC &amp; GriD or SEQ ID NO: 5, 7. 
     In some embodiments, the reductase is an enoate reductase (old yellow enzyme) classified, for example, under EC 1.3.1.31 or EC 1.6.99.1 such as the gene product of SEQ ID NO: 16-22. 
     In some embodiments, the dehydrogenase is an aldehyde dehydrogenase classified, for example, under EC 1.2.1.—such as EC 1.2.1.3. 
     In some embodiments, the mutase is a lysine 2,3-aminomutase classified, for example, under EC 5.4.3.2 such as SEQ ID NO: 26. 
     In some embodiments, the ammonia lyase is a 3-butyryl-CoA ammonia lyase classified, for example, under EC 4.3.1.14 such as SEQ ID NO: 23. 
     Enzymes Generating the Terminal Carboxyl Groups in the Biosynthesis of C6 Building Blocks 
     As depicted in  FIG. 1 ,  FIG. 2 , and  FIG. 3 , a terminal carboxyl group can be enzymatically formed using an aldehyde dehydrogenase, a thioesterase, a CoA-transferase, or a CoA-ligase. 
     In some embodiments, the first terminal carboxyl group leading to the synthesis of adipic acid is enzymatically formed by an aldehyde dehydrogenase classified, for example, under EC 1.2.1.3 (Guerrillot &amp; Vandecasteele, Eur. J. Biochem., 1977, 81, 185-192). See, e.g.,  FIG. 3 . 
     In some embodiments, the second terminal carboxyl group leading to the synthesis of a C6 building block is enzymatically formed by an acyl-CoA hydrolase or thioesterase classified under EC 3.1.2.-, such as the gene product of YciA, tesB, Acot13, SEQ ID NO: 1 or SEQ ID NO: 2 (see, for example, Cantu et al., Protein Science, 2010, 19, 1281-1295; Zhuang et al., Biochemistry, 2008, 47(9), 2789-2796; or Naggert et al., Journal of Biological Chemistry, 1991, 266(17), 11044-11050, Jing et al., BMC Biochemistry, 2011, 12, 44), See, e.g.,  FIG. 3 . 
     In some embodiments, the second terminal carboxyl group leading to the synthesis of a C6 building block is enzymatically formed by a CoA-transferase such as a glutaeonate CoA-transferase classified, for example, under EC 2.8.3.12. See, e.g.,  FIG. 3 . 
     In some embodiments, the second terminal carboxyl group leading to the synthesis of a C6 building block is enzymatically formed by a reversible CoA-ligase such as succinate CoA-transferase classified under EC 6.2.1.5. See, e.g.,  FIG. 3 . 
     In some embodiments, the second terminal carboxyl group leading to the synthesis of adipic acid is enzymatically formed by an aldehyde dehydrogenase classified, for example, under EC 1.2.1.63, such as the gene product of ChnE (Iwaki et al., Appl. Environ. Microbial., 1999, 65(11), 5158-5162). See,  FIG. 3 . 
     Enzymes Generating the Terminal Amine Groups in the Biosynthesis of C6 Building Blocks 
     As depicted in  FIG. 5 ,  FIG. 6 , and  FIG. 7  a terminal amine group can be enzymatically formed using a ω-transaminase. 
     In some embodiments, a terminal amine group is enzymatically formed by a ω-transaminase classified, for example, under EC 2.6.1.-, e.g., EC 2.6.1.18, EC 2.6.1.19, EC 2.6.1.29, EC 2.6.1.48, or EC 2.6.1.82 such as that obtained from  Chromobacterium violaceum  (Genbank Accession No. AAQ59697.1),  Pseudomonas aeruginosa  (Genbank Accession No. AAG08191.1),  Pseudomonas syringae  (Genbank Accession No. AAY39893.1),  Rhodobacter sphaeroides  (Genbank Accession No, ABA81135.1),  Vibrio fluvialis  (Genbank Accession No. AEA39183.1),  Streptomyces griseus,  or  Clostridium viride.  See,  FIG. 3 . 
     An additional ω-transaminase that can be used in the methods and hosts described herein is from  Escherichia coli  (Genbank Accession No. AAA57874.1). Some of the ω-transaminases classified, for example, under EC 2.6.1.29 or EC 2.6.1.82 are diamine ω-transaminases. 
     In some embodiments, the first terminal amine group leading to the synthesis of 6-aminohexanoic acid is enzymatically formed by a ω-transaminase classified under EC 2.6.1.18, such as that obtained from  Vibrio fluvialis  or  Chromobacterium violaceum,  EC 2.6.1.19, such as that obtained from  Streptomyces griseus,  or EC 2.6.1.48, such as that obtained from  Clostridium viride.    
     The reversible ω-transaminase from  Chromobacterium violaceum  has demonstrated analogous activity accepting 6-aminohexanoic acid as amino donor, thus forming the first terminal amine group in adipate seminaldehyde (Kaulmann et al., Enzyme and Microbial Technology, 2007, 41, 628-637). 
     The reversible 4-aminobutyryl: 2-oxoglutarate transaminase from  Streptomyces griseus  has demonstrated analogous activity for the conversion of 6-aminohexanoic acid to adipate semialdehyde (Yonaha et al., Eur. J. Biochem., 1985, 146, 101 - 106). 
     The reversible 5-aminovalerate transaminase from  Clostridium viride  has demonstrated analogous activity for the conversion of 6-aminohexanoic acid to adipate semialdehyde (Barker et al., The Journal of Biological Chemistry, 1987, 262(19), 8994-9003). 
     In some embodiments, the second terminal amine group leading to the synthesis of hexamethylenediamine is enzymatically formed by a transaminase classified under EC 2.6.1.29 or classified under EC 2.6.1.82, such as the gene product of YgjG. 
     The gene product of ygjG accepts a broad range of diamine carbon chain length substrates, such as putrescine, cadaverine and spermidine (Samsonova et al., BMC Microbiology, 2003, 3:2). 
     The diamine transaminase from  E. coli  strain B has demonstrated activity for 1,6 diaminohexane (Kim, The Journal of Chemistry, 1963, 239(3), 783-786) 
     Enzymes Generating the Terminal Hydroxyl Groups in the Biosynthesis of C6 Building Blocks 
     As depicted in  FIG. 8 , the terminal hydroxyl group can be enzymatically forming using an alcohol dehydrogenase. 
     In some embodiments, the first terminal hydroxyl group leading to the synthesis of 1,6 hexanediol is enzymatically formed by an alcohol dehydrogenase classified, for example, under EC 1,1.1.2 such as the gene product of YMR318C or an alcohol dehydrogenase classified, for example, under EC 1.1.1.258 such as the gene product of ChnI). 
     In some embodiments, the second terminal hydroxyl group leading to the synthesis of 1,6 hexanediol is enzymatically formed by an alcohol dehydrogenase classified under EC 1.1.1.- (e.g., 1, 2, 21, or 184). 
     Biochemical Pathways 
     Pathways to (S) 2-Aminopimelate and (R) 2-Aminopimelate as Precursor Leading to Central Precursors to C6 Building Blocks 
     In some embodiments, (S) 2-aminopimelate is synthesized from the central metabolite, meso-2,6-diaminopimelate, by conversion of meso-2,6-diaminopimelate to (S)-2-amino-6-oxopimelate by a diaminopimelate dehydrogenase (classified for example under EC 1.4.1.16); followed by conversion of (S)-2-amino-6-oxopimelate to (S,R) 2-amino-6-hydroxypimelate by a (R)-2-hydroxylsocaproate dehydrogenase (classified for example under EC 1.1.1.337) such as the gene product of LdhA or a (R) 2-hydroxyglutarate dehydrogenase such as the gene product of HgdH; followed by conversion of (S,R) 2-amino-6-hydroxypimelate to (R,S) 2-hydroxy-6-aminopimeloyl-CoA by a glutaconate CoA-transferase (classified, for example, under EC 2.8.3.12) such as the gene product of GctAB; followed by conversion of (R,S) 2-hydroxy-6-aminopimeloyl-CoA to (S) 6-amino-2,3-dehydropimeloyl-CoA by a 2-hydroxylsocaproyl-CoA dehydratase such as SEQ ID NO: 28 activated SEQ ID NO: 27 or (R)-2-hydroxyglutryl-CoA dehydratase such as SEQ ID NO: 25 activated by SEQ ID NO: 24; followed by conversion of (S) 6-amino-2,3-dehydropimeloyl-CoA to (S) 6-amino-2,3-dehydropimelate by a glutaconate CoA-transferase (classified, for example, under EC 2.8.3.12); followed by conversion to (S) 2-amino-7-oxohept-6-enoate by a carboxylate reductase classified, for example, under EC 1.2.99.6) such as the gene product of car &amp; npt, GriC &amp; GriD or a carboxylate reductase such as SEQ ID NO: 5, 7; followed by conversion to (S) 2-amino-7-oxoheptanoate by an enoate reductase (classified, for example, under EC 1.3.1.31 or EC 1.6.99.1) such as the gene product of SEQ ID NO: 16-22; followed by conversion to (S) 2-aminopimelate by an aldehyde dehydrogenase (classified, for example, under EC 1.2.1.3). See  FIG. 1 . 
     In some embodiments, (S)-2-amino-6-oxopimelate in  FIG. 1  is substituted with the central precursor N-Acetyl-L-2-amino-6-oxopimelate. 
     In some embodiments, (S)-2-amino-6-oxopimelate in  FIG. 1  is substituted with the central precursor N-Succinyl-2-L-amino-6-oxoheptanedioate. 
     In some embodiments, (R) 2-aminopimelate is synthesized from the central metabolite, meso-2,6-diaminopimelate, by conversion of meso-2,6-diaminopimelate to (S,R) 3,6 diaminopimelate by a lysine 2,3-aminomutase (classified, for example, under EC 5.4.3.2) such SEQ ID NO: 26; followed by conversion of (S,R) 3,6 diaminopimelate to (S,R) 3,6 diaminopimeloyl-CoA by a succinate-CoA ligase (classified, for example, under EC 6.2.1.5); followed by conversion of (S,R) 3,6 diaminopimeloyl-CoA to (R) 6-amino-2,3-dehydropimelloyl-CoA by a 3-aminobutyl-CoA ammonia lyase (classified, for example, under EC 4.3.1.14) such as SEQ ID NO: 23; followed by the conversion of (R) 6-amino-2,3-dehydropimeloyl-CoA to (R) 6-amino-2,3-dehydropimelate by a thioesterase (classified, for example, under EC 3.1.2.-) such as SEQ ID NO: 1-2 or the gene product of YciA, tesB or acot13 or by a CoA-transferase (classified, for example, under EC 2.8.3.-) such as the gene product of thnH; followed by conversion to (R) 2-amino-7-oxohept-6-enoate by a carboxylate reductase (classified, for example, under EC 1.2.99.6) such as the gene product of car &amp; npt, GriC &amp; GriD or the carboxylate reductase SEQ ID NO: 5,7; followed by conversion to (R) 2-amino-7-oxoheptanoate by an enoate reductase (classified, for example, under EC 1.3.1.31) such as SEQ ID NO: 16-22; followed by conversion to (R) 2-aminopimelate by an aldehyde dehydrogenase (classified, for example, under EC 1.2.1.3). See  FIG. 2 . 
     Pathways using (S) 2-Aminopimelate or (R) 2-Aminopimelate as Central Precursor to Adipic Acid. 
     In some embodiments, adipic acid is synthesized from the central precursor (S) aminopimelate or (R) 2-aminopimelate by conversion of (S) 2-aminopimelate to 2-oxopimelate by an L-specific alpha-aminotransferase (classified under EC 2.6.1.—such as EC 2.6.1.39 or EC 2.6.1.42) such as the gene product of ilvE or by conversion of (R) 2-aminopimelate to 2-oxopimelate by a D-specific alpha-aminotransferase (classified under EC 2.6.1,—such as EC 2.6.1.21) such as the gene product of D-AAAT; followed by conversion of 2-oxopimelate to adipate semialdehyde by a branch-chain-2-oxoacid decarboxylase (classified, for example, under EC 4.1.1.—such as EC 4.1.1.43, EC 4.1.1.71, EC 4.1.1.72 or EC 4.1.1.74) such as SEQ ID NO: 34 or the gene product of kivD or kdca or an acetolactate synthase (classified, for example, under EC 2.2.1.6) such as the gene product of ilvB &amp; ilvN; followed by conversion of adipate semialdehyde to adipic acid by an aldehyde dehydrogenase (classified, for example, under EC 1.2.1.—such as EC 1.2.1.3, EC 1.2.1.16, EC 1.2.1.20, EC 1.2.1.63, EC 1.2.1.79) such as the gene product of ChnE, CpnE or ThnG. See  FIG. 3 . 
     In some embodiments, 2-oxopimelate obtained as described above is converted to adipyl-CoA by a dehydrogenase complex (classified, for example, under EC 1.2.4.2, EC 1.8.1.4, and EC 2.3.1.61); followed by conversion to adipic acid by a thioesterase (classified, for example, under EC 3.1.2,-) such as SEQ ID NO: 1-2 or the gene product of YciA, tesB or acot13 or by a glutaconate CoA-transferase (classified under, for example, EC 2.8.3.12) or a reversible succinate CoA-ligase (classified, for example, under EC 6.2.1.5). See  FIG. 3 . 
     Pathway using (R) 2-Aminopimelate or (S) 2-Aminopimelate as Central Precursor to 6-Aminohexanoate and ε-Caprolactam 
     In some embodiments, 6-aminohexanoic acid is synthesized from the central precursor (S) 2-aminopimelate, by conversion of (S) 2-aminopimelate to 6-aminohexanoic acid by a decarboxylase (classified, for example, under EC 4.1.1.—such as EC 4.1.1.15, EC 4.1.1.17, EC 4.1.1.18 or EC 4.1.1.19) such as SEQ ID NO: 29-32. See  FIG. 4 . 
     In some embodiments, 6-aminohexanoic acid is synthesized from the central precursor (R) 2-aminopimelate by conversion of (R) 2-aminopimelate to 6-aminohexanoic acid by a decarboxylase (classified, for example, under EC 4.1,1.—such as EC 4.1.1.20) such as SEQ ID NO: 33. See  FIG. 4 . 
     In some embodiments, c-caprolactam is synthesized from the central precursor hexanoic acid by conversion of 6-aminohexanoic acid to ε-caprolactam by a hydrolase (classified, for example, under EC 3.5.2,-). See  FIG. 4 . 
     In some embodiments, 6-aminohexanoic acid is synthesized from the central precursor (S) 2-aminopimelate or (R) 2-aminopimelate by conversion of (S) 2-aminopimelate to 2-oxopimelate by an L-specific alpha-aminotransferase (classified under EC 2.6.1.—such as EC 2.6.1.39 or EC 2.6.1.42) such as the gene product of ilvE or by conversion of (R) 2-aminopimelate to 2-oxopimelate by a D-specific alpha-aminotransferase (classified under EC 2.6.1.—such as EC 2.6.1.21) such as the gene product of D-AAAT; followed by conversion of 2-oxopimelate to adipate semialdehyde by a branch-chain-2-oxoacid decarboxylase (classified, for example, under EC 4.1.1.—such as EC 4.1.1.43, EC 4.1.1.71, EC 4.1.1.72 or EC 4.1.1.74) such as SEQ ID NO: 34 or the gene product of klvD or kdca or an acetolactate synthase (classified, for example, under EC 2.2.1.6) such as the gene product of ilvB &amp; ilvN; followed by conversion of adipate semialdehyde to 6-aminohexanoic acid by an ω-transaminase (classified, for example, under EC 2.6.1—such as EC 2.6.1.18, EC 2.6.1.19, or EC 2.6.1.48, EC 2.6.1.29, or EC 2.6.1.82) such as SEQ ID NO 8-13. See  FIGS. 1, 2 and 4 . 
     Pathway using 6-Aminohexanoic Acid as Central Precursor to Hexamethylenediamine 
     In some embodiments, hexamethylenediamine is synthesized from the central precursor, 6-aminohexanoic acid, by conversion of 6-aminohexanoic acid to 6-aminohexanal by a carboxylate reductase (classified under, for example, EC 1.2.99.6) such as the gene product of car alongside the gene product of npt or the gene product of GriC &amp; GriD (Suzuki et al., J. Antibiot., 2007, 60(6), 380 387); followed by conversion of 6-aminohexanal to hexamethylenediamine by a ω-transaminase (classified, for example, under EC 2.6.1.18, EC 2.6.1.19, 2.6.1.48, EC 2.6.1.29, or EC 2.6.1.82) such as SEQ ID NO: 8-13. See  FIG. 5 . 
     The carboxylate reductase encoded by the gene product of car and enhancer npt has broad substrate specificity, including terminal difunctional C4 and C5 carboxylic acids (Venkitasubramanian et al., Enzyme and Microbial Technology, 2008, 42, 130-137). 
     In some embodiments, 6-aminohexanoic acid is synthesized from the central precursor (S) 2-aminopimelate or (R) 2-aminopimelate by conversion of (S) 2-aminopimelate to 2-oxopimelate by an L-specific alpha-aminotransferase (classified under EC 2.6.1.—such as EC 2.6.1.39 or EC 2.6.1.42) such as the gene product of ilvE or by conversion of (R) 2-aminopimelate to 2-oxopimelate by a D-specific alpha-aminotransferase (classified under EC 2.6.1.—such as EC 2.6.1.21) such as the gene product of D-AAAT; followed by conversion of 2-oxopimelate to adipate semialdehyde by a branch-chain-2-oxoacid decarboxylase (classified, for example, under EC 4.1.1.—such as EC 4.1.1.43, EC 4.1.1.71, EC 4.1.1.72 or EC 4.1.1.74) such as SEQ ID NO: 34 or the gene product of kivD or kdca or an acetolactate synthase (classified, for example, under EC 2.2.1.6) such as the gene product of ilvB &amp; ilvN; followed by conversion of adipate semialdehyde to 1,6 hexanedial by a carboxylate reductase (classified, for example, under EC 1.2.99.6) such as SEQ ID NO: 7; followed by conversion of 1,6-hexanedial to 6-aminohexanal by an ω-transaminase (classified, for example, under EC 2.6.1.—such as EC 2.6.1.18, EC 2.6.1.19, or EC 2.6.1.48, EC 2.6.1.29, or EC 2.6.1.82); followed by conversion of 6-aminohexanal to hexamethylenediamine by a ω-transaminase (classified, for example, under EC 2.6.1.—such as EC 2.6.1.18, EC 2.6.1.19, or EC 2.6.1.48, EC 2.6.1.29, or EC 2.6.1.82) such as SEQ ID NO: 8-13. See  FIG. 1, 2 and 5 . 
     In some embodiments, hexamethylenediamine is synthesized from the central precursor, 6-aminohexanoic acid, by conversion of 6-aminohexanoic acid to N6-acetyl-6-aminohexanoic acid by a N-acetyltransferase classified, for example, under EC 2.3.1.32; followed by conversion of N6-acetyl-6-aminohexanoic acid to N6-acetyl-6-aminohexanal by a carboxylate reductase classified, for example, under EC 1.2.99.6 such as SEQ ID NO: 5-7 or the gene product of GriC &amp; GriD (Suzuki et al., J. Antibiot., 2007, 60(6), 380-387); followed by conversion of N6-acetyl-6-aminohexanal to N6-acetyl-1,6-diaminohexane by a ω-transaminase (classified, for example, under EC 2.6.1.18, EC 2.6.1.19, EC 2.6.1.29, EC 2.6.1.48 or EC 2.6.1.82) such as SEQ ID NO: 8-13; followed by conversion of N6-acetyl-1,6-diaminohexane to hexamethylenediamine by a deacetylase (classified, for example, under EC 3.5.1.17). See  FIG. 6 . 
     Pathway using 6-Hydroxyhexanoic Acid as Central Precursor to Hexamethylenediamine 
     In some embodiments, hexamethylenediamine is synthesized from the central precursor, 6-hydroxyhexanoic acid, by conversion of 6-hydroxyhexanoic acid to 6-hydroxyhexanal by a carboxylate reductase (classified, for example, under EC 1.2.99.6) such as SEQ ID NO: 3-7 or the gene product of car alongside the gene product of npt or the gene product of GriC &amp; GriD (Suzuki et al., J. Antibiot., 2007, 60(6), 380 387); followed by conversion of 6-hydroxyhexanal to 1-amino-6-hydroxy-hexane by a transaminase (classified, for example, under EC 2.6.1.18, EC 2.6.1.19, EC 2.6.1.29, EC 2.6.1.48 or EC 2.6.1.82) such as SEQ ID NO: 8-13; followed by conversion of 1-amino-6-hydroxy-hexane to 6-aminohexanal by an alcohol dehydrogenase classified, for example, under EC 1.1.1.1 encoded by YMR318C, YqhD or the protein having GenBank Accession No. CAA81612.1 (from  Geobacillus stearothermophilus ); followed by conversion of 6-aminohexanal to hexamethylenediamine by a ω-transaminase (classified, for example, under EC 2.6.1.18, EC 2.6.1.19, 2.6.1.48, EC 2.6.1.29, or EC 2.6.1.82.) such as SEQ ID NO: 8-13. See  FIG. 7 . 
     Pathways using (R) 2-Aminopimelate or (S) 2-Aminopimelate as Central Precursor to 1,6-Hexanediol 
     In some embodiments, adipic acid is synthesized from the central precursor (S) 2-aminopimelate or (R) 2-aminopimelate by conversion of (S) 2-aminopimelate to 2-oxopimelate by an L-specific alpha-aminotransferase (classified under EC 2.6.1.—such as EC 2.6.1.39 or EC 2.6.1.42) such as the gene product of ilvE or by conversion of (R) 2-aminopimelate to 2-oxopimelate by D-specific alpha-aminotransferase (classified under EC 2.6.1.—such as EC 2.6.1.21) such as the gene product of D-AAAT; followed by conversion of 2-oxopimelate to adipate semialdehyde by a branch-chain-2-oxoacid decarboxylase (classified, for example, under EC 4.1.1.—such as EC 4.1.1.43, EC 4.1.1.71, EC 4.1.1.72 or EC 4.1.1.74) such as SEQ ID NO: 34 or the gene product of kivD or kdca or an acetolactate synthase (classified, for example, under EC 2.2.1.6) such as the gene product of ilvB &amp; ilbN; followed by conversion of adipate semialdehyde to 6-hydroxyhexanoic acid by an alcohol dehydrogenase (classified, for example, under EC 1.1.1.—such as EC 1.1.1.2 or EC 1.1.1.258) such as encoded by YMR318C, ChnD, or gabD. See,  FIG. 8 . 
     In some embodiments, 1,6 hexanediol is synthesized from the central precursor 6-hydroxyhexanoic acid by conversion of 6-hydroxyhexanoic acid to 6-hydroxyhexanal by a carboxylate reductase (classified, for example, under EC 1.2.99.6) such as SEQ ID NO: 3-7; followed by conversion of 6-hydroxyhexanal to 1,6 hexanediol by an alcohol dehydrogenase (classified, for example, under EC 1.1.1.- such as EC 1.1.1.1, :EC 1.1.1.2, EC 1.1.1.21, or EC 1.1.1.184) such as encoded by YMR318C, YqhD or CAA81612.1 (Liu et al., Microbiology, 2009, 155, 2078-2085). 
     Cultivation Strategy 
     In some embodiments, one or more C6 building blocks are biosynthesized in a recombinant host using anaerobic, aerobic or micro-aerobic cultivation conditions. In some embodiments, the cultivation strategy entails nutrient limitation such as nitrogen, phosphate or oxygen limitation. 
     In some embodiments in which (S) 2-aminopimelate is produced as a central precursor, a cultivation strategy entails either achieving an anaerobic or micro-aerobic cultivation condition. 
     In some embodiments in which (R) 2-aminopimelate is produced as a central precursor, a cultivation strategy entails either achieving an anaerobic, aerobic or micro-aerobic cultivation condition. 
     In some embodiments, a cell retention strategy using, for example, ceramic hollow fiber membranes is employed to achieve and maintain a high cell density during either fed-batch or continuous fermentation. 
     In some embodiments, the cultivation strategy entails culturing under conditions of nutrient limitation either via nitrogen, phosphate or oxygen limitation. 
     In some embodiments, the principal carbon source fed to the fermentation in the synthesis of one or more C6 building blocks can derive from biological or non-biological feed stocks. 
     In some embodiments, the biological feedstock can be or can derive from, monosaccharides, disaccharides, lignocellulose, hemicellulose, cellulose, lignin, levulinic acid and formic acid, triglycerides, glycerol, fatty acids, agricultural waste, condensed distillers&#39; solubles, or municipal waste. 
     The efficient catabolism of crude glycerol stemming from the production of biodiesel has been demonstrated in several microorganisms such as  Escherichia coli, Cupriavidus necator, Pseudomonas oleavorans, Pseudomonas putida  and  Yarrowia lipolytica  (Lee et al.,  Appl. Biochem. Biotechnol.,  2012, 166:1801-1813; Yang et al.,  Biotechnology for Biofuels,  2012, 5:13; Meijnen et al.  Appl. Microhiol. Biotechnol.,  2011, 90:885 893). 
     The efficient catabolism of lignocellulosic-derived levulinic acid has been o demonstrated in several organisms such as  Cupriavidus necator  and  Pseudomonas putida  in the synthesis of 3-hydroxyvalerate via the precursor propanoyl-CoA (Jaremko and Yu, 2011, supra; Martin and Prather,  J. Biotechnol.,  2009, 139:61 67). 
     The efficient catabolism of lignin-derived aromatic compounds such as benzoate analogues has been demonstrated in several microorganisms such as  Pseudomonas putida, Cupriavidus necator  (Bugg et al.,  Current Opinion in Biotechnology,  2011, 22, 394-400; Pérez-Pantoja et al.,  FEMS Microbiol. Rev.,  2008, 32, 736-794). 
     The efficient utilization of agricultural waste, such as olive mill waste water has been demonstrated in several microorganisms, including  Yarrowia lipolytica  (Papanikolaou et al.,  Bioresour. Technol.,  2008, 99(7):2419-2428). 
     The efficient utilization of fermentable sugars such as monosaccharides and disaccharides derived from cellulosic, hemicellulosic, cane and beet molasses, cassava, corn and other agricultural sources has been demonstrated for several microorganism such as  Escherichia coli, Corynebacterium glutamicum  and  Lactobacillus delbrueckii  and  Lactococcus lactis  (see, e.g., Hermann et al,  J. Biotechnol.,  2003, 104:155-172; Wee et al.,  Food Technol. Biotechnol.,  2006, 44(2):163-172; Ohashi et al.,  J. Bioscience and Bioengineering,  1999, 87(5):647-654). 
     The efficient utilization of furfural, derived from a variety of agricultural lignocellulosic sources, has been demonstrated for  Cupriavidus necator  (Li et al.,  Biodegradation,  2011, 22:1215-1225). 
     In some embodiments, the non-biological feedstock can be or can derive from natural gas, syngas, CO 2 /H 2 , methanol, ethanol, benzoate, non-volatile residue (NVR) or a caustic wash waste stream from cyclohexane oxidation processes, or terephthalic acid/isophthalic acid mixture waste streams. 
     The efficient catabolism of methanol has been demonstrated for the methylotrophic yeast  Pichia pastoris.    
     The efficient catabolism of ethanol has been demonstrated for  Clostridium kluyveri  (Seedorf et al.,  Proc. Natl. Acad. Sci. USA,  2008, 105(6) 2128-2133). 
     The efficient catabolism of CO 2  and H 2 , which may be derived from natural gas and other chemical and petrochemical sources, has been demonstrated for  Cupriavidus necator  (Prybylski et al.,  Energy, Sustainability and Society,  2012, 2:11). 
     The efficient catabolism of syngas has been demonstrated for numerous microorganisms, such as  Clostridium ljungdahlii  and  Clostridium autoethanogenum  (Kopke et al.,  Applied and Environmental Microbiology,  2011, 77(15):5467-5475). 
     The efficient catabolism of the non-volatile residue waste stream from cyclohexane processes has been demonstrated for numerous microorganisms, such as  Delftia acidovorans  and  Cupriavidus necator  (Ramsay et al.,  Applied and Environmental Microbiology,  1986, 52(1):152-156). 
     In some embodiments, the host microorganism is a prokaryote. For example, the prokaryote can be a bacterium from the genus  Escherichia  such as  Escherichia coli;  from the genus  Clostridia  such as  Clostridium ljungdahlii, Clostridium autoethanogenum  or  Clostridium ktuyveri;  from the genus  Corynebacteria  such as  Corynebacterium glutamicum;  from the genus  Cupriavidus  such as  Cupriavidus necator  or  Cupriavidus metallidurans;  from the genus  Pseudomonas  such as  Pseudomonas fluorescens, Pseudomonas putida  or  Pseudomonas oleavorans;  from the genus  Delftia  such as  Delftia acidovorans;  from the genus  Bacillus  such as  Bacillus subtillis;  from the genus  Lactobacillus  such as  Lactobacillus delbrueckii;  or from the genus  Lactococcus  such as  Lactococcus lactis.  Such prokaryotes also can be a source of genes to construct recombinant host cells described herein that are capable of producing one or more C6 building blocks. 
     In some embodiments, the host microorganism is a eukaryote. For example, the eukaryote can be a filamentous fungus, e.g., one from the genus  Aspergillus  such as  Aspergillus niger.  Alternatively, the eukaryote can be a yeast, e.g., one from the genus  Saccharomyces  such as  Saccharomyces cerevisiae;  from the genus  Pichia  such as  Pichia pastoris;  or from the genus  Yarrowia  such as  Yarrowia lipolytica;  from the genus  Issaichenkia  such as  Issathenkia orientalis;  from the genus  Debaryomyces  such as  Debaryomyces hansenii ; from the genus  Arxula  such as  Arxsula adenoinivorans;  or from the genus  Kluyveromyces  such as  Kluyveromyces lactis . Such eukaryotes also can be a source of genes to construct recombinant host cells described herein that are capable of o producing one or more C6 building blocks. 
     Metabolic Engineering 
     The present document provides methods involving less than all the steps described for all the above pathways. Such methods can involve, for example, one, two, three, four, five, six, seven, eight, nine, ten, or more of such steps. Where less than all the steps are included in such a method, the first step can be any one of the steps listed. 
     Furthermore, recombinant hosts described herein can include any combination of the above enzymes such that one or more of the steps, e.g., one, two, three, four, five, six, seven, eight, nine, ten, or more of such steps, can be performed within a recombinant host. This document provides host cells of any of the genera and species listed and genetically engineered to express one or more (e.g., two, three, four, five, six, seven, eight, nine, 10, 11, 12 or more) recombinant forms of any of the enzymes recited in the document. Thus, for example, the host cells can contain exogenous nucleic acids encoding enzymes catalyzing one or more of the steps of any of the pathways described herein. 
     In addition, this document recognizes that where enzymes have been described as accepting CoA-activated substrates, analogous enzyme activities associated with [acp]-bound substrates exist that are not necessarily in the same enzyme class. 
     Also, this document recognizes that where enzymes have been described accepting (R)-enantiomers of substrate, analogous enzyme activities associated with (S)-enantiomer substrates exist that are not necessarily in the same enzyme class. 
     This document also recognizes that where an enzyme is shown to accept a particular co-factor, such as NADPH, or co-substrate, such as acetyl-CoA, many enzymes are promiscuous in terms of accepting a number of different co-factors or co-substrates in catalyzing a particular enzyme activity. Also, this document recognizes that where enzymes have high specificity for e.g., a particular co-factor such as NADH, an enzyme with similar or identical activity that has high specificity for the co-factor NADPH may be in a different enzyme class. 
     In some embodiments, the enzymes in the pathways outlined in section 4.5 are the result of enzyme engineering via non-direct or rational enzyme design approaches with aims of improving activity, improving specificity, reducing feedback inhibition, reducing repression, improving enzyme solubility, changing stereo-specificity, or changing co-factor specificity. 
     In some embodiments, the enzymes in the pathways outlined in section 4.5 are gene dosed (i.e., overexpressed by having a plurality of copies of the gene in the host organism), into the resulting genetically modified organism via episomal or chromosomal integration approaches. 
     In some embodiments, genome-scale system biology techniques such as Flux Balance Analysis are utilized to devise genome scale attenuation or knockout strategies for directing carbon flux to a C6 building block. 
     Attenuation strategies include, but are not limited to; the use of transposons, homologous recombination (double cross-over approach), mutagenesis, enzyme inhibitors and RNA interference (RNAi). 
     In some embodiments, fluxomic, metabolomic and transcriptomal data are utilized to inform or support genome-scale system biology techniques, thereby devising genome scale attenuation or knockout strategies in directing carbon flux to a C6 building block. 
     In some embodiments, the host microorganism&#39;s tolerance to high concentrations of a C6 building block is improved through continuous cultivation in a selective environment. 
     In some embodiments, the host microorganism&#39;s biochemical network is attenuated or augmented to (1) ensure the intracellular availability of oxaloacetate, (2) create an NADPH imbalance that may only be balanced via the formation of one or more C6 building blocks, (3) prevent degradation of central metabolites, central precursors leading to and including C6 building blocks and (4) ensure efficient efflux from the cell. 
     In some embodiments, the anaplerotic reactions from glycolysis leading into the Krebs cycle to augment oxaloacetate are overexpressed in the host. 
     In some embodiments where the host microorganism uses the lysine biosynthesis pathway via meso-2,6-diaminopimelate, the genes encoding the synthesis of lysine from 2-oxoglutarate via 2-oxoadipate are gene dosed into the host organisms. 
     In some embodiments where the host microorganism uses the lysine biosynthesis pathway via 2-oxoadipate, the genes encoding the synthesis of lysine via meso-2,6-diaminopimelate are gene dosed into the host organisms. 
     In some embodiments, where pathways require excess NADPH co-factor in the synthesis of a C6 building block, a puridine nucleotide transhydrogenase gene such as UdhA is overexpressed in the host organisms (Brigham et al.,  Advanced Biofuels and Bioproducts,  2012, Chapter 39, 1065-1090), 
     In some embodiments, where pathways require excess NADPH co-factor in the synthesis of a C6 building block, a glyceraldehyde-3P-dehydrogenase gene such as GapN is overexpressed in the host organisms (Brigham et al., 2012, supra). 
     In some embodiments, where pathways require excess NADPH co-factor in the synthesis of a C6 building block, a gene encoding a malic enzyme, such as mseA or maeB, is overexpressed in the host (Brigham et al., 2012, supra). 
     In some embodiments, where pathways require excess NADPH co-factor in the synthesis of a C6 building block, a gene encoding a glucose-6-phosphate dehydrogenase such as overexpressed in the host (Lim et al.  Journal of Bioscience and Bioengineering,  2002, 93(6), 543-549). 
     In some embodiments, where pathways require excess NADPH co-factor in the synthesis of a C6 building block, a gene encoding a fructose 1,6 diphosphatase such as) fbp is overexpressed in the host (Becker et al.,  Journal of Biotechnology,  2007, 132, 99-109). 
     In some embodiments, where pathways require excess NADPB co-factor in the synthesis of a C5 building block, an endogenous gene encoding a triose phosphate isomerase (EC 5.3.1.1) is attenuated. 
     In some embodiments, where pathways require excess NADPH co-factor in the synthesis of a C6 building block, an endogenous gene encoding a glucose dehydrogenase o such as the gene product of gdh is overexpressed in the host (Satoh et al., Journal of Bioscience and Bioengineering, 2003, 95(4), 335-341). 
     In some embodiments, endogenous genes encoding enzymes facilitating the conversion of NADPH to NADH are attenuated, such as the NADH generation cycle that may be generated via inter-conversion of a glutamate dehydrogenase in EC 1.4.1.2 (NADH-specific) and EC 1.4.1.4 (NADPH-specific). 
     In some embodiments, an endogenous gene encoding a glutamate dehydrogenase (EC 1.4.1.3) that can utilize both NADH and NADPH as co-factors is attenuated. 
     In some embodiments using hosts that naturally accumulate polyhydroxyalkanoates, one or more endogenous genes encoding polymer synthase enzymes can be attenuated in the host strain. 
     In some embodiments, β-oxidation enzymes degrading central metabolites and central precursors leading to and including C6 building blocks are attenuated. 
     In some embodiments, enzymes activating C6 building blocks via Coenzyme A esterification such as CoA-ligases are attenuated. 
     In some embodiments, the efflux of a C6 building block across the cell membrane to the extracellular media is enhanced or amplified by genetically engineering structural modifications to the cell membrane or increasing any associated transporter activity for a C6 building block. 
     Producing C6 Building Blocks Using a Recombinant Host 
     Typically, one or more C6 building blocks can be produced by providing a host microorganism and culturing the provided microorganism with a culture medium containing a suitable carbon source as described above. In general, the culture media and/or culture conditions can be such that the microorganisms grow to an adequate density and produce a C6 building block efficiently. For large-scale production processes, any method can be used such as those described elsewhere (Manual of Industrial Microbiology and Biotechnology, 2 nd  Edition, Editors: A. L. Demain and J. E. Davies, ASM Press; and Principles of Fermentation Technology, P. F. Stanbury and A. Whitaker, Pergamon), Briefly, a large tank (e.g., a 100 gallon, 200 gallon, 500 gallon, or more tank) containing an appropriate culture medium is inoculated with a particular microorganism. After inoculation, the microorganism is incubated to allow biomass to be produced. Once a desired biomass is reached, the broth containing the microorganisms can be transferred to a second tank. This second tank can be any size. For example, the second tank can be larger, smaller, or the same size as the first tank. Typically, the second tank is larger than the first such that additional culture medium can be added to the broth from the first tank. In addition, the culture medium within this second tank can be the same as, or different from, that used in the first tank. 
     Once transferred, the microorganisms can be incubated to allow for the production of a C6 building block. Once produced, any method can be used to isolate C6 building blocks. For example, C6 building blocks can be recovered selectively from the fermentation broth via adsorption processes. In the case of adipic acid and 6-aminoheptanoic acid, the resulting eluate can be further concentrated via evaporation, crystallized via evaporative and/or cooling crystallization, and the crystals recovered via centrifugation. In the case of hexamethylenediamine and 1,6-hexanediol, distillation may be employed to achieve the desired product purity. 
     EXAMPLES 
     Example 1 
     Enzyme Activity of ω-Transaminase using Adipate Semialdehyde as Substrate and Forming 6-Aminohexanoate 
     A nucleotide sequence encoding a His-tag was added to the genes from  Chromobacterium violaceum, Pseudomonas aeruginosa, Pseudomonas syringae, Rhodobacter sphaeroides,  and  Vibrio Fluvialis  encoding the ω-transaminases of SEQ ID NOs: 8, 9, 10, 11 and 13, respectively (see  FIG. 20E  and  FIG. 20F ) such that N-terminal HIS tagged ω-transaminases could be produced. Each of the resulting modified genes was cloned into a pET21a expression vector under control of the T7 promoter and each expression vector was transformed into a BL21[DE3]  E. coli  host. The resulting recombinant  E. coli  strains were cultivated at 37° C. in a 250 mL shake flask culture containing 50 mL LB media and antibiotic selection pressure, with shaking at 230 rpm. Each culture was induced overnight at 16° C, using 1 mM IPTG. 
     The pellet from each induced shake flask culture was harvested via centrifugation. Each pellet was resuspended and lysed via sonication. The cell debris was separated from the supernatant via centrifugation and the cell free extract was used immediately in enzyme activity assays. 
     Enzyme activity assays in the reverse direction (i.e., 6-aminohexanoate to adipate semialdehyde) were performed in a buffer composed of a final concentration of 50 mM HEPES buffer (pH=7.5), 10 mM 6-aminohexanoate, 10 mM pyruvate and 100 μM pyridoxyl 5′ phosphate. Each enzyme activity assay reaction was initiated by adding cell free extract of the o-transaminase gene product or the empty vector control to the assay buffer containing the 6-aminohexanoate and incubated at 25° C. for 24 h, with shaking at 250 rpm. The formation of L-alanine from pyruvate was quantified via RP-HPLC. 
     Each enzyme only control without 6-aminohexanoate demonstrated low base line conversion of pyruvate to L-alanine. See  FIG. 14 . The gene product of SEQ ID NO 8, SEQ ID NO 10, SEQ ID NO 11 and SEQ ID NO 13 accepted 6-aminohexanote as substrate as confirmed against the empty vector control. See  FIG. 15 . 
     Enzyme activity in the forward direction (i.e., adipate semialdehyde to 6-aminohexanoate) was confirmed for the transaminases of SEQ ID NO 8, SEQ ID NO 9, SEQ ID NO 10, SEQ ID NO 11 and SEQ ID NO 13. Enzyme activity assays were performed in a buffer composed of a final concentration of 50 mM HEPES buffer (pH=7.5), 10 mM. adipate semialdehyde, 10 mM L-alanine and 100 μM pyridoxyl 5′ phosphate. Each enzyme activity assay reaction was initiated by adding a cell free extract of the co-transaminase gene product or the empty vector control to the assay butler containing the adipate semialdehyde and incubated at 25° C. for 4 h, with shaking at 250 rpm. The formation of pyruvate was quantified via RP-HPLC. 
     The gene product of SEQ ID NO 8, SEQ ID NO 9, SEQ ID NO 10, SEQ ID NO 11 and SEQ ID NO 13 accepted adipate semialdehyde as substrate as confirmed against the empty vector control. See  FIG. 16 . The reversibility of the ω-transaminase activity was confirmed, demonstrating that the ω-transaminases of SEQ NO 8, SEQ ID NO 9, SEQ ID NO 10, SEQ ID NO 11 and. SEQ ID NO 13 accepted adipate semialdehyde as substrate and synthesized 6-aminohexanoate as a reaction product. 
     Example 2 
     Enzyme Activity of Carboxylate Reductase using 6-Hydroxyhexanoate as Substrate and Forming 6-Hydroxyhexanal 
     A nucleotide sequence encoding a His-tag was added to the genes from  Mycobacterium marinum, Mycobacterium smegmatis, Mycobacterium smegmatis, Segniliparus rugosus, Mycobacterium massiliense,  and  Segniliparus rotundus  that encode the carboxylate reductases of SEQ NOs: 3-7, respectively (see  FIGS. 20A-20E ) such that N-terminal HIS tagged carboxylate reductases could be produced. Each of the modified genes was cloned into a pET Duet expression vector alongside a sfp gene encoding a His-tagged phosphopantetheine transferase from  Bacillus subtilis,  both under control of the T7 promoter. Each expression vector was transformed into a BL21[DE3] E. coli  host. Each resulting recombinant  E. coli  strain was cultivated at 37° C. in a 250 mL shake flask culture containing 50 mL LB media and antibiotic selection pressure, with shaking at 230 rpm. Each culture was induced overnight at 37° C. using an auto-induction media. 
     The pellet from each induced shake flask culture was harvested via centrifugation. Each pellet was resuspended and lysed via sonication. The cell debris was separated from the supernatant via centrifugation. The carboxylate reductases and phosphopantetheine transferase were purified from the supernatant using Ni-affinity chromatography, diluted 10-fold into 50 mM HEPES buffer (pH=7.5) and concentrated via ultrafiltration. 
     Enzyme activity (i.e., 6-hydroxyhexanoate to 6-hydroxyhexanal) assays were performed in triplicate in a buffer composed of a final concentration of 50 mM HEPES buffer (pH=7.5), 2 mM 6-hydroxyhexanal, 10 mM MgCl 2 , 1 mM ATP, and 1 mM NADPH. Each enzyme activity assay reaction was initiated by adding purified carboxylate reductase and phosphopantetheine transferase or the empty vector control to the assay buffer containing the 6-hydroxyhexanoate and then incubated at room o temperature for 20 min. The consumption of NADPH was monitored by absorbance at 340 nm. Each enzyme only control without 6-hydroxyhexanoate demonstrated low base line consumption of NADPH. See  FIG. 9 . 
     The gene products of SEQ ID NO 3-7, enhanced by the gene product of sfp, accepted 6-hydroxyhexanoate as substrate as confirmed against the empty vector control (see  FIG. 11 ), and synthesized 6-hydroxyhexanal. 
     Example 3 
     Enzyme Activity of ω-Transaminase for 6-Aminohexanol, Forming 6-Oxoliexanol 
     A nucleotide sequence encoding an N-terminal His-tag was added to the  Chromobacterium violaceum, Pseudomonas aeruginosa, Pseudomonas syringae, Rhodobacter sphaeroides, Escherichia coli,  and  Vibrio fluvialis  genes encoding the ω-transaminases of SEQ ID NOs: 8-13, respectively (see  FIG. 20E  and  FIG. 20F ) such that N-terminal HIS tagged ω-transaminases could be produced. The modified genes were cloned into a pET21a expression vector under the T7 promoter. Each expression vector was transformed into a BL21.[DE3]  E. coli  host. Each resulting recombinant  E. coli  strain were cultivated at 37° C. in a 250 mL shake flask culture containing 50 mL LB media and antibiotic selection pressure, with shaking at 230 rpm. Each culture was induced overnight at 16° C. using 1 mM IPTG. 
     The pellet from each induced shake flask culture was harvested via centrifugation. Each pellet was resuspended and lysed via sonication. The cell debris was separated from the supernatant via centrifugation and the cell free extract was used immediately in enzyme activity assays. 
     Enzyme activity assays in the reverse direction (i.e., 6-aminohexanol to 6-oxohexanol) were performed in a buffer composed of a final concentration of 50 mM HEPES buffer (pH=7.5), 10 mM 6-aminohexanol, 10 mM pyruvate, and 100 nM pyridoxyl 5′ phosphate. Each enzyme activity assay reaction was initiated by adding cell free extract of the ω-transaminase gene product or the empty vector control to the assay buffer containing the 6-aminohexanol and then incubated at 25° C. for 4 h, with shaking at 250 rpm. The formation of L-alanine was quantified via RP-HPLC. 
     Each enzyme only control without 6-aminohexanol had low base line conversion of pyruvate to L-alanine. See  FIG. 14 . 
     The gene products of SEQ ID NO 8-13 accepted 6-aminohexanol as substrate as confirmed against the empty vector control (see  FIG. 19 ) and synthesized 6-oxohexanol as reaction product. Given the reversibility of the ω-transaminase activity (see Example 1), it can be concluded that the gene products of SEQ ID 8-13 accept 6-aminohexanol as substrate and form 6-oxohexanol. 
     Example 4 
     Enzyme Activity of ω-Transaminase using Hexamethylenediamine as Substrate and Forming 6-Aminohexanal 
     A nucleotide sequence encoding an N-terminal His-tag was added to the  Chromobacterium violaceum, Pseudomonas aeruginosa, Pseudomonas syringae, Rhodobacter sphaeroides, Escherichia coli , and  Vibrio fluvialis  genes encoding the ω-transaminases of SEQ ID NOs: 8-13, respectively (see  FIG. 20E  and  FIG. 20F ) such that N-terminal HIS tagged ω-transaminases could be produced. The modified genes were cloned into a pET21a expression vector under the T7 promoter. Each expression vector was transformed into a BL21.[DE3]  E. coli  host. Each resulting recombinant  E. coli  strain were cultivated at 37° C. in a 250 mL shake flask culture containing 50 mL LB media and antibiotic selection pressure, with shaking at 230 rpm. Each culture was induced overnight at 16° C. using 1 mM IPTG. 
     The pellet from each induced shake flask culture was harvested via centrifugation. Each pellet was resuspended and lysed via sonication. The cell debris was separated from the supernatant via centrifugation and the cell free extract was used immediately in enzyme activity assays. 
     Enzyme activity assays in the reverse direction (i.e., hexamethylenediamine to 6-aminohexanal) were performed in a buffer composed of a final concentration of 50 mM HEPES buffer (pH=7.5), 10 mM hexamethylenediamine, 10 mM pyruvate, and 100 μM pyridoxyl 5′ phosphate. Each enzyme activity assay reaction was initiated by adding cell free extract of the ω-transaminase gene product or the empty vector control to the assay buffer containing the hexamethylenediamine and then incubated at 25° C. for 4 h, with shaking at 250 rpm. The formation of L-alanine was quantified via RP-HPLC. 
     Each enzyme only control without hexamethylenediamine had low base line conversion of pyruvate to L-alanine. See  FIG. 14 . 
     The gene products of SEQ ID NO 8-13 accepted hexamethylenediamine as substrate as confirmed against the empty vector control (see  FIG. 17 ) and synthesized 6-aminohexanal as reaction product. Given the reversibility of the ω-transaminase activity (see Example 1), it can be concluded that the gene products of SEQ ID NOs: 8-13 accept 6-aminohexanal as substrate and form hexamethylenediamine. 
     Example 5 
     Enzyme Activity of Carboxylate Reductase for N6-Acetyl-6-Aminohexanoate, Forming N6-Acetyl-6-Aminohexanal 
     The activity of each of the N-terminal His-tagged carboxylate reductases of SEQ ID NOs: 5-7 (see Example 2, and  FIGS. 20C-20E ) for converting N6-acetyl-6-aminohexanoate to N6-acetyl-6-aminohexanal was assayed in triplicate in a buffer composed of a final concentration of 50 mM HEPES buffer (pH=7.5), 2 mM N6-acetyl-6-aminohexanoate, 10 mM MgCl 2 , 1 mM ATP, and 1 mM NADPH. The assays were initiated by adding purified carboxylate reductase and phasphopantetheine transferase or the empty vector control to the assay buffer containing the N6-acetyl-6-aminohexanoate then incubated at room temperature for 20 min. The consumption of NADPH was monitored by absorbance at 340 nm. Each enzyme only control without N6-acetyl-6-aminohexanoate demonstrated low base line consumption of NADPH. See  FIG. 9 . 
     The gene products of SEQ ID NO 5-7, enhanced by the gene product of accepted N6-acetyl-6-aminohexanoate as substrate as confirmed against the empty vector control (see  FIG. 12 ), and synthesized N6-acetyl-6-aminohexanal. 
     Example 6 
     Enzyme Activity of ω-Transaminase using N6-Acetyl-1,6-Diaminohexane, and Forming N6-Acetyl-6-Aminohexanal 
     The activity of the N-terminal His-tagged ω-transaminases of SEQ ID NOs: 8-13 (see Example 4, and  FIG. 20E  and  FIG. 20F ) for converting N6-acetyl-1,6-diaminohexane to N6-acetyl-6-aminohexanal was assayed using a buffer composed of a final concentration of 50 mM HEPES butler (pH=7.5), 10 mM. N6-acetyl-1,6-diaminohexane, 10 mM pyruvate and 100 μM pyridoxyl 5′ phosphate. Each enzyme activity assay reaction was initiated by adding a cell free extract of the co-transaminase or the empty vector control to the assay buffer containing the N6-acetyl-1,6-diaminohexane then incubated at 25° C. for 4 h, with shaking at 250 rpm. The formation of L-alanine was quantified via RP-HPLC. 
     Each enzyme only control without N6-acetyl-1,6-diaminohexane demonstrated low base line conversion of pyruvate to L-alanine. See  FIG. 14 . 
     The gene product of SEQ ID NO 8-13 accepted N6-acetyl-1,6-diaminohexane as substrate as confirmed against the empty vector control (see  FIG. 18 ) and synthesized N6-acetyl-6-aminohexanal as reaction product. 
     Given the reversibility of the ω-transaminase activity (see example 1), the gene products of SEQ ID 8-13 accept N6-acetyl-6-aminohexanal as substrate forming N6-acetyl-1,6-diaminohexane. 
     Example 7 
     Enzyme Activity of Carboxylate Reductase using Adipate Semialdehyde as Substrate and Forming Hexanedial 
     The N-terminal His-tagged carboxylate reductase of SEQ ID NO 7 (see Example 2 and  FIG. 20E ) was assayed using adipate semialdehyde as substrate. The enzyme activity assay was performed in triplicate in a buffer composed of a final concentration of 50 mM HEPES buffer (pH=7.5), 2 mM adipate semialdehyde, 10 mM MgCl 2 , 1 mM ATP and 1 mM NADPH. The enzyme activity assay reaction was initiated by adding purified carboxylate reductase and phosphopanteiheine transferase or the empty vector control to the assay buffer containing the adipate semialdehyde and then incubated at room temperature for 20 min. The consumption of NADPH was monitored by absorbance at 340 nm. The enzyme only control without adipate semialdehyde o demonstrated low base line consumption of NADPH. See  FIG. 9 . 
     The gene product of SEQ ID NO 7, enhanced by the gene product of sfp, accepted adipate semialdehyde as substrate as confirmed against the empty vector control (see  FIG. 13 ) and synthesized hexanedial. 
     Other Embodiments 
     It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.