Antifreeze proteins (AFPs) and antifreeze glycoproteins (AFGPs) are the key to survival for fish, insects, plants and other organisms that endure subzero temperatures. This diverse group of proteins inhibits the growth of ice crystals and limits freezing injury. The binding of AFPs to ice increases the ice surface curvature that develops between adsorbed AFPs, thus creating a gap between the melting and freezing points (termed as thermal hysteresis, TH). The AFPs we study adsorb exclusively to prism/pyramidal planes, which inhibits ice growth along the a-axis, but allows for step-by-step growth along the c-axis, resulting in a bipyramidal crystal shape. We predict that as AFPs adsorb more rapidly to the prism/pyramidal planes, the ensuing steps will be inhibited more rapidly, resulting in less elongated crystals. We used a custom-made nanoliter osmometer with temperature stability and resolution of ±0.002 °C and governed by a LabVIEW program. This system allows for the isolation and growth of microns-sized ice crystals. The c-to-a ratio, which is the length of the c-axis divided by the length of the a-axis is used to quantify ice crystal morphology. The c-to-a ratios of AFP type III and AFGP1-5 were measured and plotted against the adsorption rate, KonC. As the adsorption rate increased, the c-to-a ratio decreased until it plateaued at a ratio of 1.7. These results demonstrate that more rapid AFP adsorption to ice crystal planes produces less elongated ice crystals. AFPs offer much promise in applications ranging from cryopreservation and cryosurgery to better food preservation and frost damage control in agriculture. This study relates AFP adsorption rate to ice crystal morphology, an understanding of which is essential in using AFPs most efficiently for their many potential applications.

Antifreeze proteins shape ice crystals to prevent freezing injury

2019 Spring National Meeting

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