Translational dynamics of antifreeze glycoprotein in supercooled water

Structure and dynamics of biomolecules in supercooled water assume a particular and distinct importance in the case of antifreeze glycoproteins (AFGPs), which function at sub-zero temperatures. To investigate whether any large-scale structural digressions in the supercooled state are correlated to the function of AFGPs, self-diffusion behavior of the AFGP8, the smallest AFGP is monitored as a function of temperature from 243 to 303 K using nuclear magnetic resonance (NMR) spectroscopy. The experimental results are compared with the hydrodynamic calculations using the viscosity of water at the same temperature range. In order to evaluate results on AFGP8, the smallest AFGP, constituting approximately two-thirds of the total AFGP fraction in fish blood serum, similar experimental and computational calculations were also performed on a set of globular proteins. These results show that even though the general trend of translational dynamics of AFGP is similar to that of the other globular proteins, AFGP8 appears to be more hydrated (approximately 30% increase in the bead radius) than the others over the temperature range studied. These results also suggest that local conformational changes such as segmental librations or hydrogen bond dynamics that are closer to the protein surface are more likely the determining dynamic factors for the function of AFGPs rather than any large-scale structural rearrangements.