Protein Domain Formation in Lipid Membranes

Abstract

Clustering of Gramicidin within a DMPC membrane has been studied with Small Angle Neutron Scattering (SANS). Hydrogen and Deuterium scatter neutrons very differently, thus deuteration allows protein scattering to be studied independent of lipid and solvent scattering (when the lipid and solvent are contrast matched). Different protein to lipid ratios were probed and a strict protocol was followed to ensure uniform vesicle size with limited polydispersity. The experiments were performed above the melting temperature of DMPC.A 100 nm deuterated lipid vesicle in deuterated solvent exhibits q-independent scattering showing that the two are truly contrast matched (see Figure 1). While the scattering obtained from lipid vesicles containing Gramicidin have significant q-dependent scattering. If the Gramicidin were uniformly distributed throughout the membrane the data should be well represented by vesicle scattering. However the vesicle fit of the data (also shown in Figure 1) clearly does not agree with the experimental scattering. Thus it is concluded that the protein is forming clusters within the lipid membrane giving rise to the difference in scattering. The system has been modeled and a 3D contrast map (inset Figure 1) has been generated. The map shows protein clustering within the membrane.View Large Image | View Hi-Res Image | Download PowerPoint Slide