Dynamics of the hydration water of antifreeze glycoproteins

Antifreeze glycoproteins (AFGPs) are unique proteins that inhibit the growth of ice by a mechanism that is still unclear. We study the dynamics of water in aqueous solutions of small and large isoforms of AFGPs using polarization-resolved femtosecond infrared spectroscopy. We find that a fraction of the water molecules is strongly slowed down by the interaction with the antifreeze glycoprotein surface. The fraction of slow water molecules scales with the size and concentration of AFGP, and is similar to the fraction of slow water observed for nonantifreeze proteins, both at room temperature and close to biologically relevant working temperatures. We observe that inhibiting AFGP antifreeze activity using borate buffer induces no changes in the dynamics of water hydrating the AFGP. Our findings support a mechanism in which the sugar unit of AFGP forms the active ice-binding site.