Role of Polar and Nonpolar Groups in the Activity of Antifreeze Proteins: A Molecular Dynamics Simulation Study

Molecular dynamics simulations have been carried out separately with the hyperactive Tenebrio molitor antifreeze protein ( TmAFP) and with its nonactive mutant at 300 K to elucidate the role of polar and nonpolar groups in the activities of antifreeze proteins (AFPs). Simulation results reveal that both polar and nonpolar groups contribute to develop the required quasi-ice-like hydration layer on the ice-binding surface (IBS) of an AFP for binding onto ice. Nonpolar groups on the IBS induce the formation of locally ordered icelike low-density waters in the hydration layer through hydrophobic interactions, and polar groups of the surface integrate these waters into a quasi-ice-like layered structure through hydrogen-bonding interactions. These contributions of polar and nonpolar groups apparently contradict the behavior of winter flounder antifreeze protein (wfAFP) mutants possibly due to switching of IBS of wfAFP upon mutation of threonine residues with valine residues.