"

From 2010.igem.org

Antifreeze proteins (AFP's) refer to a class of polypeptides, with a polyphyletic ancestry, produced by certain animals (like insects and fishes), plants and fungi that allow them to survive in freezing environments and to help them in maintain the body fluidity. (Simulation)

The sea water in cold region is freeze at -1.9C owing to dissolved solutes. To the animals don’t freeze at this temperatures, their blood must have lower freezing point. The quality of the AFP's to decrease freezing point is not caused number of solute molecules. Instead of this AFP’s bind to small ice crystals surfaces to inhibit growth and recrystallization of ice in the cell membranes that would be fatal in animals

There are many kinds of AFP's synthesize by different organisms:

Type I AFP

• Found in winter flounder, longhorn sculpin and shorthorn sculpin.

• Consist of a single, long, amphipathic alpha helix 4kD approximately.

Type I-hyp AFP (where hyp stands for hyperactive)

• Found in righteye flounders.

• It is considerably better at depressing freezing temperature than most fish AFPs

Type II AFP

• Found in sea raven, smelt and herring.

• They are cysteine-rich globular proteins containing five disulfide bonds

Type III AFP

• Found in Antarctic eelpout.
• They exhibit similar overall hydrophobicity at ice binding surfaces to type I AFPs.

Type IV AFP

• Are found in longhorn sculpins.
• They are alpha helical proteins rich in glutamate and glutamine.

Type V AFP

• Are the hyperactive AFPs found in insects
• Throughout the length of the amino acid, at least every sixth is a cysteine residue. They are also hyperactive

Plant AFP

• They have much weaker thermal hysteresis activity when compared to other AFPs.
• Their physiological function is likely in inhibiting the recrystallization of ice rather than in the preventing ice formation

Mechanisms of action

AFP's possesses the ability to bind to the ice crystals surface, inhibiting the formation of ice. The growing ice surface becomes energetically unfavorable for further absorption of water molecules proportionately with the surface curvature, leading to the termination of ice growth. This AFP-induced inhibition of ice crystal growth can be detected macroscopically as a depression in the freezing temperature (Tf) of the solution without alteration of the melting temperature (Tm) ([Tf –Tm]). This is called thermal hysteresis. (Chattopadhyay; 2007) (Davies and Hew; 1990)

Various processes are involved in the formation of solid phase of the water, among others, the interaction between ions or molecules leads to the formation of nucleus. The nucleation is the formation of the new centers from which spontaneous growth can occur; this processes determines the size and distribution of produced crystals. Large crystals may eventually be formed from fine crystals by a process called ripening.There are a lot of ions and other particles Inside the cells. So when the temperature decreases the nucleation process arise in the cytoplasm and for this reason the cells die.

---

Chattopadhyay M. K; (2007); Antifreeze Proteins of Bacteria; Resonance p 25-30[1]

Davies, Peter L. and Hew, Choy L.; (1990); Biochemistry of fish antifreeze proteins; The FASEB journal; Vol. 4 p 2460-2468[2]

Scotter, A. J.; et al. (2006). "The basis for hyperactivity of antifreeze proteins". Cryobiology 53 (2): 229–239