ABSTRACT
The deconstruction and transformation of chitin uses enzymes that facilitate an essential environmental metabolic process. Different classes and families of chitinases act at different stages of chitin degradation, and various mechanisms and pathways are used. Three significant pathways include lytic polysaccharide monooxygenases (LPMOs), chitinases, and deacetylases/chitosanases. LPMOs are copper-dependent enzymes that catalyze the cleavage of glycosidic bonds in crystalline regions of chitin using an oxidative mechanism and contribute to the efficiency of biomass degradation by glycoside hydrolases. Chitinases belonging to two different glycoside hydrolases, GH18 and GH19, degrade chitin throughout a retaining or inverting mechanism producing oxidized carbohydrates. The presence of carbohydrate-binding modules increases the local concentration of enzymes and the overall efficiency of the hydrolytic machinery. Chitin deacetylases include enzymes that remove the acetyl groups in the substrates. Chitosanases hydrolyze chitosan into oligomers and dimers. Some families of chitinases utilize retaining catalytic mechanisms, while others proceed via inverting mechanisms.
