BPS2026 – Molecular dynamics simulations: Insight into effects of polymer osmolytes on membrane protein hydration

Water plays an important role in the structure and dynamics of membrane proteins; however, the exact contribution to protein activation remains under investigation 1 . Here, we investigated rhodopsin, a prototypical G-protein-coupled receptor (GPCR), using polymer osmotic stress to probe hydration changes during membrane protein activation. In these experiments, hydrophilic polymers such as polyethylene glycol (PEG) change how water is organized, showing that osmolytes, water, and proteins are closely linked during activation. Our experiments revealed that water is not a passive solvent but rather an active participant in rhodopsin conformational transitions. To understand the interplay between lipids, polymers, and water in membrane protein function, atomic level studies are required that are experimentally challenging. Molecular dynamics (MD) simulations provide insight as they offer atomistic detail about how individual water molecules interact with protein residues and lipid surroundings, while revealing structural rearrangements during activation. Our theoretical MD simulations complement experimental data by bridging physical chemistry and biology, allowing for a comprehensive understanding of how water influences the activation of membrane proteins. We integrate knowledge from polymer physical chemistry, such as polymer lattice models, osmolyte effects, and macromolecular crowding, to enhance our understanding of the role of water. Advancements of computational simulations, particularly hybrid Monte Carlo methods, reveal the role of water at the atomistic level which is essential for understanding the structure and functions of membrane proteins. By combining both experimental and computational methods, we achieve a more complete picture of how hydration governs membrane protein activation, connecting molecular interactions with biological mechanisms. A deeper understanding of these mechanisms has the potential to open new opportunities in biophysical research and advance applications in drug design. 1 Menon, C.S.K. et. al., (2025). Biophys. J. , in press.