Hsp90 middle domain phosphorylation initiates a complex conformational program to recruit the ATPase-stimulating cochaperone Aha1

Phosphorylation of Tyr313 in Hsp90 enhances the binding to its activator Aha1, but the underlying mechanism is unknown. Here, the authors study the structural consequences of Tyr313 phosphorylation, showing that it serves as a conformational switch in Hsp90 that enables Aha1 recruitment.