Tau is a developmentally regulated axonal protein that stabilizes and bundles microtubules (MTs). Its hyperphosphorylation is thought to cause detachment from MTs and subsequent aggregation into fibrils implicated in Alzheimer’s disease. It is unclear which tau residues are crucial for tau-MT interactions, where tau binds on MTs, and how it stabilizes them. We used cryo–electron microscopy to visualize different tau constructs on MTs, and computational approaches to generate atomic models of tau-tubulin interactions. The conserved tubulin-binding repeats within tau adopt similar extended structures along the crest of the protofilament, stabilizing the interface between tubulin dimers. Our structures explain the effect of phosphorylation on MT affinity and lead to a model of tau repeats binding in tandem along protofilaments, tethering together tubulin dimers and stabilizing polymerization interfaces.

A number of microtubule-stabilizing agents have demonstrated or predicted potential as anticancer agents, but a detailed structural basis for their mechanism of action is still lacking. We have obtained high-resolution (3.9 – 4.2 Å) cryo-EM reconstructions of microtubules stabilized by the taxane-site binders Taxol and zampanolide, and by peloruside, which targets a distinct, non-taxoid pocket on β-tubulin. We find that each molecule has unique distinct structural effects on the microtubule lattice structure. Peloruside acts primarily at lateral contacts and has an effect on the “seam” of heterologous interactions, enforcing a conformation more similar to that of homologous (i.e. non-seam) contacts by which it regularizes the microtubule lattice. In contrast, binding of either Taxol or zampanolide induces microtubule heterogeneity. In doubly-bound microtubules, peloruside overrides the heterogeneity induced by Taxol-binding. Our structural analysis illustrates distinct mechanisms of these drugs for stabilizing the microtubule lattice, and is of relevance to the possible use of combinations of microtubule-stabilizing agents to regulate microtubules activity and improve therapeutic potential.

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