Ganglioside-enriched microdomains in the presynaptic neuronal membrane play a key role in the initiation of amyloid beta-protein (All) assembly related to Alzheimer's disease. We previously isolated lipids from a detergent-resistant membrane microdomain fraction of synaptosomes prepared from aged mouse brain and found that spherical AB assemblies were formed on A beta-sensitive ganglioside nanoclusters (ASIGN) of reconstituted lipid bilayers in the synaptosomal fraction. In the present study, we investigated the role of oligosaccharides in A beta fibril formation induced by ganglioside-containing mixed lipid membranes that mimic the features of ASIGN. Ganglioside nanoclusters were constructed as ternary mixed lipid bilayers composed of ganglioside (GM1, GM2, GM3, GD1a, or GT1b), sphingomyelin, and cholesterol, and their surface topography was visualized by atomic force microscopy. A beta fibril formation on the nanocluster was strongly induced in the presence of 10 mol % ganglioside, and A beta-sensitive features were observed at cholesterol contents of 35-55 mol %. GM1-, GD1a-, and GT1b-containing membranes induced longer fibrils than those containing GD1b and GM2, indicating that the terminal galactose of GM1 along with N-acetylneuraminic acid accelerates protofibril elongation. These results demonstrate that A beta fibril formation is induced by ASIGN that are highly enriched ganglioside nanoclusters with a limited number of components and that the generation and elongation of AB protofibrils are regulated by the oligosaccharide structure of gangliosides.