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 mg/mL), 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 mM ADP 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.