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Protein Science (2004), 13:567-574. Published by Cold Spring Harbor Laboratory Press. Copyright © 2004 The Protein Society
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Nucleotide-induced switch in oligomerization of the AAA+ ATPase ClpB

Vladimir Akoev1, Edward P. Gogol2, Micheal E. Barnett1 and Michal Zolkiewski1

1 Department of Biochemistry, Kansas State University, Manhattan, Kansas 66506, USA
2 School of Biological Sciences, University of Missouri-Kansas City, Kansas City, Missouri 64110, USA

(RECEIVED September 5, 2003; FINAL REVISION November 19, 2003; ACCEPTED November 23, 2003)



Abstract

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, ATP{gamma}S, 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 ATP{gamma}S. 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.

Keywords: ClpB; AAA ATPase; molecular chaperone; protein association; nucleotide binding; analytical ultracentrifugation

Abbreviations: ATP{gamma}S • adenosine 5'-O-thiotriphosphate

Reprint requests to: Michal Zolkiewski, Department of Biochemistry, 104 Willard Hall, Kansas State University, Manhattan, KS 66506, USA; e-mail: michalz{at}ksu.edu; fax: (785) 532-7278.

Article and publication are at http://www.proteinscience.org/cgi/doi/10.1110/ps.03422604.


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