Characterization of a Type II L-Asparaginase from the Halotolerant <i>Bacillus subtilis</i> CH11

Abstract

L-asparaginases from bacterial sources have been used in antineoplastic treatments and the food industry. A type II L-asparaginase encoded by the N-truncated gene ansZP21 of halotolerant Bacillus subtilis CH11 isolated from Chilca salterns in Peru was expressed using a heterologous system in Escherichia coli BL21 (DE3)pLysS. The recombinant protein was purified using one-step nickel affinity chromatography and exhibited an activity of 234.38 U mg−1 and a maximum catalytic activity at pH 9.0 and 60 °C. The enzyme showed a homotetrameric form with an estimated molecular weight of 155 kDa through gel filtration chromatography. The enzyme half-life at 60 °C was 3 h 48 min, and L-asparaginase retained 50% of its initial activity for 24 h at 37 °C. The activity was considerably enhanced by KCl, CaCl2, MgCl2, mercaptoethanol, and DL-dithiothreitol (p-value Vmax and Km were 145.2 µmol mL−1 min−1 and 4.75 mM, respectively. These findings evidence a promising novel type II L-asparaginase for future industrial applications.

Keywords

• L-asparaginase II
• <i>Bacillus subtilis</i>
• saline environment
• biochemical characterization