How Antifreeze Proteins Walk On Ice

Molecular simulations reveal how antifreeze proteins bind to ice to allow fish to withstand sub-zero temperatures.

AsianScientist (May 1, 2018) – A research group in Japan has identified a molecular binding mechanism that helps prevent non-mammalian creatures from freezing in sub-zero temperatures. They published their findings in the Journal of the American Chemical Society.

Antifreeze glycoproteins (AFGPs)—proteins with sugar moieties attached to them—are produced in polar fishes to inhibit the growth of ice crystals. The mechanism by which AFGPs interact with ice to enact their antifreeze effects has remained a mystery. This is because the attached sugars of AFGPs do not have a specific three-dimensional shape. Without rigidity, it is difficult to image the protein to better understand its structure and function.

In this study, the researchers led by Assistant Professor Kenji Mochizuki of the Institute for Fiber Engineering at Shinshu University in Japan used molecular simulations to model AFGPs and examine how they interact with the ice.

Mochizuki examined AFGP8, the shortest protein in the AFGP family, and found that it is segregated into hydrophilic and hydrophobic groups. The hydrophobic groups adsorb to the ice surface, forming a thin film over the ice. However, the adsorption of AFGP8 to the flat surface of ice is weak, so AFGP8 moves across the ice surface until it selectively binds to regions where ice crystals are growing, inhibiting ice recrystallization. Mochizuki dubbed this movement ‘walking.’

“We thought that the flexible feature of antifreeze glycoproteins might yield a unique binding manner,” Mochizuki said. “We found that antifreeze glycoproteins show various binding conformations and walk on ice surfaces until they come across a step of ice.”

This finding has potential applications in the preservation of food and biological tissue under extreme temperatures. The researchers intend to continue studying AFGPs to examine their mechanisms more precisely, and hopefully design artificial proteins or polymers which exhibit stronger antifreeze activities.

The article can be found at: Mochizuki & Molinero (2018) Antifreeze Glycoproteins Bind Reversibly to Ice via Hydrophobic Groups.


Source: Shinshu University; Photo: Pexels.
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