Multi-path asymmetric reactions of racemic epoxides mediated by an engineered Escherichia coli overexpressing SfEH2, a newfound epoxide hydrolase from Streptomyces fradiae SF-2

To enrich ‘epoxide hydrolase (EH) tool cabinet’ for preparing enantiopure epoxides and 1,2-diols, a novel microbial EH, Sf EH2, was identified from Streptomyces fradiae SF-2. Bioinformatics analysis indicated that Sf EH2 has typical structural characteristics of α/β-hydrolase fold superfamily. Its coding gene, sfeh 2, was then codon-optimized and amplified. A recombinant (re) Sf EH2-expressing E. coli BL21(DE3) strain ( E. coli / sfeh 2) was constructed through DNA manipulations. Substrate spectrum assay including fifteen common racemic ( rac -) epoxides by E. coli / sfeh 2 showed that re Sf EH2 displayed the highest and best complementary regioselectivities (regioselectivity coefficients, α R = 89.7% and β S = 91.4%) towards rac - 14a , as well as the highest enantioselectivity (enantiomeric ratio, E = 15.3) in S -type towards rac - 15a . Molecular docking simulation revealed that Sf EH2 preferentially attacked C α of ( R )- 14a and C β of ( S )- 14a geometrically. In kinetic parameter analysis, the K m R (5.74 mM) of purified re Sf EH2 for ( R )- 15a was 1.76-fold lower than K m S (10.09 mM) for ( S )- 15a . At last, using 50 mg dry cell weight/mL E. coli / sfeh 2, the scale-up enantioconvergent hydrolysis of 100 mM rac - 14a at 30 °C for 6.0 h afforded ( S )- 14b with 80.9% ee p and 90.1% yield, while the kinetic resolution of 150 mM rac - 15a retained ( S )- 15a with >99.0% ee s and 42.2% yield.