Marine teleosts from polar oceans can be protected from freezing in icysea-water by serum antifreeze proteins (AFPs) or glycoproteins (AFGPs) [<cite idref="PUB00005033"/>].These function by binding to, and preventing the growth of, ice crystalswithin the fish. Despite functional similarity, the proteins arestructurally diverse and include glycosylated and at least 3 non-glycosylated forms: the AFGP of nototheniids and cod are polymers of atripeptide repeat, Ala-Ala-Thr, with a disaccharide attached to thethreonine residue; type I AFPs are Ala-rich, alpha-helical peptidesfound in flounder and sculpin; type II AFPs of sea-raven, smelt andherring 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 Ca<sup>2+</sup>-dependent lectins. This domain is present in a superfamily ofproteins that bind sugars specifically through contact with a calciumion. The extent of similarity within the superfamily is confined to short motifs and single amino acids at intervals throughout the protein.