Enantioselective reductions of ethyl 2-oxo-4-phenylbutyrate by Saccharomyces cerevisiae dehydrogenases

A set of fusion proteins consisting of glutathione S-transferase linked to the N-terminus of putative dehydrogenases produced by baker’s yeast (Saccharomyces cerevisiae) was screened for the reduction of ethyl 2-oxo-4-phenylbutyrate in the presence of NADH and NADPH. Two dehydrogenases—Ypr1p and Gre2p—rapidly reduced this α-ketoester, providing the (R)- and (S)-alcohol, respectively, with high stereoselectivities. The same enzymes were over-expressed in their native forms in Escherichia coli and growing cells of the engineered strains could also be used to carry out the reductions without the need for exogenous cofactor. These results demonstrate the power of genomic fusion protein libraries to identify appropriate biocatalysts rapidly and expedite process development.