Thermodynamic Properties of the β-glucosidase from Thermotoga maritima Extend the Upper Limit of Thermophilicity

Enzymes from thermophilic organisms are believed to be strong candidates for industrial applications due to their ability to withstand temperature-induced enzyme inactivation. The present study demonstrated molecular cloning, over-expression, purification and characterization of β-glucosidase from Thermotoga maritima. The bglA gene with a capacity to encode a 51 kDa enzyme was heterologously expressed in E. coli M15. The enzyme was produced @130 mgL-1 in LB media and @440 mgL-1 in Dubos salt medium accounting 40-47 % of total cellular soluble proteins when lactose was used as an inducer. The enzyme showed a peak activity between pH and temperature range of 5.0-7.0 and 80-100 °C, respectively. The activity was fairly stable up to 140 °C. The turnover rate (kcat) of the enzyme was 187.1±20 s-1, whereas the Km and Vmax values were 0.56 mM and 238±2.4 IU mg-1 protein, respectively. The enzyme was shown to have half-life of 136, 71 and 12.6 h at 80, 90 and 100 °C, respectively. Thermodynamics parameters including melting temperature (130 °C), activation energy for inactivation (36.92 kJmole-1), enthalpy (33.73 kJmole-1), Gibb’s free energy (127.96 kJmole-1) and entropy (-246.46 Jmole-1K-1) have shown that the enzyme have enhanced hydrophobic interactions to prevent its thermal unfolding. These features endorse the industrial applications of the enzyme.