(A) The left panel shows a cutaway view of the ssrA tag in the recognition complex (pdb code 6WRF), emphasizing the blocked axial channel. The right panel shows the ssrA tag in this complex in stick representation with semi-transparent density, and emphasizes key contacts with specific pore-1, pore-2, or RKH loops of ClpX. (B) The left panel shows a cutaway view of the ssrA tag in the intermediate complex (pdb code 6WSG), highlighting the open ClpX channel and movement of the degron deeper into the axial channel. The right panel shows that five pore-1 loops of ClpX interact with the tag with a two-residue periodicity. (C) The pore loops of ClpX can adopt multiple conformations, facilitating flexible interactions with substrate peptides.