Expression of Two Novel [beta]-Glucosidases from Chaetomium atrobrunneum in Trichoderma reesei and Characterization of the Heterologous Protein Products

Two novel GH3 family thermostable [beta]-glucosidases from the filamentous fungus Chaetomium atrobrunneum (CEL3a and CEL3b) were expressed in Trichoderma reesei, purified by two-step ion exchange chromatography, and characterized. Both enzymes were active over a wide range of pH as compared to Neurospora crassa [beta]-glucosidase GH3-3, which was also expressed in T. reesei and purified. The optimum temperature of both C. atrobrunneum enzymes was around 60 °C at pH 5, and both enzymes had better thermal and pH stability and higher resistance to metallic compounds and to glucose inhibition than GH3-3. They also showed higher activity against oligosaccharides composed of glucose units and linked with [beta]-1,4-glycosidic bonds and moreover, had higher affinity for cellotriose over cellobiose. In hydrolysis tests against Avicel cellulose and steam-exploded sugarcane bagasse, performed at 45 °C, particularly the CEL3a enzyme performed similarly to N. crassa GH3-3 [beta]-glucosidase. Taking into account the thermal stability of the C. atrobrunneum [beta]-glucosidases, they both represent promising alternatives as enzyme mixture components for improved cellulose saccharification at elevated temperatures.