Effects of Congo red on aβ(1-40) fibril formation process and morphology (original) (raw)

Characterization of Aβ aggregation mechanism probed by congo red

Journal of Biomolecular Structure and Dynamics, 2012

β-Amyloid peptide (Aβ) aggregates are toxic to neuron and the main cause of Alzheimer's disease (AD). The role of congo red (CR) on Aβ aggregation is controversial in aqueous solution. Both prevention and promotion of Aβ aggregation have been proposed, suggesting that CR may interact with Aβ of different structural conformations resulting in different effects on Aβ aggregation behavior. CR with these characteristics can be applied to probe the molecular mechanism of Aβ aggregation. Therefore, in the present study, we used CR as a probe to study the Aβ aggregation behavior in sodium dodecyl sulfate (SDS) condition. Our results show that Aβ 40 adopts two short helices at Q15-S26 and K28-L34 in the SDS environment. CR can interact with the helical form of Aβ 40 , and the main interaction site is located at the first helical and hydrophobic core region, residues 17-25, which is assigned as a discordant helix region. Furthermore, CR may prevent Aβ 40 undergoing α-helix to β-strand conversion, and therefore aggregation through stabilizing the helical conformation of discordant helix in SDS environment, suggesting that the discordant helix plays a key role on the conformational stabilization of Aβ. Our present study implies that any factors or molecules that can stabilize the discordant helical conformation may also prevent the Aβ aggregation in membrane associated state. This leads to a new therapeutic strategy for the development of lead compounds to AD.

Alzheimer's beta-amyloid: insights into fibril formation and structure from Congo red binding

Sub Cellular Biochemistry, 2005

We consider here the chemistry of Congo red (CR), its binding equilibrium to Alzheimer's beta-amyloid, and the kinetics of beta-amyloid formation. Spectroscopic UV/V is measurements for the pH- and time-dependence binding of CR to Abeta analogues are analysed by Scatchard binding and the theory of nucleation-dependent fibril formation. CR likely binds electrostatically to the imidazolium sidechains of histidine residues that are exposed at the surface of amyloid fibrils. As revealed by atomic models of the Abeta protofilament, such as the nanotube beta-helix and parallel beta-sheet, the regular arrangement of histidines likely acts as a template for the end-to-end J-aggregation of CR molecules, which produces a red shift in UV/V is absorption.

Aβ Fibrillogenesis: Kinetic Parameters for Fibril Formation from Congo Red Binding

Journal of Structural Biology, 2000

Using Scatchard analysis, we have formulated as a function of time and pH the relationship between the binding of Congo red to Alzheimer's ␤-amyloid and the aggregation number (i.e., monomer concentration within fibrils) as defined by nucleation-dependent self-assembly. This provides a basis on which to determine the kinetic parameters for fibril formation from the observed concentration of bound Congo red.

Silver ions as em marker of congo red ligation sites in amyloids and amyloid-like aggregates

Acta Biochimica Polonica, 2016

Congo red (CR) which is known to act as selective amyloid ligand may when binds to these protein forms reflect their internal molecular structure. The disclosure by EM of sites binding the dye and their distribution in amyloids and amyloid-like aggregates formed in vitro is the focus of our work. In order to produce the required contrast, CR has been indirectly combined with metal via including by intercalation of Titan yellow (TY) which exhibits relatively strong affinity for silver ions. The resulting combined ligand retains its ability to bind to proteins which it owes to CR and can easily be detected in EM studies thanks to TY less active in penetration to proteins. We have found however that in protein aggregates where unfolding is stabilized by aggregation and therefore irreversible, TY alone may serve as both ligand and metal carrier.The formation of ordered structures in amyloids were studied using IgG light chains with amyloidogenic properties, converted into amyloids throu...

Self-Assembly of β-Amyloid 42 Is Retarded by Small Molecular Ligands at the Stage of Structural Intermediates

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 A␤42. 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 A␤42 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 A␤42-induced toxicity. Hit compounds were further assayed for binding to A␤42, radical scavenger activity, and their influence on the assembly structure of A␤42. One compound, Ro 90-7501, was found to efficiently retard mature fibril formation, while extended polymeric A␤42 sheets and fibrillar intermediates are accumulated. Ro 90-7501 may serve as a prototypic inhibitor for A␤42 fibril formation and as a tool for studying the molecular mechanism of fibril assembly.

Circular dichroism and aggregation studies of amyloid beta (11-8) fragment and its variants

Acta Biochimica Polonica, 2005

Aggregation of Abeta peptides is a seminal event in Alzheimer's disease. Detailed understanding of Abeta assembly would facilitate the targeting and design of fibrillogenesis inhibitors. Here comparative conformational and aggregation studies using CD spectroscopy and thioflavine T fluorescence assay are presented. As a model peptide, the 11-28 fragment of Abeta was used. This model peptide is known to contain the core region responsible for Abeta aggregation. The structural and aggregational behaviour of the peptide was compared with the properties of its variants corresponding to natural, clinically relevant mutants at positions 21-23 (A21G, E22K, E22G, E22Q and D23N). In HFIP (hexafluoro-2-propanol), a strong alpha-helix inducer, the CD spectra revealed an unexpectedly high amount of beta-sheet conformation. The aggregation process of Abeta(11-28) variants provoked by water addition to HFIP was found to be consistent with a model of an alpha-helix-containing intermediate. The...

Supramolecular structural constraints on Alzheimer's beta-amyloid fibrils from electron microscopy and solid-state nuclear magnetic resonance

Biochemistry, 2002

We describe electron microscopy (EM), scanning transmission electron microscopy (STEM), and solid-state nuclear magnetic resonance (NMR) measurements on amyloid fibrils formed by the 42-residue beta-amyloid peptide associated with Alzheimer's disease (Abeta(1)(-)(42)) and by residues 10-35 of the full-length peptide (Abeta(10)(-)(35)). These measurements place constraints on the supramolecular structure of the amyloid fibrils, especially the type of beta-sheets present in the characteristic amyloid cross-beta structural motif and the assembly of these beta-sheets into a fibril. EM images of negatively stained Abeta(10)(-)(35) fibrils and measurements of fibril mass per length (MPL) by STEM show a strong dependence of fibril morphology and MPL on pH. Abeta(10)(-)(35) fibrils formed at pH 3.7 are single "protofilaments" with MPL equal to twice the value expected for a single cross-beta layer. Abeta(10)(-)(35) fibrils formed at pH 7.4 are apparently pairs of protofilament...

Atomic force microscopy to study molecular mechanisms of amyloid fibril formation and toxicity in Alzheimer’s disease

Drug Metabolism Reviews, 2014

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by dementia and memory loss for which no cure or effective prevention is currently available. Neurodegeneration in AD is linked to formation of amyloid plaques found in brain tissues of Alzheimer's patients during post-mortem examination. Amyloid plaques are composed of amyloid fibrils and small oligomers-insoluble protein aggregates. Although amyloid plaques are found on the neuronal cell surfaces, the mechanism of amyloid toxicity is still not well understood. Currently, it is believed that the cytotoxicity is a result of the nonspecific interaction of small soluble amyloid oligomers (rather than longer fibrils) with the plasma membrane. In recent years, nanotechnology has contributed significantly to understanding the structure and function of lipid membranes and to the study of the molecular mechanisms of membrane-associated diseases. We review the current state of research, including applications of the latest nanotechnology approaches, on the interaction of lipid membranes with the amyloid-b (Ab) peptide in relation to amyloid toxicity. We discuss the interactions of Ab with model lipid membranes with a focus to demonstrate that composition, charge and phase of the lipid membrane, as well as lipid domains and rafts, affect the binding of Ab to the membrane and contribute to toxicity. Understanding the role of the lipid membrane in AD at the nanoscale and molecular level will contribute to the understanding of the molecular mechanism of amyloid toxicity and may aid into the development of novel preventive strategies to combat AD.