Characterization of a novel thermostable GH45 endoglucanase from Chaetomium thermophilum and its biodegradation of pectin.

A novel thermostable endoglucanase (CTendo45) encoding gene was cloned from Chaetomium thermophilum and heterologously expressed in Pichia pastoris. Sequence alignment indicated that the CTendo45 enzyme belonged to glycoside hydrolase family 45. The recombinant enzyme was purified by Ni2+ affinity chromatography, and its apparent molecular mass was estimated to be 32 kDa by SDS-PAGE. The purified enzyme displayed maximum activity at 70°C and pH 4. CTendo45 was stable at 60°C for 1 h, and residual activities of 78.9% and 65.6% were estimated after 1 h at 70°C and 80°C, respectively. Ca2+, Zn2+, Mg2+, Cu2+ and Mn2+ were found to have beneficial effects on the enzyme activity to different degrees. The specific activity of purified CTendo45 was 1.52 IU mg-1 and the Km value was 59.6 μg ml-1 with a sodium carboxymethyl cellulose substrate. Moreover, CTendo45 exhibited high hydrolysis activity towards pectin, and the hydrolysis products were mainly galacturonic acid oligosaccharides. CTendo45 is the first reported bifunctional enzyme in glycoside hydrolase family 45 from C. thermophilum that is able to hydrolyze both cellulose and pectin. The biochemical properties of this recombinant CTendo45 make it a potentially effective glycoside hydrolase for industrial applications.