Model membrane morphology and crosslinking of oxidized lipids with proteins

Model membranes composed of thion-phosphatidylcholine, cardiolipin, and cytochrome c have been studied by 31P NMR, polyacrylamide gel electrophoresis, gel filtration, fluorescence, and freeze-fracturing. Covalent binding of oxidized phospholipids to cytochrome c was shown to result in the formation of high-molecular-weight oligomeric complexes via Schiff base formation between a protein molecule and aldehydes produced upon peroxidation of phospholipids. The initial steps of the protein oligomerization lead to the appearance of intramembranous particles (IMPs) of various size and distribution on freeze-fractured faces of these model membranes. In the final phase of the crosslinking between cytochrome c and oxidized products of cardiolipin there is a breakdown of membrane vesicles and formation of globular lipoprotein complexes which are seen as globular particles. It is believed that the covalent linking between the products of phospholipid peroxidation and membrane proteins causes the oligomerization of membrane proteins and structural alteration in the hydrophobic region of other models also and, perhaps, in biological membranes.