ANTIFREEZE PROTEINS BIND INDEPENDENTLY TO ICE

It has been suggested that cooperative interactions between antifreeze proteins (AFPs) on the ice surfaces are required for complete inhibit ion of ice crystal growth. To test this hypothesis, a 7-kDa type III A FP was linked through its N-terminus to thioredoxin (12 kDa) or maltos e-binding protein (42 kDa). The resultant 20-kDa and 50-kDa fusion pro teins were larger in diameter than free AFP and thus precluded any ext ensive AFP-AFP contacts on the ice surface. Both fusion proteins were at least as active as free AFP at virtually all concentrations tested. By these criteria, AFPs function independently of each other and do n ot require specific intermolecular interactions to bind tightly to ice .