Improvement of carbonyl reductase activity for the bioproduction of tert-butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate.

tert-Butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate ((3R,5S)-CDHH) is a key chiral intermediate for the side chain synthesis of rosuvastatin. In this study, random mutagenesis, site-saturation mutagenesis and combinatorial mutagenesis methods were applied to improve the activity of a synthesized stereoselective short chain carbonyl reductase (SCR) to prepare (3R,5S)-CDHH. After screened by high-throughput screening method and high-performance liquid chromatography, mut-Phe145Met/Thr152Ser and mut-Phe145Tyr/Thr152Ser, were obtained, and the enzyme activities of mutants were improved by 1.60- and 1.91-fold compared with parent enzyme, respectively. The catalytically efficiencies (kcat/Km) of mut-Phe145Met/Thr152Ser and mut-Phe145Tyr/Thr152Ser exhibited 5.11- and 8.07-fold improvements in initial activity toward (S)-6-chloro-5-hydroxy-3-oxohexanoate ((S)-CHOH), respectively. In the asymmetric reduction, mut-Phe145Tyr/Thr152Ser catalyzed 500 g L-1 of (S)-CHOH to produce (3R,5S)-CDHH with >99% yield and >99% e.e., and the highest space-time yield achieved at 752.76 mmol L-1 h-1 g-1 wet cell weight within 8 h bioconversion. This study provides a foundation for the preparation of (3R,5S)-CDHH by carbonyl reductase.