For the first time, scientists have discovered how 'antifreeze' in polar animals’ blood keeps them alive in subzero conditions.
To survive in frigid polar regions, several cold-blooded species have independently developed antifreeze molecules that lock onto ice crystals, but not liquid water.
However, the secret behind the mechanism was a mystery for researchers till now.
Now scientists have used a combination of X-ray and neutron diffraction to gain insight into the mechanism, reports New Scientist.
Biological antifreeze proteins (AFPs) safeguard organisms from freezing to death by binding to ice crystals, and stop their growth.
However, AFPs must not attach to liquid water otherwise the organism would dehydrate and die, according to Matthew Blakeley at the Laue-Langevin Institute in Grenoble, France.
X-ray diffraction has already shown that the surface of the AFPs that binds to ice is covered in tiny hydrophobic spikes.
Now, using neutron diffraction, Blakeley and his colleagues managed to catch four water molecules at the ice-binding surface of AFPs from a fish, the ocean pout (Zoarces americanus).
The water molecules formed an arc resembling part of a six-molecule ring characteristic of ice crystals. At the centre of each ring is a nanoscale hole.
Crucially, the hole in the centre of the partial ring was occupied by one of the hydrophobic spikes. The distance between spikes suggests that each would fall inside one of the holes if an ice crystal were present.
While this formidable array of hydrophobic spikes deflects liquid water molecules from the protein, their alignment with the ice holes means they fit neatly into ice, said Blakeley,
"It's almost like a lock and key," he said.
Peter Davies at Queen’s University in Kingston, Ontario, Canada, and his team confirmed this picture.
Davies said they glimpsed 60 water molecules - not just four - on an AFP using X-ray diffraction. Again, the spikes slotted into holes in the water''s structure.
The findings could provide benefits in cancer treatments, to protect healthy tissue while freezing destroys tumours.