Antifreeze Proteins Help Snow Fleas Get through Winter

Biochemistry

A species of snow flea, a wingless insect commonly known as a springtail, has developed a powerful set of molecular helpers that allow it to remain active in the cold of winter: two antifreeze proteins (AFPs) that lower the freezing point of its body fluids by nearly 6 °C (Science 2005, 310, 461). The proteins, isolated and sequenced by Laurie A. Graham and Peter L. Davies of Queen's University in Kingston, Ontario, are among the most effective AFPs ever observed.

AFPs work by binding to the surfaces of ice crystals as they start to form, inhibiting further growth. AFPs were first discovered in fish over 30 years ago, and versions are now known in plants, bacteria, and two other insects-a beetle and a moth. In 2000, Davies and his colleagues reported the protein structure of the beetle and moth AFPs and studied their ice-binding properties.

The glycine-rich snow flea proteins are quite different from the threonine-rich beetle and moth AFPs, the researchers note. One of the snow flea proteins has a mass of 6.5 kilodaltons, while the other has a mass of 15.7 kDa. The larger protein appears to be just a longer version of the smaller one. It's also the more active of the two molecules and the most effective AFP discovered so far.

The finding helps shed light on AFP evolution in insects and could lead to potential protein-based antifreeze applications, such as frost-resistant crops.