Glycoside hydrolase family 18 chitinases: The known and the unknown

Glycoside hydrolase family 18 (GH18) chitinases, which catalyze the biodegradation of β-1,4 glycosidic bond in amino polysaccharides via a substrate-assisted retention mechanism, are widely distributed in nature and have diverse functions. Many organisms produce several GH18 chitinases which take part in multiple physiological processes, including tissue degradation and remodeling, nutrition uptake, invasion and pathogenesis as well as immune response regulation. Because of their physiological importance, mounting crystallographic investigations have been conducted for GH18 chitinases, and their inhibitors have also been developed. However, there is still much unclear concerning these enzymes, such as the explicit mechanisms underlying their involvement in disease development, the direct connection of structure to processivity, and selectivity of the inhibitors. In this article, research progress on biological function, structural information and inhibition of GH18 chitinases has been reviewed and the remaining uncertainties are highlighted. This review may also facilitate those who intent to develop drugs or agrochemicals based on these enzymes.