Identification and Characterization of a Novel Halohydrin Dehalogenase from Bradyrhizobium erythrophlei and Its Performance in Preparation of Both Enantiomers of Epichlorohydrin

Abstract

The new halohydrin dehalogenase-like gene (HheB8) in the genome of Bradyrhizobium erythrophlei was identified, synthesized and expressed in Escherichia coli. The encoded protein (HheB8) was purified to homogeneity as a molecular mass of 26 kDa and characterized using the model substrate of 1,3-dicholoro-2-propanol (1,3-DCP). The purified HheB8 was optimally active at pH 9.5 and 45 °C, and highly stable at pH 6.0–8.0 and 40 °C or below. The enzyme displayed a very broad substrate specificity, exhibiting good enantioselectivity for the transformation of prochiral 1,3-DCP and 1,3-dibromo-2-propanol to (R)-ECH (92.3% enantiomeric excess ee) and (R)-epibromohydrin (81.3% ee). For all tested epoxides, except styrene oxide, the (R)-enantiomer was converted first, affording (S)-isomer in 99% ee. Furthermore, the potential for using a single HHDH to enantioselectively produce both enantiomers of ECH was analyzed. The bioconversion process for production of (R)-ECH from 1,3-DCP by the recombinant HheB8 was developed and a maximum ee of 93.4% was achieved. Kinetically resolved racemic ECH (30 mM) to provide (S)-ECH with 99% ee and 33.4% yield. To the best of our knowledge, this is the first report of HheB8 used as biocatalyst in the production of enantiopure ECH. Therefore, this recombinant HHDH could be a potential candidate for application in the synthesis of chiral chemicals from prochiral halohydrins and racemic epoxides.