The Mechanism of Hsp90 ATPase Stimulation by Aha1.
Hsp90 is a dimeric molecular chaperone responsible for the folding, maturation, and activation of hundreds of substrate proteins called 'clients'. Numerous co-chaperone proteins regulate progression through the ATP-dependent client activation cycle. The most potent stimulator of the Hsp90 ATPase activity is the co-chaperone Aha1p. Only one molecule of Aha1p is required to fully stimulate the Hsp90 dimer despite the existence of two, presumably identical, binding sites for this regulator. Using ATPase assays with Hsp90 heterodimers, we find that Aha1p stimulates ATPase activity by a three-step mechanism via the catalytic loop in the middle domain of Hsp90. Binding of the Aha1p N domain to the Hsp90 middle domain exerts a small stimulatory effect but also drives a separate conformational rearrangement in the Hsp90 N domains. This second event drives a rearrangement in the N domain of the opposite subunit and is required for the stimulatory action of the Aha1p C domain. Furthermore, the second event can be blocked by a mutation in one subunit of the Hsp90 dimer but not the other. This work provides a foundation for understanding how post-translational modifications regulate co-chaperone engagement with the Hsp90 dimer.
Department of Cell Biology, 514 Medical Sciences Building, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada.
Annemarie
A
Wolmarans
Department of Biochemistry, 416 Medical Sciences Building, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada.
Brian
B
Lee
Department of Biochemistry, 416 Medical Sciences Building, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada.
Leo
L
Spyracopoulos
Department of Cell Biology, 514 Medical Sciences Building, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada.
Paul
P
LaPointe
D000251:Adenosine Triphosphatases / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D020816:Amino Acid Motifs; D020134:Catalytic Domain; D018833:Chaperonins / Q000737:chemistry*; D004789:Enzyme Activation; D004926:Escherichia coli; D018841:HSP90 Heat-Shock Proteins / Q000737:chemistry*; D007700:Kinetics; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry*
C475092:AHA1 protein, S cerevisiae; C074510:HSP82 protein, S cerevisiae; D018841:HSP90 Heat-Shock Proteins; D029701:Saccharomyces cerevisiae Proteins; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D018833:Chaperonins