Characterization of a novel aldo-keto reductase with anti-Prelog stereospecificity from Corallococcus sp. EGB

The asymmetric reduction of prochiral ketones is a promising process for synthesis of optically active alcohols. The aldo-keto reductase (AKR) is an attractive candidate of biocatalyst, due to its high enantioselectivity and environmentally friendly reaction conditions. In this work, nine putative AKR encoding genes from Corallococcus sp. EGB were cloned and expressed in Escherichia coli. Of these produced enzymes (CoAKRs), CoAKR7 exhibited reductive activity to various ketones and ketoesters, especially very high activity toward ethyl 4-chloro-3-oxobutanoate (COBE) with NADPH as the coenzyme. The CoAKR7 was optimally active at pH 7.0 and 50 °C. The apparent K_m and V_max for COBE was 14.18 U/mg and 0.269 mM, respectively. Moreover, CoAKR7 catalyzed an anti-Prelog reduction of COBE to (S)-ethyl-4-chloro-3-hydroxybutanoate (CHBE) with e.e. >99%. Enzyme-substrate-cofactor docking analysis elucidated the molecular mechanism of the substrate stereospecificity, providing basis for protein engineering of these enzymes for applications in the synthesis of valuable chemicals.