Identification of halohydrin dehalogenase mutants that resist COBE inhibition

The biocatalytic cascade conversion of ethyl 4-chloroacetoacetate (COBE) to ethyl (R)-4-cyano-3-hydroxybutyrate ((R)-HN) for the preparation of atorvastatin represents significant economic and environmental benefits, and is catalyzed by alcohol dehydrogenase and halohydrin dehalogenase (HHDH). However, as the activity of HHDH is inhibited by COBE, the cascade reaction is an inefficient one-pot reaction. In this study, substrate inhibition kinetics analysis was performed and the inhibition by COBE was found to be competitive reversible inhibition. Molecular simulation analysis was used to determine the inhibition mechanism by COBE. The results showed that COBE bound to the active center of HHDH via the formation of hydrogen bonds with the OH groups of S132 and Y145. Site saturation mutagenesis of residues around the active site and at the entrance of the access tunnel was performed, and two target mutant residues were identified, F136 and W249. Small focused mutagenesis on these two residues was performed and the F136V/W249F mutant was successfully found to relieve the activity inhibition of HHDH by COBE. The half inhibiting concentration of mutant F136V/W249F was found to be 20-fold higher than wild-type HHDH. The efficiency of the multi-enzymatic one-pot system for the synthesis of (R)-HN from COBE using mutant F136V/W249F was improved significantly.