The article presents the crystal structure of the full-length yeast Hsp90 chaperone complexed with an ATP analogue and the co-chaperone p23/Sba1. This structure reveals the 'closed' state of the Hsp90 chaperone, characterized by extensive inter-domain and inter-strand interactions, and detailed conformational changes in the N-terminal domain upon ATP binding. The structure also elucidates how p23/Sba1 stabilizes the closed state by binding to specific regions of the Hsp90 dimer. Contrary to previous expectations, the closed Hsp90 does not enclose its client proteins but provides a bipartite binding surface whose formation and disruption are coupled to the chaperone's ATPase cycle. The study confirms the ATPase-coupled molecular clamp mechanism and provides insights into the ATP-dependent activation of client proteins by Hsp90.The article presents the crystal structure of the full-length yeast Hsp90 chaperone complexed with an ATP analogue and the co-chaperone p23/Sba1. This structure reveals the 'closed' state of the Hsp90 chaperone, characterized by extensive inter-domain and inter-strand interactions, and detailed conformational changes in the N-terminal domain upon ATP binding. The structure also elucidates how p23/Sba1 stabilizes the closed state by binding to specific regions of the Hsp90 dimer. Contrary to previous expectations, the closed Hsp90 does not enclose its client proteins but provides a bipartite binding surface whose formation and disruption are coupled to the chaperone's ATPase cycle. The study confirms the ATPase-coupled molecular clamp mechanism and provides insights into the ATP-dependent activation of client proteins by Hsp90.