Characterization of Aβ aggregation mechanism probed by congo red (original) (raw)
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Effects of Congo red on aβ(1-40) fibril formation process and morphology
ACS chemical neuroscience, 2010
Alzheimer's disease (AD), an age-related neurodegenerative disorder, is the most common form of dementia, and the seventh-leading cause of death in the United States. Current treatments offer only symptomatic relief; thus, there is a great need for new treatments with disease-modifying potential. One pathological hallmark of AD is so-called senile plaques, mainly made up of β-sheet-rich assemblies of 40- or 42-residue amyloid β-peptides (Aβ). Hence, inhibition of Aβ aggregation is actively explored as an option to prevent or treat AD. Congo red (CR) has been widely used as a model antiamyloid agent to prevent Aβ aggregation. Herein, we report detailed morphological studies on the effect of CR as an antiamyloid agent, by circular dichroism spectroscopy, photo-induced cross-linking reactions, and atomic force microscopy. We also demonstrate the effect of CR on a preaggregated sample of Aβ(1-40). Our result suggests that Aβ(1-40) follows a different path for aggregation in the pres...
Assembly and aggregation properties of synthetic Alzheimer's A4/beta amyloid peptide analogs
Journal of Biological …, 1992
The amyloid A4 or 8 peptide is a major component of extracellular amyloid deposits that are a characteristic feature of Alzheimer's disease. We synthesized a series of peptide analogs of the A418 peptide which are progressively longer at their carboxyl termini, including 42-and 39-residue peptides which represent the major forms of the A418 peptide in senile plaque and the hereditary cerebral hemorrhage with amyloidosis form, respectively.
Journal of Structural Biology, 2000
Assembly of the amyloid- peptide (A) into fibrils and its deposition in distinct brain areas is considered responsible for the pathogenesis of Alzheimer's disease (AD). Thus, inhibition of fibril assembly is a potential strategy for therapeutic intervention. Electron cryomicroscopy was used to monitor the initial, native assembly structure of A42. In addition to the known fibrillar intermediates, a nonfibrillar, polymeric sheet-like structure was identified. A temporary sequence of supramolecular structures was revealed with (i) polymeric A42 sheets during the onset of assembly, inversely related to the appearance of (ii) fibril intermediates, which again are time-dependently replaced by (iii) mature fibrils. A cell-based primary screening assay was used to identify compounds that decrease A42-induced toxicity. Hit compounds were further assayed for binding to A42, radical scavenger activity, and their influence on the assembly structure of A42. One compound, Ro 90-7501, was found to efficiently retard mature fibril formation, while extended polymeric A42 sheets and fibrillar intermediates are accumulated. Ro 90-7501 may serve as a prototypic inhibitor for A42 fibril formation and as a tool for studying the molecular mechanism of fibril assembly.
The Aggregation Paths and Products of Aβ42 Dimers Are Distinct from Those of the Aβ42 Monomer
Biochemistry
Extracts of Alzheimer's disease (AD) brain that contain what appear to be SDS-stable amyloid βprotein (Aβ) dimers potently block LTP and impair memory consolidation. Brain-derived dimers can be physically separated from Aβ monomer, consist primarily of Aβ42 and resist denaturation by powerful chaotropic agents. In nature, covalently cross-linked Aβ dimers could be generated in only one of two different ways-either by the formation of a dityrosine (DiY) or an isopeptide ε-(γ-glutamyl)-lysine (Q-K) bond. We enzymatically cross-linked recombinant Aβ42 monomer to produce DiY and Q-K dimers and then applied a range of biophysical methods to study their aggregation. Both Q-K and DiY dimers aggregate to form soluble assemblies distinct from the fibrillar aggregates formed by Aβ monomer. These results suggest that Aβ dimers allow the formation of soluble aggregates akin to those in aqueous extracts of AD brain. Thus it seems that Aβ dimers may play an important role in determining the formation of soluble rather than insoluble aggregates.
Surfactant-induced conformational transition of amyloid β-peptide
European Biophysics Journal With Biophysics Letters, 2009
Accumulating evidence suggests that Aβ1–42–membrane interactions may play an important role in the pathogenesis of Alzheimer’s disease. However, the mechanism of this structural transition remains unknown. In this work, we have shown that submicellar concentrations of sodium dodecyl sulfate (SDS) can provide a minimal platform for Aβ1–42 self-assembly. To further investigate the relation between Aβ1–42 structure and function, we analyzed peptide conformation and aggregation at various SDS concentrations using circular dichroism (CD), Fourier transform infrared spectroscopy, and gel electrophoresis. These aggregates, as observed via atomic force microscopy, appeared as globular particles in submicellar SDS with diameters of 35–60 nm. Upon sonication, these particles increased in disc diameter to 100 nm. Pyrene I 3/I 1 ratios and 1-anilinonaphthalene-8-sulfonic acid binding studies indicated that the peptide interior is more hydrophobic than the SDS micelle interior. We have also used Forster resonance energy transfer between N-terminal labeled pyrene and tyrosine (10) of Aβ1–42 in various SDS concentrations for conformational analysis. The results demonstrate that SDS at submicellar concentrations accelerates the formation of spherical aggregates, which act as niduses to form large spherical aggregates upon sonication.
Bifunctional Compounds for Controlling Metal-Mediated Aggregation of the Aβ 42 Peptide
Journal of the American Chemical Society, 2012
Abnormal interactions of Cu and Zn ions with the amyloid β (Aβ) peptide are proposed to play an important role in the pathogenesis of Alzheimer's disease (AD). Disruption of these metal-peptide interactions using chemical agents holds considerable promise as a therapeutic strategy to combat this incurable disease. Reported herein are two bifunctional compounds (BFCs) L1 and L2 that contain both amyloid-binding and metal-chelating molecular motifs. Both L1 and L2 exhibit high stability constants for Cu 2+ and Zn 2+ and thus are good chelators for these metal ions. In addition, L1 and L2 show strong affinity toward Aβ species. Both compounds are efficient inhibitors of the metal-mediated aggregation of the Aβ 42 peptide and promote disaggregation of amyloid fibrils, as observed by ThT fluorescence, native gel electrophoresis/Western blotting, and transmission electron microscopy (TEM). Interestingly, the formation of soluble Aβ 42 oligomers in presence of metal ions and BFCs leads to an increased cellular toxicity. These results suggest that for the Aβ 42 peptide -in contrast to the Aβ 40 peptide, the previously employed strategy of inhibiting Aβ aggregation and promoting amyloid fibril dissagregation may not be optimal for the development of potential AD therapeutics, due to formation of neurotoxic soluble Aβ 42 oligomers.
ACS Chemical Neuroscience, 2010
Neuronal cytotoxicity observed in Alzheimer's disease (AD) is linked to the aggregation of β-amyloid peptide (Aβ) into toxic forms. Increasing evidence points to oligomeric materials as the neurotoxic species, not Aβ fibrils; disruption or inhibition of Aβ self-assembly into oligomeric or fibrillar forms remains a viable therapeutic strategy to reduce Aβ neurotoxicity. We describe the synthesis and characterization of amyloid aggregation mitigating peptides (AAMPs) whose structure is based on the Aβ "hydrophobic core" Aβ 17-20 , with R,R-disubstituted amino acids (RRAAs) added into this core as potential disrupting agents of fibril selfassembly. The number, positional distribution, and side-chain functionality of RRAAs incorporated into the AAMP sequence were found to influence the resultant aggregate morphology as indicated by ex situ experiments using atomic force microscopy (AFM) and transmission electron microscopy (TEM). For instance, AAMP-5, incorporating a sterically hindered RRAA with a diisobutyl side chain in the core sequence, disrupted Aβ 1-40 fibril formation. However, AAMP-6, with a less sterically hindered RRAA with a dipropyl side chain, altered fibril morphology, producing shorter and larger sized fibrils (compared with those of Aβ 1-40). Remarkably, RRAA-AAMPs caused disassembly of existing Aβ fibrils to produce either spherical aggregates or protofibrillar structures, suggesting the existence of equilibrium between fibrils and prefibrillar structures.
Mechanisms for the inhibition of amyloid aggregation by small ligands
Bioscience Reports, 2016
The formation of amyloid aggregates is the hallmark of systemic and neurodegenerative disorders, also known as amyloidoses. Many proteins have been found to aggregate into amyloid-like fibrils and this process is recognized as a general tendency of polypeptides. Lysozyme, an antibacterial protein, is a well-studied model since it is associated in human with systemic amyloidosis and that is widely available from chicken eggs (HEWL, hen egg white lysozyme). In the present study we investigated the mechanism of interaction of aggregating HEWL with rosmarinic acid and resveratrol, that we verified to be effective and ineffective, respectively, in inhibiting aggregate formation. We used a multidisciplinary strategy to characterize such effects, combining biochemical and biophysical methods with molecular dynamics (MD) simulations on the HEWL peptide 49–64 to gain insights into the mechanisms and energy variations associated to amyloid formation and inhibition. MD revealed that neither re...
Alzheimer's disease (AD), the most common form of senile dementia, is associated with the progressive accumulation of plaques and tangles within the neuronal cell. The plaques are composed of amyloid (Aβ) peptide fragments with a high propensity for aggregation. Metal ion binding to Aβ peptide has been known to alter the aggregation of the peptide and to be involved in the pathogenecity of Alzheimer's. Earlier investigations suggest that the N terminal hydrophilic region of the peptide exhibit preferential ligand binding capabilities and, thus initiate the onset of aggregation events. The complexation events with metals like zinc, copper, aluminium, and small molecules like betaine and curcumin, reported in this paper provide a molecular level appreciation of the binding characteristics of the Aβ (1-12) peptide fragments and the variations thereof. Our data show notable conformational changes induced due the binding of these ligands, suggesting plausible clues to explore these molecules as potential inhibitors and neuro-protective agents for AD.