Membrane Structure and Dynamics Studied with NMR Spectroscopy

Abstract

Biomembranes mediate the diverse functions of life and comprise mainly lipids and proteins, together with carbohydrates associated with the cellular and organelle surfaces. Present knowledge indicates that the lipids typically form a bilayer containing proteins that span the membrane or are attached to its surface. The lipid and protein moieties are amphiphilic, i.e., part of the molecule is polar and preferentially associated with water, whereas part is nonpolar and only sparingly soluble in aqueous media. The hydrophobic effect (Tanford, 1980) is thus an important determinant of the self-assembly of the lipids and proteins into biological membranes. In the liquid-crystalline state, as found in native membranes, the polar head groups of the lipids are on the exterior of the bilayer; whereas the nonpolar hydrocarbon chains are sequestered away from water, within the membrane interior. The lipid bilayer represents the fundamental permeability barrier to the passage of ions and polar molecules into or out of a cell or organelle. In addition the bilayer lipids play a role in the vectorial organization of membrane components. On the other hand, the distinctive functions of biological membranes are largely due to proteins, which may be influenced by lipid-protein interactions.