What are chitinases?
Chitinases are hydrolytic enzymes able to cleave the β-1,4-glycosidic bond between two N-acetylglucosamine residues (GlcNAc-GlcNAc). Hence, they can depolymerise chitin polymers and oligomers, typically yielding chitobiose and chitotriose as products. Chitinases have the Enzyme Commission number EC 188.8.131.52, and according to the CAZY classification of Carbohydrate Active enZYmes, most of them belong to the Glycoside Hydrolase (GH) families GH18 and GH19. Some chitinases in the GH18 family can also cleave the glycosidic linkage between an N-acetylglucosamine and a glucosamine residue (GlcNAc-GlcN), while some chitinases in the GH19 family can also cleave the glycosidic linkage between a glucosamine and an N-acetylglucosamine residue (GlcN-GlcNAc), but chitinases as a rule do not cleave the linkage between two glucosamine residues (GlcN-GlcN). Thus, the specificity of GH18 chitinases may be described as GlcNAc-X (where X is GlcNAc or GlcN) while that of GH19 chitinases is X-GlcNAc. Consequently, chitinases can also partially hydrolyse partially acetylated chitosans (but not polyglucosamine). Based on their modes of action, chitinases are classified as endo- or exo-acting enzymes, and they can act processively or non-processively.