Heterologous Expression and Characterization of an Endoglucanase from a Symbiotic Protist of the Lower Termite, Reticulitermes speratus

RsSymEG, an endoglucanase of glycosyl hydrolase family (GHF) 7 encoded by a transcript isolated from the symbiotic protist of the termite Reticulitermes speratus, is expressed in Aspergillus oryzae. Interestingly, purified RsSymEG1 has a relatively higher specific activity (603 μmol min−1 mg−1 protein) and Vmax value (769.6 unit/mg protein) than previously reported data for GHF7 endoglucanase of Trichoderma ressei. It also has the same Km value (1.97 mg/ml) with Clostridium cellulolyticum enzymes that contain cellulose binding module, a property indicative of high affinity to substrate, though no cellulose binding module is found within it. Thin-layer chromatography analysis revealed that RsSymEG1 preferentially hydrolyzes the β-1,4-cellulosic linkage of cellodextrins into cellobiose and glucose.