Dynamics of water of hydration near disaccharides strongly depends on solute topology: mapping density fluctuations, rotational anisotropy and h-bond exchange mechanism around disaccharides

comunicação em posterDisaccharides such as trehalose are abundant components of cells and may alter the phase behavior or dynamics of phospholipid bilayers: for example, trehalose is a cryoprotectant of lipid bilayers. The origin of this and other effects of disaccharides on membranes is still under debate. One possibility is that some disaccharides alter the dynamics of water of hydration relative to the bulk, and that interactions between the water of hydration of disaccharides and the phospholipids lead to changes in bilayer properties. We address this issue by investigating the dynamics of water near disaccharides kojibiose and trehalose using classical atomistic molecular dynamics simulations and transition state theory. Our results indicate that the cryoprotectant trehalose and the non-cryoprotectant kojibiose differ in the rotational dynamics of their water of hydration, with the subpopulation of water molecules nearest to the central linking oxygen being significantly slower for trehalose. Interestingly, this effect results from differences in both solute chemistry and topology: identical functional groups may interact differently with water depending on the orientation of neighboring groups, in agreement with existing reports on proteins. In contrast to observations on topologically simple solutes, our results indicate that topologically complex solutes such as disaccharides induce unexpected changes in the free energy landscape associated with rotation of water molecules. These results suggest that theoretical models to predict water dynamics near solutes, relevant for example to understand how water dynamics influences protein folding or diffusion through polysaccharide brushes, must account for both solute chemistry and topology