Antifreeze protein

Antifreeze protein (pronunciation: an-tee-freez pro-teen) is a type of protein that is produced by certain types of organisms such as fish, plants, insects, and bacteria. These proteins have the ability to inhibit the formation of ice in the organisms' tissues, allowing them to survive in extremely cold environments.

Etymology

The term "antifreeze protein" is derived from its function. The prefix "anti-" comes from the Greek word "anti" meaning "against", and "freeze" is derived from the Old English "freosan" meaning "to turn to ice". The word "protein" comes from the Greek "proteios" meaning "primary" or "in the lead".

Function

Antifreeze proteins work by binding to small ice crystals to prevent them from becoming larger. This process is known as 'ice recrystallization inhibition' (IRI). The proteins essentially lower the freezing point of water inside the organism, below the freezing point of the surrounding environment. This is a form of 'thermal hysteresis' and is crucial for the survival of many organisms in extreme cold conditions.

Types of Antifreeze Proteins

There are several types of antifreeze proteins, each found in different types of organisms. These include:

Type I AFPs: These are found in teleost fish and are relatively small proteins.
Type II AFPs: These are found in Antarctic eelpouts and are much larger than Type I AFPs.
Type III AFPs: These are found in northern pouts and are medium-sized proteins.
Antifreeze glycoproteins (AFGPs): These are found in Arctic cods and are composed of a protein backbone with attached sugar molecules.