Crystal Structures And Catalytic Mechanism Of L-Erythro-3,5-Diaminohexanoate Dehydrogenase And Rational Engineering For Asymmetric Synthesis Of Beta-Amino Acids

Amino acid dehydrogenases (AADHs) have shown considerable potential as biocatalysts in the asymmetric synthesis of chiral amino acids. However, compared to the widely studied alpha-AADHs, limited knowledge is available about beta-AADHs that enable the synthesis of beta-amino acids. Herein, we report the crystal structures of a l-erythro-3,5-diaminohexanoate dehydrogenase and its variants, the only known member of beta-AADH family. Crystal structure analysis, site-directed mutagenesis studies and quantum chemical calculations revealed the differences in the substrate binding and catalytic mechanism from alpha-AADHs. A number of rationally engineered variants were then obtained with improved activity (by 110-800 times) toward various aliphatic beta-amino acids without an enantioselectivity trade-off. Two beta-amino acids were prepared by using the outstanding variants with excellent enantioselectivity (>99 % ee) and high isolated yields (86-87 %). These results provide important insights into the molecular mechanism of 3,5-DAHDH, and establish a solid foundation for further design of beta-AADHs for the asymmetric synthesis of beta-amino acids.