4. Antifreeze proteins: effective adaptation to low temperatures

Abstract

Adaptation to low temperature presents manifold challenges. In particular, extreme environments, like the polar regions, require organisms to make sophisticated adjustments at the molecular, cellular and organismal levels. Chilling slows cellular function, alters protein-protein interactions, and reduces membrane fluidity, among other effects. Further, freezing temperatures induce ice crystal growth, which disrupts cellular processes, and is often lethal when formed intracellularly. If species are unfit to cope, high mortality rates can result. An effective strategy for cold resistance is the expression of antifreeze proteins (AFPs) - a class of polypeptides that allow survival in cold environments. AFPs and AFGPs (antifreeze glycoproteins) are relatively high molecular mass molecules that have the ability to stabilize membranes during chilling and control ice crystal growth during freezing of cells and tissues. One class of AFGPs and six classes of AFPs (AFP types I-V, and plant) have been identified in a wide variety of species. These proteins confer efficient, highly effective protection against low-temperature damage. The majority of early studies on AFPs focused on polar fish species (AFGP and AFP types I-IV), but have more recently expanded to include other vertebrates, insects, plants, fungi, and bacteria. The aim of this project is to review low-temperature adaptation, AFP evolution and mechanisms of function, as well as current applications in research and medicine.