Hyperactive Antifreeze Proteins

Hyperactive antifreeze proteins naturally secreted by an insect known as the spruce budworm, prevent it from freezing to death during winters in North American forests. Ohio University's Ido Braslavsky (braslavs@helios.phy.ohiou.edu) and his colleagues presented studies of these potent yet nontoxic proteins at this week’s APS Meeting.

Found in several other species such as snow fleas, the hyperactive proteins bind to ice, modify its crystalline shape, and prevent ice from growing further, effectively reducing the freezing point of ice for an organism that excretes them. These nontoxic substances have more recently been renamed "ice structuring proteins" (ISPs) to distinguish them from the toxic antifreeze products for automobiles.

Extracting ISPs from biological sources has many potential applications, such as preserving organs and blood products, protecting against agricultural frost damage, and even preventing frostbite. These natural proteins are currently used in some "light" ice cream products to improve their texture, but those ISPs, derived from fish, are much less potent.

How the hyperactive versions inhibit ice from growing is a topic of interest to Braslavsky's group and their collaborators, such as Peter Davies from Queen's University (daviesp@post.queensu.ca). The researchers attached fluorescent molecules, derived from jellyfish, to the protein.

Through a microscope, they watched how the fluorescing ISPs inhibited ice crystals from growing. They observed that the ISPs prevent ice crystals from expanding in their normal disk-shaped form. Instead, they inhibit ice growth in certain directions and cause the crystals to grow in altered shapes.

While a fish ISP promotes the growth of a "bipyramidal" ice-crystal form that looks like two pyramids whose bases are attached to each other, the spruce budworm ISP blocks growth in the preferred direction of the pyramid's apexes. Using the fluorescence microscopy they watched the proteins attached to the ice blocking growth in this direction. (Meeting Paper J35.8, http://meetings.aps.org/Meeting/MAR07/Event/58982; for more information, see http://www.phy.ohiou.edu/~braslavs/APS2007/)