Determination of asymmetric structure of ganglioside-DPPC mixed vesicle using SANS, SAXS, and DLS

Functions of mammalian cell membrane microdomains being rich in glycosphingolipids, so-called rafts, are now one of the current hot topics in cell biology from the intimate relation to cell adhesion and signaling. However, little is known about the role of glycosphingolipids in the formation and stability of the domains. By the use of the inverse contrast variation method in small-angle neutron scattering (SANS), combined with small-angle x-ray scattering (SAXS) and dynamic light scattering (DLS), we have determined an asymmetric internal structure of the bilayer of the small unilamellar vesicle (SUV) of monosialoganglioside (G(M1))-dipalmitoylphosphatidylcholine (DPPC) mixture ([G(M1)]:[DPPC] = 0.1:1). A direct method using a shell-model fitting with a size distribution function describes consistently all experimental results of SANS, SAXS, and DLS. We have found that G(M1) molecules predominantly localize at SUV outer surface to form a highly hydrophilic layer which is dehydrated with the rise of temperature from 25 degrees C to 55 degrees C accompanied by the conformational change of the oligosaccharide chains. The average SUV size determined is approximately 200 A, which is comparable to the reported value 260 +/- 130 A of glycosphingolipids microdomains. The present results suggest that the preferential asymmetric distribution of gangliosides is essential to define the size and stability of the domains.