The importance of hydration for inhibiting ice recrystallization with C-linked antifreeze glycoproteins

The role of hydration in modulating solution conformation, molecular recognition, and biological activity of oligosaccharides, proteins, and nucleotides is widely recognized but is often neglected when investigating many biological processes such as the mechanism by which biological antifreezes inhibit the growth of ice. We have investigated the relationship between carbohydrate configuration and recrystallization-inhibition (RI) activity in functional C-linked antifreeze glycoprotein (AFGP) analogues using a series of analogues 1-4. While analogues 1-4 did not show any thermal hysteresis (TH) activity, 1 did exhibit weak dynamic ice shaping indicating that this compound had the ability to interact with the ice lattice. The D-mannose and D-talose analogues (3 and 4, respectively) exhibited very weak RI activity with mean largest grain size values similar to phosphate buffered saline, the negative control. D-Glucose analogue 2 exhibited moderate RI activity while D-galactose analogue 1 was the most potent analogue with RI activity comparable to the native AFGP 8. These results suggest that the configuration of the carbohydrate moiety in C-linked AFGP analogues is extremely important and modulates recrystallization-inhibition activity. It seems likely that differences in hydration for each C-linked pyranose alter the compatibility of the carbohydrate moiety with the three-dimensional hydrogen-bonded network of supercooled bulk water. Consequently, the energy associated with transferring a water molecule to the ice lattice changes and can result in inhibition of ice growth. These results emphasize the importance of continued studies to further elucidate the role of hydration in antifreeze activity.