7alpha-hydroxysteroid dehydrogenase mutant, coding gene and application

The invention belongs to the technical field of biology, and particularly relates to a 7alpha-hydroxysteroid dehydrogenase mutant, a coding gene and application. According to the invention, the 5th site, 17th site, 192 site, 198 site, 201 site and 205 site of an amino acid sequence of wild type 7 alpha-hydroxysteroid dehydrogenase derived from Escherichia coli are subjected to single mutation or multi-site combined mutation, and the 7 alpha-hydroxysteroid dehydrogenase mutant is obtained through screening. In the process of catalyzing chenodeoxycholic acid to be converted into 7-ketolithocholic acid (a precursor substance for synthesizing ursodesoxycholic acid), the enzyme activity of the 7 alpha-hydroxysteroid dehydrogenase mutant is further improved on the basis of wild type 7 alpha-hydroxysteroid dehydrogenase with higher enzyme activity, and through determination, the maximum pure enzyme activity can be improved by 156%, and the 7 alpha-hydroxysteroid dehydrogenase mutant can be used for preparing 7-ketol