Degradation of hemicelluloses, the second most abundant polysaccharides in nature. Contains two catalytic domains with mannanase and endoglucanase activities. Random hydrolysis of (1->4)-beta-D-mannosidic linkages in mannans, galactomannans and glucomannans. Endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans. Optimum pH is 6. Optimum temperature is 80 degrees Celsius. In the N-terminal section; belongs to the glycosyl hydrolase 5 (cellulase A) family. In the C-terminal section; belongs to the glycosyl hydrolase 44 (cellulase J) family.