Antifreeze Protein Activity: From Ice Binding to Ice Growth Inhibition

Antifreeze proteins (AFPs) lower the freezing point of water without affecting the melting point appereciably. To elucidate the behavior of AFPs, a series of simulations are conducted using Tenebrio molitor antifreeze protein (TmAFP) as a paradigm protein. This review highlights important findings obtained from those studies. Explicit solvent molecular dynamics simulations illustrate that, in order to get adsorbed on to the ice surfaces, a very specific kind of hydration structure and dynamics are developed on the ice-binding surface (IBS) of TmAFP. The complementary arrangement of water molecules and protein residues in the ice-bound state of the protein is determined from heterogeneous ice nucleation simulation on a model IBS. The result shows that the regular structure of ice is not maintained at the protein-ice interface. Water molecules are found to form five-membered hydrogen-bonded rings with protein residues. It is further demonstrated that TmAFP carries its own binding motif while it is present freely in solution. Hydrophobic and hydrogen bonding interactions together contribute to form such motif on the IBS of the protein. Further, the growth of ice in presence of the protein bound to an ice plane is found to be inhibited by the Kelvin effect.