Electron paramagnetic resonance studies of spectrin-phospholipid associations

The interaction of spectrin, a peripheral cytoplasmic protein of the erythrocyte membrane, with synthetic phospholipids was characterized by density gradient centrifugation, electron microscopy, and the paramagnetic resonance of nitroxide spin labels. The organic solvent 2-chloroethanol, which favors the stability of hydrophobic surfaces on proteins, was utilized in the formation of the protein-lipid systems. Spectrin, upon dialysis to remove 2-chloroethanol, was found to associate into extensive network-like aggregates and in the presence of dipalmitoylphosphatidylcholine, the spectrin aggregates were found to associate with liposomes formed during dialysis. This interaction, which was significantly enhanced by the presence of dipalmitoylphosphatidylethanolamine, was found to reduce the mobility of fatty acid spin labels incorporated into the lipid regions of the lipid-protein associations. Evidence was found which suggests that spectrin tends to stabilize the phospholipid vesicles against fusion and decrease lipid mobility, particularly near the polar bilayer surfaces.