Simultaneous single-molecule fluorescence and conductivity studies reveal distinct classes of Abeta species on lipid bilayers.
The extracellular senile plaques prevalent in brain tissue in Alzheimer's disease (AD) are composed of amyloid fibrils formed by the Abeta peptide. These fibrils have been traditionally believed to be featured in neurotoxicity; however, numerous recent studies provide evidence that cytotoxicity in AD may be associated with low-molecular weight oligomers of Abeta that associate with neuronal membranes and may lead to membrane permeabilization and disruption of the ion balance in the cell. The underlying mechanism leading to disruption of the membrane is the subject of many recent studies. Here we report the application of single-molecule optical detection, using fluorescently labeled human Alphabeta40, combined with membrane conductivity measurements, to monitor the interaction of single-oligomeric peptide structures with model planar black lipid membranes (BLMs). In a qualitative study, we show that the binding of Alphabeta to the membrane can be described by three distinctly different behaviors, depending on the Alphabeta monomer concentration. For concentrations much below 10 nM, there is uniform binding of monomers over the surface of the membrane with no evidence of oligomer formation or membrane permeabilization. Between 10 nM and a few hundred nanomolar, the uniform monomer binding is accompanied by the presence of peptide species ranging from dimers to small oligomers. The dimers are not found to permeabilize the membrane, but the larger oligomers lead to permeabilization with individual oligomers producing ion conductances of <10 pS/pore. At higher concentrations, perhaps beyond physiologically relevant concentrations, larger extended and dynamic structures are found with large conductances (hundreds of picosiemens), suggesting a major disruption of the membrane.
Schauerte
Joseph A
JA
Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA. schauert@umich.edu
Wong
Pamela T
PT
Wisser
Kathleen C
KC
Ding
Hao
H
Steel
Duncan G
DG
Gafni
Ari
A
D000682:Amyloid / Q000737:chemistry; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D004553:Electric Conductivity; D005456:Fluorescent Dyes; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry*; D009842:Oligopeptides / Q000737:chemistry*; D010446:Peptide Fragments / Q000737:chemistry*; D010539:Permeability; D011485:Protein Binding; D013050:Spectrometry, Fluorescence
D000682:Amyloid; D016229:Amyloid beta-Peptides; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D009842:Oligopeptides; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40)