endoglucanases

Endoglucanases are enzymes that hydrolyze internal β-1,4-glycosidic bonds in cellulose and other beta-glucans, producing new chain ends. Classified as glycoside hydrolases (EC 3.2.1.4), they primarily act on the amorphous regions of cellulose, in contrast to exoglucanases that cleave from chain ends and β-glucosidases that release glucose from the resulting cellobiose and short cello-oligosaccharides.

Most endoglucanases employ either retaining or inverting catalytic mechanisms and use one or two carboxylate residues (often glutamate or aspartate) as acid/base and nucleophile. Structures commonly feature TIM-barrel or beta-sandwich folds and may include carbohydrate-binding modules that enhance interaction with crystalline cellulose. Substrate specificity varies: many favor amorphous cellulose or soluble substrates like carboxymethyl cellulose, while others act on mixed-linkage glucans or lichenin.

Endoglucanases are distributed across multiple glycoside hydrolase families, including GH5, GH7, GH9, GH12, GH44, and GH45, among others. They are produced by bacteria, fungi, and some other microorganisms, and are key players in lignocellulose degradation. Industrially important sources include fungi such as Trichoderma reesei and Humicola species, and various bacterial strains.

In practical applications, endoglucanases are used in enzyme cocktails for biomass pretreatment and saccharification, aiding cellulose breakdown to fermentable sugars for biofuels and bioproducts. Their efficiency depends on stability, temperature, pH, and substrate accessibility. In nature, they contribute to cellulose digestion in ruminants and wood-feeding insects through synergistic action with other cellulases. Activity is commonly measured using carboxymethyl cellulose as a substrate (CMCase assay).