title: Structures of asymmetric ClpX hexamers reveal nucleotide-dependent motions in a AAA+ protein-unfolding machine.
abstract: ClpX is a AAA+ machine that uses the energy of ATP binding and hydrolysis to unfold native proteins and translocate unfolded polypeptides into the ClpP peptidase. The crystal structures presented here reveal striking asymmetry in ring hexamers of nucleotide-free and nucleotide-bound ClpX. Asymmetry arises from large changes in rotation between the large and small AAA+ domains of individual subunits. These differences prevent nucleotide binding to two subunits, generate a staggered arrangement of ClpX subunits and pore loops around the hexameric ring, and provide a mechanism for coupling conformational changes caused by ATP binding or hydrolysis in one subunit to flexing motions of the entire ring. Our structures explain numerous solution studies of ClpX function, predict mechanisms for pore elasticity during translocation of irregular polypeptides, and suggest how repetitive conformational changes might be coupled to mechanical work during the ATPase cycle of ClpX and related molecular machines.
authors.affiliation: Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Steven E
authors.initials: SE
authors.lastname: Glynn
authors.forename: Andreas
authors.initials: A
authors.lastname: Martin
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Nager
authors.forename: Tania A
authors.initials: TA
authors.lastname: Baker
authors.forename: Robert T
authors.initials: RT
authors.lastname: Sauer
mesh_terms: D000074183:ATPases Associated with Diverse Cellular Activities; D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D049071:Endopeptidase Clp / Q000737:chemistry* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism*; D009711:Nucleotides / Q000378:metabolism; D011487:Protein Conformation; D017510:Protein Folding
chemical_list: D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; D009711:Nucleotides; D049071:Endopeptidase Clp; D000251:Adenosine Triphosphatases; C088072:ClpX protein, E coli; D000074183:ATPases Associated with Diverse Cellular Activities