title: Coordinated gripping of substrate by subunits of a AAA+ proteolytic machine.
abstract: Hexameric ATP-dependent proteases and protein remodeling machines use conserved loops that line the axial pore to apply force to substrates during the mechanical processes of protein unfolding and translocation. Whether loops from multiple subunits act independently or coordinately in these processes is a critical aspect of the mechanism but is currently unknown for any AAA+ machine. By studying covalently linked hexamers of the Escherichia coli ClpX unfoldase bearing different numbers and configurations of wild-type and mutant pore loops, we show that loops function synergistically, and the number of wild-type loops required for efficient degradation is dependent on the stability of the protein substrate. Our results support a mechanism in which a power stroke initiated in one subunit of the ClpX hexamer results in the concurrent movement of all six pore loops, which coordinately grip and apply force to the substrate.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Ohad
authors.initials: O
authors.lastname: Iosefson
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Nager
authors.affiliation: 1] Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA. [2] Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Tania A
authors.initials: TA
authors.lastname: Baker
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Sauer
mesh_terms: D049069:ATP-Dependent Proteases / Q000737:chemistry*; D000074183:ATPases Associated with Diverse Cellular Activities; D000251:Adenosine Triphosphatases / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000378:metabolism; D049071:Endopeptidase Clp / Q000737:chemistry; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry; D018832:Molecular Chaperones / Q000737:chemistry; D009154:Mutation; D010447:Peptide Hydrolases / Q000737:chemistry*; D058767:Protein Unfolding; D013379:Substrate Specificity; D014178:Translocation, Genetic
chemical_list: D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; D000255:Adenosine Triphosphate; D010447:Peptide Hydrolases; D049069:ATP-Dependent Proteases; D049071:Endopeptidase Clp; D000251:Adenosine Triphosphatases; C088072:ClpX protein, E coli; D000074183:ATPases Associated with Diverse Cellular Activities