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摘要
ClpB is a hexameric molecular chaperone that, together with the DnaK system, has the ability to disaggregate stress-denatured proteins. The hexamer is a highly dynamic complex, able to reshuffle subunits. To further characterize the biological implications of the ClpB oligomerization state, the association equilibrium of the wildtype (wt) protein and of two deletion mutants, which lack part or the whole M domain, was quantitatively analyzed under different experimental conditions, using several biophysical [analytical ultracentrifugation, composition-gradient (CG) static light scattering, and circular dichroism] and biochemical (ATPase and chaperone activity) methods. We have found that (i) ClpB self-associates from monomers to form hexamers and higher-order oligomers that have been tentatively assigned to dodecamers, (ii) oligomer dissociation is not accompanied by modifications of the protein secondary structure, (iii) the M domain is engaged in intersubunit interactions that stabilize the protein hexamer, and (iv) the nucleotide-induced rearrangement of ClpB affects the protein oligomeric core, in addition to the proposed radial extension of the M domain. The difference in the stability of the ATP- and ADP-bound states [Delta Delta G((ATP-ADP)) = -10 kJ/mol] might explain how nucleotide exchange promotes the conformational change of the protein particle that drives its functional cycle.
- 出版日期2011-3-29
