Characterization of ML-005, a Novel Metaproteomics-Derived Esterase.

A novel gene encoding for a lipolytic enzyme, designated ML-005, was recently identified using a functional metaproteomics approach. We heterologously expressed this protein in and biochemically characterized it. ML-005 exhibited lipolytic activity toward short-chained substrates with the preferred substrate being -nitrophenyl-butyrate, suggesting that ML-005 is an esterase. According to homology analysis and site-directed mutagenesis, the catalytic triad of the enzyme was identified as Ser-99, Asp-164, and His-191. Its optimal pH was determined to be at pH 8. Optimal activity was observed at 45°C. It also exhibited temperature, pH and salt tolerance. Residual relative activity after incubating at 50-60°C for 360 min was above 80% of its initial activity. It showed tolerance over a broad range of pH (5-12) and retained most of its initial activity. Furthermore, incubating ML-005 in 1 - 5M NaCl solution had negligible effect on its activity. DTT, EDTA, and ß-mercaptoethanol had no significant effect on ML-005's activity. However, addition of PMSF led to almost complete inactivation consistent with ML-005 being a serine hydrolase. ML-005 remains stable in the presence of a range of metal ions, but addition of Cu significantly reduces its relative activity. Organic solvents have an inhibitory effect on ML-005, but it retained 21% of activity in 10% methanol. SDS had the most pronounced inhibitory effect on ML-005 among all detergents tested and completely inactivated it. Furthermore, the V of ML-005 was determined to be 59.8 μM/min along with a K of 137.9 μM. The k of ML-005 is 26 s and k/K is 1.88 × 10 M s.