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

Abstract

In order to excavate microbial epoxide hydrolases (EHs) with desired catalytic properties, a novel EH, SfEH1, was identified based on the genome annotation of Streptomyces fradiae and sequence alignment analysis with local protein library. The SfEH1-encoding gene, sfeh1, was then cloned and over-expressed in soluble form in Escherichia coli/BL21(DE3). The optimal temperature and pH of recombinant SfEH1 (reSfEH1) and reSfEH1-expressing E. coli (E. coli/sfeh1) were both determined as 30 ℃ and 7.0, also indicating that the influences of temperature and pH on reSfEH1's activities were more obvious than those of E. coli/sfeh1 whole cells. Subsequently, using E. coli/sfeh1 as catalyst, its catalytic properties towards thirteen common mono-substituted epoxides were tested, in which E. coli/sfeh1 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.

Keywords: (R)-1,2-Hexanediol; (R)-1,2-Pentanediol; Enantioconvergent hydrolysis; Epoxide hydrolase; Streptomyces fradiae.