Surviving winter with antifreeze proteins

Publisher Summary The rigors of cold climates have resulted in the evolution of unique, hyperactive antifreeze proteins that bind to microscopic ice crystals. Some insects, those that are freeze tolerant, upregulate metabolic pathways for the production of cryoprotectants, such as sugars or polyhydroxy alcohols. Freeze-tolerant insects raise their supercooling point, with some producing ice nucleators to ensure freezing at high subzero temperatures, and they may also accumulate other macromolecules, such as enzymes for anaerobic glycolysis. Most studied overwintering insects, have an alternative strategy for winter survival and are freeze susceptible. To avoid freezing, these insects decrease their supercooling points. They synthesize low molecular weight cryoprotectants to lower the freezing point of their hemolymph. To avoid inoculating ice, they seal themselves in cocoons or hibemacula and eliminate materials that could act as ice nucleators. Some freeze-susceptible insects may also synthesize thermal hysteresis proteins (THPs), which depress the hemolymph freezing point, relative to the melting point, by inhibiting the growth of ice until the nonequilibrium freezing point is reached. Although thermal hysteresis (TH) activity was originally described in insects, the subsequent discovery and extensive characterization of proteins with similar properties from fish, termed antifreeze proteins (AFPs), has prescribed a name change on the insect proteins. Two freeze-susceptible species, spruce budworm and mealworm beetles represent promising candidates for the purification of AFPs, because both can be reared under laboratory conditions.