Figure 9. Structure of Hsp90–Rar1–Sgt1 and Hsp90–Rar1–Sba1 co-chaperone complexes.

(A) Structure of the N-terminal domains of Hsp90 (green) in complex with the CS domain of Sgt1 (magenta) and the CHORD II domain of Rar1 (cyan). Recruitment of Rar1 into the Hsp90 complex stimulates ATP hydrolysis producing a stable ADP-bound Hsp90 complex. The lid segment is shown in red and bound ADP in blue stick representation. Broken blue lines represent hydrogen bonds. (B) Structure of the closed conformation of Hsp90 in complex with Sba1 (cyan). Hsp90 is represented by the lid (red), the N-terminal segment of the N-terminus (yellow) and a segment of the middle domain (green). The bound ATP is shown as a yellow stick representation. Arg³⁸⁰ is seen to interact with the γ-phosphate of ATP in the catalytically active state of Hsp90. Broken blue lines represent hydrogen bonds.