<p>O-Glycosyl hydrolases <db_xref db="EC" dbkey="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 [<cite idref="PUB00004870"/>, <cite idref="PUB00005266"/>]. This classification is available on the CAZy (CArbohydrate-Active EnZymes) web site.</p><p>Family 56 (<db_xref db="CAZY" dbkey="GH56"/>) encompasses a group of hyaluronidases (<db_xref db="EC" dbkey="3.2.1.35"/>)that includes venom hyaluronidases [<cite idref="PUB00004814"/>] and mammalian sperm surface proteins (PH-20).</p><p>Allergies are hypersensitivity reactions of the immune system to specific substances called allergens (such as pollen, stings, drugs, or food) that, in most people, result in no symptoms. A nomenclature system has been established for antigens (allergens) that cause IgE-mediated atopic allergies in humans [WHO/IUIS Allergen Nomenclature Subcommittee King T.P., Hoffmann D., Loewenstein H., Marsh D.G., Platts-Mills T.A.E., Thomas W. Bull. World Health Organ. 72:797-806(1994)]. This nomenclature system is defined by a designation that is composed ofthe first three letters of the genus; a space; the first letter of thespecies name; a space and an arabic number. In the event that two speciesnames have identical designations, they are discriminated from one anotherby adding one or more letters (as necessary) to each species designation.</p><p> The allergens in this family include allergens with the following designations: Api m 2, Dol m 2 and Ves v 2.</p> <p>The venom of <taxon tax_id="7460">Apis mellifera</taxon> (honeybee) contains several biologically-active peptides andtwo enzymes, one of which is a hyaluronidase [<cite idref="PUB00004814"/>]. The amino acid sequence of bee venom hyaluronidase contains 349 amino acids, and includes fourcysteines and a number of potential glycosylation sites [<cite idref="PUB00004814"/>]. The sequence shows a high degree of similarity to PH-20, a membrane protein of mammaliansperm involved in sperm-egg adhesion, supporting the view that hyaluronidases play a role in fertilisation [<cite idref="PUB00004814"/>].</p>