Membrane hydration and structure on a subnanometer scale as seen by high resolution solid state nuclear magnetic resonance: POPC and POPC/C12EO4 model membranes

Abstract

The position on a subnanometer scale and the dynamics of structurally important water in model membranes was determined using a combination of proton magic-angle spinning NMR (MAS) with two-dimensional NOESY NMR techniques. Here, we report studies on phosphocholine lipid bilayers that were then modified by the addition of a nonionic surfactant that is shown to dehydrate the lipid. These studies are supplemented by 13C magic-angle spinning NMR investigations to get information on the dynamics of segmental motions of the membrane molecules. It can be shown that the hydrophilic chain of the surfactant is positioned at least partially within the hydrophobic core of the lipid bilayer. With the above NMR approach, we are able to establish molecular contacts between water and the lipid headgroup as well as with certain groups of the hydrocarbon chains and the glycerol backbone. This is possible because high resolution proton and 13C-NMR spectra of multilamellar bilayer membranes are obtained using MAS. A phase-sensitive NOESY must also be applied to distinguish positive and negative cross-peaks in the two-dimensional plot. These studies have high potential to investigate membrane proteins hydration and structural organization in a natural lipid bilayer surrounding.