Physical Basis of Functioning of Antifreeze Protein

Antifreeze proteins, expressed in cold-blooded organisms, prevent ice formation in their bodies, and thus help them to survive in extremely cold winter temperatures. However, the mechanism of action of these proteins is still not clear. In any case, it is not simply a decrease in the temperature of normal ice formation. In this work, investigating the ice-binding protein (a mutant form of the antifreeze protein cfAFP from the spruce budworm Choristoneura fumiferana, which overwinters in needles), we showed that this antifreeze protein does not at all lower the freezing point of water and, paradoxically, increases the melting point of ice. On the other hand, calculations based on the theory of crystallization show that at temperatures of 0 degrees to -30 degrees C ice can only appear on surfaces that contact water, but not in the body of water. These facts suggest a new perspective on the role of antifreeze proteins: their task is not (as it is commonly believed) to bind with nascent ice crystals already formed in the organism and stop their growth, but to bind to those surfaces, on which ice nuclei can appear, and thus completely inhibit the ice formation in supercooled water or biological fluid.