Journal of Physical Chemistry B, Vol.118, No.40, 11613-11621, 2014
Local Water Dynamics around Antifreeze Protein Residues in the Presence of Osmolytes: The Importance of Hydroxyl and Disaccharide Groups
Antifreeze proteins (AFP) and antifreeze glycoproteins (AFGP) are synthesized by various organisms to enable their cells to survive low temperature environments like in the polar regions. The presence of antifreeze proteins leads to a temperature difference between the melting and freezing poing of the solution known as thermal hysteresis. It is nowadays common knowledge that the antifreeze activity of AFPs is mainly determined by a short range effect which includes a direct binding to the ice phase. Recently, experimental findings also revealed a long-range effect which implies a significant retardation of the water dynamics to facilitate the ice-binding process specifically for AFGPs. The aim of this work is to examine the dynamics of water molecules around different antifreeze protein residue by using atomistic molecular dynamics simulations. A prototype of AFP from antarctic notothenioids with the main subunit alanine-alanine threonine (AAT) and a mutant (polyalanine) together with the residues of an antifreeze glycoprotein (AFGP) were simulated and compared with respect to their influence on the local water shell. The analysis of the water hydrogen bond characteristics and the dipolar relaxation times reveals a strong retardation effect of the water dynamics around the AFGP prototype. Our numerical results reveal the significant importance of polar units like threonine and disaccharides for the direct binding of water molecules in terms of hydrogen bonds and a significant retardation of water dynamics. In addition, a considerable change of the hydration dynamics is additionally observed in the presence of asmolytes like urea and hydroxyectoine. Our findings indicate that this effect is even more pronounced in the presence of kosmotropic osmolytes.