Thermodynamic Properties of the β-glucosidase from Thermotoga maritima Extend the Upper Limit of Thermophilicity
Muhammad A. Mehmood,
Muhammad I. Rajoka.
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.
Keywords: β-glucosidase, heterologous expression, low-cost production, Thermotoga maritima, thermophilic.
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