If the freezing point of fish blood is -0.9 ° Celsius, how are Antarctic fish able to keep moving at a temperature like -1.8 ° C?

You're not the only one to ask, researchers have wondered for 50 years, and it known that fish in the Arctic have a special sort of antifreeze, similar to what we put in cars, but just how these special frost protection proteins work has been unclear.

Ruhr-University Bochum researchers recently used terahertz spectroscopy to find out and say they have now unraveled the underlying mechanism by recording and analyzing the collective motion of water molecules and proteins.  Result:  The water molecules, which move one way in liquid water, move much differently in the presence of the proteins – "the disco dance becomes a minuet" says Prof. Dr. Martina Havenith (Physical Chemistry II of Bochum.

The subject of the current investigations was the anti-freeze glycoproteins of the Antarctic toothfish Dissostichus mawsoni.

Macropteris maculatus
Macropteris maculatus, with anti-freeze glycoproteins structure.   Credit: Konrad Meister

"We could see that the protein has an especially long-range effect on the water molecules around it. We speak of an extended dynamical hydration shell", says co-author Konrad Meister.  "This effect, which prevents ice crystallization, is even more pronounced at low temperatures than at room temperature," added  Havenith.

To freeze the water, lower temperatures were necessary. Complexation of the AFP by borate reduced the antifreeze activity but the researchers found no change in the terahertz 'dance' so the results provided evidence for a new model of how AFGPs prevent water from freezing: Antifreeze activity is not achieved by a single molecular binding between the protein and the water, but instead AFP perturbs the aqueous solvent over long distances.

They say they investigation demonstrated for the first time a direct link between the function of a protein and its signature in the terahertz range.

Citation: Simon Ebbinghaus, Konrad Meister, Benjamin Born, Arthur L. DeVries, Martin Gruebele and Martina Havenith, 'Antifreeze Glycoprotein Activity Correlates with Long-Range Protein−Water Dynamics',  J. Am. Chem. Soc., Articles ASAP (As Soon As Publishable) Publication Date (Web): August 16, 2010 (Communication) DOI: 10.1021/ja1051632

The studies were funded by the Volkswagen Foundation.