Cryo-EM structures of the CLPB double-heptamer in the apo-state and the CLPB^E425Q double-hexamer in the substrate-bound state.

(A) Domain organization of H. sapiens CLPB. CLPB is composed of an MTS, a short hydrophobic stretch (S), an LH, 4 ankyrin-repeat (ANK) motifs, an NBD, and a CTD. (B) Representative 2D classification averages of CLPB and CLPBE425Q datasets. (C, D) The density maps of the double-heptamer (C) and double-hexamer (D), superimposed with the models of CLPB. The density maps are shown in the side and top (ATPase ring) views. The higher-order oligomer is mediated by ANK domains. The substrate was labeled as yellow. LH, linker helix; NBD, nucleotide-binding domain.