| Dr. Harman 2005-04-25, 11:49 am |
| Krebs MR, Bromley EH, Donald AM.
P&C Group, Cavendish Laboratory, university of Cambridge, Madingley
Road, Cambridge CB3 0HE, UK. mrhk2@cam.ac.uk
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.
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