Michler’s Hydrol Blue: A Sensitive Probe for Amyloid Fibril Detection (original) (raw)
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The phenomenon of abnormal protein aggregation currently attracts ever growing attention due to its involvement in etiology of a number of so-called conformational diseases, including neurological disorders, type II diabetes, prion diseases, etc. In vivo, transformation of polypeptide chain into partially folded aggregation-prone conformation can be initiated by protein-lipid interactions. Lipid bilayer, a basic structural element of biological membranes, may act as an effective catalyst of fibrillogenesis, providing an environment where protein molecules adopt conformation and orientation promoting their assembly into protofibrillar and fibrillar structures. Identification of amyloid fibrils in protein-lipid systems with widely employed spectroscopic criteria involving amyloid-specific dyes Congo Red (CR) or Thioflavin T (ThT) may be complicated by interferences of spectral responses from protein-and lipid-bound dye species. To circumvent this problem, all optical amyloid markers must be thoroughly characterized with respect of their lipid-associating abilities. In the present study, the interactions between CR and model lipid membranes composed of phosphatidylcholine (PC) and its mixtures with anionic lipid cardiolipin (CL), cationic detergent cetyltrimethylammoniumbromide (CTAB) and cholesterol (Chol) have been examined using absorption spectroscopy technique. It was found that CR can effectively interact with PC, PC:Chol and PC:CTAB bilayers. The observed shifts of absorption maxima suggest that the dye is capable of penetrating into interfacial region of uncharged model membranes, while remaining at the bilayer surface in positively charged membranes. No CR binding to negatively charged bilayers has been detected. Differential absorption spectra of the lipid-bound dye exhibited maximum at 524 nm, the value different from that characteristic of amyloid-bound dye (545 nm). These findings suggest that CR can be used for detection of amyloid growth in protein-lipid systems, especially for identification of amyloid fibrils induced by anionic lipids.
New fluorescent probes for detection and characterization of amyloid fibrils
Chemical Physics Letters, 2010
The applicability of the novel fluorescent probes, aminoderivative of benzanthrone ABM, squaraine dye SQ-1 and polymethine dye V2 to identification and structural analysis of amyloid fibrils has been evaluated using the lysozyme model system in which fibrillar aggregates have been formed in concentrated ethanol solution. The association constant, binding stoichiometry and molar fluorescence of the bound dye have been determined. ABM was found to surpass classical amyloid marker ThT in the sensitivity to the presence of fibrillar aggregates. Resonance energy transfer measurements involving ABM-SQ-1 and SQ-1-V2 donor-acceptor pairs yielded the limits for fractal-like dimension of lysozyme fibrils.
A comparison of amyloid fibrillogenesis using the novel fluorescent compound K114
Journal of Neurochemistry, 2003
Proteinaceous inclusions with amyloidogenic properties are a common link between many neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Histological and in vitro studies of amyloid fibrils have advanced the understanding of protein aggregation, and provided important insights into pathogenic mechanisms of these neurodegenerative brain amyloidoses. The classical amyloid dyes Congo Red (CR) and thioflavin T and S, have been used extensively to detect amyloid inclusions in situ. These dyes have also been utilized to monitor the maturation of amyloid fibrils assembled from monomer subunits in vitro. Recently, the compound (trans,trans)-1-bromo-2,5-bis-(3-hydroxycarbonyl-4-hydroxy)styrylbenzene (BSB), derived from the structure of CR, was shown to bind to a wide range of amyloid inclusions in situ. More importantly it was also used to label brain amyloids in live animals. Herein, we show that an analogue of BSB, (trans,trans)-1-bromo-2,5-bis-(4-hydroxy)styrylbenzene (K114), recognizes amyloid lesions, and has distinctive properties which allowed the quantitative monitoring of the formation of amyloid fibrils assembled from the amyloid-b peptide, a-synuclein, and tau.
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.
ACS Chemical Neuroscience, 2013
Alzheimer's disease (AD) is a devastating neurodegenerative disease most notably characterized by the misfolding of amyloid-β (Aβ) into fibrils and its accumulation into plaques. In this Article, we utilize the affinity of Aβ fibrils to bind metal cations and subsequently imprint their chirality to bound molecules to develop novel imaging compounds for staining Aβ aggregates. Here, we investigate the cationic dye ruthenium red (ammoniated ruthenium oxychloride) that binds calcium-binding proteins, as a labeling agent for Aβ deposits. Ruthenium red stained amyloid plaques red under light microscopy, and exhibited birefringence under crossed polarizers when bound to Aβ plaques in brain tissue sections from the Tg2576 mouse model of AD. Staining of Aβ plaques was confirmed via staining of the same sections with the fluorescent amyloid binding dye Thioflavin S. In addition, it was confirmed that divalent cations such as calcium displace ruthenium red, consistent with a mechanism of binding by electrostatic interaction. We further characterized the interaction of ruthenium red with synthetic Aβ fibrils using independent biophysical techniques. Ruthenium red exhibited birefringence and induced circular dichroic bands at 540 nm upon binding to Aβ fibrils due to induced chirality. Thus, the chirality and cation binding properties of Aβ aggregates could be capitalized for the development of novel amyloid labeling methods, adding to the arsenal of AD imaging techniques and diagnostic tools.
Trimethine cyanine dyes as fluorescent probes for amyloid fibrils: The effect of N,N′-substituents
Analytical Biochemistry, 2015
The effect of various N,N 0 -substituents in the molecule of benzothiazole trimethine cyanine dye on its ability to sense the amyloid aggregates of protein was studied. The dyes are low fluorescent when free and in the presence of monomeric proteins, but their emission intensity sharply increases in complexes with aggregated insulin and lysozyme, with the fluorescence quantum yield reaching up to 0.42.