Atomic model of microtubule-bound tau
Tau is a developmentally regulated protein found in axons, whose physiological role is to stabilize and bundle microtubules (MTs). Hyper-phosphorylation of tau is thought to cause its detachment from MTs and subsequent aggregation into pathological fibrils that have been implicated in Alzheimers disease pathogenesis. Despite its known MT binding role, there is no consensus regarding which tau residues are crucial for tau-MT interactions, where on the MT tau binds, and how binding results in MT stabilization. We have used cryo-EM to visualize the interaction of different tau constructs with MTs at high resolution (3.2-4.8 [A]) and used computational approaches to generate atomic models of tau-tubulin interactions. Our work shows that the highly conserved tubulin-binding repeats within tau adopt very similar structures in their interactions with the MT. Each tau repeat binds the MT exterior and adopts an extended structure along the crest of the protofilament (PF), interacting with both - and {beta}-tubulin, thus stabilizing the interface between tubulin dimers. Our structures agree with and explain previous biochemical data concerning the effect of phosphorylation on MT affinity and lead to a model in which tau repeats bind in tandem along a PF, tethering together tubulin dimers and stabilizing longitudinal polymerization interfaces. These structural findings could establish a basis of future treatments aiming at the selective stabilization of tau-MT interactions.