Tau stabilizes microtubules by binding at the interface between tubulin heterodimers

Significance Tau is an important microtubule-associated protein. Although the structure–function relationship of Tau has been intensively studied for many years primarily by molecular biology and biochemical approaches, little is still known about the molecular mechanisms by which Tau interacts with microtubules and promotes microtubule assembly. Here, we provide detailed insight into the Tau–microtubule association by using NMR spectroscopy and mass spectrometry. We show that Tau binds to microtubules by using small groups of residues, which are important for pathological aggregation of Tau. We further show that Tau stabilizes a straight protofilament conformation by binding to a hydrophobic pocket in between tubulin heterodimers. Our work is thus relevant to normal Tau action development and in Tau-related neurodegenerative diseases. The structure, dynamic behavior, and spatial organization of microtubules are regulated by microtubule-associated proteins. An important microtubule-associated protein is the protein Tau, because its microtubule interaction is impaired in the course of Alzheimer’s disease and several other neurodegenerative diseases. Here, we show that Tau binds to microtubules by using small groups of evolutionary conserved residues. The binding sites are formed by residues that are essential for the pathological aggregation of Tau, suggesting competition between physiological interaction and pathogenic misfolding. Tau residues in between the microtubule-binding sites remain flexible when Tau is bound to microtubules in agreement with a highly dynamic nature of the Tau–microtubule interaction. By binding at the interface between tubulin heterodimers, Tau uses a conserved mechanism of microtubule polymerization and, thus, regulation of axonal stability and cell morphology.