Deep sea freeze

Why don’t fish freeze in the ocean? They have an antifreeze protein in their blood, and scientists have just uncovered the mechanism of how this protein works.

Ocean temperatures of -1.8°C should be enough to freeze any fish – especially since the freezing point of their blood is around -0.9°C – but Antarctic fish are still able to keep moving and until recently, scientists were puzzled at how.

Scientists from the Ruhr Universität Bochum used terahertz spectroscopy to record the motion of water molecules and antifreeze proteins (AFP) in the blood of the Antarctic toothfish. They discovered that AFP in the blood affects water molecules in its vicinity preventing ice crystallisation. However, the AFP doesn’t bind to water – just its presence is enough to stop freezing.

“We could see that the protein has an especially long-range effect on the water molecules around it,” said co-author Konrad Meister, “We speak of an extended dynamical hydration shell.”

“This effect, which prevents ice crystallisation, is even more pronounced at low temperatures than at room temperature,” said Professor Martina Havenith.

Using terahertz radiation, the researchers showed that water molecules – which usually perform a permanent dance in liquid water, constantly forming new bonds – perform a more ordered dance in the presence of proteins.

Researchers found that when in a complex with borate, the antifreeze activity of the AFP was strongly reduced and that there was no change in the terahertz dance.

The results provide evidence of a new model of how AFP prevents water from freezing. It suggests activity is not achieved by a single molecular bonding between the water and protein but that the protein disturbs the aqueous solvent over long distances.

The investigation – funded by the Volkswagen Foundation – showed for the first time a direct link between a protein and its signature in the terahertz range.