Cloning, expression and characterization of esterase from Pseudomonas putida 3SK

Abstract

Pseudomonas putida 3SK, a solvent resistant strain, produced extracellular lipase. We observed that there was another lipolytic enzyme, which had no lipase activity in P. putida 3SK. This lipolytic enzyme, an esterase, was cloned in Escherichia coli and sequenced. The cloned esterase gene, which designated estA, had single open reading frame of 1941 nucleotides. The estA gene encoded a protein of 646 amino acids and was predicted to belong to the GDSL family of lipolytic enzymes. The consensus motif GxSxxDxG, which was a characteristic feature of the GDSL lipolytic enzymes, was found in estA. A putative catalytic triad, $Ser^{38}$, $Asp^{172}$, and $His^{313}$ was also determined. The calculated molecular weight was 69.6kDa and theoretical isoelectric point (pI) was 4.68. The esterase expressed in E. coli was purified by Ni-NTA affinity chromatography and FPLC gel filtration chromatography. The molecular weight of the purified esterase was about 65kDa and judging from the immunoblot analysis, an esterase from P. putida 3SK was extracellular enzyme. The optimum pH and temperature were pH 11 and 50℃, respectively. In the study of effect of organic solvents, DMF was the most effective solvent among the solvents tested for the p-nitrophenyl myristate hydrolysis. On the basis of substrate specificity and sensitivity toward various inhibitors, P. putida 3SK esterase appears to be an acetylesterase (E.C. 3.1.1.6).