Cloning, homology modeling, and reaction mechanism analysis of a novel cis-epoxysuccinate hydrolase from Klebsiella sp.

The gene encoding a novel cis-epoxysuccinate hydrolase, which hydrolyzes cis-epoxysuccinate to L (+)-tartaric acid, was cloned from Klebsiella sp. BK-58 and expressed in Escherichia coli. The ORF was 825 bp encoding a mature protein of 274 amino acids with a molecular mass of 30.1 kDa. Multiple sequence alignment showed that the enzyme belonged to the haloacid dehalogenase-like super family. Homology modeling and site-directed mutagenesis were performed to investigate the structural characteristics of the enzyme. Its overall structure consisted of a core domain formed by six-stranded parallel β-sheets flanked by seven α-helices and a subdomain that had a four helix bundle structure. Residues D48, T52, R85, N165, K195, Y201, A219, H221, and D224 were catalytically important forming the active pocket between the two domains. An (18)O-labeling study suggested that the catalytic reaction of the enzyme proceeded through a two-step mechanism.