Enantioconvergent hydrolysis of racemic 1,2-epoxypentane and 1,2-epoxyhexane by an engineered Escherichia coli strain overexpressing a novel Streptomyces fradiae epoxide hydrolase

In order to excavate microbial epoxide hydrolases (EHs) with desired catalytic properties, a novel EH, Sf EH1, was identified based on the genome annotation of Streptomyces fradiae and sequence alignment analysis with local protein library. The Sf EH1-encoding gene, sfeh 1, was then cloned and over-expressed in soluble form in Escherichia coli /BL21(DE3). The optimal temperature and pH of recombinant Sf EH1 (re Sf EH1) and re Sf EH1-expressing E. coli ( E. coli / sfeh 1) were both determined as 30 ℃ and 7.0, also indicating that the influences of temperature and pH on re Sf EH1′s activities were more obvious than those of E. coli / sfeh 1 whole cells. Subsequently, using E. coli / sfeh 1 as catalyst, its catalytic properties towards thirteen common mono-substituted epoxides were tested, in which E. coli / sfeh 1 had the highest activity of 28.5 U/g dry cells for rac -1,2-epoxyoctane ( rac - 6a ), and ( R )-1,2-pentanediol (( R )- 3b ) (or ( R )-1,2-hexanediol (( R )- 4b )) with up to 92.5% (or 94.1%) ee p was obtained at almost 100% conversion ratio. Regioselectivity coefficients (α S and β R ) displayed in the enantioconvergent hydrolysis of rac - 3a (or rac - 4a ) were calculated to be 98.7% and 93.8% (or 95.2% and 98.9%). Finally, the reason of the high and complementary regioselectivity was confirmed by both kinetic parameter analysis and molecular docking simulations .