Understanding substrate specificity and enantioselectivity of carbonyl reductase from Candida parapsilosis ATCC 7330 (CpCR): Experimental and modeling studies

The whole cells of Candida parapsilosis ATCC 7330 are a well-established biocatalyst used for oxidation and reduction of various organic compounds to generate chiral synthons. Recombinantly expressed carbonyl reductase (CpCR) from the same strain reduces aryl alpha-ketoesters to their respective optically pure alcohols but preferentially reduces aliphatic and aryl aldehydes to primary alcohols. The prochiral substrates viz. aryl alpha-ketoester [Ethyl-2-oxo-4-phenylbutanoate], aryl ketone [Acetophenone] and aliphatic beta-ketoester [Ethyl-4,4,4-trifloro-3-oxo-butanoate] get reduced to (R)-alcohols with CpCR while an aryl ketoaldehyde [2-oxo-2-phenylacetaldehyde] gives the (S)-alcohol. The optimal orientation required for the high conversion and desired enantioselectivity was analyzed by docking the alpha/beta ketoesters, ketoaldehyde and a ketone with a modeled CpCR. Aryl alpha-ketoester, having the lowest free energy (-8.43 kcal/mol), shows the most favorable binding with CpCR (Interaction Energy = 7.9 kcal/mol). Also, the close proximity of aryl alpha-ketoester to the cofactor NADPH (2.82 angstrom) facilitates a better Pro R hydride transfer as compared to other substrates.