Thioflavin T Interaction with Acetylcholinesterase: New Evidence of 1:1 Binding Stoichiometry Obtained with Samples Prepared by Equilibrium Microdialysis

Anna I. Sulatskaya, Georgy N Rychkov, Maksim I. Sulatsky, Natalia P. Rodina, Irina M. Kuznetsova, Konstantin K. Turoverov

Index: 10.1021/acschemneuro.8b00111

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Abstract

The aim of the present work was investigation of the fluorescent dye thioflavin T (ThT) binding to acetylcholinesterase (AChE). ThT is an effectively used test for the protease activity, as well as a probe for amyloid fibril formation. Despite the extended and active investigation of the ThT – AChE binding, there is still no common view on the stoichiometry of this interaction. In particular, there is a hypothesis explaining the spectral properties of the bound to AChE dye and high quantum yield of its fluorescence by formation of dimers or excimers of ThT. In order to confirm or deny this hypothesis we proposed a new experimental approach for examination of the ThT – AChE interaction based on spectroscopic investigation of samples prepared by equilibrium microdialysis. This approach allowed to prove the 1/1 ThT/AChE binding stoichiometry. The increase of the ThT fluorescence quantum yield and lifetime accompanying its binding to AChE can be explained by the molecular rotor nature of this dye. Together with the coincidence of the positions of free and AChE-bound ThT fluorescence spectra, the obtained results prove the groundlessness of the hypotheses about ThT aggregation while binding to AChE. The model of ThT localization in the active site of AChE was proposed by using molecular docking simulations. These results also allowed us to suggest the key role of aromatic residues in the ThT – AChE interaction, as observed for some amyloid fibrils.