Fish from the polar regions only know one season : Winter. Temperatures are freezing, sometimes reaching -2°C ! But thanks to the salt, the seawater stays liquid. Fish, however, are not so salty. So why don’t they become solid blocks of ice? The notothenoid fish live in the chilly waters of the Antarctica and have devised very sophisticated ways of surviving extreme conditions. Thanks to the singular properties of antifreeze gylcopeptides, their body fluids remain fluid in ice-laden waters.
Antifreeze proteins diffuse into many parts of a fishes’ body, to protect cells from ice crystals which would perforate the cells and cause them to explode. How do antifreeze proteins work? They check the development of budding ice crystals thanks to a particular structure in their primary sequence: a succession of 3 amino acids (threonine – alanine (or proline) – alanine) which is repeated many times. Every threonine carries a molecule of sugar, which imparts to the overall antifreeze protein an affinity for water. The moment an ice crystal starts to form, antifreeze glycopeptides are attracted to the molecules of water surrounding it. In doing so, the nascent crystal is coated with a film of antifreeze proteins and, as a result, is unable to recruit further water molecules. Consequently, any further growth is interrupted.
Antifreeze proteins are particularly aggressive antifreeze agents. Such substances could be used to preserve human tissues such as sperm for example. Indeed, in the freezing process, one third is lost! The use of antifreeze proteins for such tissue samples could help to save a greater fraction. Antifreeze proteins could also be used to help preserve organs which frequently have to cover great distances before they are transplanted.