Nucleotide‐induced switch in oligomerization of the AAA+ ATPase ClpB

• Published in: Protein science Vol. 13; no. 3; pp. 567 - 574
• Main Authors: Akoev, Vladimir, Gogol, Edward P., Barnett, Micheal E., Zolkiewski, Michal
• Format: Journal Article
• Language: English
• Published: Bristol Cold Spring Harbor Laboratory Press 01-03-2004
• Subjects: AAA ATPase; adenosine 5′‐O‐thiotriphosphate; Adenosine Diphosphate - chemistry; Adenosine Triphosphate - analogs & derivatives; Adenosine Triphosphate - chemistry; analytical ultracentrifugation; ATPγS; Chromatography, Agarose; ClpB; Endopeptidase Clp; Escherichia coli Proteins - chemistry; Heat-Shock Proteins - chemistry; Microscopy, Electron; molecular chaperone; Molecular Chaperones - chemistry; nucleotide binding; Nucleotides - chemistry; Osmolar Concentration; protein association; Protein Binding; Protein Structure, Quaternary; Recombinant Proteins - chemistry; Ultracentrifugation
• ISSN: 0961-8368; 1469-896X
• DOI: 10.1110/ps.03422604

ClpB is a member of the bacterial protein‐disaggregating chaperone machinery and belongs to the AAA+ superfamily of ATPases associated with various cellular activities. The mechanism of ClpB‐assisted reactivation of strongly aggregated proteins is unknown and the oligomeric state of ClpB has been under discussion. Sedimentation equilibrium and sedimentation velocity show that, under physiological ionic strength in the absence of nucleotides, ClpB from Escherichia coli undergoes reversible self‐association that involves protein concentration‐dependent populations of monomers, heptamers, and intermediate‐size oligomers. Under low ionic strength conditions, a heptamer becomes the predominant form of ClpB. In contrast, ATPγS, a nonhydrolyzable ATP analog, as well as ADP stabilize hexameric ClpB. Consistently, electron microscopy reveals that ring‐type oligomers of ClpB in the absence of nucleotides are larger than those in the presence of ATPγS. Thus, the binding of nucleotides without hydrolysis of ATP produces a significant change in the self‐association equilibria of ClpB: from reactions supporting formation of a heptamer to those supporting a hexamer. Our results show how ClpB and possibly other related AAA+ proteins can translate nucleotide binding into a major structural transformation and help explain why previously published electron micrographs of some AAA+ ATPases detected both six‐ and sevenfold particle symmetry.