Highly regio- and enantio-selective hydrolysis of two racemic epoxides by GmEH3, a novel epoxide hydrolase from Glycine max

A novel epoxide hydrolase from Glycine max, designated GmEH3, was excavated based on the computer-aided analysis. Then, gmeh3, a GmEH3-encoding gene, was cloned and successfully expressed in E. coli Rosetta(DE3). Among the ten investigated rac-epoxides, GmEH3 possessed the highest and best complementary regioselectivities (regioselectivity coefficients, α_S = 93.7% and β_R = 97.2%) in the asymmetric hydrolysis of rac-m-chlorostyrene oxide (5a), and the highest enantioselectivity (enantiomeric ratio, E = 55.6) towards rac-phenyl glycidyl ether (7a). The catalytic efficiency (k_cat^S/K_m^S = 2.50 mM^-1 s^-1) of purified GmEH3 for (S)-5a was slightly higher than that (k_cat^R/K_m^R = 1.52 mM^-1 s^-1) for (R)-5a, whereas the k_cat/K_m (5.16 mM^-1 s^-1) for (S)-7a was much higher than that (0.09 mM^-1 s^-1) for (R)-7a. Using 200 mg/mL wet cells of E. coli/gmeh3 as the biocatalyst, the scale-up enantioconvergent hydrolysis of 150 mM rac-5a at 25 °C for 1.5 h afforded (R)-5b with 90.2% ee_p and 95.4% yield_p, while the kinetic resolution of 500 mM rac-7a for 2.5 h retained (R)-7a with over 99% ee_s and 43.2% yield_s. Furthermore, the sources of high regiocomplementarity of GmEH3 for (S)- and (R)-5a as well as high enantioselectivity towards rac-7a were analyzed via molecular docking (MD) simulation.

Keywords: Epoxide hydrolase; Glycine max; Molecular docking simulation; Phenyl glycidyl ether; Regio- and enantio-selective hydrolysis; m-Chlorostyrene oxide.