Molecular recognition and binding of thermal hysteresis proteins to ice

Molecular recognition and binding are two very important processes in virtu ally all biological and chemical processes. An extremely interesting system involving recognition and binding is that of thermal hysteresis proteins a t the ice-water interface. These proteins are of great scientific interest because of their antifreeze activity. Certain fish, insects and plants livi ng in cold weather regions are known to generate these proteins for surviva l. A detailed molecular understanding of how these proteins work could assi st in developing synthetic analogs for use in industry. Although the shapes of these proteins vary from completely ar-helical to globular, they perfor m the same function, It is the shapes of these proteins that control their recognition and binding to a specific face of ice. Thermal hysteresis prote ins modify the morphology of the ice crystal, thereby depressing the freezi ng point. Currently there are three hypotheses proposed with respect to the antifreez e activity of thermal hysteresis proteins. From structure-function experime nts, ice etching experiments, X-ray structures and computer modeling at the ice-vacuum interface, the first recognition and binding hypothesis was pro posed and stated that a lattice match of the ice oxygens with hydrogen-bond ing groups on the proteins was important. Additional mutagenesis experiment s and computer simulations have lead to the second hypothesis, which assert ed that the hydrophobic portion of the amphiphilic helix of the type I ther mal hysteresis proteins accumulates at the ice-water interface. A third hyp othesis, also based on mutagenesis experiments and computer simulations, su ggests that the thermal hysteresis proteins accumulate in the ice-water int erface and actually influence the specific ice plane to which the thermal h ysteresis protein ultimately binds. The first two hypotheses emphasize the aspect of the protein 'binding or accumulating' to specific faces of ice, w hile the third suggests that the protein assists in the development of the binding site. Our modeling and analysis supports the third hypothesis, howe ver, the first two cannot be completely ruled out at this time. The objecti ve of this paper is to review the computational and experimental efforts du ring the past 20 years to elucidate the recognition and binding of thermal hysteresis proteins at the ice-vacuum and ice-water interface. Copyright (C ) 2000 John Whey & Sons, Ltd.