Binding of thioflavin T by albumins: An underestimated role of protein oligomeric heterogeneity.

Amyloid fibrils formation is the well-known hallmark of various neurodegenerative diseases. Thioflavin T (ThT)-based fluorescence assays are widely used to detect and characterize fibrils, however, if performed in bioliquids, the analysis can be biased due to the presence of other, especially abundant, proteins. Particularly, it is known that albumin may bind ThT, although the binding mechanism remains debatable.

Thioflavin T fluoresces as excimer in highly concentrated aqueous solutions and as monomer being incorporated in amyloid fibrils.

Fluorescence of thioflavin T (ThT) is a proven tool for amyloid fibrils study. The correct model of ThT binding to fibrils is crucial to clarify amyloid fibrils structure and mechanism of their formation. Although there are convincing evidences that ThT has molecular rotor nature, implying it's binding to fibrils in monomer form, speculations concerning ThT binding to fibrils in aggregated forms appear in literature so far.

High Fluorescence Anisotropy of Thioflavin T in Aqueous Solution Resulting from Its Molecular Rotor Nature.

Thioflavin T (ThT) is widely used to study amyloid fibrils while its properties are still debated in the literature. By steady-state and femtosecond time-resolved fluorescence we showed that, unlike small sized rigid molecules, the fluorescence anisotropy value of the free ThT in aqueous solutions is very high, close to the limiting value. This is determined by the molecular rotor nature of ThT, where the direction of the ThT transition dipole moment S₀ → S₁* is not changed either by the internal rotation of the ThT benzothiazole and aminobenzene rings relative to each other in the excited state, because the axis of this rotation coincides with the direction of the transition dipole moment, or by the rotation of the ThT molecule as a whole, because the rate of this process is 3 orders of magnitude smaller than the rate of the internal rotation which leads to the fluorescence quenching.

[Investigation of the kinetics of insulin amyloid fibrils formation].

Investigation of the structure of ordered protein aggregates--amyloid fibrils, the influence of the native structure of the protein and the environment on the process of fibrillation is currently the subject of intensive research. The present work is devoted to the study of the kinetics of insulin amyloid fibrils formation at low pH values (which are produced at many stages of the isolation and purification of the protein) using a fluorescent probe thioflavin T (ThT). It has been shown that the increase of fluorescence intensity of ThT during the formation of amyloid fibrils is described by a sigmoidal curve, in which 3 areas can be distinguished: the lag phase, the growth and the plateau, which characterize the various stages of fibril formation.

Fluorescence quantum yield of thioflavin T in rigid isotropic solution and incorporated into the amyloid fibrils.

In this work, the fluorescence of thioflavin T (ThT) was studied in a wide range of viscosity and temperature. It was shown that ThT fluorescence quantum yield varies from 0.0001 in water at room temperature to 0.