Nucleotide-dependent oligomerization of ClpB from Escherichia coli

Self-association of ClpB (a mixture of 95- and 80-kDa subunits) has been st udied with gel filtration chromatography, analytical ultracentrifugation, a nd electron microscopy. Monomeric ClpB predominates at low protein concentr ation (0.07 mg/mL), while an oligomeric form is highly populated at >4 mg/m L. The oligomer formation is enhanced in the presence of 2 mM ATP or adenos ine 5'-O-thiotriphosphate (ATP gamma S). In contrast, 2 mM ADP inhibits ful l oligomerization of ClpB. The apparent size of the ATP- or ATP gamma S-ind uced oligomer, as determined by gel filtration, sedimentation velocity and electron microscopy image averaging, and the molecular weight, as determine d by sedimentation equilibrium, are consistent with those of a ClpB hexamer . These results indicate that the oligomerization reactions of ClpB are sim ilar to those of other Hsp100 proteins.