Primary structure and catalytic mechanism of the epoxide hydrolase from Agrobacterium radiobacter AD1

被引:147
作者
Rink, R [1 ]
Fennema, M [1 ]
Smids, M [1 ]
Dehmel, U [1 ]
Janssen, DB [1 ]
机构
[1] UNIV GRONINGEN, DEPT BIOCHEM, GRONINGEN BIOMOL SCI & BIOTECHNOL INST, NL-9747 AG GRONINGEN, NETHERLANDS
关键词
D O I
10.1074/jbc.272.23.14650
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The epoxide hydrolase gene from Agrobacterium radiobacter AD1, a bacterium that is able to grow on epichlorohydrin as the sole carbon source, was cloned by means of the polymerase chain reaction with two degenerate primers based on the N-terminal and C-terminal sequences of the enzyme, The epoxide hydrolase gene coded for a protein of 294 amino acids with a molecular mass of 34 kDa, An identical epoxide hydrolase gene was cloned from chromosomal DNA of the closely related strain A, radiobacter CFZ11, The recombinant epoxide hydrolase was expressed up to 40% of the total cellular protein content in Escherichia coli BL21(DE3) and the purified enzyme had a k(cat) of 21 s(-1) with epichlorohydrin, Amino acid sequence similarity of the epoxide hydrolase with eukaryotic epoxide hydrolases, haloalkane dehalogenase from Xanthobacter autotrophicus GJ10, and bromoperoxidase A2 from Streptomyces aureofaciens indicated that it belonged to the alpha/beta-hydrolase fold family, This conclusion was supported by secondary structure predictions and analysis of the secondary structure with circular dichroism spectroscopy. The catalytic triad residues of epoxide hydrolase are proposed to be Asp(107), His(275), and Asp(246). Replacement of these residues to Ala/Glu, Arg/Gln, and Ala, respectively, resulted in a dramatic loss of activity for epichlorohydrin, The reaction mechanism of epoxide hydrolase proceeds via a covalently bound ester intermediate, as was shown by single turnover experiments with the His(275) --> Arg mutant of epoxide hydrolase in which the ester intermediate could be trapped.
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页码:14650 / 14657
页数:8
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