Background: Hsp100 chaperones cooperate with Hsp70 chaperones to disaggregate and reactivate heat-denatured proteins. Results: Mutations in the interface region between NBD1 and M domains of Hsp100 result in a hyperactive protein toxic to the cell. Conclusion:The interaction between M and NBD1 domains is crucial for regulation of Hsp100 activity. Significance: A novel important aspect of the Hsp100 mechanism of action is described.

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Besides its beneficial role in thermotolerance, the chaperone protein Hsp104 is involved in the inheritance of yeast Saccharomyces cerevisiae prions. Guanidine hydrochloride was previously shown to interfere with Hsp104 chaperone activity in vivo, thus impairing thermotolerance and resulting in prion curing. It was also reported that guanidine inhibits Hsp104 ATPase and disaggregation activity. We show that in vitro guanidine significantly inhibits the disaggregation activity of ClpB, the bacterial orthologue of Hsp104. However, guanidine exerts opposite effects on the ATPase activities of Hsp104 and ClpB. While the ATPase activity of Hsp104 is inhibited, the analogous ClpB activity is stimulated several-fold. Mutation of the universally conserved aspartic acid residue in position 184 to serine (D184S) in HSP104 and the analogous mutation in clpB (D178S) resulted in chaperones with lower disaggregating and ATPase activities. The activities of such changed chaperones are not influenced by guanidine, which suggests the role of this residue in the interaction with guanidine.Electronic supplementary materialThe online version of this article (doi:10.1007/s12192-011-0312-4) contains supplementary material, which is available to authorized users.