초록
<P>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>3–1</SUB>) 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>3–1</SUB> increased to 942 g L<SUP>–1</SUP> day<SUP>–1</SUP>, in contrast to 141 g L<SUP>–1</SUP> day<SUP>–1</SUP> 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.</P><P><B>Graphic Abstract</B><BR><IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jafcau/2017/jafcau.2017.65.issue-6/acs.jafc.6b05428/production/images/medium/jf-2016-05428d_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jf6b05428'>ACS Electronic Supporting Info</A></P>