MODELING STUDIES OF BINDING OF SEA RAVEN TYPE-II ANTIFREEZE PROTEIN TO ICE

Certain plants, insects, and fish living In cold environments prevent tissue damage due to freezing by producing antifreeze proteins or anti freeze glycoproteins that inhibit ice growth below the normal equilibr ium freezing point of water in a noncolligative fashion. In polar fish these macromolecules, taking into account their structural characteri stics. are grouped into three broad classes, namely Type I, Type II, a nd Type III. In this paper we report the results of our studies on the stereospecific binding of sea raven, a Type IJ antifreeze protein (AF P) to (111) hexagonal bipyramidal faces of ice. Earlier studies of Typ e I and Type III AFP have shown that stereospecific binding of these p roteins, recognizing specific planes of ice, is essential for their no ncolligative antifreeze point depression. Moreover, as it has been sho wn for the AFT of Type I, this binding also occurs along specific vect ors on these planes and also is enantioselective, distinguishing betwe en the mirror related directions. In this study we will show, by using molecular modeling, that the fold of Type II AFP could facilitate a s tereospecific mode of interaction with (111) planes of ice. Similar to Type I AFP, preferential directionality of binding was also observed in the simulations.