Sequential binding of zinc triggers tau aggregation

Tau protein has been extensively studied due to its key roles in microtubular cytoskeleton regulation and in the formation of aggregates found in some neurodegenerative diseases. Recently it has been shown that zinc is able to induce tau aggregation by interacting with several binding sites. However, precise location of these sites and the molecular mechanism of zinc-induced aggregation remain unknown. Here we used Isothermal Titration Calorimetry (ITC) and Nuclear Magnetic Resonance (NMR) to identify zinc binding sites on hTau40 isoform. These experiments revealed three distinct zinc binding sites on tau, located in the N-terminal part (H14, H32, H94, and H121), the repeat region (H299, C322, H329 and H330) and the C-terminal part (H362, H374, H388 and H407). We then demonstrated that one zinc ion binds first to the repeat region, thus allowing the binding of a second zinc ion to the C-terminal part, while the N-terminal site is independant. Using molecular simulations, we modeled the structure of each site in complex with zinc. Finally, using turbidity and Dynamic Light Scattering (DLS) assays, we showed that the C-terminal site (in particular H388 and H407) is critical for zinc-induced aggregation of tau. Our study highlights key residues involved in zinc induced aggregation of tau. Given the clinical importance of tau aggregation, our findings pave the way for designing potential therapies for tauopathies. Based on our results, we propose a model of zinc-induced aggregation of tau, allowing a better understanding of both the physiological and pathological processes associated with tau-zinc interaction.