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Alzheimer's disease (AD) is associated with progressive accumulation of amyloid-β (Aβ) cross-β fibrils in the brain. Aβ species tightly associated with GM1 ganglioside, a glycosphingolipid abundant in neuronal membranes, promote amyloid fibril formation; therefore, they could be attractive clinical targets. However, the active conformational state of Aβ in GM1-containing lipid membranes is still unknown. The present solid-state nuclear magnetic resonance study revealed a nonfibrillar Aβ assemblage characterized by a double-layered antiparallel β-structure specifically formed on GM1 ganglioside clusters. Our data show that this unique assemblage was not transformed into fibrils on GM1-containing membranes but could promote conversion of monomeric Aβ into fibrils, suggesting that a solvent-exposed hydrophobic layer provides a catalytic surface evoking Aβ fibril formation. Our findings offer structural clues for designing drugs targeting catalytically active Aβ conformational species for the development of anti-AD therapeutics.

Physiological and pathological functions of glycans are promoted through their clustering effects as exemplified by a series of gangliosides, sialylated glycosphingolipids, which serve as acceptors for bacterial toxins and viruses. Furthermore, ganglioside GM1 clusters on neuronal cell membranes specifically interact with amyloidogenic proteins, triggering their conformational transitions and leading to neurodegeneration. Here we develop a self-assembled spherical complex that displays a cluster of the GM1 pentasaccharide, and successfully demonstrate its ability to interact with amyloid β and α-synuclein. Due to the lack of hydrophobic lipid moieties, which would stably trap these cohesive proteins or give rise to toxic aggregates, this artificial cluster enabled NMR spectroscopic characterization of the early encounter stage of protein interactions with its outer carbohydrate moieties, which were not observable with previous glycan clusters., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The ganglioside GM1 mediates various physiological and pathological processes mainly through the formation of GM1 clusters on cell surfaces. Therefore, detailed characterization of conformational properties of the glycan moiety of GM1 and the structures and interactions of this glycosphingolipid in membrane environments is necessary for better understanding of the clustering-coupled functional promotion. Nuclear magnetic resonance (NMR) spectroscopy has provided conformational information of GM1 in solution as well as in membrane-like environments. Recently, sophisticated paramagnetism-assisted NMR approaches combined with molecular dynamics simulations have enabled the quantitative exploration of conformational spaces of a series of gangliosides, including GM1, taking into account their minor conformations. NMR techniques have also been successfully applied to investigations of the dynamic interactions of GM1 clusters with amyloidogenic proteins such as amyloid β and α-synuclein associated with neurodegenerative disorders. Further integration of experimental and computational approaches will open up new possibilities to provide structural views of the more complicated heterogeneous systems exemplified by microdomains involving GM1.

Gangliosides are targets for a variety of pathologically relevant proteins, including amyloid beta (Abeta), an important component implicated in Alzheimer's disease (AD). To provide a structural basis for this pathogenic interaction associated with AD, we conducted NMR analyses of the Abeta interactions with gangliosides using lyso-GM1 micelles as a model system. Our NMR data revealed that the sugar-lipid interface is primarily perturbed upon binding of Abeta to the micelles, underscoring the importance of the inner part of the ganglioside cluster for accommodating Abeta in comparison with the outer carbohydrate branches that provide microbial toxin- and virus-binding sites., (Copyright 2010 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.)