The impact of the glycan headgroup on the nanoscopic segregation of gangliosides.

Abstract Gangliosides form an important class of receptor lipids containing a large oligosaccharide headgroup whose ability to self-organize within lipid membranes results in the formation of nanoscopic platforms. Despite of their biological importance, the molecular basis for the nanoscopic segregation of gangliosides is not clear. In this work, we investigated the role of the ganglioside headgroup on the nanoscale organisation of gangliosides. We studied the effect of the reduction in the number of sugar units of the ganglioside oligosaccharide chain on the ability of gangliosides GM1, GM2 and GM3 to spontaneously self-organize into lipid nanodomains. To reach nanoscopic resolution and to identify molecular forces that drive ganglioside segregation, we combined an experimental technique MC-FRET offering high lateral and trans-bilayer resolution with molecular dynamics (MD) simulations. We show the ganglioside headgroup plays a key role in ganglioside self-assembly despite the negative charge of the sialic acid group. The nanodomains range from 7 to 120 nm in radius and are majorly composed of the surrounding bulk lipids, with gangliosides being a minor component of the nanodomains. The interactions between gangliosides are dominated by the hydrogen bonding network between the headgroups that facilitates ganglioside clustering. The N-acetylgalactosamine sugar moiety of GM2, however, seems to impair the stability of these clusters by disrupting hydrogen bonding of neighbouring sugars, which is in agreement with a broad size distribution of GM2 nanodomains. The simulations suggest that the formation of nanodomains are likely accompanied by several conformational changes in the gangliosides, which, however, have little impact on the solvent exposure of these receptor groups. Overall, this work identifies the key physicochemical factors that drive nanoscopic segregation of gangliosides.