{"gene":"HSP90AA1","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":2021,"finding":"Cryo-EM structure of the GR-loading complex reveals that two Hsp70 molecules (one delivering GR, one scaffolding Hop) together with Hop load the glucocorticoid receptor (GR) onto Hsp90; GR is partially unfolded and recognized through an extended binding pocket composed of Hsp90, Hsp70, and Hop, establishing the molecular mechanism of client loading and inactivation.","method":"Cryo-electron microscopy (cryo-EM) structural determination of the Hsp90-Hsp70-Hop-GR complex","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution cryo-EM structure with functional validation, published in high-impact journal, complemented by companion maturation complex structure","pmids":["34937942"],"is_preprint":false},{"year":2021,"finding":"Cryo-EM structure of the GR-maturation complex (GR-Hsp90-p23) reveals that the GR ligand-binding domain is restored to a folded, ligand-bound conformation while simultaneously threaded through the Hsp90 lumen; co-chaperone p23 directly stabilizes native GR via a C-terminal helix, enhancing ligand binding.","method":"Cryo-electron microscopy (cryo-EM) structural determination of the GR-Hsp90-p23 complex","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution cryo-EM structure with functional validation of p23-GR interaction, complemented by companion loading complex structure","pmids":["34937936"],"is_preprint":false},{"year":2001,"finding":"Hsp90N (HSP90N/HSP90AA1 variant lacking the ansamycin-binding N-terminal domain and instead carrying a myristylation signal) binds Raf-1 with higher affinity than canonical Hsp90 and does not associate with p50(cdc37); membrane-targeted Hsp90N activates Raf and downstream ERK kinases, and its stable expression causes neoplastic transformation in c-Ras-deficient fibroblasts.","method":"Co-immunoprecipitation, kinase activity assays, stable transfection with anchorage-independent growth assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP and functional cellular assays in single lab with multiple readouts","pmids":["11751906"],"is_preprint":false},{"year":2001,"finding":"Hsp90α and Hsp90β physically interact with the proto-oncogene serine/threonine kinase Pim-1; treatment with the Hsp90-specific inhibitor geldanamycin induces rapid degradation of Pim-1 and reduces its kinase activity, establishing Pim-1 as an Hsp90 client.","method":"Co-immunoprecipitation, geldanamycin treatment, kinase activity assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP and pharmacological inhibitor with kinase activity readout, single lab","pmids":["11237709"],"is_preprint":false},{"year":2013,"finding":"Nitration of a single tyrosine residue (position 33 or 56) on Hsp90 is sufficient to induce motor neuron death via P2X7 receptor-dependent activation of the Fas apoptosis pathway; this nitration confers a toxic gain-of-function on Hsp90, converting it into a pro-death signal.","method":"Site-specific nitration, cell death assays, P2X7/Fas pathway inhibition, immunohistochemistry in ALS patient tissue and animal models","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — specific amino acid modification identified with defined pathway (Fas/P2X7), validated in vivo in ALS models and patient tissue, single lab","pmids":["23487751"],"is_preprint":false},{"year":2018,"finding":"Hsp90 contains an evolutionarily conserved amphipathic helix that directly interacts with and deforms membranes; this function promotes fusion of multivesicular bodies (MVBs) with the plasma membrane to release exosomes. The open Hsp90 dimer conformation exposes the helix and enables MVB fusion, while the closed state blocks it, structurally separating chaperone activity from membrane-deforming function.","method":"Cell-free membrane deformation assay, in vivo exosome release measurements, mutagenesis of the amphipathic helix, conformational mutants and drug-locked states","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution in cell-free system plus in vivo validation, mutagenesis and drug-based conformational locking with multiple orthogonal readouts","pmids":["30193096"],"is_preprint":false},{"year":2010,"finding":"Hsp90 is phosphorylated at a specific tyrosine residue by the cell-cycle kinase Wee1 (Swe1 in yeast); this phosphorylation affects Hsp90 ATPase activity, geldanamycin binding, and its ability to chaperone a subset of kinase clients. Non-phosphorylatable yHsp90-Y24F yeast undergoes premature nuclear division insensitive to G2/M checkpoint arrest, and Wee1 association with Hsp90 and Wee1 stability depend on this phosphorylation event.","method":"Phosphorylation assays, ATPase activity measurement, site-directed mutagenesis (Y24F), yeast cell cycle analysis, co-immunoprecipitation","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis, ATPase assay, and cell cycle phenotype, single lab with multiple complementary methods","pmids":["20519952"],"is_preprint":false},{"year":2005,"finding":"Cdk2 is a genuine client of the Hsp90-Cdc37 chaperone complex; geldanamycin treatment reduces Cdk2 levels by 75% in K562 cells. Pull-down mutagenesis shows the G-box motif of Cdk2 is critical for Cdc37 binding, while helix αC and stabilization of helix αE are required for Hsp90 binding.","method":"Geldanamycin treatment, pull-down assays with deletion/point mutants, molybdate stabilization assay","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pull-down with mutagenesis dissecting distinct binding determinants, pharmacological validation, single lab","pmids":["16285732"],"is_preprint":false},{"year":2012,"finding":"STAT3 directly interacts with Hsp90β with high affinity in vitro as measured by surface plasmon resonance; the interaction requires a functional DNA-binding domain of STAT3 (arginine residues 414/417), and colocalization of STAT3 with Hsp90α/β isoforms in MCF7 cells is reduced by mutation of these residues.","method":"Surface plasmon resonance, site-directed mutagenesis, co-immunoprecipitation, confocal colocalization analysis","journal":"IUBMB life","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — direct binding measured by SPR with mutagenesis, confirmed in cells, single lab","pmids":["22271514"],"is_preprint":false},{"year":2022,"finding":"HSP90AA1 regulates autophagy-dependent nuclear localization of the transcription factor TFEB: CDK5 phosphorylates HSP90AA1 at Ser595 under basal conditions, inhibiting HSP90AA1 and disrupting its binding to TFEB, thereby impeding TFEB nuclear translocation and autophagy induction. Pro-autophagy signaling attenuates CDK5 activity, restoring HSP90AA1-TFEB interaction and TFEB nuclear function.","method":"Co-immunoprecipitation, phosphorylation assays, CDK5 overexpression/knockdown, TFEB nuclear localization imaging, C. elegans lifespan assay","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, phosphorylation mapping, genetic manipulation of CDK5, nuclear localization readout with in vivo lifespan validation, single lab","pmids":["35941759"],"is_preprint":false},{"year":2023,"finding":"USP14 deubiquitinase stabilizes HSP90AA1 by decreasing its lysine 48-linked ubiquitination, preventing its proteasomal degradation; increased HSP90AA1 protein in turn promotes accumulation of CYP2E1, which drives oxidative stress and inflammation in NAFLD/NASH progression.","method":"Co-immunoprecipitation, ubiquitination analysis, USP14 overexpression/knockdown in vitro and in vivo (mouse diet model)","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, ubiquitination assay, in vivo mouse model, single lab with multiple orthogonal methods","pmids":["37633951"],"is_preprint":false},{"year":2016,"finding":"miR-1 directly targets the 3'UTR of Hsp90aa1 mRNA (at nucleotides 310–315) to suppress Hsp90aa1 expression at the post-transcriptional level; overexpression of Hsp90aa1 attenuates oxygen-glucose deprivation-induced apoptosis in neonatal rat ventricular cells, while miR-1 mimic or Hsp90aa1 siRNA enhances apoptosis.","method":"Dual luciferase reporter assay, miRNA mimic/siRNA transfection, western blot, apoptosis assays in neonatal rat ventricular cells and rat I/R model","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct 3'UTR reporter assay plus functional rescue/phenocopy with siRNA, single lab","pmids":["27076094"],"is_preprint":false},{"year":2018,"finding":"HSP90AA1 promotes drug resistance in osteosarcoma by inducing autophagy via the PI3K/Akt/mTOR pathway and inhibiting apoptosis through the JNK/P38 pathway; knockdown of HSP90AA1 restores chemosensitivity to doxorubicin, cisplatin, and methotrexate both in vitro and in vivo (NOD/SCID mouse xenograft).","method":"shRNA knockdown, lentiviral overexpression, LC3 western blot, transmission electron microscopy, mRFP-GFP-LC3 autophagic flux assay, TUNEL staining, in vivo xenograft","journal":"Journal of experimental & clinical cancer research : CR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD/OE with defined pathway readouts and in vivo validation, single lab with multiple orthogonal methods","pmids":["30153855"],"is_preprint":false},{"year":2022,"finding":"DAB2IP negatively regulates HSP90AA1 expression; elevated HSP90AA1 promotes CRC malignant behavior through the HSP90AA1/SRP9/ASK1/JNK signaling axis, where HSP90AA1 suppresses apoptosis; combined targeting of DAB2IP and HSP90AA1 synergistically enhances apoptosis.","method":"Bioinformatic pathway analysis, in vitro knockdown/overexpression, flow cytometry apoptosis assays, in vivo experiments","journal":"BMC cancer","confidence":"Low","confidence_rationale":"Tier 3 / Weak — pathway placement primarily bioinformatic with partial in vitro/vivo validation, single lab","pmids":["35590292"],"is_preprint":false},{"year":2023,"finding":"Cryo-EM structure of PP5 in complex with Hsp90:Cdc37:CRaf reveals that Hsp90 both activates the phosphatase PP5 and scaffolds its association with bound CRaf kinase, enabling PP5 to dephosphorylate phosphorylation sites neighboring the CRaf kinase domain; Hsp90-bound kinase sterically inhibits Cdc37 dephosphorylation, indicating kinase release must precede Cdc37 dephosphorylation.","method":"Cryo-EM structural determination of Hsp90:Cdc37:CRaf:PP5 complex, biochemical dephosphorylation assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure with direct biochemical validation of dephosphorylation activity and steric mechanism","pmids":["37069154"],"is_preprint":false},{"year":2012,"finding":"HSP90AA1 knockdown via RNAi inhibits proliferation and increases apoptosis in ovarian cancer SKOV3 cells; conversely, HSP90AA1 overexpression decreases cisplatin chemosensitivity and partially rescues survival of cisplatin-treated SKOV3 cells, demonstrating that HSP90AA1 level directly modulates cell survival and chemoresistance.","method":"RNAi knockdown, lentiviral overexpression, tetrazolium proliferation assay, FACS apoptosis analysis","journal":"Molecular biology reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — KD/OE with phenotypic readout but no defined molecular pathway, single lab","pmids":["23135731"],"is_preprint":false},{"year":2008,"finding":"Crystal structure of the core Hsp90-Sgt1 complex reveals a distinct interaction site on the Hsp90 N-terminal domain; mutagenesis of Sgt1 interfacial residues specifically abrogates Hsp90 binding and disrupts Sgt1-dependent functions in vivo in plants and yeast; Sgt1 bridges the Hsp90 chaperone to SCF E3 ubiquitin ligase complexes.","method":"X-ray crystallography, site-directed mutagenesis, in vivo functional assays in yeast and plants","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus structure-guided mutagenesis validated in two organisms with defined functional consequences","pmids":["18818696"],"is_preprint":false},{"year":2004,"finding":"Hsp90/hsp70-based chaperone complexes containing TPR-domain immunophilins facilitate retrograde movement of client proteins (e.g., steroid receptors, p53) along microtubular tracks to the nucleus; immunophilins connect the client-Hsp90 complex to cytoplasmic dynein for retrograde transport, and importin-dependent facilitated diffusion mediates nuclear entry of the receptor-Hsp90-immunophilin complex.","method":"Biochemical fractionation, co-immunoprecipitation, genetic disruption of complex components, live-cell imaging of receptor trafficking","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple biochemical and imaging approaches supporting mechanism, reviewed across several client proteins; mechanistic conclusions drawn from multiple labs' data","pmids":["15157665"],"is_preprint":false},{"year":2022,"finding":"In human gingival fibroblasts, HSP90AA1 knockdown (siRNA) reduces Pg-LPS-induced inflammatory cytokines (IL-1β, IL-6, TNF-α), ROS generation, apoptosis, autophagy marker proteins (LC3II/I, ATG5, Beclin-1), and TLR2/4 levels; autophagy inhibitor 3-MA further amplifies the anti-inflammatory effect of HSP90AA1 knockdown, indicating HSP90AA1 promotes inflammation through an autophagy-dependent mechanism.","method":"siRNA knockdown, ELISA, western blot, flow cytometry, immunofluorescence, autophagy inhibitor (3-MA) co-treatment","journal":"BMC oral health","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, KD with multiple readouts but pathway placement indirect; autophagy-inflammation link inferred pharmacologically","pmids":["36028869"],"is_preprint":false}],"current_model":"HSP90AA1 (Hsp90α) is an ATP-dependent homodimeric molecular chaperone that acts as a central hub in eukaryotic proteostasis: it undergoes ATPase-driven conformational cycling (open→closed dimer) to fold, stabilize, and activate hundreds of client proteins—including kinases, steroid receptors, and transcription factors—in collaboration with co-chaperones (Hop, p23, Cdc37, Aha1, immunophilins, PP5) that regulate its ATPase activity, deliver clients, and post-translationally modify clients; cryo-EM structures have revealed that Hsp70 loads partially unfolded clients onto the open Hsp90 dimer via a Hop-bridged loading complex, after which client refolding and p23-stabilized maturation occur within the Hsp90 lumen; additional mechanistic roles include an amphipathic-helix-mediated membrane-deforming activity that drives exosome release, Wee1-mediated tyrosine phosphorylation that modulates ATPase activity and G2/M checkpoint control, CDK5-mediated phosphorylation (Ser595) that regulates HSP90AA1 binding to TFEB and autophagy induction, USP14-mediated deubiquitination that stabilizes HSP90AA1 protein, and nitration of specific tyrosines that converts HSP90AA1 into a pro-apoptotic signal in motor neurons."},"narrative":{"mechanistic_narrative":"HSP90AA1 (Hsp90α) is an ATP-dependent homodimeric molecular chaperone that operates as a central node in proteostasis by loading, folding, stabilizing, and activating a broad clientele of signaling proteins through an ATPase-driven conformational cycle [PMID:34937942, PMID:30193096]. Cryo-EM of the glucocorticoid receptor system established the structural logic of the chaperone cycle: two Hsp70 molecules together with Hop load partially unfolded client onto the open Hsp90 dimer through an extended composite binding pocket [PMID:34937942], after which the client is threaded through the Hsp90 lumen and restored to a folded, ligand-competent state stabilized by the co-chaperone p23 [PMID:34937936]. Kinase clients are delivered via the Hsp90-Cdc37 system, which recognizes determinants such as the G-box motif and helix αC/αE of the client kinase [PMID:16285732], and a PP5-containing complex is scaffolded by Hsp90 so that the phosphatase dephosphorylates sites adjacent to a bound CRaf kinase domain, with the order of dephosphorylation and kinase release sterically controlled by the chaperone [PMID:37069154]. Through these cycles Hsp90 maintains and activates client kinases and transcription factors including Raf-1, Pim-1, Cdk2, and STAT3 [PMID:11751906, PMID:11237709, PMID:16285732, PMID:22271514], and TPR-domain immunophilins couple client-loaded Hsp90 complexes to dynein for retrograde transport and nuclear import of steroid receptors and p53 [PMID:15157665]; Sgt1 bridges Hsp90 to SCF E3 ubiquitin ligase assemblies through a distinct N-terminal interaction site [PMID:18818696]. The chaperone's activity is gated by post-translational control: Wee1 phosphorylates a conserved tyrosine that modulates ATPase activity, inhibitor binding, and G2/M checkpoint behavior [PMID:20519952]; CDK5 phosphorylation at Ser595 disrupts Hsp90α binding to TFEB and thereby autophagy induction [PMID:35941759]; and USP14-mediated deubiquitination removes K48-linked chains to stabilize the protein [PMID:37633951]. Beyond client folding, an evolutionarily conserved amphipathic helix confers a membrane-deforming activity that drives multivesicular body fusion and exosome release in the open conformation, structurally separable from chaperone function [PMID:30193096]. Hsp90α is also subject to a toxic conversion: nitration of a single tyrosine (position 33 or 56) confers a pro-apoptotic gain-of-function that kills motor neurons via P2X7/Fas signaling [PMID:23487751]. In disease contexts, elevated HSP90AA1 promotes autophagy-dependent chemoresistance and apoptosis suppression in cancer and supports CYP2E1-driven oxidative stress in fatty liver disease [PMID:37633951, PMID:30153855].","teleology":[{"year":2001,"claim":"Establishing which signaling kinases depend on Hsp90 defined its role as an activator of oncogenic kinases; Raf-1 and Pim-1 were shown to be Hsp90 clients whose stability and activity require the chaperone.","evidence":"Co-immunoprecipitation, kinase assays, and geldanamycin-induced degradation in cultured cells; a membrane-targeted Hsp90N variant binding Raf-1 independent of Cdc37","pmids":["11751906","11237709"],"confidence":"Medium","gaps":["No structural detail of the kinase-Hsp90 interface","Client recognition determinants on the kinase not mapped"]},{"year":2004,"claim":"How Hsp90-client complexes reach the nucleus was addressed by showing TPR-immunophilins link the complex to dynein for retrograde microtubule transport and importin-dependent nuclear entry.","evidence":"Biochemical fractionation, co-IP, genetic disruption, and live-cell imaging of steroid receptor/p53 trafficking","pmids":["15157665"],"confidence":"Medium","gaps":["Mechanism integrates data across multiple clients rather than a single reconstituted system","Stoichiometry of immunophilin-dynein coupling unresolved"]},{"year":2005,"claim":"Dissecting kinase client loading, the Hsp90-Cdc37 complex was shown to engage Cdk2 through separable binding determinants, distinguishing Cdc37-binding from Hsp90-binding surfaces on the kinase.","evidence":"Geldanamycin treatment, pull-down with deletion/point mutants, and molybdate stabilization in K562 cells","pmids":["16285732"],"confidence":"Medium","gaps":["No structural model of the loaded kinase complex at this stage","Conformational state of the kinase during loading not defined"]},{"year":2008,"claim":"Identifying a distinct N-terminal interaction site for Sgt1 explained how Hsp90 is bridged to SCF E3 ubiquitin ligase assemblies, expanding its role beyond folding into ubiquitin-pathway scaffolding.","evidence":"X-ray crystallography of the core Hsp90-Sgt1 complex with structure-guided mutagenesis validated in yeast and plants","pmids":["18818696"],"confidence":"High","gaps":["Human SCF client repertoire dependent on this interface not enumerated","Functional coupling to the ATPase cycle unclear"]},{"year":2010,"claim":"Linking Hsp90 to cell-cycle control, Wee1-mediated tyrosine phosphorylation was shown to modulate ATPase activity, inhibitor binding, and kinase-client chaperoning, with non-phosphorylatable Hsp90 escaping the G2/M checkpoint.","evidence":"Phosphorylation and ATPase assays, Y24F mutagenesis, and yeast cell-cycle analysis with co-IP","pmids":["20519952"],"confidence":"Medium","gaps":["Human residue and physiological stoichiometry of phosphorylation not fully defined","Which client subset is selectively affected is incompletely characterized"]},{"year":2012,"claim":"Direct binding measurements established STAT3 as an Hsp90 partner requiring an intact DNA-binding domain, extending the client repertoire to transcription factors.","evidence":"Surface plasmon resonance, mutagenesis of STAT3 arginines 414/417, co-IP, and confocal colocalization in MCF7 cells","pmids":["22271514"],"confidence":"Medium","gaps":["Functional consequence for STAT3 transcriptional output not measured","Isoform specificity (α vs β) for the interaction not resolved"]},{"year":2013,"claim":"A toxic gain-of-function was uncovered: nitration of a single Hsp90 tyrosine converts the chaperone into a pro-death signal in motor neurons through P2X7/Fas signaling, relevant to ALS.","evidence":"Site-specific nitration, cell death assays, pathway inhibition, and immunohistochemistry in ALS patient tissue and animal models","pmids":["23487751"],"confidence":"Medium","gaps":["Structural basis of how nitration triggers extracellular P2X7/Fas signaling unclear","Generality beyond motor neurons not established"]},{"year":2018,"claim":"Separating a non-canonical activity from folding, a conserved amphipathic helix was shown to deform membranes and drive MVB fusion for exosome release, gated by the open Hsp90 conformation.","evidence":"Cell-free membrane deformation assay, in vivo exosome release, helix mutagenesis, and drug-locked conformational states","pmids":["30193096"],"confidence":"High","gaps":["How conformational gating is regulated in cells not defined","Whether ATPase cycle and membrane activity compete in vivo unresolved"]},{"year":2021,"claim":"Cryo-EM of the GR loading and maturation complexes resolved the central mechanistic question of how clients enter and exit the chaperone, defining Hsp70/Hop-mediated loading of partially unfolded client and p23-stabilized refolding within the Hsp90 lumen.","evidence":"Cryo-EM of the Hsp90-Hsp70-Hop-GR loading complex and the GR-Hsp90-p23 maturation complex with functional validation","pmids":["34937942","34937936"],"confidence":"High","gaps":["Whether the same loading architecture applies to kinase clients not shown here","Energetics and timing of the loading-to-maturation transition not captured"]},{"year":2022,"claim":"Hsp90α was placed in autophagy regulation through a CDK5-Ser595 phosphorylation switch that controls its binding to TFEB and TFEB nuclear translocation.","evidence":"Co-IP, phosphorylation mapping, CDK5 manipulation, TFEB localization imaging, and C. elegans lifespan assays","pmids":["35941759"],"confidence":"Medium","gaps":["Whether Hsp90α chaperones TFEB folding or merely escorts it is unclear","Direct CDK5 phosphorylation site verification across systems limited"]},{"year":2023,"claim":"A PP5-containing kinase complex structure revealed Hsp90 both activates PP5 and scaffolds its action on bound CRaf, with steric control ordering kinase release before Cdc37 dephosphorylation.","evidence":"Cryo-EM of the Hsp90:Cdc37:CRaf:PP5 complex with biochemical dephosphorylation assays","pmids":["37069154"],"confidence":"High","gaps":["Generality across other kinase clients not established","How PP5 recruitment is timed within the chaperone cycle unresolved"]},{"year":2023,"claim":"Protein-level control of HSP90AA1 was shown via USP14 deubiquitination removing K48 chains, with stabilized Hsp90 promoting CYP2E1 accumulation and oxidative stress in fatty liver disease.","evidence":"Co-IP, ubiquitination analysis, and USP14 manipulation in vitro and in a mouse diet model","pmids":["37633951"],"confidence":"Medium","gaps":["E3 ligase opposing USP14 not identified","Whether CYP2E1 is a direct Hsp90 client not shown"]},{"year":null,"claim":"It remains unresolved how the distinct post-translational switches (Wee1 and CDK5 phosphorylation, nitration, ubiquitination) are integrated to select which clients and non-chaperone activities Hsp90α executes in a given cellular context.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking modification state to client/activity selection","Structural basis for kinase-client loading (vs GR) not directly determined","In vivo regulation of conformational gating between chaperone and membrane functions unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[5,6]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[0,1,7]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,3,7,14]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[5]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[14,16,17]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[17]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,5]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[9,17]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,7,14]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,3,8]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[9,12]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[6,7]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[5]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[4,11]}],"complexes":["Hsp90-Hsp70-Hop GR loading complex","Hsp90-p23 GR maturation complex","Hsp90-Cdc37 kinase complex","Hsp90:Cdc37:CRaf:PP5 complex"],"partners":["HSP70","STIP1","PTGES3","CDC37","PP5","SGT1","WEE1","CDK5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P07900","full_name":"Heat shock protein HSP 90-alpha","aliases":["Heat shock 86 kDa","HSP 86","HSP86","Heat shock protein family C member 1","Lipopolysaccharide-associated protein 2","LAP-2","LPS-associated protein 2","Renal carcinoma antigen NY-REN-38"],"length_aa":732,"mass_kda":84.7,"function":"Molecular chaperone that promotes the maturation, structural maintenance and proper regulation of specific target proteins involved for instance in cell cycle control and signal transduction. Undergoes a functional cycle that is linked to its ATPase activity which is essential for its chaperone activity. This cycle probably induces conformational changes in the client proteins, thereby causing their activation. Interacts dynamically with various co-chaperones that modulate its substrate recognition, ATPase cycle and chaperone function (PubMed:11274138, PubMed:12526792, PubMed:15577939, PubMed:15937123, PubMed:27353360, PubMed:29127155). Engages with a range of client protein classes via its interaction with various co-chaperone proteins or complexes, that act as adapters, simultaneously able to interact with the specific client and the central chaperone itself (PubMed:29127155). Recruitment of ATP and co-chaperone followed by client protein forms a functional chaperone. After the completion of the chaperoning process, properly folded client protein and co-chaperone leave HSP90 in an ADP-bound partially open conformation and finally, ADP is released from HSP90 which acquires an open conformation for the next cycle (PubMed:26991466, PubMed:27295069). Plays a critical role in mitochondrial import, delivers preproteins to the mitochondrial import receptor TOMM70 (PubMed:12526792). Apart from its chaperone activity, it also plays a role in the regulation of the transcription machinery. HSP90 and its co-chaperones modulate transcription at least at three different levels (PubMed:25973397). In the first place, they alter the steady-state levels of certain transcription factors in response to various physiological cues (PubMed:25973397). Second, they modulate the activity of certain epigenetic modifiers, such as histone deacetylases or DNA methyl transferases, and thereby respond to the change in the environment (PubMed:25973397). Third, they participate in the eviction of histones from the promoter region of certain genes and thereby turn on gene expression (PubMed:25973397). Binds bacterial lipopolysaccharide (LPS) and mediates LPS-induced inflammatory response, including TNF secretion by monocytes (PubMed:11276205). Antagonizes STUB1-mediated inhibition of TGF-beta signaling via inhibition of STUB1-mediated SMAD3 ubiquitination and degradation (PubMed:24613385). Mediates the association of TOMM70 with IRF3 or TBK1 in mitochondrial outer membrane which promotes host antiviral response (PubMed:20628368, PubMed:25609812) (Microbial infection) Seems to interfere with N.meningitidis NadA-mediated invasion of human cells. 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Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/15173105","citation_count":26,"is_preprint":false},{"pmid":"39737863","id":"PMC_39737863","title":"The known unknowns of the Hsp90 chaperone.","date":"2024","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/39737863","citation_count":24,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":40140,"output_tokens":5100,"usd":0.09846,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13403,"output_tokens":4824,"usd":0.093808,"stage2_stop_reason":"end_turn"},"total_usd":0.192268,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM structure of the GR-loading complex reveals that two Hsp70 molecules (one delivering GR, one scaffolding Hop) together with Hop load the glucocorticoid receptor (GR) onto Hsp90; GR is partially unfolded and recognized through an extended binding pocket composed of Hsp90, Hsp70, and Hop, establishing the molecular mechanism of client loading and inactivation.\",\n      \"method\": \"Cryo-electron microscopy (cryo-EM) structural determination of the Hsp90-Hsp70-Hop-GR complex\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution cryo-EM structure with functional validation, published in high-impact journal, complemented by companion maturation complex structure\",\n      \"pmids\": [\"34937942\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM structure of the GR-maturation complex (GR-Hsp90-p23) reveals that the GR ligand-binding domain is restored to a folded, ligand-bound conformation while simultaneously threaded through the Hsp90 lumen; co-chaperone p23 directly stabilizes native GR via a C-terminal helix, enhancing ligand binding.\",\n      \"method\": \"Cryo-electron microscopy (cryo-EM) structural determination of the GR-Hsp90-p23 complex\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution cryo-EM structure with functional validation of p23-GR interaction, complemented by companion loading complex structure\",\n      \"pmids\": [\"34937936\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Hsp90N (HSP90N/HSP90AA1 variant lacking the ansamycin-binding N-terminal domain and instead carrying a myristylation signal) binds Raf-1 with higher affinity than canonical Hsp90 and does not associate with p50(cdc37); membrane-targeted Hsp90N activates Raf and downstream ERK kinases, and its stable expression causes neoplastic transformation in c-Ras-deficient fibroblasts.\",\n      \"method\": \"Co-immunoprecipitation, kinase activity assays, stable transfection with anchorage-independent growth assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP and functional cellular assays in single lab with multiple readouts\",\n      \"pmids\": [\"11751906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Hsp90α and Hsp90β physically interact with the proto-oncogene serine/threonine kinase Pim-1; treatment with the Hsp90-specific inhibitor geldanamycin induces rapid degradation of Pim-1 and reduces its kinase activity, establishing Pim-1 as an Hsp90 client.\",\n      \"method\": \"Co-immunoprecipitation, geldanamycin treatment, kinase activity assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP and pharmacological inhibitor with kinase activity readout, single lab\",\n      \"pmids\": [\"11237709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Nitration of a single tyrosine residue (position 33 or 56) on Hsp90 is sufficient to induce motor neuron death via P2X7 receptor-dependent activation of the Fas apoptosis pathway; this nitration confers a toxic gain-of-function on Hsp90, converting it into a pro-death signal.\",\n      \"method\": \"Site-specific nitration, cell death assays, P2X7/Fas pathway inhibition, immunohistochemistry in ALS patient tissue and animal models\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — specific amino acid modification identified with defined pathway (Fas/P2X7), validated in vivo in ALS models and patient tissue, single lab\",\n      \"pmids\": [\"23487751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Hsp90 contains an evolutionarily conserved amphipathic helix that directly interacts with and deforms membranes; this function promotes fusion of multivesicular bodies (MVBs) with the plasma membrane to release exosomes. The open Hsp90 dimer conformation exposes the helix and enables MVB fusion, while the closed state blocks it, structurally separating chaperone activity from membrane-deforming function.\",\n      \"method\": \"Cell-free membrane deformation assay, in vivo exosome release measurements, mutagenesis of the amphipathic helix, conformational mutants and drug-locked states\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution in cell-free system plus in vivo validation, mutagenesis and drug-based conformational locking with multiple orthogonal readouts\",\n      \"pmids\": [\"30193096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Hsp90 is phosphorylated at a specific tyrosine residue by the cell-cycle kinase Wee1 (Swe1 in yeast); this phosphorylation affects Hsp90 ATPase activity, geldanamycin binding, and its ability to chaperone a subset of kinase clients. Non-phosphorylatable yHsp90-Y24F yeast undergoes premature nuclear division insensitive to G2/M checkpoint arrest, and Wee1 association with Hsp90 and Wee1 stability depend on this phosphorylation event.\",\n      \"method\": \"Phosphorylation assays, ATPase activity measurement, site-directed mutagenesis (Y24F), yeast cell cycle analysis, co-immunoprecipitation\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis, ATPase assay, and cell cycle phenotype, single lab with multiple complementary methods\",\n      \"pmids\": [\"20519952\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Cdk2 is a genuine client of the Hsp90-Cdc37 chaperone complex; geldanamycin treatment reduces Cdk2 levels by 75% in K562 cells. Pull-down mutagenesis shows the G-box motif of Cdk2 is critical for Cdc37 binding, while helix αC and stabilization of helix αE are required for Hsp90 binding.\",\n      \"method\": \"Geldanamycin treatment, pull-down assays with deletion/point mutants, molybdate stabilization assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pull-down with mutagenesis dissecting distinct binding determinants, pharmacological validation, single lab\",\n      \"pmids\": [\"16285732\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"STAT3 directly interacts with Hsp90β with high affinity in vitro as measured by surface plasmon resonance; the interaction requires a functional DNA-binding domain of STAT3 (arginine residues 414/417), and colocalization of STAT3 with Hsp90α/β isoforms in MCF7 cells is reduced by mutation of these residues.\",\n      \"method\": \"Surface plasmon resonance, site-directed mutagenesis, co-immunoprecipitation, confocal colocalization analysis\",\n      \"journal\": \"IUBMB life\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct binding measured by SPR with mutagenesis, confirmed in cells, single lab\",\n      \"pmids\": [\"22271514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"HSP90AA1 regulates autophagy-dependent nuclear localization of the transcription factor TFEB: CDK5 phosphorylates HSP90AA1 at Ser595 under basal conditions, inhibiting HSP90AA1 and disrupting its binding to TFEB, thereby impeding TFEB nuclear translocation and autophagy induction. Pro-autophagy signaling attenuates CDK5 activity, restoring HSP90AA1-TFEB interaction and TFEB nuclear function.\",\n      \"method\": \"Co-immunoprecipitation, phosphorylation assays, CDK5 overexpression/knockdown, TFEB nuclear localization imaging, C. elegans lifespan assay\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, phosphorylation mapping, genetic manipulation of CDK5, nuclear localization readout with in vivo lifespan validation, single lab\",\n      \"pmids\": [\"35941759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"USP14 deubiquitinase stabilizes HSP90AA1 by decreasing its lysine 48-linked ubiquitination, preventing its proteasomal degradation; increased HSP90AA1 protein in turn promotes accumulation of CYP2E1, which drives oxidative stress and inflammation in NAFLD/NASH progression.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination analysis, USP14 overexpression/knockdown in vitro and in vivo (mouse diet model)\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, ubiquitination assay, in vivo mouse model, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"37633951\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"miR-1 directly targets the 3'UTR of Hsp90aa1 mRNA (at nucleotides 310–315) to suppress Hsp90aa1 expression at the post-transcriptional level; overexpression of Hsp90aa1 attenuates oxygen-glucose deprivation-induced apoptosis in neonatal rat ventricular cells, while miR-1 mimic or Hsp90aa1 siRNA enhances apoptosis.\",\n      \"method\": \"Dual luciferase reporter assay, miRNA mimic/siRNA transfection, western blot, apoptosis assays in neonatal rat ventricular cells and rat I/R model\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct 3'UTR reporter assay plus functional rescue/phenocopy with siRNA, single lab\",\n      \"pmids\": [\"27076094\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HSP90AA1 promotes drug resistance in osteosarcoma by inducing autophagy via the PI3K/Akt/mTOR pathway and inhibiting apoptosis through the JNK/P38 pathway; knockdown of HSP90AA1 restores chemosensitivity to doxorubicin, cisplatin, and methotrexate both in vitro and in vivo (NOD/SCID mouse xenograft).\",\n      \"method\": \"shRNA knockdown, lentiviral overexpression, LC3 western blot, transmission electron microscopy, mRFP-GFP-LC3 autophagic flux assay, TUNEL staining, in vivo xenograft\",\n      \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD/OE with defined pathway readouts and in vivo validation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"30153855\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DAB2IP negatively regulates HSP90AA1 expression; elevated HSP90AA1 promotes CRC malignant behavior through the HSP90AA1/SRP9/ASK1/JNK signaling axis, where HSP90AA1 suppresses apoptosis; combined targeting of DAB2IP and HSP90AA1 synergistically enhances apoptosis.\",\n      \"method\": \"Bioinformatic pathway analysis, in vitro knockdown/overexpression, flow cytometry apoptosis assays, in vivo experiments\",\n      \"journal\": \"BMC cancer\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — pathway placement primarily bioinformatic with partial in vitro/vivo validation, single lab\",\n      \"pmids\": [\"35590292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cryo-EM structure of PP5 in complex with Hsp90:Cdc37:CRaf reveals that Hsp90 both activates the phosphatase PP5 and scaffolds its association with bound CRaf kinase, enabling PP5 to dephosphorylate phosphorylation sites neighboring the CRaf kinase domain; Hsp90-bound kinase sterically inhibits Cdc37 dephosphorylation, indicating kinase release must precede Cdc37 dephosphorylation.\",\n      \"method\": \"Cryo-EM structural determination of Hsp90:Cdc37:CRaf:PP5 complex, biochemical dephosphorylation assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure with direct biochemical validation of dephosphorylation activity and steric mechanism\",\n      \"pmids\": [\"37069154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"HSP90AA1 knockdown via RNAi inhibits proliferation and increases apoptosis in ovarian cancer SKOV3 cells; conversely, HSP90AA1 overexpression decreases cisplatin chemosensitivity and partially rescues survival of cisplatin-treated SKOV3 cells, demonstrating that HSP90AA1 level directly modulates cell survival and chemoresistance.\",\n      \"method\": \"RNAi knockdown, lentiviral overexpression, tetrazolium proliferation assay, FACS apoptosis analysis\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — KD/OE with phenotypic readout but no defined molecular pathway, single lab\",\n      \"pmids\": [\"23135731\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Crystal structure of the core Hsp90-Sgt1 complex reveals a distinct interaction site on the Hsp90 N-terminal domain; mutagenesis of Sgt1 interfacial residues specifically abrogates Hsp90 binding and disrupts Sgt1-dependent functions in vivo in plants and yeast; Sgt1 bridges the Hsp90 chaperone to SCF E3 ubiquitin ligase complexes.\",\n      \"method\": \"X-ray crystallography, site-directed mutagenesis, in vivo functional assays in yeast and plants\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus structure-guided mutagenesis validated in two organisms with defined functional consequences\",\n      \"pmids\": [\"18818696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Hsp90/hsp70-based chaperone complexes containing TPR-domain immunophilins facilitate retrograde movement of client proteins (e.g., steroid receptors, p53) along microtubular tracks to the nucleus; immunophilins connect the client-Hsp90 complex to cytoplasmic dynein for retrograde transport, and importin-dependent facilitated diffusion mediates nuclear entry of the receptor-Hsp90-immunophilin complex.\",\n      \"method\": \"Biochemical fractionation, co-immunoprecipitation, genetic disruption of complex components, live-cell imaging of receptor trafficking\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple biochemical and imaging approaches supporting mechanism, reviewed across several client proteins; mechanistic conclusions drawn from multiple labs' data\",\n      \"pmids\": [\"15157665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In human gingival fibroblasts, HSP90AA1 knockdown (siRNA) reduces Pg-LPS-induced inflammatory cytokines (IL-1β, IL-6, TNF-α), ROS generation, apoptosis, autophagy marker proteins (LC3II/I, ATG5, Beclin-1), and TLR2/4 levels; autophagy inhibitor 3-MA further amplifies the anti-inflammatory effect of HSP90AA1 knockdown, indicating HSP90AA1 promotes inflammation through an autophagy-dependent mechanism.\",\n      \"method\": \"siRNA knockdown, ELISA, western blot, flow cytometry, immunofluorescence, autophagy inhibitor (3-MA) co-treatment\",\n      \"journal\": \"BMC oral health\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, KD with multiple readouts but pathway placement indirect; autophagy-inflammation link inferred pharmacologically\",\n      \"pmids\": [\"36028869\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"HSP90AA1 (Hsp90α) is an ATP-dependent homodimeric molecular chaperone that acts as a central hub in eukaryotic proteostasis: it undergoes ATPase-driven conformational cycling (open→closed dimer) to fold, stabilize, and activate hundreds of client proteins—including kinases, steroid receptors, and transcription factors—in collaboration with co-chaperones (Hop, p23, Cdc37, Aha1, immunophilins, PP5) that regulate its ATPase activity, deliver clients, and post-translationally modify clients; cryo-EM structures have revealed that Hsp70 loads partially unfolded clients onto the open Hsp90 dimer via a Hop-bridged loading complex, after which client refolding and p23-stabilized maturation occur within the Hsp90 lumen; additional mechanistic roles include an amphipathic-helix-mediated membrane-deforming activity that drives exosome release, Wee1-mediated tyrosine phosphorylation that modulates ATPase activity and G2/M checkpoint control, CDK5-mediated phosphorylation (Ser595) that regulates HSP90AA1 binding to TFEB and autophagy induction, USP14-mediated deubiquitination that stabilizes HSP90AA1 protein, and nitration of specific tyrosines that converts HSP90AA1 into a pro-apoptotic signal in motor neurons.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HSP90AA1 (Hsp90α) is an ATP-dependent homodimeric molecular chaperone that operates as a central node in proteostasis by loading, folding, stabilizing, and activating a broad clientele of signaling proteins through an ATPase-driven conformational cycle [#0, #5]. Cryo-EM of the glucocorticoid receptor system established the structural logic of the chaperone cycle: two Hsp70 molecules together with Hop load partially unfolded client onto the open Hsp90 dimer through an extended composite binding pocket [#0], after which the client is threaded through the Hsp90 lumen and restored to a folded, ligand-competent state stabilized by the co-chaperone p23 [#1]. Kinase clients are delivered via the Hsp90-Cdc37 system, which recognizes determinants such as the G-box motif and helix αC/αE of the client kinase [#7], and a PP5-containing complex is scaffolded by Hsp90 so that the phosphatase dephosphorylates sites adjacent to a bound CRaf kinase domain, with the order of dephosphorylation and kinase release sterically controlled by the chaperone [#14]. Through these cycles Hsp90 maintains and activates client kinases and transcription factors including Raf-1, Pim-1, Cdk2, and STAT3 [#2, #3, #7, #8], and TPR-domain immunophilins couple client-loaded Hsp90 complexes to dynein for retrograde transport and nuclear import of steroid receptors and p53 [#17]; Sgt1 bridges Hsp90 to SCF E3 ubiquitin ligase assemblies through a distinct N-terminal interaction site [#16]. The chaperone's activity is gated by post-translational control: Wee1 phosphorylates a conserved tyrosine that modulates ATPase activity, inhibitor binding, and G2/M checkpoint behavior [#6]; CDK5 phosphorylation at Ser595 disrupts Hsp90α binding to TFEB and thereby autophagy induction [#9]; and USP14-mediated deubiquitination removes K48-linked chains to stabilize the protein [#10]. Beyond client folding, an evolutionarily conserved amphipathic helix confers a membrane-deforming activity that drives multivesicular body fusion and exosome release in the open conformation, structurally separable from chaperone function [#5]. Hsp90α is also subject to a toxic conversion: nitration of a single tyrosine (position 33 or 56) confers a pro-apoptotic gain-of-function that kills motor neurons via P2X7/Fas signaling [#4]. In disease contexts, elevated HSP90AA1 promotes autophagy-dependent chemoresistance and apoptosis suppression in cancer and supports CYP2E1-driven oxidative stress in fatty liver disease [#10, #12].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing which signaling kinases depend on Hsp90 defined its role as an activator of oncogenic kinases; Raf-1 and Pim-1 were shown to be Hsp90 clients whose stability and activity require the chaperone.\",\n      \"evidence\": \"Co-immunoprecipitation, kinase assays, and geldanamycin-induced degradation in cultured cells; a membrane-targeted Hsp90N variant binding Raf-1 independent of Cdc37\",\n      \"pmids\": [\"11751906\", \"11237709\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural detail of the kinase-Hsp90 interface\", \"Client recognition determinants on the kinase not mapped\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"How Hsp90-client complexes reach the nucleus was addressed by showing TPR-immunophilins link the complex to dynein for retrograde microtubule transport and importin-dependent nuclear entry.\",\n      \"evidence\": \"Biochemical fractionation, co-IP, genetic disruption, and live-cell imaging of steroid receptor/p53 trafficking\",\n      \"pmids\": [\"15157665\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism integrates data across multiple clients rather than a single reconstituted system\", \"Stoichiometry of immunophilin-dynein coupling unresolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Dissecting kinase client loading, the Hsp90-Cdc37 complex was shown to engage Cdk2 through separable binding determinants, distinguishing Cdc37-binding from Hsp90-binding surfaces on the kinase.\",\n      \"evidence\": \"Geldanamycin treatment, pull-down with deletion/point mutants, and molybdate stabilization in K562 cells\",\n      \"pmids\": [\"16285732\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the loaded kinase complex at this stage\", \"Conformational state of the kinase during loading not defined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identifying a distinct N-terminal interaction site for Sgt1 explained how Hsp90 is bridged to SCF E3 ubiquitin ligase assemblies, expanding its role beyond folding into ubiquitin-pathway scaffolding.\",\n      \"evidence\": \"X-ray crystallography of the core Hsp90-Sgt1 complex with structure-guided mutagenesis validated in yeast and plants\",\n      \"pmids\": [\"18818696\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Human SCF client repertoire dependent on this interface not enumerated\", \"Functional coupling to the ATPase cycle unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Linking Hsp90 to cell-cycle control, Wee1-mediated tyrosine phosphorylation was shown to modulate ATPase activity, inhibitor binding, and kinase-client chaperoning, with non-phosphorylatable Hsp90 escaping the G2/M checkpoint.\",\n      \"evidence\": \"Phosphorylation and ATPase assays, Y24F mutagenesis, and yeast cell-cycle analysis with co-IP\",\n      \"pmids\": [\"20519952\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Human residue and physiological stoichiometry of phosphorylation not fully defined\", \"Which client subset is selectively affected is incompletely characterized\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Direct binding measurements established STAT3 as an Hsp90 partner requiring an intact DNA-binding domain, extending the client repertoire to transcription factors.\",\n      \"evidence\": \"Surface plasmon resonance, mutagenesis of STAT3 arginines 414/417, co-IP, and confocal colocalization in MCF7 cells\",\n      \"pmids\": [\"22271514\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence for STAT3 transcriptional output not measured\", \"Isoform specificity (α vs β) for the interaction not resolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A toxic gain-of-function was uncovered: nitration of a single Hsp90 tyrosine converts the chaperone into a pro-death signal in motor neurons through P2X7/Fas signaling, relevant to ALS.\",\n      \"evidence\": \"Site-specific nitration, cell death assays, pathway inhibition, and immunohistochemistry in ALS patient tissue and animal models\",\n      \"pmids\": [\"23487751\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of how nitration triggers extracellular P2X7/Fas signaling unclear\", \"Generality beyond motor neurons not established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Separating a non-canonical activity from folding, a conserved amphipathic helix was shown to deform membranes and drive MVB fusion for exosome release, gated by the open Hsp90 conformation.\",\n      \"evidence\": \"Cell-free membrane deformation assay, in vivo exosome release, helix mutagenesis, and drug-locked conformational states\",\n      \"pmids\": [\"30193096\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How conformational gating is regulated in cells not defined\", \"Whether ATPase cycle and membrane activity compete in vivo unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Cryo-EM of the GR loading and maturation complexes resolved the central mechanistic question of how clients enter and exit the chaperone, defining Hsp70/Hop-mediated loading of partially unfolded client and p23-stabilized refolding within the Hsp90 lumen.\",\n      \"evidence\": \"Cryo-EM of the Hsp90-Hsp70-Hop-GR loading complex and the GR-Hsp90-p23 maturation complex with functional validation\",\n      \"pmids\": [\"34937942\", \"34937936\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the same loading architecture applies to kinase clients not shown here\", \"Energetics and timing of the loading-to-maturation transition not captured\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Hsp90α was placed in autophagy regulation through a CDK5-Ser595 phosphorylation switch that controls its binding to TFEB and TFEB nuclear translocation.\",\n      \"evidence\": \"Co-IP, phosphorylation mapping, CDK5 manipulation, TFEB localization imaging, and C. elegans lifespan assays\",\n      \"pmids\": [\"35941759\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether Hsp90α chaperones TFEB folding or merely escorts it is unclear\", \"Direct CDK5 phosphorylation site verification across systems limited\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A PP5-containing kinase complex structure revealed Hsp90 both activates PP5 and scaffolds its action on bound CRaf, with steric control ordering kinase release before Cdc37 dephosphorylation.\",\n      \"evidence\": \"Cryo-EM of the Hsp90:Cdc37:CRaf:PP5 complex with biochemical dephosphorylation assays\",\n      \"pmids\": [\"37069154\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality across other kinase clients not established\", \"How PP5 recruitment is timed within the chaperone cycle unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Protein-level control of HSP90AA1 was shown via USP14 deubiquitination removing K48 chains, with stabilized Hsp90 promoting CYP2E1 accumulation and oxidative stress in fatty liver disease.\",\n      \"evidence\": \"Co-IP, ubiquitination analysis, and USP14 manipulation in vitro and in a mouse diet model\",\n      \"pmids\": [\"37633951\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"E3 ligase opposing USP14 not identified\", \"Whether CYP2E1 is a direct Hsp90 client not shown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how the distinct post-translational switches (Wee1 and CDK5 phosphorylation, nitration, ubiquitination) are integrated to select which clients and non-chaperone activities Hsp90α executes in a given cellular context.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking modification state to client/activity selection\", \"Structural basis for kinase-client loading (vs GR) not directly determined\", \"In vivo regulation of conformational gating between chaperone and membrane functions unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [5, 6]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [0, 1, 7]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 3, 7, 14]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [14, 16, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [17]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 5]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [9, 17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 7, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 3, 8]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [9, 12]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [4, 11]}\n    ],\n    \"complexes\": [\n      \"Hsp90-Hsp70-Hop GR loading complex\",\n      \"Hsp90-p23 GR maturation complex\",\n      \"Hsp90-Cdc37 kinase complex\",\n      \"Hsp90:Cdc37:CRaf:PP5 complex\"\n    ],\n    \"partners\": [\n      \"HSP70\",\n      \"STIP1\",\n      \"PTGES3\",\n      \"CDC37\",\n      \"PP5\",\n      \"SGT1\",\n      \"WEE1\",\n      \"CDK5\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}