Nucleotide‐dependent oligomerization of C1pB from Escherichia coli

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Abstract
Self‐association of ClpB (a mixture of 95‐ and 80‐kDa subunits) has been studied with gel filtration chromatography, analytical ultracentrifugation, and electron microscopy. Monomeric ClpB predominates at low protein concentration (0.07 mg0mL), while an oligomeric form is highly populated at >4 mg/mL. The oligomer formation is enhanced in the presence of 2 mM ATP or adenosine 5′‐O‐thiotriphosphate (ATPγS). In contrast, 2 mMADP inhibits full oligomerization of ClpB. The apparent size of the ATP‐ or ATPγS‐induced oligomer, as determined by gel filtration, sedimentation velocity and electron microscopy image averaging, and the molecular weight, as determined by sedimentation equilibrium, are consistent with those of a ClpB hexamer. These results indicate that the oligomerization reactions of ClpB are similar to those of other Hsp100 proteins.