Freeze Protector Is Protein-free

For the first time, researchers have found a natural high-molecular-weight antifreeze molecule that does not contain protein. The find may someday be applied in the food industry or in tissue cryopreservation for organ transplants.

Many living things that must survive in cold habitats contain molecules that adsorb to the surface of ice, thereby lowering the freezing point of bodily fluids and protecting tissues from inhospitable temperatures. Every ice-binding antifreeze found so far has contained protein. Now, a multi-institution team led by University of Notre Dame researchers Kent R. Walters Jr., Anthony S. Serianni, and John G. Duman has isolated a polysaccharide antifreeze from adult darkling beetles, Upis ceramboides, which live deep in the Alaska interior (Proc. Natl. Acad. Sci. USA 2009, 106, 20210).

Both the beetles and their larvae survive harsh Alaska winters, but the adults bear the brunt of the cold, hiding in dry crevices in trees without the benefit of snow cover to insulate them, Walters says. Adult beetles freeze at –6 °C, but the ice-binding agent helps prevent this from harming them, he suggests. They can tolerate temperatures as low as –60 °C.

The isolated ice-binding factor lowers water’s freezing point by 3.7 °C, on par with the most active antifreeze proteins. Although the team hasn’t fully determined the agent’s structure, their spectroscopic and biochemical work suggests it contains a lipid component and a disaccharide core with β-(1→4)-linked mannose and xylose units (shown).

The team surmises that factors of this type might be found in other creatures, too. “It will be interesting to see if ice-binding factors from other freeze-tolerant animals are similar to this or, like the antifreeze proteins, are extremely diverse,” says Peter L. Davies, an expert in antifreeze proteins at Queen’s University, in Ontario.