MAPT and Classical progressive supranuclear palsy: In this work, using a combination of Cryo-EM, in-cell experiments and biophysical analysis, the authors decoded the aggregation propensity of tau, revealing 5 central hot spots in its primary sequence and identify PAM4 as short segment that determines both the structure, as well as the cellular propagation of tau aggregates extracted from Alzheimer’s disease, corticobasal degeneration, and progressive supranuclear palsy patients.