Can Antarctic microalgae produce ice-binding proteins?

Abstract

Attempts to use natural antifreeze proteins to protect cells and tissues from freezing damage have had mixed results (1). Some success has been achieved in preventing hemolysis of red blood cells (2,3) and maintaining sperm motility (4,5). There is some evidence that the protective effect of the antifreeze proteins is due to their ability to inhibit the recrystallization of ice. Ice-binding proteins (IBPs

formerly called ice-active substances, or IASs) from an Antarctic sea ice diatom (6) and other Antarctic photosynthetic organisms (7) can inhibit the recrystallization of ice at concentrations in the microgram ml-1 range. At natural concentrations in seawater, the IBPs cause pitting and other changes in the habit of ice crystals, which are an indication that they adsorb to the ice surface (8). Other evidence of ice binding by IBPs is their preferential incorporation in the ice phase of partially frozen solutions (9) and incorporation in ice hemispheres (6). Unlike antifreeze proteins, the IBPs do not significantly lower the freezing point. Rather their function appears to be prevention of damage in the frozen state as they have been shown to increase survival of diatoms subjected to a freeze-thaw cycle (6,10). These latter results encouraged us to evaluate the ability of an algal IBP to reduce freezing damage to another cell type, red blood cells.