Endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans. Glycan metabolism; cellulose degradation. Homodimer. Predicted to be exported by the Tat system. The position of the signal peptide cleavage has been experimentally proven. Belongs to the glycosyl hydrolase 6 (cellulase B) family.