pDimers of Aβ (amyloid β-protein) are believed to play an important role in Alzheimer9s disease. In the absence of sufficient brain-derived dimers, we studied one of the only possible dimers that could be produced iin vivo/i, [Aβ]subDiY/sub (dityrosine cross-linked Aβ). For comparison, we used the Aβ monomer and a design dimer cross-linked by replacement of Sersup26/sup with cystine [AβS26C]sub2/sub. We showed that similar to monomers, unaggregated dimers lack appreciable structure and fail to alter long-term potentiation. Importantly, dimers exhibit subtly different structural propensities from monomers and each other, and can self-associate to form larger assemblies. Although [Aβ]subDiY/sub and [AβS26C]sub2/sub have distinct aggregation pathways, they both populate bioactive soluble assemblies for longer durations than Aβ monomers. Our results indicate that the link between Aβ dimers and Alzheimer9s disease results from the ability of dimers to further assemble and form synaptotoxic assemblies that persist for long periods of time./p
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