Antifreeze proteins: effective adaptations of organisms for low temperature survival

Adaptation to low temperature presents many challenges. On a cellular level, structural integrity and metabolism are profoundly affected in cold temperatures, and at freezing temperatures, ice crystal formation must be prevented or controlled for an organism to survive. Antifreeze proteins (AFP) and glycoproteins (AFGP) are protective molecules expressed by organisms to effectively cope with these challenges. These proteins are extremely effective at protecting tissues from chilling and freezing damage, and are active at low concentrations compared to other cryoprotectants, such as glycerol. Many organisms can prevent ice crystal formation in their tissues by supercooling, where the freezing point of cellular fluid is decreased below the normal freezing point of water. Those that can tolerate freezing use ice nucleating proteins (INP) and AFPs to restrict the growth and coalescence of ice crystals. Studies on the evolution of AFPs and AFGPs in polar species reveal that the genes arose from a variety of mechanisms - including lateral gene transfer, gene duplication and convergent evolution - in response to climate change. AFPs directly bind to ice crystal faces, slowing or preventing crystal growth and coalescence. They also act to reduce membrane permeability by interacting with bilayer lipids, thereby preventing leakage during chilling. Practical applications of these molecules include tissue preservation, cold tolerance in crops and food animals, frozen food storage, and freeze-proof surface coatings.