Interaction of Winter Flounder Antifreeze Protein With Ice

Abstract

Interpretation of crystallographic and mutational studies of antifreeze proteins (AFPs) requires molecular modeling of AFPs with ice. Most models proposed so far suggested H-bonds as the major driving force of AFP-ice association. However, the bulk water offers optimal network of H-bonds and van der Waals contacts to the isolated AFP and ice suggesting that corresponding components of free energy would not decrease upon AFP-ice association. In an attempt to resolve this controversy, we Monte Carlominimized complexes of several AFPs with taking into account, in addition to nonbonded interactions and H-bonds, the hydration potential for proteins (Augspurger and Scheraga, 1996). Parameters of the hydration potential for ice were developed basing on an assumption that at the melting temperature the free energy of water-ice association is small. Simulations demonstrate that desolvation of hydrophobic groups in the AFPs upon their fitting to the grooves at the ice surface presents the major stabilizing contributions to the free energy of AFP-ice binding. Our results explain available data on structure of AFPs and their mutational analyses, in particular, a paradoxical fact that substitution of Thr residues to Val does not affect potency of Winter Flounder AFP.