Fu_2013_Appl.Microbiol.Biotechnol_97_3965

A novel cold-adapted lipolytic enzyme gene, est97, was identified from a high Arctic intertidal zone sediment metagenomic library. The deduced amino acid sequence of Est97 showed low similarity with other lipolytic enzymes, the maximum being 30 % identity with a putative lipase from Vibrio caribbenthicus. Common features of lipolytic enzymes, such as the GXSXG sequence motif, were detected. The gene product was over-expressed in Escherichia coli and purified. The recombinant Est97 (rEst97) hydrolysed various rho-nitrophenyl esters with the best substrate being rho-nitrophenyl hexanoate (K m and k cat of 39 muM and 25.8 s(-1), respectively). This esterase activity of rEst97 was optimal at 35 degrees C and pH 7.5 and the enzyme was unstable at temperatures above 25 degrees C. The apparent melting temperature, as determined by differential scanning calorimetry was 39 degrees C, substantiating Est97 as a cold-adapted esterase. The crystal structure of rEst97 was determined by the single wavelength anomalous dispersion method to 1.6 A resolution. The protein was found to have a typical alpha/beta-hydrolase fold with Ser144-His226-Asp197 as the catalytic triad. A suggested, relatively short lid domain of rEst97 is composed of residues 80-114, which form an alpha-helix and a disordered loop. The cold adaptation features seem primarily related to a high number of methionine and glycine residues and flexible loops in the high-resolution structures.