Analysis of shorthorn sculpin antifreeze protein stereospecific binding to (2-1 0) faces of ice.

In this paper we report the results of our studies on the stereospecific binding of shorthorn sculpin antifreeze protein (AFP) to (2 -1 0) secondary prism faces of ice. Using ice crystal growth and etching techniques together with molecular modeling, molecular dynamics, and energy minimization, we explain the nature of preferential binding of shorthorn sculpin AFP along the [1 2 2] direction on (2- 1 0) planes. In agreement with ice etching studies, the mechanism of preferential binding suggested by molecular modeling explains why the binding of shorthorn sculpin AFP occurs along [1 2 2] and not along its mirror symmetry-related direction [-1 -2 2] on (2 -1 0). This binding mechanism is based on the protein-crystal surface enantioselective recognition that utilizes both alpha-helical protein backbone matching to the (2 -1 0) surface topography and matching of side chains of polar/charged residues with specific water molecule positions in the ice surface. The mechanisms of winter flounder and shorthorn sculpin antifreeze binding to ice are compared.