Engineering a hydroxysteroid dehydrogenase to improve its soluble expression for the asymmetric reduction of cortisone to 11β-hydrocortisone

11 beta-Hydrocortisone (11 beta-HC) is an important anti-inflammatory drug and intermediate for the synthesis of other steroids. One of the methods for the synthesis of 11 beta-HC is the asymmetric reduction of cortisone catalyzed by a highly regioselective and stereoselective 11 beta-hydroxysteroid dehydrogenase (11 beta-HSDH). However, this process has been prohibited by the poor soluble expression of the membrane-anchoring protein 11 beta-HSDH in prokaryotes. To overcome this obstacle, a mutant III-1G1 (Phe80Leu/Thr105Ser/Ala260Thr/Tyr274Stop) truncated at position 274 with improved yield of soluble protein was stepwise obtained from the 11 beta-HSDH from guinea pig by random mutagenesis combining with structural complementation assay and C-terminal truncating library screening. The improved 11 beta-HSDH mutant and glucose dehydrogenase (GDH) from Bacillus subtilis were coexpressed in Escherichia coli. The resulting whole-cell biocatalyst catalyzed the reduction of cortisone to 11 beta-HC with 98 % conversion in 20 h, laying foundation for the development of an asymmetric reduction process for the production of 11 beta-HC.