Resveratrol Selectively Remodels Soluble Oligomers and Fibrils of Amyloid Aβ into Off-pathway Conformers

Abstract

Misfolded proteins associated with diverse aggregation disorders assemble not only into a single toxic conformer but rather into a suite of aggregated conformers with unique biochemical properties and toxicities. To what extent small molecules can target and neutralize specific aggregated conformers is poorly understood. Therefore, we have investigated the capacity of resveratrol to recognize and remodel five conformers (monomers, soluble oligomers, non-toxic oligomers, fibrillar intermediates, and amyloid fibrils) of the A␤1-42 peptide associated with Alzheimer disease. We find that resveratrol selectively remodels three of these conformers (soluble oligomers, fibrillar intermediates, and amyloid fibrils) into an alternative aggregated species that is non-toxic, high molecular weight, and unstructured. Surprisingly, resveratrol does not remodel non-toxic oligomers or accelerate A␤ monomer aggregation despite that both conformers possess random coil secondary structures indistinguishable from soluble oligomers and significantly different from their ␤-sheet rich, fibrillar counterparts. We expect that resveratrol and other small molecules with similar conformational specificity will aid in illuminating the conformational epitopes responsible for A␤-mediated toxicity.Despite the remarkable fidelity of protein folding in diverse cellular environments, defects do occur that are linked to an array of protein aggregation diseases. In many such disorders (e.g. Alzheimer (1-4), Parkinson (5, 6), Huntington (7-9), and Prion (10, 11) diseases) specific peptides of unrelated sequence aggregate into similar types of assemblies ranging from soluble, low molecular weight oligomers to insoluble, high molecular weight amyloid fibrils (1, 12).A particularly intriguing aspect of protein misfolding is that a single polypeptide chain can adopt multiple aggregated conformations with unique biological activities (13). Such conformational diversity was first observed for the mammalian prion protein PrP (14 -21). Different infectious prion conformations of PrP, known as strains or variants, encipher unique prion diseases through differences in their aggregate structure (14,16,19,(22)(23)(24). More recently, polymorphic aggregate structures have been formed in vitro and identified in vivo for many other proteins (25-39). However, the biological consequence of such conformational diversity and which conformers are most toxic remains poorly defined.Aggregated A␤ conformers associated with Alzheimer disease also display such conformational diversity (30,32,33,38,40). The A␤ peptide self-assembles through multiple pathways in which several intermediates are transiently populated (41-46). These conformers, which range from dimers and soluble oligomers to fibrillar oligomers and protofibrils, are typically classified either by size or structure. Even though size is an important characteristic of different A␤ conformers, it is now clear that aggregates of the same size can have unique structures (44, 47). These recent findings have been illumi...

Small-molecule conversion of toxic oligomers to nontoxic β-sheet–rich amyloid fibrils

“…A stabilization of -sheet-rich, nontoxic, spherical A conformations was observed with the compound scyllo-inositol 47 , while the polyphenol EGCG was shown to convert A42 peptides into non-toxic, unstructured oligomers 18 . A similar result was obtained more recently with the compound resveratrol that selectively remodels soluble oligomers and fibrils of A42 peptides into offpathway conformers 48 . Thus, small molecules can have different effects on A42 polymerization, leading to the stabilization of aggregate species with very distinct conformations, morphologies and biological properties.…”

Suppression of Amyloid β A11 Antibody Immunoreactivity by Vitamin C

“…In Vitro Assay of A␤42 A11 Immunoreactivity-The conversion of monomeric A␤42 to A11-positive soluble oligomers can be monitored by in vitro assays (52,53). We adopted the latter procedure.…”

Structure-based design of conformation- and sequence-specific antibodies against amyloid β

“…Therefore, we first assembled the Aβ conformers as we described previously (30)(31)(32) and deposited each of them on nitrocellulose membranes. We detected each Aβ conformer using sequence-specific monoclonal antibodies that recognize the N terminus (6E10; Aβ residues 1-16), middle region (4G8; Aβ residues 18-22), and C terminus (9F1; Aβ residues 34-39) of Aβ (Fig.…”