Direct three-dimensional visualization of membrane disruption by amyloid fibrils

Abstract

[eng] Protein misfolding and aggregation cause serious degenerativeconditions such as Alzheimer’s, Parkinson, and prion diseases. Damageto membranes is thought to be one of the mechanisms underlyingcellular toxicity of a range of amyloid assemblies. Previousstudies have indicated that amyloid fibrils can cause membraneleakage and elicit cellular damage, and these effects are enhancedby fragmentation of the fibrils. Here we report direct 3D visualizationof membrane damage by specific interactions of a lipid bilayerwith amyloid-like fibrils formed in vitro from β2-microglobulin(β2m). Using cryoelectron tomography, we demonstrate that fragmentedβ2m amyloid fibrils interact strongly with liposomes andcause distortions to the membranes. The normally spherical liposomesform pointed teardrop-like shapes with the fibril ends seenin proximity to the pointed regions on the membranes. Moreover,the tomograms indicated that the fibrils extract lipid from the membranesat these points of distortion by removal or blebbing of theouter membrane leaflet. Tiny (15–25 nm) vesicles, presumably formedfrom the extracted lipids, were observed to be decorating the fibrils.The findings highlight a potential role of fibrils, and particularly fibrilends, in amyloid pathology, and report a previously undescribed classof lipid–protein interactions in membrane remodelling.