The glycoside hydrolase family 18 family contains enzymes with chitinase (chitinase class III group) or endo-β-N-acetylglucosaminidase activity as well as non-catalytic proteins. The family also includes various glycoproteins from mammals such as cartilage glycoprotein and the oviduct-specific glycoproteins. Some family members from animals also contain a pertrophin-like chitin-binding domain, which is also found in chitin binding proteins without chitinase activity, particularly peritrophic matrix proteins of insects [1]. Class III chitinases from plants have bifunctional activities as chitinases and lysozymes [2].
Chitinases from mites (group 15 and 18 mite allergens) are highly glycosylated major allergens [3]. In addition, they are major mite allergens for cats and dogs [4]. Group 18 allergens contain a C-terminal peritrophin domain. Group 12 mite allergens also contain a peritrophin domain, but lack a catalytic domain. Some plant allergens belong to the chitinase class III family. Hevamine (Hev b 14) is a bifunctional chitinase/lysozyme from Hevea brasiliensis and a minor natural rubber latex allergen [5].
Family-defining Pfam domains (at least one of these domains is present in each family member):
| Pfam domain | Pfam clan | ||
| PF00704 | Glycosyl hydrolases family 18 | CL0058 | Tim barrel glycosyl hydrolase superfamily |
| PF01607 | Chitin binding Peritrophin-A domain | CL0155 | Carbohydrate binding domain 14/19 clan |
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