The biological conversion of cellulose to glucose generally requires three types of hydrolytic enzymes: (1) Endoglucanases which cut internal beta-1,4-glucosidic bonds; (2) Exocellobiohydrolases that cut the disaccharide cellobiose from the non-reducing end of the cellulose polymer chain; (3) Beta-1,4-glucosidases which hydrolyze the cellobiose and other short cello-oligosaccharides to glucose. Active against carboxymethylcellulose, beta-glucan and lichenan. Hydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose and cellotetraose, releasing cellobiose from the non-reducing ends of the chains. Optimum pH is 5.5. Optimum temperature is 57 degrees Celsius. Has a modular structure: a carbohydrate-binding module (CBM) at the N-terminus, a linker rich in threonines, and a C-terminal exocellobiohydrolase catalytic module. The genes for catalytic modules and CBMs seem to have evolved separately and have been linked by gene fusion. Belongs to the glycosyl hydrolase 6 (cellulase B) family.