Role of Nonpolar Amino Acid Functional Groups in the Surface Orientation-Dependent Adsorption of Natural and Synthetic Antifreeze Peptides on Ice

The aim of this study is to investigate the significance of nonpolar functional groups in the surface orientation-dependent adsorption of natural and synthetic antifreeze proteins (AFPs) on ice. We investigate using nanoliter osmometry, ice etching, and circular dichroism spectroscopy a series of nine designed α-helical peptides to probe the nature of their selectivity between the bipyramidal {201} and the secondary prismatic {21̅0} faces of ice, identified earlier as the preferred faces for adsorption of winter flounder (WF) and shorthorn sculpin type I AFPs, respectively. Complementarities between the AFP’s surface features, comprised chiefly of nonpolar groups, and the well-defined sites on ice surface, allow close contact. Because our experimental studies demonstrate that the function of AFPs relies on participation of both polar and nonpolar residues in the ice surface adsorption, we carry out computational modeling to explore both kinds of contacts at the ice surface. On the basis of results of semiempirical quantum mechanical calculations of the WF AFP/ice system, we propose and discuss a new model for the binding of WF AFP to the {201} surface of ice, in a groove formed between {21̅0} and {011} facets.