GM1 Ganglioside Inhibits β-Amyloid Oligomerization Induced by Sphingomyelin

beta-Amyloid (A beta) oligomers are neurotoxic and implicated in Alzheimer's disease. Neuronal plasma membranes may mediate formation of A beta oligomers in vivo. Membrane components sphingomyelin and GM(1) have been shown to promote aggregation of A beta; however, these studies were performed under extreme, non-physiological conditions. We demonstrate that physiological levels of GM(1), organized in nanodomains do not seed oligomerization of A beta(40) monomers. We show that sphingomyelin triggers oligomerization of A beta(40) and that GM(1) is counteractive thus preventing oligomerization. We propose a molecular explanation that is supported by all-atom molecular dynamics simulations. The preventive role of GM(1) in the oligomerization of A beta(40) suggests that decreasing levels of GM(1) in the brain, for example, due to aging, could reduce protection against A beta oligomerization and contribute to the onset of Alzheimer's disease.