Interaction of chondroitin sulfate with zwitterionic lipid membranes

Chondroitin sulfates (CSs) are important components of the extracellular matrix and side chains of membrane proteoglycans. These polysaccharides are, therefore, likely to interact with plasma membranes and play a significant role in modulating cellular functions. So far, the details of the processes occurring at the interface between the extracellular matrix and cellular membranes are not fully understood. In this study, we used experimental methods and atomic-scale molecular dynamics (MD) simulations to reveal the molecular picture of the interactions between CS and phosphocholine (PC) membranes, used as a simplified model of cell membranes. MD simulations reveal that the polysaccharide associates to the PC bilayer as a result of electrostatic interactions between the positively charged quaternary ammonium groups of choline and the negatively charged sulfate groups of CS. Compared to an aqueous medium, the adsorbed polysaccharide chains adopt more elongated conformations, which facilitates the electrostatic interactions with the membrane, and have a high degree of freedom to change their conformations and to adhere to and detach from the membrane surface. Penetrating slightly between the polar groups of the bilayer, they form a loosely anchored layer, but do not intrude into the hydrophobic region of the PC bilayer. The CS adsorption spread the PC headgroups apart, which is manifested by an increase in the value of the area pre lipid. The expansion of the lipid polar groups weakens the dispersion interactions between the lipid acyl chains. As a result, the lipid membrane in the membrane-polysaccharide contact areas becomes more fluid. Our outcomes may help to understand in detail the interaction of chondroitin sulfate with zwitterionic membranes at the molecular level, which is of biological interest since many biological processes depend on lipid-CS interactions.