ClpXP is an ATP-dependent protease in which the ClpX AAA+ motor binds, unfolds, and translocates specific protein substrates into the degradation chamber of ClpP. We present cryo-EM studies of the E. coli enzyme that show how asymmetric hexameric rings of ClpX bind symmetric heptameric rings of ClpP and interact with protein substrates. Subunits in the ClpX hexamer assume a spiral conformation and interact with two-residue segments of substrate in the axial channel, as observed for other AAA+ proteases and protein-remodeling machines. Strictly sequential models of ATP hydrolysis and a power stroke that moves two residues of the substrate per translocation step have been inferred from these structural features for other AAA+ unfoldases, but biochemical and single-molecule biophysical studies indicate that ClpXP operates by a probabilistic mechanism in which five to eight residues are translocated for each ATP hydrolyzed. We propose structure-based models that could account for the functional results.
PDB files for the structures determined here have been deposited in the PDB under accession codes 6PPE, 6PP8, 6PP7, 6PP6, 6PP5, 6POS, 6POD, 6PO3, and 6PO1.
6PPERCSB Protein Data Bank, 6PPE.
6PP8RCSB Protein Data Bank, 6PP8.
6PP7RCSB Protein Data Bank, 6PP7.
6PP6RCSB Protein Data Bank, 6PP6.
6PP5RCSB Protein Data Bank, 6PP5.
6POSRCSB Protein Data Bank, 6POS.
6PODRCSB Protein Data Bank, 6POD.
6PO3RCSB Protein Data Bank, 6PO3.
6PO1RCSB Protein Data Bank, 6PO1.
- Robert T Sauer
- Tania A Baker
- Stephen C Harrison
- Tristan A Bell
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- James M Berger, Johns Hopkins University School of Medicine, United States
© 2020, Fei et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.