Fig. 4. Interactions of conserved residues that stabilize the open proteasome conformation. The clusters of Tyr8, Asp9, Pro17 and Tyr26 side chains that stabilize the open pore structure are shown explicitly with yellow carbon atoms. (A) Top view of the yeast proteasome α-subunits as seen in the complex with PA26. (B) Enlarged view of the central region of (A). (C) Close up view of the cluster outlined in (B). Hydrogen bonding interactions are shown by dotted lines.