Metabolic pathway of 6-aminohexanoate in the nylon oligomer-degrading bacterium Arthrobacter sp. KI72: identification of the enzymes responsible for the conversion of 6-aminohexanoate to adipate

Appl Microbiol Biotechnol. 2018 Jan;102(2):801-814. doi: 10.1007/s00253-017-8657-y. Epub 2017 Nov 29.


Arthrobacter sp. strain KI72 grows on a 6-aminohexanoate oligomer, which is a by-product of nylon-6 manufacturing, as a sole source of carbon and nitrogen. We cloned the two genes, nylD 1 and nylE 1 , responsible for 6-aminohexanoate metabolism on the basis of the draft genomic DNA sequence of strain KI72. We amplified the DNA fragments that encode these genes by polymerase chain reaction using a synthetic primer DNA homologous to the 4-aminobutyrate metabolic enzymes. We inserted the amplified DNA fragments into the expression vector pColdI in Escherichia coli, purified the His-tagged enzymes to homogeneity, and performed biochemical studies. We confirmed that 6-aminohexanoate aminotransferase (NylD1) catalyzes the reaction of 6-aminohexanoate to adipate semialdehyde using α-ketoglutarate, pyruvate, and glyoxylate as amino acceptors, generating glutamate, alanine, and glycine, respectively. The reaction requires pyridoxal phosphate (PLP) as a cofactor. For further metabolism, adipate semialdehyde dehydrogenase (NylE1) catalyzes the oxidative reaction of adipate semialdehyde to adipate using NADP+ as a cofactor. Phylogenic analysis revealed that NylD1 should be placed in a branch of the PLP-dependent aminotransferase sub III, while NylE1 should be in a branch of the aldehyde dehydrogenase superfamily. In addition, we established a NylD1/NylE1 coupled system to quantify the aminotransferase activity and to enable the conversion of 6-aminohexaoate to adipate via adipate semialdehyde with a yield of > 90%. In the present study, we demonstrate that 6-aminohexanoate produced from polymeric nylon-6 and nylon oligomers (i.e., a mixture of 6-aminohexaoate oligomers) by nylon hydrolase (NylC) and 6-aminohexanoate dimer hydrolase (NylB) reactions are sequentially converted to adipate by metabolic engineering technology.

Keywords: 4-Aminobutyrate; 6-Aminohexanoate; Adipate; Aldehyde dehydrogenase; Aminotransferase; Bioconversion.

MeSH terms

  • Adipates / metabolism*
  • Alanine / metabolism
  • Aminocaproic Acid / metabolism*
  • Arthrobacter / enzymology*
  • Arthrobacter / genetics
  • Bacterial Proteins / metabolism
  • Escherichia coli
  • Glutamic Acid / metabolism
  • Glycine / metabolism
  • Hydrolases / metabolism
  • Metabolic Engineering
  • Metabolic Networks and Pathways*
  • Nylons / metabolism*
  • Pyridoxal Phosphate / metabolism
  • Substrate Specificity
  • Transaminases / metabolism


  • Adipates
  • Bacterial Proteins
  • Nylons
  • Glutamic Acid
  • Pyridoxal Phosphate
  • Transaminases
  • Hydrolases
  • Alanine
  • Glycine
  • Aminocaproic Acid