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. Author manuscript; available in PMC: 2010 Nov 13.
Published in final edited form as: Cell. 2009 Nov 13;139(4):744–756. doi: 10.1016/j.cell.2009.09.034

Figure 1. Asymmetric Structures of ClpX Hexamers.

Figure 1

(A) Model for protein unfolding and degradation by the ClpXP protease. Cutaway view showing how the degradation tag of a protein substrate could initially bind in the pore of ClpX. ATP-dependent translocation could then lead to unfolding and degradation of the polypeptide by ClpP.

(B) Domain structures of wild-type ClpX and the covalently linked ClpX-ΔN trimer.

(C) Portion of the refined 2Fo-Fc electron-density map (contoured at 1σ) for the nucleotide-bound hexamer.

(D) Surface representation of the nucleotide-bound ClpX hexamer, viewed from the top or ClpP-distal face. Each subunit is a different color. The large and small AAA+ domains of two adjacent subunits are labeled.

(E) Side views of the nucleotide-free (top) and nucleotide-bound (bottom) hexamers in mixed surface/cartoon representation. The staggered positions of the small AAA+ domains in chain A (blue), in chain B (green), and in chain C (red) are shown.

(F) The large AAA+ domains of a type-1 subunit (chain A) and type-2 subunit (chain C) from the nucleotide-bound hexamer are shown in the same orientation, revealing a large change in the relative orientation of the attached small AAA+ domains. In the small domains, only the helix formed by residues 333-344 is shown in cartoon representation.