Preparation of (S)-epichlorohydrin using a novel halohydrin dehalogenase by selective conformation adjustment.

Chiral epichlorohydrin (ECH) is an attractive intermediate for chiral pharmaceuticals and chemicals preparation. The asymmetric synthesis of chiral ECH using 1,3-dicholoro-2-propanol (1,3-DCP) catalyzed by a haloalcohol dehalogenase (HHDH) was considered as a feasible approach. However, the reverse ring opening reaction caused low optical purity of chiral ECH, thus severely restricts the industrial application of HHDHs. In the present study, a novel selective conformation adjustment strategy was developed with an engineered HheC_PS to regulate the kinetic parameters of the forward and reverse reactions, based on site saturation mutation and molecular simulation analysis. The HheC_PS mutant E85P was constructed with a markable change in the conformation of (S)-ECH in the substrate pocket and a slight impact on the interaction between 1,3-DCP and the enzyme, which resulted in the kinetic deceleration of the reverse reactions. Compared with HheC_PS, the catalytic efficiency (k_cat(S)-ECH/K_m(S)-ECH) of the reversed reaction dropped to 0.23-fold (from 0.13 to 0.03 mM^-1 s^-1), while the catalytic efficiency (k_cat(1,3-DCP)/K_m(1,3-DCP)) of the forward reaction only reduced from 0.83 to 0.71 mM^-1 s^-1. With 40 mM 1,3-DCP as substrate, HheC_PS E85P catalyzed the synthesis of (S)-ECH with the yield up to 55.35% and the e.e. increased from 92.54 to >99%. Our work provided an effective approach for understanding the stereoselective catalytic mechanism as well as the green manufacturing of chiral epoxides.