Antifreeze protein, type I (IPR000104)

Short name: Antifreeze_1

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 and depressing the non-equilibrium freezing point to below that of the melting point.

Despite functional similarity, antifreeze proteins are structurally diverse and include glycosylated and at least 3 non-glycosylated forms: the AFGP of nototheniids and cods are polymers of a tripeptide repeat, Ala-Ala-Thr, with a disaccharide attached to the threonine residue; type I AFPs are 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. Non-homologous antifreeze proteins have also been identified in insects and plants [PMID: 12171656].

Type I AFPs are Ala-rich, amphiphilic, alpha-helical proteins [PMID: 8344924]. The ice-binding sites of all AFPs are relatively flat and hydrophobic and have an uninterupted section of alanines running the length of the approximately 16.5A helix repeat. Based on the energy-minimised structure [PMID: 1738160], a model has been proposed to describe the binding of the protein to ice crystals, whereby the protein binds to an ice nucleation structure, in a zipper-like fashion, via hydrogen bonding of the methyl-group of threonine side chains (with an 11-residue period) to oxygen atoms in the ice lattice. The growth of ice crystals is thus stopped, or retarded, and the freezing point depressed. The high lysince content of these peptides may serve to promote the solubility of these proteins.

GO terms

Biological Process

No terms assigned in this category.

Molecular Function

GO:0050825 ice binding

Cellular Component

No terms assigned in this category.

Contributing signatures

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