The Clone, Expression and Site-directed Mutagenesis of 3-Ketosteroid-Delta (1)-Dehydrogenase from Arthrobacter Simplex / 现代生物医学进展

ABSTRACT

Objective:In this study,a prokaryotic expression of the 3-ketosteroid-Delta (1)-dehydrogenase (KSDD) which came from Arthrobacter simplex was built.Moreover,in order to investigate the catalytic mechanism of KSDD and improve its stability,the structure of KSDD was predicted by computer and the critical sites were confirmed by site-directed mutations.Methods:The recombinant plasmid was constructed by eukaryotic expression vector pET-22b and the recombinant strain was constructed and expressed in Escherichia coli BL21 (DE3).High-performance liquid chromatography was used to determine the transformation rate of 4-AD to ADD.The KSDD structure and key sites were predicted by SWISS-MODEL.Site-directed mutations for the amino acid residues of key sites were constructed and activities of the mutations were detected.Results:The recombinant strain E.coli pET-22-ksdd was successfully constructed.It was induced to express the dehydrogenase by IPTG and the conversion rate of 4-AD to ADD was 27％ at 21 ℃.The structure of 3-ketosteroid-Delta (1)-dehydrogenase and the four key sites was analyzed by SWISS-MODEL.Four mutants,Y120R,Y320L,Y488F and G492Y were constructed.Mutants Y120R and Y488F were inactivated,so they were proved to be the key active sites of KSDD.The conversion rate of mutant Y320L was consistent with that of wild type,but the stability at 37 ℃ was improved.The conversion rate of mutant G492Y was 1.2 times of the wild type and the stability has been improved at 37 ℃.Conclusions:At present,there are few studies about the structure and catalytic mechanism of dehydrogenase.The active sites of the enzyme were verified by this study,which laid the foundation for the further study of the properties of the enzyme KSDD.