Comprehensively understanding enzymatic stereoselectivity will assist in the creation of new enzymes for producing optically pure compounds for chemical applications. The essential features for selecting enantiomers are controlled by particular residues or regions of the enzymes. We report a stereoselective mechanism in the D-2-haloacid dehalogenase HadD AJ1, in which L288 is identified as a gatekeeper in the access channel that strictly recognizes D-enantiomers. Mutagenesis of L288 to isoleucine (I) enlarges the size of the channel and allows the enzyme to accommodate L-enantiomers. Furthermore, the wing flip of I288 induces hydrophobic interactions with the L-enantiomer and directly affects the catalytic efficiency. The results illustrate the dynamic catalytic mechanisms of Leu-Ile gatekeepers and provide knowledge for unveiling the basis of stereospecificity in biocatalysts.
Keywords: biocatalyst; enzyme; molecular dynamics; protein engineering; stereoselectivity.
© 2018 Federation of European Biochemical Societies.