exoglucanase

Exoglucanase, also known as a cellobiohydrolase, is a type of cellulase enzyme that hydrolyzes the ends of cellulose chains, releasing cellobiose as the primary product (and sometimes glucose). Acting in a processive manner, exoglucanases peel away disaccharide units from either the reducing or nonreducing end of crystalline or amorphous cellulose, functioning alongside other cellulases to convert cellulose into soluble sugars.

Exoglucanases are classified within glycoside hydrolase families, notably GH6 and GH7, with members in GH9 and GH48 also exhibiting exocellulase activity. They are typically secreted by cellulolytic organisms such as fungi and bacteria and often possess a cellulose-binding module that anchors the catalytic domain to the substrate. Well-known fungal examples include Cel7A (CBH I) and Cel6A (CBH II). The enzyme activity is catalogued as EC 3.2.1.91 (cellobiohydrolase).

In industrial contexts, exoglucanases are key components of enzyme cocktails used for biomass conversion and biofuel production, where they work in concert with endoglucanases and β-glucosidases to maximize saccharification. Their performance depends on substrate crystallinity and accessibility, enzyme–substrate binding, and product inhibition by cellobiose and glucose. Beyond biofuels, exoglucanases have relevance in textile processing and pulp and paper applications that involve cellulose modification and degradation.