Characterization of a novel alkaline esterase from <i>Altererythrobacter epoxidivorans</i> CGMCC 1.7731<sup>T</sup>

<p>A novel esterase gene (<i>e25</i>) was identified from <i>Altererythrobacter epoxidivorans</i> CGMCC 1.7731<sup>T</sup> by genome sequence screening. The <i>e25</i> gene is 948 nucleotides in length and encodes a 315 amino acid protein (E25) with a predicted molecular mass of 33,683 Da. A phylogenetic tree revealed that E25 belongs to the hormone-sensitive lipase (HSL) family of lipolytic enzymes. An activity assay of E25 showed that it exhibited the highest catalytic efficiency when using <i>p</i>-nitrophenyl caproate (C6) as a substrate. The optimum pH and temperature were determined to be approximately pH 9 and 45°C, and the <i>K</i><sub>m</sub> and <i>V</i><sub>max</sub> values were 0.12 mM and 1,772 µmol/min/mg, respectively. After an incubation at 40°C for 80 min, E25 retained 75% of its basal activity. The enzyme exhibited good tolerance to metal cations, such as Ba<sup>2+</sup>, Ca<sup>2+</sup>, and Cu<sup>2+</sup> (10 mM), but its activity was strongly inhibited by Co<sup>2+</sup>, Ni<sup>2+</sup>, Mn<sup>2+</sup>, and Zn<sup>2+</sup>. The E25 enzyme was stimulated by glycerol and retained over 60% of its basal activity in the presence of 1% Tween-80 and Triton X-100. Overall, the activity of E25 under alkaline conditions and its organic solvent and detergent tolerance indicate that E25 could be useful as a novel industrial catalyst in biotechnological applications.</p>