Type-2 ice-structuring protein (IPR002353)

Short name: AntifreezeII

Overlapping homologous superfamilies

Family relationships



Marine teleosts from polar oceans can be protected from freezing in icy sea-water by serum antifreeze proteins (AFPs) or glycoproteins (AFGPs) [PMID: 7540906]. These function by binding to, and preventing the growth of, ice crystals within the fish. Despite functional similarity, the proteins are structurally diverse and include glycosylated and at least 3 non-glycosylated forms: the AFGP of nototheniids and cod are polymers of a tripeptide repeat, Ala-Ala-Thr, with a disaccharide attached to the threonine residue; type I AFPs are Ala-rich, alpha-helical peptides found in flounder and sculpin; type II AFPs of sea-raven, smelt and herring are Cys-rich proteins; and type III AFPs, found in Eel pouts, are rich in beta-structure. Although no direct structural information is available for type II AFPs, their sequences are similar to the carbohydrate recognition domain (CRD) of Ca2+-dependent lectins. This domain is present in a superfamily of proteins that bind sugars specifically through contact with a calcium ion. The extent of similarity within the superfamily is confined to short motifs and single amino acids at intervals throughout the protein.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.