The binding of thioflavin-T to amyloid fibrils: localisation and implications

• Published in: Journal of structural biology 2005, Vol.149 (1), p.30-37
• Main Authors: Krebs, M.R.H., Bromley, E.H.C., Donald, A.M.
• Format: Article
• Language: English
• Subjects: Amyloid - chemistry; Amyloid - metabolism; Amyloid fibrils; Animals; Binding Sites; Cattle; Confocal microscopy; Congo red; Fluorescent Dyes - chemistry; Insulin - metabolism; Lactoglobulins - metabolism; Microscopy, Confocal; Particle Size; Protein Binding; Spherulites; Thiazoles - chemistry; Thiazoles - metabolism; Thioflavin-T
• ISSN: 1047-8477; 1095-8657
• DOI: 10.1016/j.jsb.2004.08.002

Amyloid fibrils are a polymeric form of protein, involving a continuous β-sheet with the strands perpendicular to the long axis of the fibril. Although typically implicated in diseases such as Alzheimer’s disease and the transmissible spongiform encephalopathies, non disease-associated protein can also be converted into amyloid fibrils. Traditionally, amyloid fibrils are identified via the use of specific dyes such as Congo red and thioflavin-T, although their specificity is ill understood. Recently, solutions of bovine insulin and bovine β-lactoglobulin have been found to form spherulites, micron-sized spherical structures containing radially arranged amyloid fibrils. When studied by confocal microscopy using polarised laser light and thioflavin-T, a consistent pattern of emission, rather than a uniform disc, was observed. This suggests the dye binds in a specific, regular fashion to amyloid fibrils. Confocal microscopy studies of thioflavin-T aligned in stretched poly-vinyl alcohol films showed that the dye dipole excitation axis lies parallel to the long molecular axis. Therefore, thioflavin-T binds to amyloid fibrils such that their long axes are parallel. We propose binding occurs in ‘channels’ that run along the length of the β-sheet. Steric interactions between dye molecules and side chains indicate why thioflavin-T fluoresces more intensely when bound to amyloid fibrils and can explain why this interaction with amyloid fibrils is specific, but with varying efficiency.