Detection of Strongly Bound Thioflavin T Species in Amyloid Fibrils by Ligand-Detected ¹H NMR

Abstract

Thioflavin T (ThT) is used widely for the detection of amyloid fibrils. Detection is based on the dramatic enhancement of its fluorescence following binding to amyloid fibrils. The biophysical basis for this effect remains poorly understood but may lie in the elucidation of ThT binding modes at the atomic level. Here, we use ThT-detected 1H NMR to identify strongly bound ThT in fibrils formed by the islet amyloid polypeptide. Our results together with the molecular rotor model of ThT proposed by others provide the basis for the characteristic amyloid-induced increase in ThT fluorescence. In the strongly bound ThT species, the rotation of the aromatic rings of ThT relative to each other is sterically hindered, and thus the transition to the nonfluorescent state of ThT is blocked. Knowledge of the interaction of ligands with amyloid assemblies may lead to the development of small molecules for the detection and inhibition of amyloid formation.