Thioflavine t interaction with amyloid βsheet structures

Thioflavine T (ThT) interacts in tissue sections with amyloid deposits comprised of a variety of protein species giving a characteristic fluorescent complex. Binding of the dye to amyloid fibrils in suspension generates an amyloid-specific fluorescent signal. This interaction with amyloid fibrils formed from different polypeptides and proteins containing antiparallel βpleated sheet secondary structure is selective, occurring strongly with amyloid fibrils formed from insulin, transthyretin, polyglycine(I), Aβ (1-40), and weakly with β₂-microglobulin. No fluorescence changes were seen with βsheet fibrillar poly-L-lysine, islet amyloid peptide (20-29), or poly-L-serine. Native forms of transthyretin, insulin, β₂-microglobulin, poly-L-lysine, Aβ1-40), or several proteins containing high percentages of βsheet were also unreactive. The affinity of the amyloid fibrils for ThT varied: (apparent K_d's 0.033 - 10 μ Amyloid A protein <insulin <ApoAII <polyglycine <transthyretin <Aβ1-40). The spectral changes induced by the different amyloid fibrils are qualitatively the same regardless of the pK_a of the interaction with ThT or the identity of the amyloid fibrils, suggesting that the quaternary and secondary, but not the primary structure of the amyloid fibrils are important in forming the amyloid fibril-specific ThT species. Thus, Thioflavine T provides a useful tool for the investigation of amyloidogenesis in a variety of systems.