Antifreeze proteins (AFPs) enable various organisms to survive subfreezing environments by inhibiting the growth of endogenous ice crystals. Antifreeze glycoproteins (AFGPs) protect Antarctic fish from freezing and include 8 isoforms, which differ mainly by their size. It is postulated that AF(G)Ps inhibit ice growth via the adsorption-inhibition mechanism, which assumes that these molecules bind irreversibly to the surface of embryonic ice crystals, thus preventing further growth. While it was experimentally substantiated that AFPs bind irreversibly to ice, these evidences are still elusive for AFGPs, and evidences for reversible binding of AFGPs had been reported.<br/>We used fluorescent microscopy and microfluidic devices to investigate the nature of ice binding of small and large AFGP isoforms. Specifically, the question whether AFGPs bind irreversibly to ice can be answered by the exchange of solutions around micron-sized ice crystals.<br/>We found that both AFGP isoforms bind irreversibly to ice as evidenced by high fluorescence intensity on the ice surface after the removal of the AFGP solution. Adsorption rate of the larger AFGP isoform to ice was found to be 50% faster than that of a globular fish AFP.<br/>These findings provide strong evidences that AFGPs bind irreversibly to ice, regardless of their size. The fact that the larger AFGP isoform binds to ice faster than a globular fish AFP suggests that the structure of AFGPs in solution is well-defined at temperatures slightly below 0 °C. These understandings will facilitate the design of novel synthetic antifreeze agents that may benefit a variety of fields, including agriculture, medicine and food.<br/>

New insights Into the ice-binding mechanism of antifreeze glycoproteins

256th National Meeting (2018)

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