InterPro domain: IPR000400

O-Glycosyl hydrolases ( 3.2.1. ) are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycosyl hydrolases, based on sequence similarity, has led to the definition of 85 different families [ 1 , 2 ]. This classification is available on the CAZy (CArbohydrate-Active EnZymes) website.

Glycoside hydrolase family 46 GH46 comprises enzymes with only one known activity; chitosanase ( 3.2.1.132 ).

Chitosanase enzymes catalyse the endohydrolysis of beta-1,4-linkages between N-acetyl-D-glucosamine and D-glucosamine residues in a partly acetylated chitosan. Chitosan is a biopolymer of beta (1,4)-linked -D-glucosamine (GlcN) residues produced by partial or full deacetylation of chitin. Chitosanases play a role in defense against pathogens such as fungi and are found in microorganisms, fungi, viruses, and plants. Microbial chitosanases whose members are the most prevalent can be divided into 3 subclasses based on the specificity of the cleavage positions for partial acetylated chitosan. Subclass I chitosanases such as N174 can split GlcN-GlcN and GlcNAc-GlcN linkages, whereas subclass II chitosanases such as Bacillus sp. no. 7-M can cleave only GlcN-GlcN linkages. Subclass III chitosanases such as MH-K1 chitosanase are the most versatile and can split both GlcN-GlcN and GlcN-GlcNAc linkages [ 3 , 4 , 5 , 6 ].

1. Conserved catalytic machinery and the prediction of a common fold for several families of glycosyl hydrolases. Proc. Natl. Acad. Sci. U.S.A. 92, 7090-4
2. Structures and mechanisms of glycosyl hydrolases. Structure 3, 853-9
3. Structural analysis shows five glycohydrolase families diverged from a common ancestor. J. Exp. Zool. 282, 127-32
4. X-ray structure of an anti-fungal chitosanase from streptomyces N174. Nat. Struct. Biol. 3, 155-62
5. Chitinases, chitosanases, and lysozymes can be divided into procaryotic and eucaryotic families sharing a conserved core. Nat. Struct. Biol. 3, 133-40
6. Chitinolytic enzymes: catalysis, substrate binding, and their application. Curr. Protein Pept. Sci. 1, 105-24