ThT as an instrument for testing and investigation of amyloid and amyloid-like fibrils

Abstract

Thioflavin T (ThT) is known to have a very low quantum yield in water solutions itself and in the presence of native and denatured proteins and their amorphous aggregates, but to form a highly fluorescent complex with amyloid and amyloid-like fibrils. A new view on ThT spectral characteristics and mechanism of interaction with amyloid fibrils was elaborated on the basis of experimental studies of solvent polarity and viscosity influence on ThT absorption, excitation and fluorescence spectra and results of quantum-chemical calculations. It was shown that presence of the methyl group at nitrogen atom in benzthiazole ring makes nonplanar conformation of ThT energetically profitable and decreases barrier of intramolecular rotation of benzthiazole and aminobenzole rings relative to each other. Due to this ThT represents a dynamic set of molecules with differently perturbed systems of π-conjugated bonds. Possibility of torsional oscillations of ThT fragments relative to each other coupled with intramolecular charge transfer in the excited state permits to refer ThT to the class of molecular rotors. The significant, by three orders, increase of quantum yield of ThT when incorporated in amyloid and amyloid-like fibrils is caused by restriction of torsional oscillations of ThT fragments relative to each other.