A new esterase showing similarity to putative dienelactone hydrolase from a strict marine bacterium, Vibrio sp GMD509

초록

Vibrio sp. GMD509, a marine bacterium isolated from eggs of the sea hare, exhibited lipolytic activity on tributyrin (TBN) plate, and the gene representing lipolytic activity was cloned. As a result, an open reading frame (ORF) consisting of 1,017 bp (338 aa) was found, and the deduced amino acid sequence of the ORF showed low similarity (< 20%) to alpha/beta hydrolases such as dienelactone hydrolases and esterase/lipase with G-X-1-S-X-2-G sequence conserved. Phylogenetic analysis suggested that the protein belonged to a new family of esterase/lipase together with various hypothetical proteins. The enzyme was overexpressed in Escherichia coli and purified to homogeneity. The purified enzyme (Vlip509) showed the best hydrolyzing activity toward p-nitrophenyl butyrate (C-4) among various p-nitrophenyl esters (C-2 to C-18), and optimal activity of Vlip509 occurred at 30 degrees C and pH 8.5, respectively. Kinetic parameters toward p-nitrophenyl butyrate were determined as K (m) (307 mu M), k(cat) (5.72 s(-1)), and k(cat)/K-m (18.61 s(-1) mM(-1)). Furthermore, Vlip509 preferentially hydrolyzed the S-enantiomer of racemic ofloxacin ester. Despite its sequence homology to dienelactone hydrolase, Vlip509 showed no dienelactone hydrolase activity. This study represents the identification of a novel lipolytic enzyme from marine environment.

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