The binding of thioflavin-T to amyloid fibrils: localisation and implications.
Amyloid fibrils are a polymeric form of protein, involving a continuous beta-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 beta-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 beta-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.
Krebs
M R H
MR
P&C Group, Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK. mrhk2@cam.ac.uk
Bromley
E H C
EH
Donald
A M
AM
D000682:Amyloid / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D052160:Benzothiazoles; D001665:Binding Sites; D002417:Cattle; D005456:Fluorescent Dyes / Q000737:chemistry; D007328:Insulin / Q000378:metabolism; D007782:Lactoglobulins / Q000378:metabolism; D018613:Microscopy, Confocal; D010316:Particle Size; D011485:Protein Binding; D013844:Thiazoles / Q000737:chemistry* / Q000378:metabolism
D000682:Amyloid; D052160:Benzothiazoles; D005456:Fluorescent Dyes; D007328:Insulin; D007782:Lactoglobulins; D013844:Thiazoles; C009462:thioflavin T