Endoglucanase (EG) that cleaves the internal beta-1,4-glucosidic bonds in cellulose. The degradation of cellulose involves an interplay between different cellulolytic enzymes. Hydrolysis starts with EGs, which cut internal glycosidic linkages to reduce the polymerization degree of the substrate and creates new chain ends for exocellobiohydrolases (CBHs). The CBH release the disaccharide cellobiose from the non-reducing end of the cellulose polymer chain. Finally, beta-1,4-glucosidases hydrolyze the cellobiose and other short cello-oligosaccharides into glucose units. Endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans. The enzyme consists of two functional domains, a catalytic core joined to a carbohydrate-binding domain (CBM) by a serine-, threonine-, and proline-rich, highly glycosylated linker sequence. Belongs to the glycosyl hydrolase 5 (cellulase A) family.