title: The co-chaperone p23 arrests the Hsp90 ATPase cycle to trap client proteins.
abstract: The action of the molecular chaperone Hsp90 is essential for the activation and assembly of an increasing number of client proteins. This function of Hsp90 has been proposed to be governed by conformational changes driven by ATP binding and hydrolysis. Association of co-chaperones and client proteins regulate the ATPase activity of Hsp90. Here, we have examined the inhibition of the ATPase activity of human Hsp90beta by one such co-chaperone, human p23. We demonstrate that human p23 interacts with Hsp90 in both the absence and presence of nucleotide with a higher affinity in the presence of the ATP analogue AMP-PNP. This is consistent with an analysis of the effect of p23 on the steady-state kinetics that revealed a mixed mechanism of inhibition. Mass spectrometry of the intact Hsp90.p23 complex determined the stoichiometry of binding to be one p23 to each subunit of the Hsp90 dimer. p23 was also shown to interact with a monomeric, truncated fragment of Hsp90, lacking the C-terminal homodimerisation domain, indicating dimerisation of Hsp90 is not a prerequisite for association with p23. Complex formation between Hsp90 and p23 increased the apparent affinity of Hsp90 for AMP-PNP and completely inhibited the ATPase activity. We propose a model where the role of p23 is to lock individual subunits of Hsp90 in an ATP-dependent conformational state that has a high affinity for client proteins.
authors.affiliation: Cambridge University, Chemical Laboratory, Lensfield Road, Cambridge CB2 1EW, UK. smclaugh@ntlworld.com
authors.forename: Stephen H
authors.initials: SH
authors.lastname: McLaughlin
authors.forename: Frank
authors.initials: F
authors.lastname: Sobott
authors.forename: Zhong-ping
authors.initials: ZP
authors.lastname: Yao
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Peter R
authors.initials: PR
authors.lastname: Nielsen
authors.forename: J Günter
authors.initials: JG
authors.lastname: Grossmann
authors.forename: Ernest D
authors.initials: ED
authors.lastname: Laue
authors.forename: Carol V
authors.initials: CV
authors.lastname: Robinson
authors.forename: Sophie E
authors.initials: SE
authors.lastname: Jackson
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors* / Q000737:chemistry; D000266:Adenylyl Imidodiphosphate / Q000737:chemistry / Q000378:metabolism; D002151:Calorimetry; D002850:Chromatography, Gel; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D019281:Dimerization; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D018832:Molecular Chaperones / Q000737:chemistry* / Q000502:physiology; D011485:Protein Binding; D011487:Protein Conformation; D021122:Protein Subunits / Q000037:antagonists & inhibitors / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D004268:DNA-Binding Proteins; D018841:HSP90 Heat-Shock Proteins; C493165:HSP90AB1 protein, human; D018832:Molecular Chaperones; D021122:Protein Subunits; C073446:protein p23; D000266:Adenylyl Imidodiphosphate; D000251:Adenosine Triphosphatases