Antifreeze Proteins in Other Species

Abstract

Ice-binding proteins (IBPs) are now recognized to include three types of proteins. (1) Antifreeze proteins (AFPs), first discovered in Antarctic fish, protect freeze-avoiding organisms from lethal ice formation of their body fluids by lowering the freezing point of aqueous solutions by a non-colligative mechanism—binding to ice crystals and preventing their growth. This results in a difference between the freezing and melting points termed thermal hysteresis (TH). AFPs prevent inoculative freezing across the body surface by exterior ice and they also promote supercooling by inhibiting potential ice nucleation surfaces. (2) Recrystallization inhibition proteins (RIPs) function primarily to inhibit recrystallization of ice in freeze-tolerant organisms (those able to freeze and survive) although they also generally produce minor TH. Note that true While AFPs inhibit recrystallization of ice, the primary function of recrystallization inhibition proteins (RIPs), although they also produce minor TH, is to inhibit recrystallization in freeze-tolerant organisms (those able to freeze and survive). (3) Adaptive ice-nucleating proteins (INPs) function in freeze-tolerant species to inhibit supercooling and promote freezing at a high subzero temperature where the resulting freezing is more easily controlled. Although INPs are best known in bacteria, AFPs and RIPs traditionally have been most studied in fish, insects, and plants. However, these proteins are also present in numerous other organisms. These “other” TH-producing organisms are the focus of this chapter. They include many types of animals such as noninsect arthropods (spiders, mites, ticks, centipedes, a crustacean, and snow fleas), mollusks, ribbon worms, fish leeches, sponges, nematodes, frogs, perhaps even mammals and birds; several fungi and numerous bacteria, and archaea. Antifreeze glycolipids will also be discussed.