Metal Complex Lipids for Fluid-Fluid Phase Separation in Coassembled Phospholipid Membranes

Cooperativity between sodium ions and water molecules facilitates lipid mobility in model cell membranes

Cellular membranes are surrounded by an aqueous buffer solution containing various ions, which influence the hydration layer of the lipid head groups. At the same time, water molecules hydrating the lipids play a major role in facilitating the organisation and dynamics of membrane lipids. Employing fluorescence microscopy imaging and fluorescence recovery after photobleaching measurements, we demonstrate that the cooperativity between water and sodium (Na+) ions is crucial to maintain lipid mobility upon the removal of the outer hydration layer of the lipid membrane. Under similar hydration conditions, lipid diffusion ceases in the absence of Na+ ions. We find that Na+ ions (and similarly K+ ions) strengthen the water clathrate cage around the lipid phosphocholine headgroup and thus prevent its breaking upon removal of bulk water. Intriguingly, Ca2+ and Mg2+ do not show this effect. In this article, we provide a detailed molecular-level picture of ion specific dependence of lipid mobility and membrane hydration properties.

Experimental and computational characterization of dynamic biomolecular interaction systems involving glycolipid glycans

On cell surfaces, carbohydrate chains that modify proteins and lipids mediate various biological functions, which are exerted not only through carbohydrate-protein interactions but also through carbohydrate-carbohydrate interactions. These glycans exhibit considerable degrees of conformational variability and often form clusters providing multiple binding sites. The integration of nuclear magnetic resonance spectroscopy and molecular dynamics simulation has made it possible to delineate the dynamical structures of carbohydrate chains. This approach has facilitated the remodeling of oligosaccharide conformational space in the prebound state to improve protein-binding affinity and has been applied to visualize dynamic carbohydrate-carbohydrate interactions that control glycoprotein-glycoprotein complex formation. Functional glycoclusters have been characterized by experimental and computational approaches applied to various model membranes and artificial self-assembling systems. This line of investigation has provided dynamic views of molecular assembling on glycoclusters, giving mechanistic insights into physiological and pathological molecular events on cell surfaces as well as clues for the design and creation of molecular systems exerting improved glycofunctions. Further development and accumulation of such studies will allow detailed understanding and artificial control of the "glycosynapse" foreseen by Dr. Sen-itiroh Hakomori.