How An Insect Version Of Antifreeze Works

Car owners might have to buy antifreeze every winter, but some creatures that survive in frigid climes make their own. Researchers have now obtained new insights into how insect antifreeze—a protein—works. The finding could help the food industry make additives that protect crops from frost or extend the shelf life of frozen foods. Antifreeze proteins derived from fish are already used in some frozen desserts.

Antifreeze proteins have a tricky job. They must bind to ice crystals to prevent their growth while engulfed by much larger amounts of liquid water. And they must do so at low concentrations, far lower than those of ethylene glycol antifreeze in a car. Some antifreeze proteins have a particular arrangement of threonine amino acids that forms an ice-binding site. But because not all antifreeze proteins share this arrangement, researchers have proposed that other interactions must also be involved.

Martina Havenith of Ruhr University in Germany and coworkers support that idea by demonstrating that an antifreeze protein affects the organization of water molecules up to 20 Å, or seven layers of water, away from the ice-binding site (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1214911110). This long-range interaction affects hydrogen bonding and likely interferes with ice formation, the authors say. The team examined an antifreeze protein from the fire-colored beetle Dendroides canadensis. They dissolved the protein in water and analyzed the water molecules’ motions with terahertz spectroscopy and computer simulations to see the long-distance action.

This is the first time scientists have shown this interaction between an antifreeze protein and water molecules, though it’s not unheard-of for water to affect protein activity, says biochemist Kim A. Sharp of the University of Pennsylvania. He cautions, though, that researchers did not study the protein at the freezing temperatures at which it’s active. But it’s still possible, he says, that long-range water ordering lets antifreeze proteins reach farther and prevent freezing more efficiently than they could with a threonine ice-binding site alone.