Biosynthesis of α-keto acids and resolution of chiral amino acids by L-amino acid deaminases from Proteus mirabilis

Chiral amino acids and their deamination products, α-keto acids, have important applications in food, medicine, and fine chemicals. In this study, two L-amino acid deaminase genes from Proteus mirabilis, PM473 of type Ⅰ and PM471 of type Ⅱ were cloned and expressed in Escherichia coli respectively, expected to achieve the chiral separation of amino acids. Extensive substrate preference testing showed that both deaminases had catalytic effects on the D-amino acid component of the D, L-amino acids, and PM473 has a wider catalytic range for amino acids. When D, L-Cys was used as the substrate, all L-Cys components and 75.1% of D-Cys were converted to mercapto pyruvate, and the remaining D-Cys was a single chiral enantiomer. Molecular docking analysis showed that the interaction between the substrate and the key residues affected the stereoselectivity of enzymes. The compatibility of hydrophobicity between the binding pocket and substrate may be the basic factor that affects the substrate selectivity. This work provides an alternative method for the production of α-keto acids and the resolution of chiral amino acids.