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Biological Chemistry

How polar fish survive subzero seas

New data may resolve debate over how antifreeze glycoproteins keep fish from freezing

by Tien Nguyen
February 12, 2018 | A version of this story appeared in Volume 96, Issue 7

Three-dimensional structure of antifreeze glycoprotein 8 with methyl groups highlighted.
Credit: J. Am. Chem. Soc.
Models show that multiple methyl groups (colored spheres) on AFGP8's peptide backbone (red ribbon) and dangling sugars bind reversibly to ice to stop its spread.

Having “ice in one’s veins” may simply suggest an unshakable demeanor for a person, but for an arctic fish, it can be deadly. Luckily, polar fish have evolved molecular defenses to keep their blood flowing in freezing waters, including so-called antifreeze glycoproteins (AFGPs), which keep ice growth at bay in fish’s blood. These floppy molecules hold promise for food and tissue cryopreservation, but exactly how they inhibit the spread of ice has been difficult for scientists to pin down experimentally. Now, using molecular dynamic simulations, Kenji Mochizuki and Valeria Molinero of the University of Utah have revealed how the smallest member of the AFGP family, AFGP8, binds to ice at the water–ice interface (J. Am. Chem. Soc. 2018, DOI: 10.1021/jacs.7b13630). They found that AFGP8’s multiple methyl groups, on both the peptide backbone and the pendant sugars, stick weakly to the ice surface. This reversible binding allows the glycoproteins to “walk” around the surface until they find a nook in the crystal, preventing ice growth, Molinero says. Hokkaido University’s Yoshinori Furukawa, whose group has reported experimental data supporting AFGPs’ reversible binding behavior, says the work is “excellent” and that it resolves a decades-long debate over the AFGP binding mechanism.


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