A cold-adapted epoxide hydrolase from a strict marine bacterium, Sphingophyxis alaskensis

Abstract

An open reading frame (ORF) encoding a putative epoxide hydrolase (EHase) was identified by analyzing the genome sequence of Sphingoplyxis alaskensis. The EHase gene (seh) was cloned and expressed in E. coli. To facilitate purification, the gene was fused in-frame to 6x histidine at the C-terminus. The recombinant EHase (rSEH) was highly soluble and could be purified to apparent homogeneity by one step of metal affinity chromatography. The purified SEH displayed hydrolyzing activities toward various epoxides such as styrene oxide, glycidyl phenyl ether, epoxyhexane, epoxybutane, epichlorohydrin, and epifluorohydrin. The optimum activity toward styrene oxide was observed at pH 6.5 and 35 degrees C. The purified SEH showed a cold-adapted property, displaying more than 40% of activity at low temperature of 10 degrees C compared with the optimum activity. Despite the catalytic efficiency, the purified SEH did not hydrolyze various epoxides enantioselectively. K-m and k(cat) of SEH toward (R)-styrene oxide were calculated as 4 +/- 0.3 mM and 7.42 s(-1), respectively, whereas K-m and k(cat) of SEH toward (S)-styrene oxide were 5.25 +/- 0.3 mM and 10.08 s(-1), respectively.