Supplementary Figure 5: Cryo-EM density maps of select subcomplexes in the human proteasome.

(a) Cryo-EM density maps of the overall organization in the proteasome. Three perpendicular views are shown. The 18 subunits in the RP are color-coded. (b) Cryo-EM density maps of the lid. The atomic models are shown on the right. In each case, two perpendicular views are shown. The solenoid folds of six Rpn subunits (Rpn3, Rpn5, Rpn6, Rpn7, Rpn9, and Rpn12) radiate from the center. (c) Cryo-EM density maps of the hexameric Rpt ring. The atomic models are shown on the right. In each case, two perpendicular views are shown. The coiled-coil of Rpt6-Rpt3 exhibits excellent density maps, in part because it is stabilized through direct interactions with Rpn3 of the Lid and Rpn2 of the base. In contrast, the other two coiled-coils, formed by Rpt4-5 and Rpt2-1, point into solvent and have discontinuous density maps, likely reflecting their dynamic conformations. (d) Cryo-EM density maps of the heptameric α-ring in two perpendicular views. The atomic model is shown in the right. (e) Cryo-EM density maps of the heptameric β-ring in two perpendicular views. The atomic model is shown in the right.