Characterization of a thermostable carboxylesterase from the hyperthermophilic bacterium Thermotoga maritima |
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Authors: | Satoshi Kakugawa Shinya Fushinobu Takayoshi Wakagi Hirofumi Shoun |
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Affiliation: | (1) Department of Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan;(2) Present address: Division of Virology, Department of Microbiology and Immunology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan |
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Abstract: | The gene encoding carboxylesterase from the hyperthermophilic bacterium Thermotoga maritima (tm0053) was cloned. The recombinant protein (EST53) was overexpressed in Escherichia coli without its NH2-terminal hydrophobic region, and with a C-terminal hexahistidine sequence. The enzyme was purified to homogeneity by heat treatment, followed by Ni2+ affinity chromatography, and then characterized. Among the p-nitrophenyl esters tested, the best substrate was p-nitrophenyl decanoate with K m and k cat values of 3.1 μM and 10.8 s−1, respectively, at 60°C and pH 7.5. The addition of O,O′-bis(2-aminoethyl)ethyleneglycol-N,N,N′,N′-tetraacetic acid decreased the esterase activity, indicating that EST53 is dependent on the presence of Ca2+ ion. In addition, its activity was inhibited by the addition of phenylmethylsulfonyl fluoride and diethyl pyrocarbonate, indicating that it contains serine and histidine residues, which play key roles in the catalytic mechanism. EST53 shows a relatively high degree of similarity to Burkholderia lipases that belong to family I.2 of the lipolytic enzymes, whereas the local sequence around the pentapeptide of EST53 is most similar to those of Bacillus lipases belonging to family I.4. |
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Keywords: | Esterase Carboxylesterase Hyperthermophilic enzyme Lipase Alpha/beta-Hydrolase Lipolytic enzyme |
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