Development of a Bioconversion System Using Saccharomyces cerevisiae Reductase YOR120W and Bacillus subtilis Glucose Dehydrogenase for Chiral Alcohol Synthesis

Reductases convert some achiral ketone compounds into chiral alcohols, which are important materials for the synthesis of chiral drugs. The Saccharomyces cerevisiae reductase YOR120W converts ethyl-4-chloro-3-oxobutanoate (ECOB) enantioselectively into (R)-ethyl-4-chloro-3- hydroxybutanoate ((R)-ECHB), an intermediate of a pharmaceutical. As YOR120W requires NADPH as a cofactor for the reduction reaction, a cofactor recycling system using Bacillus subtilis glucose dehydrogenase was employed. Using this coupling reaction system, 100 mM ECOB was converted to (R)-ECHB. A homology modeling and site-directed mutagenesis experiment were performed to determine the NADPH-binding site of YOR120W. Four residues (Q29, K264, N267, and R270) were suggested by homology and docking modeling to interact directly with 2`-phosphate of NADPH. Among them, two positively charged residues (K264 and R270) were experimentally demonstrated to be necessary for NADPH 2`-phosphate binding. A mutant enzyme (Q29E) showed an enhanced enantiomeric excess value compared with that of the wild-type enzyme.