The large conformational changes of Hsp90 are only weakly coupled to ATP hydrolysis.
The molecular chaperone heat-shock protein 90 (Hsp90) is one of the most abundant proteins in unstressed eukaryotic cells. Its function is dependent on an exceptionally slow ATPase reaction that involves large conformational changes. To observe these conformational changes and to understand their interplay with the ATPase function, we developed a single-molecule assay that allows examination of yeast Hsp90 dimers in real time under various nucleotide conditions. We detected conformational fluctuations between open and closed states on timescales much faster than the rate of ATP hydrolysis. The compiled distributions of dwell times allow us to assign all rate constants to a minimal kinetic model for the conformational changes of Hsp90 and to delineate the influence of ATP hydrolysis. Unexpectedly, in this model ATP lowers two energy barriers almost symmetrically, such that little directionality is introduced. Instead, stochastic, thermal fluctuations of Hsp90 are the dominating processes.
Mickler
Moritz
M
Physik-Department, IMETUM, CeNS, James-Franck-Strasse 1, 85748 Garching, Germany.
Hessling
Martin
M
Ratzke
Christoph
C
Buchner
Johannes
J
Hugel
Thorsten
T
D000255:Adenosine Triphosphate / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods; D018841:HSP90 Heat-Shock Proteins / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D020836:Protein Structure, Quaternary; D012441:Saccharomyces cerevisiae / Q000737:chemistry*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism*
C074510:HSP82 protein, S cerevisiae; D018841:HSP90 Heat-Shock Proteins; D029701:Saccharomyces cerevisiae Proteins; D000255:Adenosine Triphosphate