{"gene":"PF3D7_0308500","run_date":"2026-09-07T10:55:51","timeline":{"discoveries":[{"year":2003,"finding":"PfHsp90 (PF3D7_0308500) exists in ~300 kDa, 11S hetero-oligomeric complexes containing PfHsp70, as shown by sedimentation analysis and size exclusion chromatography. Geldanamycin (GA) inhibits PfHsp90 and arrests parasite transition from ring to trophozoite stage (LD50 0.2 µM), and selectively inhibits PfHsp90 phosphorylation in GA-treated cultures.","method":"Sedimentation analysis, size exclusion chromatography, homology modeling of GA-binding pocket, flow cytometry for stage analysis, metabolic labeling","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal biochemical methods (sedimentation, SEC, metabolic labeling, stage-specific growth assays) in a single focused study on PfHsp90","pmids":["12584193"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"Full-length recombinant PfHsp90 has the highest ATPase activity of all known Hsp90s (6-fold higher than human Hsp90); GA inhibits this ATPase activity more robustly than it inhibits human Hsp90. Mass spectrometry identified an acetylation site on PfHsp90 that overlaps with the Aha1 and p23 binding domain, and treatment with a histone deacetylase inhibitor caused partial dissociation of the PfHsp90 complex.","method":"In vitro ATPase assay with recombinant full-length protein, mass spectrometry, histone deacetylase inhibitor treatment with complex analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic reconstitution with recombinant protein, orthogonal MS-based PTM identification, and functional inhibitor validation","pmids":["20837488"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2003,"finding":"PfHsp90 binds ATP in vitro, and this binding is specifically inhibited by geldanamycin. PfHsp90 mRNA is mainly expressed in ring and trophozoite stages, while the protein is found in all asexual erythrocytic stages.","method":"Recombinant protein expression, ATP-binding assay, in vitro growth inhibition assay, Western blot for stage-specific expression","journal":"Malaria journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct in vitro ATP-binding assay on recombinant protein with inhibitor specificity, single lab, two methods","pmids":["14514358"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7, W2"}]},{"year":2004,"finding":"PfHsp90 forms a multi-chaperone complex containing PfHsp70, PfPP5, and tubulin during heat shock. Inhibition of this complex by geldanamycin disrupts the complex and inhibits temperature-dependent progression from ring to trophozoite stage. Heat shock-mediated growth promotion is dependent on the PfHsp90 multi-chaperone complex.","method":"Co-immunoprecipitation, geldanamycin inhibition, flow cytometry for stage analysis, heat-shock treatment","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP identifying complex components with functional phenotypic validation, single lab","pmids":["15339915"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2001,"finding":"PfPP5, a TPR-domain serine/threonine phosphatase, physically associates with PfHsp90 in vivo, as demonstrated by co-immunoprecipitation of native proteins from P. falciparum.","method":"Co-immunoprecipitation of native parasite proteins","journal":"BMC microbiology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single co-IP experiment, but replicated as part of the broader PfHsp90 complex shown in PMID:15339915","pmids":["11737864"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"finding":"PfFKBP35 (an immunophilin with TPR domain) associates with PfHsp90 via its TPR domain in vivo. Geldanamycin and ascomycin inhibit P. falciparum growth synergistically, and parasitic calcineurin (PfCN) also associates with PfHsp90 in vivo; GA inhibits the PfCN-PfHsp90 association.","method":"Co-immunoprecipitation, domain-deletion analysis, synergy growth inhibition assay","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP for two distinct client/co-chaperone interactions, functional synergy assay, single lab","pmids":["15850699","15811524"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"Crystal structure of the N-terminal ATP-binding domain of PfHsp90 (PF3D7_0308500) was solved in apo and ADP-bound states at 2.3 Å resolution. The structure shows high similarity to human Hsp90 and contains a principal drug-binding pocket that likely binds geldanamycin in an identical manner to human Hsp90.","method":"X-ray crystallography","journal":"Proteins","confidence":"High","confidence_rationale":"Tier 1 / Moderate — high-resolution crystal structure in two states (apo and ADP-bound), single lab but rigorous structural method","pmids":["20635416"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"finding":"PfHop co-localizes with PfHsp90 and PfHsp70 in trophozoite-stage parasites and is present in a complex with both chaperones, as shown by gel filtration and co-immunoprecipitation.","method":"Co-immunoprecipitation, gel filtration, immunofluorescence co-localization","journal":"Cell stress & chaperones","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — gel filtration plus co-IP as orthogonal methods, replicated by later studies","pmids":["22005844"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"finding":"The crystal structure of the PfFKBP35 TPR domain was solved, and surface plasmon resonance and NMR confirmed direct interaction between the PfFKBP35-TPR domain and the PfHsp90 C-terminal pentapeptide (MEEVD). Mutational analysis of positively charged clamp residues showed all were important for Hsp90 C-terminal peptide binding.","method":"X-ray crystallography, surface plasmon resonance, NMR, site-directed mutagenesis","journal":"Protein science","confidence":"High","confidence_rationale":"Tier 1 / Strong — structure plus SPR plus NMR plus mutagenesis, multiple orthogonal methods in one study","pmids":["19691130"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"Pfp23 (P. falciparum co-chaperone p23) physically interacts with PfHsp90 using purified recombinant proteins. Pfp23 suppresses the ATPase activity of PfHsp90 in vitro. Site-directed mutagenesis identified residues K91, H93, W94, and K96 in Pfp23 as crucial for binding PfHsp90.","method":"Recombinant protein interaction assay, ATPase assay, site-directed mutagenesis, homology modeling","journal":"Cellular and molecular life sciences","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with mutagenesis, multiple orthogonal methods, single lab","pmids":["20140477"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"finding":"PfAha1 interacts with PfHsp90 as demonstrated by split-ubiquitin assay (in vivo) and GST pull-down (in vitro). The interaction is dependent on MgCl2 and ATP, competed by Pfp23, and sensitive to high salt. Residue N108 in PfAha1 is essential for PfHsp90 interaction. PfAha1 stimulates PfHsp90 ATPase activity.","method":"Split-ubiquitin assay, GST pull-down, site-directed mutagenesis, ATPase assay, bio-computational modelling","journal":"The international journal of biochemistry & cell biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution plus mutagenesis plus in vivo and in vitro interaction assays, multiple orthogonal methods, single lab","pmids":["22100910"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2012,"finding":"Harmine specifically inhibits PfHsp90 ATP-binding domain with a KD of 40 µM (surface plasmon resonance). Site-directed mutagenesis revealed Arg98 in PfHsp90 is essential for harmine selectivity over human Hsp90.","method":"Surface plasmon resonance, site-directed mutagenesis, in vitro growth inhibition","journal":"Antimicrobial agents and chemotherapy","confidence":"High","confidence_rationale":"Tier 1 / Moderate — SPR binding with mutagenesis to identify the selectivity determinant, two orthogonal methods, single lab","pmids":["22615284"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"finding":"Differences in the conformational dynamics of the ATP-binding pocket between PfHsp90 and human Hsp90 enable selective inhibitor binding. Novel 7-azaindole compounds bind exclusively to recombinant N-terminal domain of PfHsp90 but not to human Hsp90 or a PfHsp90 mutant engineered to have 'human-like' dynamics.","method":"Structure-based virtual screening, in vitro binding assay, yeast complementation system, mutagenesis","journal":"Journal of medicinal chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — structure-guided approach with mutagenesis and yeast complementation validation, multiple orthogonal methods, single lab","pmids":["24580531"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"finding":"PfHsp90 interacts either directly or indirectly with the P. falciparum chloroquine resistance transporter (PfCRT), as identified by LC-MS/MS pulldown. Inhibition of PfHsp90 with PU-H71 synergizes with chloroquine against P. falciparum in vitro and in a P. berghei mouse model.","method":"LC-MS/MS interactome (pulldown), SPR binding assay, ATPase assay, flow cytometry, P. berghei mouse model","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — MS-based pulldown for PfCRT interaction; functional synergy validated in two models; indirect interaction cannot be ruled out","pmids":["24098696"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":2021,"finding":"PfAP2-HS, an ApiAP2 transcription factor, activates transcription of hsp90 (PF3D7_0308500) at elevated (febrile) temperatures. Parasites lacking PfAP2-HS have reduced heat-shock survival and growth defects at 37°C. The main PfAP2-HS binding site in the genome coincides with a tandem G-box motif in the hsp70-1 promoter.","method":"Conditional knockdown/knockout, chromatin immunoprecipitation, transcriptomics, survival assays","journal":"Nature microbiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockouts with defined phenotypic readout plus ChIP for binding site, replicated across multiple assays, rigorous controls","pmids":["34400833"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"PfHsp90 acts as a transcriptional repressor of PfSIR2A and PfSIR2B at febrile temperatures. PfHsp90 is present at PfSIR2A and PfSIR2B promoter proximal regions, helps recruit H3K9me3 (heterochromatic mark), and its inhibition by 17-AAG or Radicicol reverses transcriptional downregulation of PfSIR2A/B.","method":"Chromatin immunoprecipitation (ChIP), inhibitor treatment (17-AAG, Radicicol), transcriptional reporter assays","journal":"Molecular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP localization to promoters with functional inhibitor-based validation, single lab","pmids":["33538363"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2022,"finding":"PfHsp90 physically interacts with PfSir2A (demonstrated by co-immunoprecipitation), and inhibition of PfHsp90 by 17-AAG or Radicicol causes depletion of PfSir2A protein and abolishes its histone deacetylase activity, leading to derepression of var genes and ribosomal silencing.","method":"Co-immunoprecipitation, chemical inhibition (17-AAG, Radicicol), HDAC activity assay, var gene expression analysis","journal":"mSphere","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus functional HDAC assay plus gene expression readout, single lab, multiple orthogonal methods","pmids":["36121150"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2024,"finding":"PfHsp90 directly promotes 26S proteasome function by chaperoning the active 26S complex. Thermal proteome profiling following PfHsp90 inhibition identified the proteasome as enriched among proteins with perturbed stability. Subsequent biochemical and cellular studies confirmed PfHsp90 promotes proteasome hydrolysis.","method":"Thermal proteome profiling, biochemical proteasome activity assays, cellular studies with selective PfHsp90 inhibitors (BX-2819, XL888, Tropane 1)","journal":"Cell chemical biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — thermal proteome profiling plus orthogonal biochemical and cellular validation in one rigorous study, multiple methods","pmids":["38492573"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2023,"finding":"Hsp90 is present on the surface of Plasmodium female gametes and is a key determinant for fertilization. Anti-HSP90 antibodies binding to the female gamete surface inhibit fertilization.","method":"Phage peptide display screening, antibody binding assay, fertilization inhibition assay","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional inhibition of fertilization by anti-HSP90 antibodies with peptide display identification, single lab, but mechanistic detail limited to localization and blocking","pmids":["38131664"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"finding":"Class 2 imidazopyridazine compounds (non-pyrimidine linker) bind to the ATP-binding site in the N-terminal domain of PfHsp90 and inhibit parasite growth at the trophozoite stage, implicating PfHsp90 inhibition as their primary mechanism of action.","method":"Compound-pulldown/target identification, in vitro growth inhibition, parasite lines expressing modified kinases (gatekeeper mutants), stage-specific growth analysis","journal":"Antimicrobial agents and chemotherapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding demonstrated with N-terminal domain plus stage-specific phenotype, but target assignment relies partly on correlative evidence; single lab","pmids":["26711771"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2020,"finding":"Violacein directly binds PfHsp90 (as well as PfHsp70-1), compromising chaperone activities in the parasite, leading to increased protein unfolding and proteasomal degradation and multi-stage growth inhibition.","method":"Chemical genomic profiling, direct binding assay (thermal shift/pull-down), ATPase assay, proteasome activity assay","journal":"ACS infectious diseases","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding demonstrated plus functional ATPase and chaperone activity assays, single lab, two orthogonal methods","pmids":["33689276"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"finding":"PfHop inhibits the ATPase activity of recombinant PfHsp90 while stimulating the ATPase activity of PfHsp70-1 in vitro. PfHop behaves primarily as an elongated dimer as characterized by small-angle X-ray scattering.","method":"In vitro ATPase assay, small-angle X-ray scattering, circular dichroism","journal":"Biochimica et biophysica acta. Proteins and proteomics","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstituted ATPase assay with recombinant proteins plus SAXS structural characterization, single lab","pmids":["31525467"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2020,"finding":"Solution structure of full-length recombinant PfHsp90 characterized by small-angle X-ray scattering reveals an open, highly elongated and flexible homodimer. PfHsp90 interacts with adenosine nucleotides via the N-terminal domain; Mg2+ is critical for strong nucleotide binding. The C-terminal domain is essential for dimerization.","method":"Small-angle X-ray scattering (SAXS), isothermal titration calorimetry/fluorescence-based nucleotide binding assays, domain-deletion constructs","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — SAXS-based solution structure plus nucleotide binding assays with domain truncations, single lab","pmids":["32679196"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"finding":"A cryptic C-terminal binding site on PfHsp90 interacts specifically with ATP; limited proteolysis experiments suggest association with ATP, dATP, and ADP but not AMP or GTP. Mutagenesis studies were used to interrogate the molecular basis of this interaction.","method":"Affinity experiments with lysine-reactive nucleotide analog and ATP resin, limited proteolysis, site-directed mutagenesis, in silico analysis","journal":"Bioorganic & medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro affinity and proteolysis assays with mutagenesis, single lab, novel finding not yet independently replicated","pmids":["40907219"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"finding":"Two p23 co-chaperones (Pfp23A and Pfp23B) are present in P. falciparum and both inhibit the ATPase activity of recombinant PfHsp90 in vitro, validating them as functional Hsp90 co-chaperones. Pfp23A is more structurally stable than Pfp23B.","method":"Recombinant protein expression, in vitro ATPase assay, thermal stability assay, small-angle X-ray scattering","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstituted ATPase assay with recombinant proteins plus SAXS, single lab","pmids":["29191421"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"finding":"Two HSP90 inhibitors (geldanamycin and AUY-922) targeting the identical ATP-binding site of PfHsp90 show dramatically different resistance profiles in P. falciparum. Conditional HSP90 knockdown increases geldanamycin sensitivity but leaves AUY-922 activity unaffected, suggesting AUY-922 may engage multiple Hsp90 family members. The A41S mutation in the ATP-binding site enhances AUY-922 binding affinity yet correlates with resistance.","method":"Drug resistance selection, yeast complementation, conditional knockdown, in vitro binding assays, in silico analysis","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional knockdown plus binding assays plus genetic epistasis, preprint not yet peer-reviewed","pmids":["41279590"],"is_preprint":true,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"PfHsp90 (PF3D7_0308500) is an essential ATP-dependent molecular chaperone that exists as a highly flexible homodimer with the highest ATPase activity among known Hsp90 orthologues; it forms multi-chaperone complexes with PfHsp70, PfHop, PfPP5, PfFKBP35, PfAha1, Pfp23, and PfCRT in the parasite cytosol, directly chaperones the 26S proteasome to promote proteasome hydrolysis, acts as a transcriptional repressor of PfSIR2A/B by recruiting H3K9me3 to their promoters, maintains PfSir2A protein stability and HDAC activity, appears on the female gamete surface where it is required for fertilization, and its transcription is activated at febrile temperatures by the ApiAP2 transcription factor PfAP2-HS; inhibition of PfHsp90 by geldanamycin or other ATP-competitive inhibitors arrests intraerythrocytic development primarily at the ring-to-trophozoite transition and causes parasite death."},"narrative":{"mechanistic_narrative":"PfHsp90 (PF3D7_0308500) is an essential ATP-dependent molecular chaperone of the intraerythrocytic malaria parasite whose inhibition arrests development at the ring-to-trophozoite transition and causes parasite death [PMID:12584193, PMID:15339915]. The full-length recombinant protein exhibits the highest ATPase activity of any known Hsp90 orthologue—roughly six-fold that of human Hsp90—and is potently inhibited by geldanamycin [PMID:20837488]; structural work shows it is an open, highly elongated and flexible homodimer whose N-terminal domain binds adenosine nucleotides in a Mg2+-dependent manner and whose C-terminal domain drives dimerization [PMID:32679196, PMID:20635416]. PfHsp90 nucleates a cytosolic multi-chaperone machine, associating with PfHsp70, PfHop, the TPR-domain phosphatase PfPP5 and immunophilin PfFKBP35 (the latter docking onto the C-terminal MEEVD pentapeptide), and its ATPase cycle is tuned by co-chaperones—stimulated by PfAha1 and suppressed by Pfp23 and PfHop [PMID:15339915, PMID:22005844, PMID:19691130, PMID:22100910, PMID:20140477, PMID:31525467]. Beyond canonical chaperoning, PfHsp90 directly promotes 26S proteasome hydrolysis [PMID:38492573] and has acquired nuclear regulatory roles at febrile temperatures: it acts as a transcriptional repressor of PfSIR2A/B by recruiting the H3K9me3 mark to their promoters and physically stabilizes PfSir2A protein and its histone deacetylase activity, thereby controlling var-gene silencing [PMID:33538363, PMID:36121150]. Its own transcription is induced at febrile temperatures by the ApiAP2 factor PfAP2-HS [PMID:34400833], and the protein is displayed on the female gamete surface where it is required for fertilization [PMID:38131664]. The conformational dynamics of its ATP-binding pocket differ from the human enzyme, a feature exploited to develop parasite-selective inhibitors [PMID:24580531, PMID:22615284].","teleology":[{"year":2003,"claim":"Establishing that PfHsp90 is a genuine, druggable chaperone required showing it binds ATP, assembles into oligomeric complexes, and that its inhibition blocks a defined developmental step.","evidence":"ATP-binding and geldanamycin-inhibition assays on recombinant protein, plus sedimentation/SEC showing ~300 kDa Hsp70-containing complexes with stage-specific growth arrest in P. falciparum","pmids":["12584193","14514358"],"confidence":"High","gaps":["Complex composition beyond Hsp70 not resolved at this stage","Direct client proteins not identified"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium falciparum","strain":"3D7, W2"}]},{"year":2005,"claim":"The identity of the co-chaperones assembling on PfHsp90 was mapped by defining TPR-domain partners that dock the chaperone into functional complexes.","evidence":"Co-immunoprecipitation of native PfPP5, PfFKBP35 and PfCN with PfHsp90, with domain-deletion and synergy growth assays in P. falciparum","pmids":["11737864","15339915","15850699","15811524"],"confidence":"Medium","gaps":["Whether these interactions are direct or bridged by other chaperones","Client proteins folded by the assembled complex unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"claim":"Quantifying the enzymatic and structural properties revealed PfHsp90 as an unusually hyperactive ATPase with a defined N-terminal drug pocket, rationalizing its inhibitor sensitivity.","evidence":"In vitro ATPase assays on full-length recombinant protein, MS-based acetylation mapping, and a 2.3 Å crystal structure of the N-terminal domain in apo and ADP states","pmids":["20837488","20635416"],"confidence":"High","gaps":["Full-length crystal structure not solved","Functional role of the acetylation site in vivo untested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"claim":"Delineating how co-chaperones tune the ATPase cycle clarified the regulatory logic of the chaperone machine.","evidence":"SPR/NMR mapping of PfFKBP35-TPR binding the C-terminal MEEVD, plus reconstituted ATPase assays and mutagenesis showing Pfp23 suppresses and PfAha1 stimulates PfHsp90 ATPase in P. falciparum proteins","pmids":["19691130","20140477","22100910","22005844"],"confidence":"High","gaps":["Order of co-chaperone loading during the catalytic cycle not established","In vivo consequences of ATPase modulation on client folding unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"claim":"Demonstrating that PfHsp90's ATP-pocket dynamics differ from the human enzyme opened a route to parasite-selective inhibitors.","evidence":"SPR with harmine identifying Arg98 as a selectivity determinant, and structure-based design of 7-azaindoles binding only the parasite N-terminal domain, validated by yeast complementation and dynamics-altering mutants","pmids":["22615284","24580531"],"confidence":"High","gaps":["Selectivity determinants not yet translated to in vivo efficacy in these studies","Impact on the assembled multi-chaperone complex not tested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"claim":"Interactome profiling linked PfHsp90 to drug-resistance machinery, connecting chaperone function to chloroquine action.","evidence":"LC-MS/MS pulldown identifying PfCRT association and PU-H71/chloroquine synergy in P. falciparum in vitro and a P. berghei mouse model","pmids":["24098696"],"confidence":"Medium","gaps":["Direct versus indirect PfCRT interaction unresolved","Mechanism by which PfHsp90 influences PfCRT function unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":2021,"claim":"The transcriptional context of PfHsp90 was defined at both ends—how its own gene is induced by heat and how it in turn controls chromatin at febrile temperatures.","evidence":"Conditional knockout/ChIP showing PfAP2-HS activates hsp90 transcription at febrile temperatures, and ChIP plus inhibitor assays showing PfHsp90 represses PfSIR2A/B by recruiting H3K9me3 in P. falciparum 3D7","pmids":["34400833","33538363"],"confidence":"Medium","gaps":["How a cytosolic chaperone accesses promoters and directs H3K9me3 mechanistically unclear","Whether repression is direct or via chaperoned nuclear factors unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2022,"claim":"The chromatin-regulatory role was refined to a direct chaperone-client relationship with a sirtuin deacetylase governing antigenic variation.","evidence":"Co-IP and inhibitor treatment (17-AAG, Radicicol) showing PfHsp90 stabilizes PfSir2A protein and HDAC activity, with var-gene derepression on inhibition in P. falciparum 3D7","pmids":["36121150"],"confidence":"Medium","gaps":["Structural basis of PfHsp90-PfSir2A recognition undefined","Contribution relative to other var-silencing pathways unquantified"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2024,"claim":"Unbiased proteome profiling identified the proteasome as a direct functional client, extending PfHsp90 beyond classical folding into proteostasis control.","evidence":"Thermal proteome profiling after PfHsp90 inhibition plus biochemical proteasome-activity assays using selective inhibitors in P. falciparum","pmids":["38492573"],"confidence":"High","gaps":["Which proteasome subunits PfHsp90 engages directly not resolved","Stoichiometry and dynamics of the chaperone-proteasome interaction unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"claim":"Solution-structure and nucleotide-binding studies mapped the conformational and cryptic-site features that distinguish PfHsp90 and complicate inhibitor targeting.","evidence":"SAXS showing an open flexible homodimer with C-terminal-driven dimerization, limited proteolysis identifying a cryptic C-terminal ATP site, and conditional-knockdown/binding assays contrasting geldanamycin versus AUY-922 resistance (bioRxiv preprint for #25)","pmids":["32679196","40907219","41279590"],"confidence":"Medium","gaps":["Physiological role of the cryptic C-terminal nucleotide site untested in vivo","Mechanism of AUY-922 resistance despite enhanced binding unresolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"How PfHsp90's diverse activities—cytosolic client folding, proteasome chaperoning, nuclear transcriptional repression, and gamete-surface fertilization function—are partitioned and regulated within a single essential chaperone remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking cytosolic chaperone activity to its nuclear and surface roles","Full endogenous client repertoire not defined","Mechanism of gamete-surface targeting unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["PfHsp90-PfHsp70 hetero-oligomeric (~300 kDa, 11S) chaperone complex [#0]","PfHsp90-PfHsp70-PfPP5-tubulin heat-shock multi-chaperone complex [#3]","PfHsp90-PfHsp70-PfHop complex [#7]","PfHsp90-26S proteasome functional association [#17]"],"partners":["PFHSP70 [#0, #3, #7]","PFPP5 (TPR-DOMAIN SER/THR PHOSPHATASE) [#4, #3]","PFFKBP35 (IMMUNOPHILIN, MEEVD-BINDING) [#5, #8]","PFCN (CALCINEURIN) [#5]","PFHOP [#7, #21]","PFP23 / PFP23A / PFP23B (CO-CHAPERONE, ATPASE SUPPRESSOR) [#9, #24]","PFAHA1 (CO-CHAPERONE, ATPASE STIMULATOR) [#10]","PFCRT (DIRECT OR INDIRECT) [#13]","PFAP2-HS (TRANSCRIPTIONAL ACTIVATOR OF HSP90) [#14]","PFSIR2A (CHAPERONE CLIENT/STABILIZED) [#16]"],"other_free_text":["Highest ATPase activity of any known Hsp90 orthologue, ~6-fold above human Hsp90 [#1]","Open, highly elongated flexible homodimer; C-terminal domain required for dimerization [#22]","N-terminal ATP-binding pocket with distinct conformational dynamics enabling parasite-selective inhibitors (harmine/Arg98, 7-azaindoles) [#11, #12, #6]","Cryptic C-terminal nucleotide-binding site selective for ATP/dATP/ADP [#23]","Inhibition (geldanamycin, 17-AAG, radicicol, PU-H71, imidazopyridazines, violacein) arrests development at ring-to-trophozoite transition and kills parasites [#0, #19, #20]","Divergent resistance profiles between geldanamycin and AUY-922 despite shared ATP-site targeting (preprint) [#25]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"12584193","id":"PMC_12584193","title":"Heat shock protein 90 function is essential for Plasmodium falciparum growth in human erythrocytes.","date":"2003","source":"The Journal of biological 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Geldanamycin (GA) inhibits PfHsp90 and arrests parasite transition from ring to trophozoite stage (LD50 0.2 µM), and selectively inhibits PfHsp90 phosphorylation in GA-treated cultures.\",\n      \"method\": \"Sedimentation analysis, size exclusion chromatography, homology modeling of GA-binding pocket, flow cytometry for stage analysis, metabolic labeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal biochemical methods (sedimentation, SEC, metabolic labeling, stage-specific growth assays) in a single focused study on PfHsp90\",\n      \"pmids\": [\"12584193\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Full-length recombinant PfHsp90 has the highest ATPase activity of all known Hsp90s (6-fold higher than human Hsp90); GA inhibits this ATPase activity more robustly than it inhibits human Hsp90. Mass spectrometry identified an acetylation site on PfHsp90 that overlaps with the Aha1 and p23 binding domain, and treatment with a histone deacetylase inhibitor caused partial dissociation of the PfHsp90 complex.\",\n      \"method\": \"In vitro ATPase assay with recombinant full-length protein, mass spectrometry, histone deacetylase inhibitor treatment with complex analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic reconstitution with recombinant protein, orthogonal MS-based PTM identification, and functional inhibitor validation\",\n      \"pmids\": [\"20837488\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PfHsp90 binds ATP in vitro, and this binding is specifically inhibited by geldanamycin. PfHsp90 mRNA is mainly expressed in ring and trophozoite stages, while the protein is found in all asexual erythrocytic stages.\",\n      \"method\": \"Recombinant protein expression, ATP-binding assay, in vitro growth inhibition assay, Western blot for stage-specific expression\",\n      \"journal\": \"Malaria journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct in vitro ATP-binding assay on recombinant protein with inhibitor specificity, single lab, two methods\",\n      \"pmids\": [\"14514358\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7, W2\"}]\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PfHsp90 forms a multi-chaperone complex containing PfHsp70, PfPP5, and tubulin during heat shock. Inhibition of this complex by geldanamycin disrupts the complex and inhibits temperature-dependent progression from ring to trophozoite stage. Heat shock-mediated growth promotion is dependent on the PfHsp90 multi-chaperone complex.\",\n      \"method\": \"Co-immunoprecipitation, geldanamycin inhibition, flow cytometry for stage analysis, heat-shock treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP identifying complex components with functional phenotypic validation, single lab\",\n      \"pmids\": [\"15339915\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PfPP5, a TPR-domain serine/threonine phosphatase, physically associates with PfHsp90 in vivo, as demonstrated by co-immunoprecipitation of native proteins from P. falciparum.\",\n      \"method\": \"Co-immunoprecipitation of native parasite proteins\",\n      \"journal\": \"BMC microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single co-IP experiment, but replicated as part of the broader PfHsp90 complex shown in PMID:15339915\",\n      \"pmids\": [\"11737864\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PfFKBP35 (an immunophilin with TPR domain) associates with PfHsp90 via its TPR domain in vivo. Geldanamycin and ascomycin inhibit P. falciparum growth synergistically, and parasitic calcineurin (PfCN) also associates with PfHsp90 in vivo; GA inhibits the PfCN-PfHsp90 association.\",\n      \"method\": \"Co-immunoprecipitation, domain-deletion analysis, synergy growth inhibition assay\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP for two distinct client/co-chaperone interactions, functional synergy assay, single lab\",\n      \"pmids\": [\"15850699\", \"15811524\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Crystal structure of the N-terminal ATP-binding domain of PfHsp90 (PF3D7_0308500) was solved in apo and ADP-bound states at 2.3 Å resolution. The structure shows high similarity to human Hsp90 and contains a principal drug-binding pocket that likely binds geldanamycin in an identical manner to human Hsp90.\",\n      \"method\": \"X-ray crystallography\",\n      \"journal\": \"Proteins\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high-resolution crystal structure in two states (apo and ADP-bound), single lab but rigorous structural method\",\n      \"pmids\": [\"20635416\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PfHop co-localizes with PfHsp90 and PfHsp70 in trophozoite-stage parasites and is present in a complex with both chaperones, as shown by gel filtration and co-immunoprecipitation.\",\n      \"method\": \"Co-immunoprecipitation, gel filtration, immunofluorescence co-localization\",\n      \"journal\": \"Cell stress & chaperones\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — gel filtration plus co-IP as orthogonal methods, replicated by later studies\",\n      \"pmids\": [\"22005844\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The crystal structure of the PfFKBP35 TPR domain was solved, and surface plasmon resonance and NMR confirmed direct interaction between the PfFKBP35-TPR domain and the PfHsp90 C-terminal pentapeptide (MEEVD). Mutational analysis of positively charged clamp residues showed all were important for Hsp90 C-terminal peptide binding.\",\n      \"method\": \"X-ray crystallography, surface plasmon resonance, NMR, site-directed mutagenesis\",\n      \"journal\": \"Protein science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — structure plus SPR plus NMR plus mutagenesis, multiple orthogonal methods in one study\",\n      \"pmids\": [\"19691130\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Pfp23 (P. falciparum co-chaperone p23) physically interacts with PfHsp90 using purified recombinant proteins. Pfp23 suppresses the ATPase activity of PfHsp90 in vitro. Site-directed mutagenesis identified residues K91, H93, W94, and K96 in Pfp23 as crucial for binding PfHsp90.\",\n      \"method\": \"Recombinant protein interaction assay, ATPase assay, site-directed mutagenesis, homology modeling\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with mutagenesis, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"20140477\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PfAha1 interacts with PfHsp90 as demonstrated by split-ubiquitin assay (in vivo) and GST pull-down (in vitro). The interaction is dependent on MgCl2 and ATP, competed by Pfp23, and sensitive to high salt. Residue N108 in PfAha1 is essential for PfHsp90 interaction. PfAha1 stimulates PfHsp90 ATPase activity.\",\n      \"method\": \"Split-ubiquitin assay, GST pull-down, site-directed mutagenesis, ATPase assay, bio-computational modelling\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution plus mutagenesis plus in vivo and in vitro interaction assays, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"22100910\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Harmine specifically inhibits PfHsp90 ATP-binding domain with a KD of 40 µM (surface plasmon resonance). Site-directed mutagenesis revealed Arg98 in PfHsp90 is essential for harmine selectivity over human Hsp90.\",\n      \"method\": \"Surface plasmon resonance, site-directed mutagenesis, in vitro growth inhibition\",\n      \"journal\": \"Antimicrobial agents and chemotherapy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — SPR binding with mutagenesis to identify the selectivity determinant, two orthogonal methods, single lab\",\n      \"pmids\": [\"22615284\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Differences in the conformational dynamics of the ATP-binding pocket between PfHsp90 and human Hsp90 enable selective inhibitor binding. Novel 7-azaindole compounds bind exclusively to recombinant N-terminal domain of PfHsp90 but not to human Hsp90 or a PfHsp90 mutant engineered to have 'human-like' dynamics.\",\n      \"method\": \"Structure-based virtual screening, in vitro binding assay, yeast complementation system, mutagenesis\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — structure-guided approach with mutagenesis and yeast complementation validation, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"24580531\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PfHsp90 interacts either directly or indirectly with the P. falciparum chloroquine resistance transporter (PfCRT), as identified by LC-MS/MS pulldown. Inhibition of PfHsp90 with PU-H71 synergizes with chloroquine against P. falciparum in vitro and in a P. berghei mouse model.\",\n      \"method\": \"LC-MS/MS interactome (pulldown), SPR binding assay, ATPase assay, flow cytometry, P. berghei mouse model\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — MS-based pulldown for PfCRT interaction; functional synergy validated in two models; indirect interaction cannot be ruled out\",\n      \"pmids\": [\"24098696\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PfAP2-HS, an ApiAP2 transcription factor, activates transcription of hsp90 (PF3D7_0308500) at elevated (febrile) temperatures. Parasites lacking PfAP2-HS have reduced heat-shock survival and growth defects at 37°C. The main PfAP2-HS binding site in the genome coincides with a tandem G-box motif in the hsp70-1 promoter.\",\n      \"method\": \"Conditional knockdown/knockout, chromatin immunoprecipitation, transcriptomics, survival assays\",\n      \"journal\": \"Nature microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockouts with defined phenotypic readout plus ChIP for binding site, replicated across multiple assays, rigorous controls\",\n      \"pmids\": [\"34400833\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PfHsp90 acts as a transcriptional repressor of PfSIR2A and PfSIR2B at febrile temperatures. PfHsp90 is present at PfSIR2A and PfSIR2B promoter proximal regions, helps recruit H3K9me3 (heterochromatic mark), and its inhibition by 17-AAG or Radicicol reverses transcriptional downregulation of PfSIR2A/B.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), inhibitor treatment (17-AAG, Radicicol), transcriptional reporter assays\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP localization to promoters with functional inhibitor-based validation, single lab\",\n      \"pmids\": [\"33538363\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PfHsp90 physically interacts with PfSir2A (demonstrated by co-immunoprecipitation), and inhibition of PfHsp90 by 17-AAG or Radicicol causes depletion of PfSir2A protein and abolishes its histone deacetylase activity, leading to derepression of var genes and ribosomal silencing.\",\n      \"method\": \"Co-immunoprecipitation, chemical inhibition (17-AAG, Radicicol), HDAC activity assay, var gene expression analysis\",\n      \"journal\": \"mSphere\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus functional HDAC assay plus gene expression readout, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"36121150\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PfHsp90 directly promotes 26S proteasome function by chaperoning the active 26S complex. Thermal proteome profiling following PfHsp90 inhibition identified the proteasome as enriched among proteins with perturbed stability. Subsequent biochemical and cellular studies confirmed PfHsp90 promotes proteasome hydrolysis.\",\n      \"method\": \"Thermal proteome profiling, biochemical proteasome activity assays, cellular studies with selective PfHsp90 inhibitors (BX-2819, XL888, Tropane 1)\",\n      \"journal\": \"Cell chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — thermal proteome profiling plus orthogonal biochemical and cellular validation in one rigorous study, multiple methods\",\n      \"pmids\": [\"38492573\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Hsp90 is present on the surface of Plasmodium female gametes and is a key determinant for fertilization. Anti-HSP90 antibodies binding to the female gamete surface inhibit fertilization.\",\n      \"method\": \"Phage peptide display screening, antibody binding assay, fertilization inhibition assay\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional inhibition of fertilization by anti-HSP90 antibodies with peptide display identification, single lab, but mechanistic detail limited to localization and blocking\",\n      \"pmids\": [\"38131664\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Class 2 imidazopyridazine compounds (non-pyrimidine linker) bind to the ATP-binding site in the N-terminal domain of PfHsp90 and inhibit parasite growth at the trophozoite stage, implicating PfHsp90 inhibition as their primary mechanism of action.\",\n      \"method\": \"Compound-pulldown/target identification, in vitro growth inhibition, parasite lines expressing modified kinases (gatekeeper mutants), stage-specific growth analysis\",\n      \"journal\": \"Antimicrobial agents and chemotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding demonstrated with N-terminal domain plus stage-specific phenotype, but target assignment relies partly on correlative evidence; single lab\",\n      \"pmids\": [\"26711771\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Violacein directly binds PfHsp90 (as well as PfHsp70-1), compromising chaperone activities in the parasite, leading to increased protein unfolding and proteasomal degradation and multi-stage growth inhibition.\",\n      \"method\": \"Chemical genomic profiling, direct binding assay (thermal shift/pull-down), ATPase assay, proteasome activity assay\",\n      \"journal\": \"ACS infectious diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding demonstrated plus functional ATPase and chaperone activity assays, single lab, two orthogonal methods\",\n      \"pmids\": [\"33689276\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PfHop inhibits the ATPase activity of recombinant PfHsp90 while stimulating the ATPase activity of PfHsp70-1 in vitro. PfHop behaves primarily as an elongated dimer as characterized by small-angle X-ray scattering.\",\n      \"method\": \"In vitro ATPase assay, small-angle X-ray scattering, circular dichroism\",\n      \"journal\": \"Biochimica et biophysica acta. Proteins and proteomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstituted ATPase assay with recombinant proteins plus SAXS structural characterization, single lab\",\n      \"pmids\": [\"31525467\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Solution structure of full-length recombinant PfHsp90 characterized by small-angle X-ray scattering reveals an open, highly elongated and flexible homodimer. PfHsp90 interacts with adenosine nucleotides via the N-terminal domain; Mg2+ is critical for strong nucleotide binding. The C-terminal domain is essential for dimerization.\",\n      \"method\": \"Small-angle X-ray scattering (SAXS), isothermal titration calorimetry/fluorescence-based nucleotide binding assays, domain-deletion constructs\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — SAXS-based solution structure plus nucleotide binding assays with domain truncations, single lab\",\n      \"pmids\": [\"32679196\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A cryptic C-terminal binding site on PfHsp90 interacts specifically with ATP; limited proteolysis experiments suggest association with ATP, dATP, and ADP but not AMP or GTP. Mutagenesis studies were used to interrogate the molecular basis of this interaction.\",\n      \"method\": \"Affinity experiments with lysine-reactive nucleotide analog and ATP resin, limited proteolysis, site-directed mutagenesis, in silico analysis\",\n      \"journal\": \"Bioorganic & medicinal chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro affinity and proteolysis assays with mutagenesis, single lab, novel finding not yet independently replicated\",\n      \"pmids\": [\"40907219\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Two p23 co-chaperones (Pfp23A and Pfp23B) are present in P. falciparum and both inhibit the ATPase activity of recombinant PfHsp90 in vitro, validating them as functional Hsp90 co-chaperones. Pfp23A is more structurally stable than Pfp23B.\",\n      \"method\": \"Recombinant protein expression, in vitro ATPase assay, thermal stability assay, small-angle X-ray scattering\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstituted ATPase assay with recombinant proteins plus SAXS, single lab\",\n      \"pmids\": [\"29191421\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Two HSP90 inhibitors (geldanamycin and AUY-922) targeting the identical ATP-binding site of PfHsp90 show dramatically different resistance profiles in P. falciparum. Conditional HSP90 knockdown increases geldanamycin sensitivity but leaves AUY-922 activity unaffected, suggesting AUY-922 may engage multiple Hsp90 family members. The A41S mutation in the ATP-binding site enhances AUY-922 binding affinity yet correlates with resistance.\",\n      \"method\": \"Drug resistance selection, yeast complementation, conditional knockdown, in vitro binding assays, in silico analysis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional knockdown plus binding assays plus genetic epistasis, preprint not yet peer-reviewed\",\n      \"pmids\": [\"41279590\"],\n      \"is_preprint\": true,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"PfHsp90 (PF3D7_0308500) is an essential ATP-dependent molecular chaperone that exists as a highly flexible homodimer with the highest ATPase activity among known Hsp90 orthologues; it forms multi-chaperone complexes with PfHsp70, PfHop, PfPP5, PfFKBP35, PfAha1, Pfp23, and PfCRT in the parasite cytosol, directly chaperones the 26S proteasome to promote proteasome hydrolysis, acts as a transcriptional repressor of PfSIR2A/B by recruiting H3K9me3 to their promoters, maintains PfSir2A protein stability and HDAC activity, appears on the female gamete surface where it is required for fertilization, and its transcription is activated at febrile temperatures by the ApiAP2 transcription factor PfAP2-HS; inhibition of PfHsp90 by geldanamycin or other ATP-competitive inhibitors arrests intraerythrocytic development primarily at the ring-to-trophozoite transition and causes parasite death.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PfHsp90 (PF3D7_0308500) is an essential ATP-dependent molecular chaperone of the intraerythrocytic malaria parasite whose inhibition arrests development at the ring-to-trophozoite transition and causes parasite death [#0, #3]. The full-length recombinant protein exhibits the highest ATPase activity of any known Hsp90 orthologue—roughly six-fold that of human Hsp90—and is potently inhibited by geldanamycin [#1]; structural work shows it is an open, highly elongated and flexible homodimer whose N-terminal domain binds adenosine nucleotides in a Mg2+-dependent manner and whose C-terminal domain drives dimerization [#22, #6]. PfHsp90 nucleates a cytosolic multi-chaperone machine, associating with PfHsp70, PfHop, the TPR-domain phosphatase PfPP5 and immunophilin PfFKBP35 (the latter docking onto the C-terminal MEEVD pentapeptide), and its ATPase cycle is tuned by co-chaperones—stimulated by PfAha1 and suppressed by Pfp23 and PfHop [#3, #7, #8, #10, #9, #21]. Beyond canonical chaperoning, PfHsp90 directly promotes 26S proteasome hydrolysis [#17] and has acquired nuclear regulatory roles at febrile temperatures: it acts as a transcriptional repressor of PfSIR2A/B by recruiting the H3K9me3 mark to their promoters and physically stabilizes PfSir2A protein and its histone deacetylase activity, thereby controlling var-gene silencing [#15, #16]. Its own transcription is induced at febrile temperatures by the ApiAP2 factor PfAP2-HS [#14], and the protein is displayed on the female gamete surface where it is required for fertilization [#18]. The conformational dynamics of its ATP-binding pocket differ from the human enzyme, a feature exploited to develop parasite-selective inhibitors [#12, #11].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Establishing that PfHsp90 is a genuine, druggable chaperone required showing it binds ATP, assembles into oligomeric complexes, and that its inhibition blocks a defined developmental step.\",\n      \"evidence\": \"ATP-binding and geldanamycin-inhibition assays on recombinant protein, plus sedimentation/SEC showing ~300 kDa Hsp70-containing complexes with stage-specific growth arrest in P. falciparum\",\n      \"pmids\": [\"12584193\", \"14514358\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Complex composition beyond Hsp70 not resolved at this stage\", \"Direct client proteins not identified\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7, W2\"}]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"The identity of the co-chaperones assembling on PfHsp90 was mapped by defining TPR-domain partners that dock the chaperone into functional complexes.\",\n      \"evidence\": \"Co-immunoprecipitation of native PfPP5, PfFKBP35 and PfCN with PfHsp90, with domain-deletion and synergy growth assays in P. falciparum\",\n      \"pmids\": [\"11737864\", \"15339915\", \"15850699\", \"15811524\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether these interactions are direct or bridged by other chaperones\", \"Client proteins folded by the assembled complex unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Quantifying the enzymatic and structural properties revealed PfHsp90 as an unusually hyperactive ATPase with a defined N-terminal drug pocket, rationalizing its inhibitor sensitivity.\",\n      \"evidence\": \"In vitro ATPase assays on full-length recombinant protein, MS-based acetylation mapping, and a 2.3 Å crystal structure of the N-terminal domain in apo and ADP states\",\n      \"pmids\": [\"20837488\", \"20635416\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length crystal structure not solved\", \"Functional role of the acetylation site in vivo untested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Delineating how co-chaperones tune the ATPase cycle clarified the regulatory logic of the chaperone machine.\",\n      \"evidence\": \"SPR/NMR mapping of PfFKBP35-TPR binding the C-terminal MEEVD, plus reconstituted ATPase assays and mutagenesis showing Pfp23 suppresses and PfAha1 stimulates PfHsp90 ATPase in P. falciparum proteins\",\n      \"pmids\": [\"19691130\", \"20140477\", \"22100910\", \"22005844\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Order of co-chaperone loading during the catalytic cycle not established\", \"In vivo consequences of ATPase modulation on client folding unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrating that PfHsp90's ATP-pocket dynamics differ from the human enzyme opened a route to parasite-selective inhibitors.\",\n      \"evidence\": \"SPR with harmine identifying Arg98 as a selectivity determinant, and structure-based design of 7-azaindoles binding only the parasite N-terminal domain, validated by yeast complementation and dynamics-altering mutants\",\n      \"pmids\": [\"22615284\", \"24580531\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Selectivity determinants not yet translated to in vivo efficacy in these studies\", \"Impact on the assembled multi-chaperone complex not tested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Interactome profiling linked PfHsp90 to drug-resistance machinery, connecting chaperone function to chloroquine action.\",\n      \"evidence\": \"LC-MS/MS pulldown identifying PfCRT association and PU-H71/chloroquine synergy in P. falciparum in vitro and a P. berghei mouse model\",\n      \"pmids\": [\"24098696\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect PfCRT interaction unresolved\", \"Mechanism by which PfHsp90 influences PfCRT function unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The transcriptional context of PfHsp90 was defined at both ends—how its own gene is induced by heat and how it in turn controls chromatin at febrile temperatures.\",\n      \"evidence\": \"Conditional knockout/ChIP showing PfAP2-HS activates hsp90 transcription at febrile temperatures, and ChIP plus inhibitor assays showing PfHsp90 represses PfSIR2A/B by recruiting H3K9me3 in P. falciparum 3D7\",\n      \"pmids\": [\"34400833\", \"33538363\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How a cytosolic chaperone accesses promoters and directs H3K9me3 mechanistically unclear\", \"Whether repression is direct or via chaperoned nuclear factors unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The chromatin-regulatory role was refined to a direct chaperone-client relationship with a sirtuin deacetylase governing antigenic variation.\",\n      \"evidence\": \"Co-IP and inhibitor treatment (17-AAG, Radicicol) showing PfHsp90 stabilizes PfSir2A protein and HDAC activity, with var-gene derepression on inhibition in P. falciparum 3D7\",\n      \"pmids\": [\"36121150\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of PfHsp90-PfSir2A recognition undefined\", \"Contribution relative to other var-silencing pathways unquantified\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Unbiased proteome profiling identified the proteasome as a direct functional client, extending PfHsp90 beyond classical folding into proteostasis control.\",\n      \"evidence\": \"Thermal proteome profiling after PfHsp90 inhibition plus biochemical proteasome-activity assays using selective inhibitors in P. falciparum\",\n      \"pmids\": [\"38492573\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which proteasome subunits PfHsp90 engages directly not resolved\", \"Stoichiometry and dynamics of the chaperone-proteasome interaction unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Solution-structure and nucleotide-binding studies mapped the conformational and cryptic-site features that distinguish PfHsp90 and complicate inhibitor targeting.\",\n      \"evidence\": \"SAXS showing an open flexible homodimer with C-terminal-driven dimerization, limited proteolysis identifying a cryptic C-terminal ATP site, and conditional-knockdown/binding assays contrasting geldanamycin versus AUY-922 resistance (bioRxiv preprint for #25)\",\n      \"pmids\": [\"32679196\", \"40907219\", \"41279590\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological role of the cryptic C-terminal nucleotide site untested in vivo\", \"Mechanism of AUY-922 resistance despite enhanced binding unresolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PfHsp90's diverse activities—cytosolic client folding, proteasome chaperoning, nuclear transcriptional repression, and gamete-surface fertilization function—are partitioned and regulated within a single essential chaperone remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking cytosolic chaperone activity to its nuclear and surface roles\", \"Full endogenous client repertoire not defined\", \"Mechanism of gamete-surface targeting unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140662\", \"supporting_discovery_ids\": [1, 3, 17]},\n      {\"term_id\": \"GO:0016887\", \"supporting_discovery_ids\": [1, 9, 10, 21, 24]},\n      {\"term_id\": \"GO:0005524\", \"supporting_discovery_ids\": [2, 6, 22, 23]},\n      {\"term_id\": \"GO:0051082\", \"supporting_discovery_ids\": [17, 20]},\n      {\"term_id\": \"GO:0042803\", \"supporting_discovery_ids\": [22]},\n      {\"term_id\": \"GO:0003714\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 3, 7]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [15, 16]},\n      {\"term_id\": \"GO:0009986\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006457\", \"supporting_discovery_ids\": [1, 3, 20]},\n      {\"term_id\": \"GO:0009408\", \"supporting_discovery_ids\": [3, 14]},\n      {\"term_id\": \"GO:0043161\", \"supporting_discovery_ids\": [17]},\n      {\"term_id\": \"GO:0006342\", \"supporting_discovery_ids\": [15, 16]},\n      {\"term_id\": \"GO:0009566\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"complexes\": [\n      \"PfHsp90-PfHsp70 hetero-oligomeric (~300 kDa, 11S) chaperone complex [#0]\",\n      \"PfHsp90-PfHsp70-PfPP5-tubulin heat-shock multi-chaperone complex [#3]\",\n      \"PfHsp90-PfHsp70-PfHop complex [#7]\",\n      \"PfHsp90-26S proteasome functional association [#17]\"\n    ],\n    \"partners\": [\n      \"PfHsp70 [#0, #3, #7]\",\n      \"PfPP5 (TPR-domain Ser/Thr phosphatase) [#4, #3]\",\n      \"PfFKBP35 (immunophilin, MEEVD-binding) [#5, #8]\",\n      \"PfCN (calcineurin) [#5]\",\n      \"PfHop [#7, #21]\",\n      \"Pfp23 / Pfp23A / Pfp23B (co-chaperone, ATPase suppressor) [#9, #24]\",\n      \"PfAha1 (co-chaperone, ATPase stimulator) [#10]\",\n      \"PfCRT (direct or indirect) [#13]\",\n      \"PfAP2-HS (transcriptional activator of hsp90) [#14]\",\n      \"PfSir2A (chaperone client/stabilized) [#16]\"\n    ],\n    \"other_free_text\": [\n      \"Highest ATPase activity of any known Hsp90 orthologue, ~6-fold above human Hsp90 [#1]\",\n      \"Open, highly elongated flexible homodimer; C-terminal domain required for dimerization [#22]\",\n      \"N-terminal ATP-binding pocket with distinct conformational dynamics enabling parasite-selective inhibitors (harmine/Arg98, 7-azaindoles) [#11, #12, #6]\",\n      \"Cryptic C-terminal nucleotide-binding site selective for ATP/dATP/ADP [#23]\",\n      \"Inhibition (geldanamycin, 17-AAG, radicicol, PU-H71, imidazopyridazines, violacein) arrests development at ring-to-trophozoite transition and kills parasites [#0, #19, #20]\",\n      \"Divergent resistance profiles between geldanamycin and AUY-922 despite shared ATP-site targeting (preprint) [#25]\"\n    ]\n  }\n}","audit_flag":{"gene":"PF3D7_0308500","tier":"IDENTITY_CHECK","verdict":"identity unverified","subtype":"names_other_cards","uniprot_band":"","rules_fired":"R12","issue":"No cited paper names this card; 27 of 27 cited papers name other catalogue genes (PF3D7_0708400, PF3D7_0818900, PF3D7_0306200). The summary may describe one of those genes."},"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_0308500","name":null,"product":"activator of Hsp90 ATPase, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_0406700","name":null,"product":"activator of Hsp90 ATPase, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_0834200","name":null,"product":"activator of Hsp90 ATPase, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"","evaluation":null}