Antifreeze protein

Antifreeze proteins (AFPs) are a class of polypeptides produced by certain vertebrates, plants, fungi and bacteria that permit their survival in subzero environments. AFPs bind to small ice crystals to inhibit growth and recrystallization of ice that would otherwise be fatal.

Function

There are many different types of AFPs, each with a unique structure and function. However, all AFPs bind to ice crystals in order to lower the freezing temperature of water. This is known as thermal hysteresis. AFPs demonstrate a larger thermal hysteresis gap than any other known substance.

Types

There are four known types of AFPs, categorized by their structure and source. These include:

• Type I AFPs are found in winter flounder and related species. They are fairly small (3-4 kDa), alanine-rich, amphipathic alpha-helices.
• Type II AFPs are found in sea raven and related species. They are cysteine-rich globular proteins (14 kDa) that contain five disulfide bonds.
• Type III AFPs are found in Antarctic eelpout and related species. They are globular (6-7 kDa) and have a similar structure to the C-type lectins.
• Antarctic bacterial AFPs are found in Antarctic bacteria. They are fairly large (54 kDa) and are composed of a series of beta-helices.

Applications

AFPs have potential applications in a variety of areas. For example, they could be used to improve the texture of frozen foods or to preserve organs for transplantation. They could also be used to enhance the frost resistance of crops.

See also

• Ice-binding protein
• Cryoprotectant
• Thermal hysteresis
• Supercooling

References

Antifreeze protein Resources
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