title: Small angle X-ray scattering analysis of Cu(2+)-induced oligomers of the Alzheimer's amyloid β peptide.
abstract: Research into causes of Alzheimer's disease and its treatment has produced a tantalising array of hypotheses about the role of transition metal dyshomeostasis, many of them on the interaction of these metals with the neurotoxic amyloid-β peptide (Aβ). Here, we have used small angle X-ray scattering (SAXS) to study the effect of the molar ratio, Cu(2+)/Aβ, on the early three-dimensional structures of the Aβ1-40 and Cu(2+)/Aβ1-42 peptides in solution. We found that at molar ratios of 0.5 copper to peptide Aβ1-40 aggregated, while Aβ1-42 adopted a relatively monodisperse cylindrical shape, and at a ratio of 1.5 copper to peptide Aβ1-40 adopted a monodisperse cylindrical shape, while Aβ1-42 adopted the shape of an ellipsoid of rotation. We also found, via in-line rapid mixing SAXS analysis, that both peptides in the absence of copper were monodisperse at very short timeframes (<2 s). Kratky plots of these scattering profiles indicated that immediately after mixing both were intrinsically disordered. Ensemble optimisation modelling reflected this, indicating a wide range of structural conformers. These data reflect the ensembles from which the Cu(2+)-promoted oligomers were derived. Our results are discussed in the light of other studies that have shown that the Cu(2+)/Aβ has a marked effect on fibril and oligomer formation by this peptide, with a higher ratio favouring the formation of cytotoxic non-amyloid oligomers. Our results are relatively consistent with previous two-dimensional studies of the conformations of these Cu(2+)-induced entities, made on a much longer time-scale than SAXS, by transmission electron microscopy and atomic force microscopy, which showed that a range of oligomeric species are formed. We propose that SAXS carried out on a modern synchrotron beamline enables studies on initial events in disordered protein folding on physiologically-relevant time-scales, and will likely provide great insight into the initiating processes of the Aβ misfolding, oligomerisation and amyloid formation.
authors: University of Melbourne, Florey Institute of Neuroscience and Mental Health, Victoria 3010, Australia.
authors: Timothy M
authors: TM
authors: Ryan
authors: Nigel
authors: N
authors: Kirby
authors: Haydyn D T
authors: HD
authors: Mertens
authors: Blaine
authors: B
authors: Roberts
authors: Kevin J
authors: KJ
authors: Barnham
authors: Roberto
authors: R
authors: Cappai
authors: Chi Le Lan
authors: Cle L
authors: Pham
authors: Colin L
authors: CL
authors: Masters
authors: Cyril C
authors: CC
authors: Curtain
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D002021:Buffers; D003300:Copper / Q000633:toxicity*; D006801:Humans; D008958:Models, Molecular; D008970:Molecular Weight; D010455:Peptides / Q000032:analysis; D055503:Protein Multimerization / Q000187:drug effects*; D053838:Scattering, Small Angle; D014961:X-Ray Diffraction
chemical_list: D016229:Amyloid beta-Peptides; D002021:Buffers; D010455:Peptides; D003300:Copper