Fig. 6: ClpP-ClpC contacts and AAA-2 ATPase activity states.

a Nucleotide-binding state of the ClpC subunits. The subunits are shown as ribbon liquorice. The nucleotides are shown as sticks colored by element; the Mg atom is in lime green, the R-fingers and the WalkerB residues are shown as sticks in magenta and yellow, respectively. The modeled nucleotide is ATPγS, but indicated as ATP for simplicity. Cryo-EM density is shown. b Schematic of the ATPase active (green) and inactive (light blue) subunits around the AAA-1 and AAA-2 rings. c Superimposition of subunits b (ADP-bound, dark blue) and c (ATP-bound orange) on the AAA-2 ATP pocket showing the position of Walker B residues D617 and E618, as well as the position of allo-W residue E620 and conserved N659. N659 reorients itself from the ADP to the ATP-bound state. N659 is positioned at intermediate positions in subunits d, e, and it is not fully visible for subunit a–f. d Interface between the inactive subunit b and active subunit c in the AAA-2 ATP pocket. Topological scheme in the top left corner is shown to facilitate the localization of the various regions. The Pc β-hairpin contacts of allo-W of subunit b and the distal part of the allo-R helix subunit b that is also contacted by the Pd β-hairpin, which in turn also contacts the P-loop of subunit c. This forms a β-hairpin network, which could define two allosteric paths toward the ATP pocket of subunit c and the P-loop/H-site region of ClpC to ClpP anchoring.