Asymmetric activation of the hsp90 dimer by its cochaperone aha1.
The chaperone Hsp90 is an ATP-dependent, dimeric molecular machine regulated by several cochaperones, including inhibitors and the unique ATPase activator Aha1. Here, we analyzed the mechanism of the Aha1-mediated acceleration of Hsp90 ATPase activity and identified the interaction surfaces of both proteins using multidimensional NMR techniques. For maximum activation of Hsp90, the two domains of Aha1 bind to sites in the middle and N-terminal domains of Hsp90 in a sequential manner. This binding induces the kinetically unfavored N terminally dimerized state of Hsp90, which primes for the hydrolysis-competent conformation. Surprisingly, this activation mechanism is asymmetric. The presence of one Aha1 molecule per Hsp90 dimer is sufficient to bridge the two subunits and to fully stimulate Hsp90 ATPase activity. This seems to functionalize the two subunits of the Hsp90 dimer in different ways, in that one subunit can be used for conformational ATPase regulation and the other for substrate protein processing.
Center for Integrated Protein Science Munich at the Department Chemie, Technische Universität München, D-85747 Garching, Germany.
Marco
M
Retzlaff
Franz
F
Hagn
Lars
L
Mitschke
Martin
M
Hessling
Frederik
F
Gugel
Horst
H
Kessler
Klaus
K
Richter
Johannes
J
Buchner
D018833:Chaperonins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D031541:Fluorescence Resonance Energy Transfer; D018841:HSP90 Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism; D007700:Kinetics; D018832:Molecular Chaperones / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
C475092:AHA1 protein, S cerevisiae; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; C113025:SBA1 protein, S cerevisiae; C542289:STI1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D018833:Chaperonins