Plasma lipoproteins, chylomicrons, VLDL and LDL differ in their lipid composition and size, which alter the surface properties and influence the distribution of exchangeable apolipoproteins, accordingly determining the fates of the particles themselves in an animal. Lipoproteins are composed of lipid emulsion particle and apolipoproteins. It is of importance to consider the relevance of surface properties of lipid particles with the interaction of apolipoproteins. In this article, the mechanism of apolipoprotein association with plasma membranes and lipoproteins, is discussed in terms of the lipid composition and surface curvature of phospholipid monolayers (emulsions) and bilayers (liposomes).
Core lipids of emulsions play roles in determining the binding behavior of apolipoproteins A-1 and E. 13C NMR and fluorescence measurements showed that the acyl chain regions of emulsion surface phosphatidylcholine (PC) monolayers are more restricted than those of liposome PC bilayers, whereas the head group regions of emulsions are more hydrated. Accordingly, interpenetration of core lipids into surface PC monolayers was presumed to occur in lipid emulsions. The interpenetration causes the separation of PC head groups and leads to enhanced apoA-1 or E binding in emulsion surface. Lipid risk factors, cholesterol, its ester, sphingomyeline and ceramide modify the structure of surface monolayers, leading to the altered apolipoprotein binding and cell association.