THIOFLAVINE-T INTERACTION WITH AMYLOID BETA-SHEET STRUCTURES

Thioflavine T (Th T) 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 beta-pleated sheet secondary structure is selective, occurring strongly with amyloid fibrils formed from insulin, transthyretin, polyglycine((), A beta(1-40), and weakly with beta(2)-microglobulin. No fluorescence changes were seen with beta-sheet fibrillar poly-L-lysine, islet amyloid peptide (20-29), or poly-L-serine. Native forms of transthyretin, insulin, beta(2)-microglobulin, poly-L-lysine, A beta(1-40), or several proteins containing high percentages of beta-sheet were also unreactive. The affinity of the amyloid fibrils for ThT varied: (apparent K-d's 0.033 - 10 mu M; Amyloid A protein < insulin < ApoAII <polyglycine < transthyretin < A beta(1-40). 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 informing the amyloid fibril-specific ThT species. Thus, Thioflavine T provides a useful tool for the investigation of amyloidogenesis in a variety of systems.