It Takes Tau to Tango: Investigating the Fuzzy Interaction between the R2-Repeat Domain and Tubulin C-Terminal Tails

Abstract

The microtubule-associated protein (MAP) tau plays a key role in the regulation of microtubule assembly and spatial organization. Tau hyperphosphorylation affects its binding on the tubulin surface and has been shown to be involved in several pathologies such as Alzheimer's disease. As the tau binding site on the microtubule lays close to the disordered and highly flexible tubulin C-terminal tails (CTTs), these are likely to impact the tau-tubulin interaction. Since the disordered tubulin CTTs are missing from the available experimental structures, we used homology modeling to build two complete models of tubulin heterotrimers with different isotypes for the β-tubulin subunit (βI/αI/βI and βIII/αI/βIII). We then performed long timescale classical Molecular Dynamics simulations for the tau-R2/tubulin assembly (in systems with and without CTTs) and analyzed the resulting trajectories to obtain a detailed view of the protein interface in the complex and the impact of the CTTs on the stability of this assembly. Additional analyses of the CTT mobility in the presence, or in the absence, of tau also highlight how tau might modulate the CTT activity as hooks that are involved in the recruitment of several MAPs. In particular, we observe a wrapping phenomenon, where the β-tubulin CTTs form a loop over tau-R2, thus stabilizing its interaction with the tubulin surface and simultaneously reducing the CTT availability for interactions with other MAPs.

nP-Collabs: Investigating Counterion-Mediated Bridges in the Multiply Phosphorylated Tau-R2 Repeat

“…We used the structure of the tau-R2 repeat (a 27 residue fragment ranging from Lys274 to Val300) extracted from the tau-tubulin assembly modeled in our previous work as a starting point. Phosphorylations were added using the CHARMM-GUI () input generator.…”

“…Following an earlier study using molecular dynamics simulation to investigate the interaction pattern in the fuzzy complex formed by the tau-R2 fragment (which comprises a strong interacting region centered around Ser289) and the tubulin surface, we phosphorylated the Ser285, Ser289 and Ser293 residues in the isolated tau-R2 fragment, which have been identified as phosphorylation sites in tauopathies. ,− Ser289, in particular, is one of the 40 phosphorylation sites found in AD brains, but not in healthy ones . Initial analyses of the conformational space explored by the multiply phosphorylated tau-R2 fragment highlighted stable structures with one or several Na + counterions bridging two or three phosphate groups, which we named n P-collab s (for n phosphate-collaborations, with n being an integer).…”

nP-collabs: Investigating counterion mediated bridges in the multiply phosphorylated tau-R2 repeat

“…We used the structure of the tau-R2 repeat (a 27 residues fragment ranging from Lys274 to Val300) extracted from the tau-tubulin assembly modeled in our previous work 37 as a starting point. Phosphorylations were added using the CHARMM-GUI 39 (https://www.charmmgui.org/) input generator.…”

“…[24][25][26][27][28][29] These approaches are also well complemented by atomistic simulations, which bring further insight on the conformational space covered by the protein, and the last decade has seen the development of numerous force-fields that were specifically parametrized for the modeling of disordered proteins. [30][31][32][33][34][35] Following an earlier study using molecular dynamics simulation to investigate the interaction pattern in the fuzzy complex 36 formed by the tau-R2 fragment (which comprises a strong interacting region centered around Ser289 37 ) and the tubulin surface, 38 we phosphorylated the Ser285, Ser289 and Ser293 residues in the isolated tau-R2 fragment, which have been identified as phosphorylation sites in tauopathies. 11,[14][15][16] Ser289, in particular, is one the 40 phosphorylations sites found in AD brains, but not in healthy ones.…”