Creation of a (<i>R</i>)-β-Transaminase by Directed Evolution of <scp>d</scp>-Amino Acid Aminotransferase

Abstract

β-Transaminases (β-TAs) have shown considerable potential as biocatalysts for the synthesis of chiral β- and γ-amino acid. Herein, a (R)-β-TA was successfully created by the directed evolution of d-amino acid aminotransferase. The specific activities of created (R)-β-TA for β-phenylalanine (1.74 U/mg) and γ-phenylbutanoic acid (1.67 U/mg) were comparable with those of naturally occurring (S)-β-TAs. Moreover, the designed (R)-β-TA also showed potential for the biocatalytic synthesis of a δ-amino acid with specific activity (0.23 U/mg), which has not yet been explored. Enantiopure (S)- and (R)-forms of various β-, γ- and δ-amino acids (>99% ee) were synthesized using engineered (R)-β-TA-mediated kinetic resolution and asymmetric synthesis, respectively.