Abstract
α-Synuclein is a membrane-interacting protein involved in Parkinson’s disease. Here we have investigated the co-association of α-synuclein and lipids from ganglioside-containing model membranes. Our study relies on the reported importance of ganglioside lipids, which are found in high amounts in neurons and exosomes, on cell-to-cell prion-like transmission of misfolded α-synuclein. Samples taken along various stages of the aggregation process were imaged using cryogenic transmission electron microscopy, and the composition of samples corresponding to the final state analyzed using NMR spectroscopy. The combined data shows that α-synuclein co-assembles with lipids from the ganglioside (GM1)-containing model membranes. The lipid-protein samples observed during the aggregation process contain non-vesicular objects not present at the final stage, thus capturing the co-existence of species under non-equilibrium conditions. A range of different lipid-protein co-assemblies are observed during the time course of the reaction and some of these appear to be transient assemblies that evolve into other co-aggregates over time. At the end of the aggregation reaction, the samples become more homogeneous, showing thin fibrillar structures heavily decorated with small vesicles. From the NMR analysis, we conclude that the ratio of GM1 to phosphatidyl choline (PC) in the supernatant of the co-aggregated samples is significantly reduced compared to the GM1/PC ratio of the lipid dispersion from which these samples were derived. Taken together, this indicates a selective uptake of GM1 into the fibrillar aggregates and removal of GM1-rich objects from the solution.
Highlights
The deposition of protein-rich aggregates and the spreading of the pathology throughout the brain are hallmarks of Parkinson’s disease (Schulz-Schaeffer, 2010)
We have in previous studies identified experimental conditions leading to reproducible α-syn aggregation kinetics (Buell et al, 2014; Grey et al, 2015; Gaspar et al, 2017; Figure 5A), making it possible to collect samples at defined stages along the aggregation process for cryo electron microscopy (cryo-EM) imaging
Lipid-protein co-aggregation leads to changes in composition, molecular organization, morphology, lipid molecular dynamics and surface properties of amyloid fibrils
Summary
The deposition of protein-rich aggregates and the spreading of the pathology throughout the brain are hallmarks of Parkinson’s disease (Schulz-Schaeffer, 2010). Associated lipids have been detected in amyloid fibrils formed in the presence of lipid membranes in vivo as well as in vitro (Halliday et al, 2005; Reynolds et al, 2011; Hellstrand et al, 2013; van Maarschalkerweerd et al, 2014). These observations imply that the lipid membrane is not a catalyzing surface but lipids are active players in the aggregation reaction. These observations imply that the lipid membrane is not a catalyzing surface but lipids are active players in the aggregation reaction. α-Syn aggregation has been linked to membrane disruption in cells and of model membranes (Davidson et al, 1998; Furukawa et al, 2006; van Rooijen et al, 2009)
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