Characterization of a novel highly thermostable esterase from the Gram-positive soil bacterium Streptomyces lividans...

A novel esterase gene (estW) from soil bacterium Streptomyces lividans TK64 was successfully cloned using a pair of homologous primers. The estW gene encoded a protein (EstW) of 289 amino acid residues with a predicted molecular weight of 31.43 kDa. Sequence alignment revealed that EstW show relatively high levels of homology to other lipolytic enzymes characterized from Streptomyces and phylogenetic analysis suggested EstW belongs to the bacterial lipase/esterase family I. The estW gene was expressed at a high level in Escherichia coli and the recombinant enzyme was purified to homogeneity. The purified EstW was characterized via hydrolysis of various p-nitrophenyl esters and the best substrate was found to be p-nitrophenyl acetate (pNPA). Maximal activity of the recombinant protein was observed at pH 8.0 and 50 °C with pNPA as the substrate. The calculated activation energy (Ea ) of the esterase reaction was 9.12 kcal/mol. Half-life of EstW at 95 °C was approximately 12.5 H, making it the most thermostable esterase among all of the known lipolytic enzymes from Streptomyces, and the thermostability of EstW was similar to those of some enzymes characterized from the thermophilic bacteria. EstW exhibited relatively high tolerance to several detergents and required no cations for its maximal activity. The unique properties of EstW, namely its high thermostability and stability in the presence of organic solvents, may render it a potential candidate for industrial applications.