Characterization of micellar and liposomal dispersions of gangliosides and phospholipids.

Abstract

Gangliosides are minor surface components of most mammalian cells, where they are located mainly in the outer leaflet of the lipid bilayer of the plasma membrane (1,2, 3). They are also present in membranes of some enveloped viruses (4). In membranes they serve as receptors for various toxins, viruses, hormones and their pattern is often drastically changed in neoplasia (1, 3, 5). The gangliosides, which are part of the lipid bilayer of the membranes differ in their lyotropic behaviour from the phospholipids and cholesterol which constitute the main lipid components of the membrane (6,38). The membrane phospholipids have two long hydrophobic chains, an interface region and a relatively small inogenic head group. They are classified as “non-soluble swelling amphipaths (6), implying that they do not form micelles but disperse spontaneously in water, forming bilayered multilamellar large liposomes (MLV) or, upon ultrasonic irradiation small unilamellar vesicles (SUV). In contrast, the gangliosides are “soluble amphipaths” (6) which form micelles in water (7). The fact that, in spite of their two long hydrophobic chains the gangliosides are classified as “soluble” amphipaths is explained by their large and highly negatively charged polar head group. Since gangliosides and phospholipids differ in their state of aggregation, their coexistance in membranes may affect or even disturb the bilayered structure. This study aimed to investigate the mutual relations between gangliosides arrl the main lipid components of the membranes. For this purpose the structural and dynamic properties of dispersions composed of well-characterized membrane lipids (either synthetic or of natural sources) and well defined, pure gangliosides were studied with the aid of physical and enzymatic methods.