ATP as a catalyst for amyloid fibrillation of tau protein

Authors: Chae Eun Heo, Hugh Inkon Kim

Published: 2020-12-07

Abstract

AbstractBackgroundIntracellular tau protein tangle is a hallmark of various neurodegenerative diseases, which include Alzheimer’s disease (AD). For this reason, characterizing the physiological factors associated with tau aggregation and the aggregation mechanism has been considered crucial for understanding tau pathology. Recent evidence implies that (i) intracellular ATP level may be dysregulated and (ii) the increased ATP level may have an influence on the tau aggregation. However, the effects of ATP on tau fibrillation and its mechanistic details are not fully elucidated.MethodsFor characterizing K18 fibrillation mechanism catalysed by ATP, we performed multiple biophysical experiments such as thioflavin assays, circular dichroism, small‐angle X‐ray scattering, and native mass spectrometry. We further measured cellular ATP amount in presence of TNFα, and intracellular tau aggregation was examined by bimolecular fluorescence complementation experiments.ResultsHerein, we report the catalytic role of ATP and its mechanistic details in tau aggregation at a molecular level for the first time. Using multiple approaches including solution small angle X‐ray scattering (SAXS), native mass spectrometry (MS) and molecular dynamics (MD) simulations, we observed that nonspecific electrostatic interactions between negatively charged triphosphate moiety in ATP and basic residues in tau K18 (i.e. four‐repeat domain of tau) direct the dimerization of K18 by charge neutralization of the protein in the early stage of the aggregation. We observed that ATP was excluded in the late stage of fibrillation and acted to accelerate K18 fibrillation even at lower stoichiometric ratios for the charge neutralization, indicating that ATP acted as a catalyst for K18 fibrillation. Moreover, our bimolecular fluorescence complementation (BiFC) and immunoblotting (IB) experiments suggested a correlation between ATP dyshomeostasis and tau aggregation in cellular environment.ConclusionWe believe that our observations would provide valuable insights into the mechanism of tau aggregation and the importance of ATP in tauopathies.