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Nat Struct Mol Biol. 2015 May;22(5):411-6. doi: 10.1038/nsmb.3012. Epub 2015 Apr 13.

Subunit asymmetry and roles of conformational switching in the hexameric AAA+ ring of ClpX.

Author information

1
Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
2
1] Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA. [2] Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.

Abstract

The hexameric AAA+ ring of Escherichia coli ClpX, an ATP-dependent machine for protein unfolding and translocation, functions with the ClpP peptidase to degrade target substrates. For efficient function, ClpX subunits must switch between nucleotide-loadable (L) and nucleotide-unloadable (U) conformations, but the roles of switching are uncertain. Moreover, it is controversial whether working AAA+-ring enzymes assume symmetric or asymmetric conformations. Here, we show that a covalent ClpX ring with one subunit locked in the U conformation catalyzes robust ATP hydrolysis, with each unlocked subunit able to bind and hydrolyze ATP, albeit with highly asymmetric position-specific affinities. Preventing U↔L interconversion in one subunit alters the cooperativity of ATP hydrolysis and reduces the efficiency of substrate binding, unfolding and degradation, showing that conformational switching enhances multiple aspects of wild-type ClpX function. These results support an asymmetric and probabilistic model of AAA+-ring activity.

PMID:
25866879
PMCID:
PMC4424054
DOI:
10.1038/nsmb.3012
[Indexed for MEDLINE]
Free PMC Article

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