Next time you pass through the frozen food aisle at the supermarket, consider what it takes to put some of those items on ice. New scientific research reveals just how the natural defenses of some organisms work against extreme cold.
Researchers at Yeshiva University have illustrated the mechanism by which antifreeze proteins from fish and plants exhibit synergistic enhancement of their ability to prevent ice from growing further. The study was led by Dr. Ran Drori, an assistant professor at Yeshiva University, and his student Tehilla Berger ’19S (who was a 2018 Kressel Scholar). These researchers formed a collaboration with Dr. Konrad Meister from the Max Planck Institute in Mainz, Germany; Dr. Arthur DeVries of the School of Molecular & Cellular Biology from the University of Illinois at Urbana-Champaign; and with Dr. Robert Eves (Department of Biochemistry) and Dr. Peter Davies (Department of Biomedical and Molecular Sciences) from Queen’s University in Kingston, Ontario, Canada.
Their findings were recently published in the Journal of the American Chemical Society. The insights could open the door to a new approach of developing combinatory synthetic crystal growth inhibitors that would rely on synergy that could help advance the frozen food industry or lead to greater cold resistance for living plants, or advances in cryopreservation of tissues and organs.
Fish that live in cold waters have special proteins in their blood stream that prevent tiny ice crystal from growing. These special proteins are named antifreeze proteins. Some fish produce up to 12 different antifreeze proteins, which vary in their ice inhibition efficiency, although their structures are similar. Curiously, the most abundant antifreeze protein in the fish’s blood is a passive antifreeze protein, which cannot inhibit ice growth on its own. Mixtures of these proteins in the laboratory showed that when adding a small amount of an active protein to a passive protein, the mixture is capable of much higher inhibitory effect.
A mixture of two-colored antifreeze proteins binding to the same ice crystal at different locations on the crystal.
“While this effect was discovered more than a decade ago, it was not clear until now how two types of antifreeze proteins can exhibit synergy,” Dr. Drori explains. “We used two types of antifreeze proteins, passive and active, and colored each one with a different dye. After mixing the two-colored proteins, we saw that each protein binds to a specific location on the ice crystal, and a better coverage of the ice crystal is achieved.”
The researchers used microfluidic devices, a technology that includes micron-sized channels enabling liquid to flow through the device. Dr. Drori used microfluidic devices to grow ice crystals in the channels and to exchange the solution around these crystals without melting them.
The team found that regardless of the structure of the antifreeze protein or its origin (fish or plant), the ability of the proteins to synergistically enhance ice inhibition was related to the specific face of the crystal that the proteins bind. Spectroscopic experiments of mixtures of antifreeze proteins provided evidence that these proteins do not interact in solution before they bind to ice.
