Probing Molecular Interactions in Biological Membranes by Solid-State NMR

Abstract

The interaction between integral membrane proteins and the lipid bilayer is vital in the regulation of many biological processes. Here we report preliminary solid-state NMR studies on two systems where interactions at the lipid/protein interface play an important role in the regulation and trafficking of integral membrane proteins.The anaesthetic octanol has been shown to interact with several sites on the nicotinic acetylcholine receptor (nAChR) one of which is in the lipid/protein interface. In preliminary studies we are investigating how octanol interacts with the lipid bilayer. Analysis of the 1H-13C dipolar couplings present in 2D dipolar/chemical shift spectra we have been able to measure changes in bilayer fluidity at pharmacologically relevant concentrations. We have been able to correlate these results with 2D-1H-NOE-MAS spectra enabling us to locate the position of the octanol within the lipid bilayer. As these methods function with isotopes at natural abundance levels, we are currently applying them to native nAChR membranes to see if changes in the order parameter profile observed in model lipid bilayers are reproduced in native receptor membranes.The interaction of proteins with lateral domains (rafts) in lipid bilayers has been proposed to play an important role in the trafficking of proteins within cells. We are utilizing exchange spectroscopy to study the partitioning of Fukutin, a protein linked to the onset of muscular dystrophy, into lipid rafts. Exchange measurements have enabled us to observe the restricted lateral diffusion of phospholipids in the presence of lateral domains formed in vesicles formed from ternary lipid mixtures. The affects of these lateral domains on the structure and oligomeric state of the Fukutin is also being probed.