Fig. 4.

ATPase ring gymnastics. (A) Structural motifs of the proteasome ATPase ring. Left: A top view of the EM density for the Rpt1-Rpt6 hexamer in the s4 state (EMDB: 9045), with the central channel of ATPase ring labeled. Middle: ATPase ring displayed as a ribbon diagram (PDB: 6EF3) rotated 90° relative to the view on the left and highlighting the N-terminal coiled coils, N-ring, ATPase motor ring, and HbYX motifs. Right: ribbon diagram structure of Rpt5 and Rpt6 (PDB: 6EF3) to illustrate the OB fold, Pore-1 loop (red), and nucleotide (oxygen, red; nitrogen, blue; phosphorus, orange). (B) Cutaway representations of the 26S proteasome in s1 (apo, EMDB: 3534) and s4 (engaged, EMDB: 3537) conformations, showing the different position of Rpn11 and change in alignment of the N-ring, ATPase motor ring, and CP. The central channel through the N-ring and ATPase motor ring is indicated by a dashed orange line. (C) Conformational switching of the human 26S proteasome between a ground state (S_A, PDB: 5VFS) and substrate processing state (S_D, PDB: 5VFP), with the CP aligned. During the transition from S_A to S_D, hRpn10’s VWA domain rotates by ~30° towards the hRpt4/hRpt5 coiled coil. The color scheme in panels (B) and (C) follows that in Fig. 1B and Fig. 3D. This figure was generated by using UCSF Chimera [182], UCSF ChimeraX [183], Adobe Illustrator (Adobe), and Adobe Photoshop (Adobe).