Isolation and characterization of a metagenome-derived thermoalkaliphilic esterase with high stability over a broad pH range.

A novel alkaliphilic esterase (EstJ) was identified from a soil metagenome of Jeju Island, Korea, using a 96-well plate-based functional assay for determination of pH dependence of activity. The amino acid sequence of EstJ showed low similarity (32-45 %) to putative α/β hydrolases derived from whole-genome sequencing studies. EstJ, although not belonging to any of the known families of bacterial lipolytic enzymes, however, it showed closest sequence identity to the family IV enzymes that are related to the mammalian hormone-sensitive lipases. The highly conserved motifs of family IV enzymes were found in EstJ, but the corresponding sequences of each motif in EstJ were unique; most particularly the -(F/Y)(F/Y/L)HGGG- motif was represented by -WMVSGG-. The purified EstJ was highly active from pH 8.5 to 10.5. More than 90 % of maximum activity was also retained over a wide pH range of 5.5-0.5 after prolonged incubation. EstJ was also moderately thermophilic with an optimum temperature of 55 °C. Therefore, EstJ is the first metagenome-derived bacterial family IV esterase possessing both highly alkaliphilic and moderately thermophilic properties.