Heterologous Expression and Biochemical Characterization of a Thermostable Endoglucanase (MtEG5-1) from Myceliophthora thermophila

Thermophilic endoglucanases have become of significant interest for effectively catalyzing the hydrolysis of cellulose. Myceliophthora thermophila is an ideal source of thermophilic enzymes. Interestingly, different hosts differently express the same enzymes. In this study, we successfully overexpressed endoglucanase (MtEG5-1) from M. thermophila in the methylotrophic yeast, Pichia pastoris GS115, via electroporation. We found that purified MtEG5-1 exhibited optimum activity levels at pH 5 and 70 °C, with 88% thermal stability after being incubated at 70 °C for 2 h. However, we observed that purified MtEG5-1 had a molecular weight of 55 kDa. The Km and Vmax values of purified MtEG5-1 were approximately 6.11 mg/mL and 91.74 μmol/min/mg at 70 °C (pH 5.0), respectively. Additionally, the optimum NaCl concentration of purified MtEG5-1 was found to be 6 g/L. Furthermore, we observed that the activity of purified MtEG5-1 was significantly enhanced by Mn2+ and was inhibited by K+. These results indicated that MtEG5-1 expressed by P. pastoris GS115 is more heat-tolerant than that expressed by A. niger and P. pastoris X33. These properties of MtEG5-1 make it highly suitable for future academic research and industrial applications.