The Reductive Amination of Carbonyl Compounds Using Native Amine Dehydrogenase from Laribacter hongkongensis

Amine dehydrogenases (AmDHs) are one of the key emerging enzymes used in the synthesis of various amines with the expense of only one ammonium ion as an amino donor, thereby, generates only water molecule as a by-product. Currently, most available AmDHs have been created through protein engineering using the existing natural L-amino acid dehydrogenase, and native AmDHs are rarely reported. In this study, a novel native AmDH from Laribacter hongkongensis (LhAmDH) was identified based on the GenBank database using a sequence-driven approach. LhAmDH showed a good activity towards various carbonyl compounds such as cyclohexanone (170 mU/mg) and isovaleraldehyde (214 mU/mg). The reductive amination of model substrate, cyclohexanone (up to 100 mM) into cyclohexylamine was successfully performed in LhAmDH and FDH system with > 99% conversion using Escherichia coli whole-cell as well as purified enzymes. Furthermore, three enzymes cascade (ω-transaminase, LhAmDH, and FDH) was designed to produce chiral amine from the corresponding ketone using inexpensive ammonium formate as sole sacrificial agent. The active site of LhAmDH residues were predicted using the protein structure homology model building program SWISS-MODEL server. In the docking analysis, cyclohexanone is well-orientated with −5.4 kcal/mol of binding energy and 3.16 A distance from side chain of E104, which is a key residue for interacting ammonia and substrate. This LhAmDH model can be used as a promising template to produce chiral amines through semi-rational design.