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ACS Chem Biol. 2016 Jun 17;11(6):1552-1560. doi: 10.1021/acschembio.6b00083. Epub 2016 Mar 30.

Highly Dynamic Interactions Maintain Kinetic Stability of the ClpXP Protease During the ATP-Fueled Mechanical Cycle.

Author information

1
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139.
2
Department of Chemistry, Brown University, Providence, RI 02912.
3
Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139.
#
Contributed equally

Abstract

The ClpXP protease assembles in a reaction in which an ATP-bound ring hexamer of ClpX binds to one or both heptameric rings of the ClpP peptidase. Contacts between ClpX IGF-loops and clefts on a ClpP ring stabilize the complex. How ClpXP stability is maintained during the ATP-hydrolysis cycle that powers mechanical unfolding and translocation of protein substrates is poorly understood. Here, we use a real-time kinetic assay to monitor the effects of nucleotides on the assembly and disassembly of ClpXP. When ATP is present, complexes containing single-chain ClpX assemble via an intermediate and remain intact until transferred into buffers containing ADP or no nucleotides. ATP binding to high-affinity subunits of the ClpX hexamer prevents rapid dissociation, but additional subunits must be occupied to promote assembly. Small-molecule acyldepsipeptides, which compete with the IGF loops of ClpX for ClpP-cleft binding, cause exceptionally rapid dissociation of otherwise stable ClpXP complexes, suggesting that the IGF-loop interactions with ClpP must be highly dynamic. Our results indicate that the ClpX hexamer spends almost no time in an ATP-free state during the ATPase cycle, allowing highly processive degradation of protein substrates.

PMID:
27003103
PMCID:
PMC5087277
DOI:
10.1021/acschembio.6b00083
[Indexed for MEDLINE]
Free PMC Article

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