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

摘要

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 α/β hydrolases such as dienelactone hydrolases and esterase/lipase with G–X1–S–X2–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 (C4) among various p-nitrophenyl esters (C2 to C18), and optimal activity of Vlip509 occurred at 30°C and pH 8.5, respectively. Kinetic parameters toward p-nitrophenyl butyrate were determined as K m (307 μM), 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.