Heterologous overexpression of Pseudomonas umsongensis halohydrin dehalogenase in Escherichia coli and its application in epoxide asymmetric ring opening reactions

A new halohydrin dehalogenase-like gene (HHDH) in the genome of Pseudomonas umsongensis YCIT1612 was identified, cloned and over-expressed in Escherichia coli. HHDH-Pu exhibited the highest sequence identity of 45% in comparison with the previously reported HHDHs. The recombinant HHDH-Pu was purified to homogeneity and its catalytic characteristics in epoxide ring opening was explored. Compared to other reported HHDHs, HHDH-Pu showed higher catalytic activity, exhibiting varied activities (2.4–50.4 U/mg) toward all the tested epoxides. It catalyzed the ring opening of epoxides with low to moderate enantioselectivity (E=1.13-10.89). Rac-PGE was found to be the most selective among the tested epoxides. In the ring opening of rac-PGE, nucleophiles such as Cl−, N3−, NO2−, Br− or SCN− were accepted. N3− was selected as the optimal nucleophile. Some parameters that may alter this bio-resolution, such as the concentration of N3−, temperature and pH were evaluated. By optimizing the reaction conditions, the residual (S)-PGE could be obtained in 23.5% yield and more than 99% ee from 40 mM rac-PGE.