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Multiple ligand binding sites on A beta(1-40) fibrils.
1Department of Molecular and Cellular Biochemistry, Chandler School of Medicine and the Center on Aging, University of Kentucky, USA. hlevine@email.uky.edu
Summary
Thioflavin T and BTA-1 bind differently to amyloid fibrils than previously thought. This suggests multiple binding sites, opening doors for selective ligand design for Alzheimer's disease and other protein misfolding diseases.
Area of Science:
- Biochemistry
- Neuroscience
- Pharmacology
Background:
- Amyloid fibrils, such as those formed by A beta(1-40), are implicated in Alzheimer's disease.
- Thioflavin T (ThT) is a common fluorescent probe for detecting amyloid fibrils.
- Understanding ligand binding to amyloid fibrils is crucial for developing diagnostic and therapeutic agents.
Purpose of the Study:
- To investigate the binding characteristics of benzothiazole ligands, specifically Thioflavin T (ThT) and BTA-1, to A beta(1-40) fibrils.
- To compare the binding of ThT and BTA-1 with other known amyloid-binding ligands like (S)-naproxen, (R)-ibuprofen, and Congo Red.
- To explore the implications of these binding properties for designing selective ligands targeting pathogenic amyloid species.
Main Methods:
- Non-competitive binding assays were used to study the interaction of ThT and BTA-1 with A beta(1-40) fibrils.
- Fluorescence displacement assays were performed to assess the competition between ThT and other ligands, including (S)-naproxen, (R)-ibuprofen, and FDDNP derivatives.
- Stoichiometry of ligand binding was determined and compared to Congo Red.
Main Results:
- ThT and BTA-1 bind to A beta(1-40) fibrils non-competitively, suggesting distinct binding sites.
- Amyloid fibril-induced fluorescence of ThT was not displaced by high concentrations of (S)-naproxen or (R)-ibuprofen.
- Benzothiazole ligand binding was significantly substoichiometric relative to A beta(1-40) monomer, unlike the 1:1 binding of Congo Red.
Conclusions:
- Amyloid fibrils possess multiple distinct ligand-binding domains.
- The binding characteristics of ThT and BTA-1 differ from other ligands, indicating unique interaction mechanisms.
- These findings support the potential for designing novel ligands with selective binding affinities for specific amyloid fibril conformations relevant to disease pathogenesis.