At sixes and sevens: Characterization of the symmetry mismatch of the ClpAP chaperone-assisted protease

Fabienne Beuron, Michael R. Maurizi, David M. Belnap, Eva Kocsis, Frank P. Booy, Martin Kessel, Alasdair C. Steven*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

122 Scopus citations

Abstract

ClpAP, a typical energy-dependent protease, consists of a proteolytic component (ClpP) and a chaperone-like ATPase (ClpA). ClpP is composed of two apposed heptameric rings, whereas in the presence of ATP or ATPγS, ClpA is a single hexameric ring. Formation of ClpAP complexes involves a symmetry mismatch as sixfold ClpA stacks axially on one or both faces of sevenfold ClpP. We have analyzed these structures by cryo-electron microscopy. Our three-dimensional reconstruction of ClpA at 29-Å resolution shows the monomer to be composed of two domains of similar size that, in the hexamer, form two tiers enclosing a large cavity. Cylindrical reconstruction of ClpAP reveals three compartments: the digestion chamber inside ClpP; a compartment between ClpP and ClpA; and the cavity inside ClpA. They are connected axially via narrow apertures, implying that substrate proteins should be unfolded to allow translocation into the digestion chamber. The cavity inside ClpA is structurally comparable to the 'Anfinsen cage' of other chaperones and may play a role in the unfolding of substrates. A geometrical description of the symmetry mismatch was obtained by using our model of ClpA and the crystal structure of ClpP (Wang et al., 1997, Cell 91, 447-456) to identify the particular side views presented by both molecules in individual complexes. The interaction is characterized by a key pair of subunits, one of each protein. A small turn (8.6°= 2π/42; equivalent to a 4-Å shift) would transfer the key interaction to another pair of subunits. We propose that nucleotide hydrolysis results in rotation, facilitating the processive digestion of substrate proteins.

Original languageEnglish
Pages (from-to)248-259
Number of pages12
JournalJournal of Structural Biology
Volume123
Issue number3
DOIs
StatePublished - Nov 1998
Externally publishedYes

Keywords

  • Clp protease
  • Electron microscopy
  • Energy-dependent proteolysis
  • Symmetry
  • Three-dimensional image reconstruction.

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