文摘
Ursodeoxycholic acid (UDCA) is the main active ingredient of natural bear bile powder with multiple pharmacological functions. 7β-Hydroxysteroid dehydrogenase (HSDH) is a key biocatalyst for the synthesis of UDCA. However, all the 7β-HSDHs reported commonly suffer from poor activity and thermostability, resulting in limited productivity of UDCA. In this study, a multiobjective directed evolution (MODE) strategy was proposed and applied to improve the activity, thermostability, and pH optimum of a 7β-HSDH. The best variant (V<sub>3–1sub>) showed a specific activity 5.5-fold higher than and a half-life 3-fold longer than those of the wild type. In addition, the pH optimum of the variant was shifted to a weakly alkaline value. In the cascade reaction, the productivity of UDCA with V<sub>3–1sub> increased to 942 g L<sup>–1sup> day<sup>–1sup>, in contrast to 141 g L<sup>–1sup> day<sup>–1sup> with the wild type. Therefore, this study provides a useful strategy for improving the catalytic efficiency of a key enzyme that significantly facilitated the bioproduction of UDCA.