Endochitinases

Endochitinases are enzymes that degrade chitin by cleaving internal β-1,4-glycosidic bonds within the polymer. This mode of action releases short chito-oligosaccharides rather than monomeric units, distinguishing endochitinases from exochitinases that dismantle the chain from the ends. Chito-oligosaccharides produced by endochitinases can vary in length and acetylation.

Most endochitinases belong to the glycoside hydrolase family 18 (GH18), with plant endochitinases often classified in GH19. Many enzymes contain a catalytic domain and, in some cases, a chitin-binding module that helps target crystalline chitin in nature. The catalytic mechanism typically involves two conserved residues, commonly an aspartate and a glutamate, functioning in a retaining reaction to hydrolyze the glycosidic bond.

Substrate specificity among endochitinases varies. They generally act on chitin, a polymer of N-acetylglucosamine, and can differ in their preference for crystalline versus soluble forms and in tolerance to substrate acetylation. Some enzymes show activity on related substrates such as chitosan, but activity profiles are diverse across organisms.

Biological roles of endochitinases include nutrient acquisition from chitin-containing organisms, such as fungi and crustaceans, as well as defense mechanisms in plants where chitin fragments act as immune elicitors. In fungi and bacteria, endochitinases contribute to cell wall remodeling and interaction with other microbes.

Industrially, endochitinases are exploited to produce defined chitooligosaccharides for applications in agriculture, medicine, and cosmetics, and for bioconversion of chitinous waste. Ongoing research focuses on improving activity toward crystalline chitin, stability under process conditions, and tailoring substrate specificity through protein engineering.