Efficient access to L-phenylglycine using a newly identified amino acid dehydrogenase from Bacillus clausii

An amino acid dehydrogenase from Bacillus clausii (BcAADH) was identified and overexpressed in Escherichia coli BL21(DE3) for the preparation of L-phenylglycine from benzoylformic acid. Recombinant BcAADH was purified to homogeneity and characterized. BcAADH could catalyse reductive amination and oxidative deamination at optimum pHs of 9.5 and 10.5. Furthermore, BcAADH has a broad substrate spectrum, displaying activities toward various aromatic and aliphatic keto acids. When coexpressed with glucose dehydrogenase from Bacillus megaterium, the potential application of BcAADH in the preparation of L-phenylglycine was investigated at a high substrate loading and low biocatalyst addition. As much as 400 mM benzoylformic acid could be fully reduced into L-phenylglycine within 6 h at > 99.9% ee. With merely 0.5 g DCW L-1, 200 mM benzoylformic acid was completely reduced, resulting in a substrate to biocatalyst ratio of 60 g g(-1), environmental factor of 4.7 and 91.7% isolation yield at gram scale. This study provides guidance for the application of BcAADH in the synthesis of chiral nonnatural amino acids.