Characterization of a novel thermostable GH7 endoglucanase from Chaetomium thermophilum capable of xylan hydrolysis

Abstract

A new endoglucanase encoding gene (ctendo7) was cloned from the thermophilic fungus Chaetomium thermophilum and heterologously expressed in Pichia pastoris. The recombinant CTendo7 enzyme was purified by Ni²⁺ affinity chromatography and subsequently characterized. CTendo7 belongs to glycoside hydrolase family 7, and exhibited considerable activity against sodium carboxymethyl cellulose (CMC-Na) and xylan of 1.91 IU/mg and 3.05 IU/mg at the optimum reaction condition of 55 °C, pH 5.0, respectively. The purified enzyme displayed relatively good thermostability. The residual endoglucanase and xylanase activities were 74.3% and 66.2% after a 60 min pre-incubation at 70 °C. Additionally, Ag⁺, Fe³⁺ and Cu²⁺ negatively affected the enzyme's activity, while the presence of 1 mM and 5 mM Mn²⁺ significantly enhanced both endoglucanase and xylanase activities. Generation of soluble oligosaccharides from lignocellulose is a critical step in bioethanol production, and it is noteworthy that CTendo7 produced cello-oligosaccharides and xylo-oligosaccharides from the continuous enzymatic saccharification of CMC-Na and xylan, respectively. This is the first detailed report on a novel bifunctional endoglucanase/xylanase enzyme from C. thermophilum. Furthermore, the excellent properties of CTendo7 distinguish it as a promising candidate for industrial lignocellulosic biomass conversion.