BINDING OF AN ANTIFREEZE POLYPEPTIDE TO AN ICE WATER INTERFACE VIA COMPUTER-SIMULATION

The interaction between a winter flounder antifreeze polypeptide and a n ice/water interface was studied using Molecular Dynamics computer si mulation techniques to study the mechanism of action of this class of antifreeze molecules. Simple Point Charge models were used for the wat er molecules, and a molecular mechanics program (CHARMM) was used to c onstruct the model for the polypeptide. A (20 (2) over bar 1) face was exposed on the ice surface, as this is believed to be the experimenta lly favored ice face for peptide binding. The polypeptide binds strong ly to the ice surface even though it was placed with its four polar th reonine (Thr) groups pointing away from the ice surface. This tested t he previously advanced hypothesis that adsorption occurs primarily bet ween these groups and the ice due to a matching of the spacing between oxygen atoms in the ice lattice and the polar Thr residues. As well a s contacts with other polar groups on the peptide, the binding to the ice produces a good steric fir of the peptide with the corrugated ice interface. The presence of the peptide did not induce any melting of t he ice at 200 K.