{"gene":"PF3D7_0708400","run_date":"2026-09-08T12:51:27","timeline":{"discoveries":[{"year":2003,"finding":"PfHsp90 exists in ~300 kDa, 11S complexes in P. falciparum that contain PfHsp70; geldanamycin (GA) inhibits parasite growth by arresting Ring-to-trophozoite transition, selectively inhibits PfHsp90 phosphorylation, and disrupts the PfHsp90 multi-chaperone complex, establishing PfHsp90 as essential for intraerythrocytic development.","method":"Sedimentation analysis, size exclusion chromatography, homology modeling of GA-binding pocket, drug inhibition assays, metabolic labeling/phosphorylation analysis, flow cytometry","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal biochemical methods (sedimentation, SEC, phosphorylation assay, growth inhibition), single lab but convergent results","pmids":["12584193"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2003,"finding":"Recombinant PfHsp90 binds ATP in vitro, and this ATP-binding activity is specifically inhibited by geldanamycin; PfHsp90 mRNA is predominantly expressed in ring and trophozoite stages while the protein is present in all asexual blood stages.","method":"Recombinant protein expression, ATP-binding assay, drug inhibition assay, stage-specific protein/mRNA analysis","journal":"Malaria journal","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vitro ATP binding and specific GA inhibition demonstrated in single lab with single method per finding","pmids":["14514358"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"},{"species":"Plasmodium falciparum","strain":"W2"}]},{"year":2004,"finding":"The PfHsp90 multi-chaperone complex, which includes PfHsp70, PfPP5, and tubulin, mediates heat shock-dependent cytoprotection and promotes Ring-to-trophozoite progression; GA disrupts this complex and blocks temperature-dependent developmental promotion.","method":"Flow cytometry, geldanamycin-based complex disruption, co-immunoprecipitation/complex isolation","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — complex composition determined by co-immunoprecipitation + functional rescue by heat shock abrogated by GA, single lab","pmids":["15339915"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2001,"finding":"PfPP5 (a tetratricopeptide repeat serine/threonine phosphatase) co-immunoprecipitates with PfHsp90 in P. falciparum, establishing a direct interaction between these two proteins in the parasite.","method":"Co-immunoprecipitation of native proteins","journal":"BMC microbiology","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single co-IP experiment, single lab","pmids":["11737864"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"finding":"PfFKBP35 associates with PfHsp90 via its TPR domain in vivo; geldanamycin and ascomycin (a FK506 derivative) act synergistically to inhibit P. falciparum erythrocytic growth, consistent with functional coupling of FKBP35 and Hsp90.","method":"Co-immunoprecipitation, drug synergy assay in cultured parasites","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP established interaction; functional synergy of inhibitors corroborates coupling, single lab","pmids":["15850699"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"finding":"Plasmodial calcineurin (PfCN) associates with PfHsp90 in vivo; GA disrupts this PfHsp90–calcineurin association but cyclosporin A does not, demonstrating that PfHsp90 is required for stabilizing the calcineurin complex in the parasite.","method":"Co-immunoprecipitation with native parasite extracts, GA and CsA treatment","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP combined with pharmacological dissection in parasite culture, single lab","pmids":["15811524"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"Full-length recombinant PfHsp90 exhibits the highest ATPase activity among known Hsp90 orthologs (6-fold higher than human Hsp90); GA inhibits PfHsp90 ATPase activity more robustly than human Hsp90. Mass spectrometry identified an acetylation site on PfHsp90 that overlaps with the Aha1 and p23 co-chaperone binding domain; treatment with a histone deacetylase inhibitor partially dissociates the PfHsp90 complex, suggesting acetylation modulates multichaperone assembly.","method":"In vitro ATPase assay with purified recombinant protein, mass spectrometry, HDAC inhibitor treatment and complex analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic reconstitution with recombinant protein, MS-identified PTM site, functional dissection with inhibitors, single lab with multiple orthogonal methods","pmids":["20837488"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"Crystal structure of the N-terminal ATP-binding domain of PfHsp90 was solved in apo and ADP-bound states at 2.3 Å resolution, revealing high structural similarity to human Hsp90 in the drug-binding pocket and confirming the same mode of geldanamycin binding.","method":"X-ray crystallography","journal":"Proteins","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure at 2.3 Å resolution, apo and ligand-bound forms, single lab","pmids":["20635416"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"finding":"PfHsp90 expressed in yeast (replacing endogenous yeast Hsp90) confers differential sensitivity to geldanamycin vs. radicicol relative to human Hsp90, demonstrating intrinsic pharmacological differences between PfHsp90 and its human ortholog in a living cellular context.","method":"Yeast complementation assay with isogenic strains, drug sensitivity comparison","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic complementation in isogenic yeast strains with drug sensitivity readout, single lab","pmids":["19320098"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"finding":"PfHop co-localizes with PfHsp70 and PfHsp90 in trophozoite-stage parasites and forms a complex with both chaperones as demonstrated by gel filtration and co-immunoprecipitation, suggesting PfHop mediates the functional interaction between PfHsp70 and PfHsp90.","method":"Immunofluorescence microscopy (co-localization), gel filtration chromatography, co-immunoprecipitation","journal":"Cell stress & chaperones","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP and gel filtration establish ternary complex; direct localization, single lab","pmids":["22005844"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"Recombinant Pfp23 (P. falciparum p23 co-chaperone) directly interacts with PfHsp90 and suppresses its ATPase activity; site-directed mutagenesis identified residues K91, H93, W94, and K96 in Pfp23 as critical for PfHsp90 binding.","method":"In vitro ATPase assay, recombinant protein interaction studies, site-directed mutagenesis, citrate synthase aggregation suppression assay","journal":"Cellular and molecular life sciences","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay (ATPase suppression), mutagenesis of binding interface, multiple orthogonal methods, single lab","pmids":["20140477"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"finding":"PfAha1 (P. falciparum Aha1 co-chaperone) interacts with PfHsp90 in an ATP- and MgCl2-dependent manner, as established by split-ubiquitin assay and GST pull-down; the interaction is competed by Pfp23. Residue N108 of PfAha1 is essential for PfHsp90 binding by site-directed mutagenesis. PfAha1 stimulates PfHsp90 ATPase activity.","method":"Split-ubiquitin yeast assay, GST pull-down, site-directed mutagenesis, ATPase activity assay","journal":"The international journal of biochemistry & cell biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro ATPase reconstitution, mutagenesis of interface residue, multiple orthogonal binding assays, single lab","pmids":["22100910"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"finding":"The TPR domain of PfFKBP35 was crystallized and its interaction with the PfHsp90 C-terminal MEEVD pentapeptide was demonstrated by surface plasmon resonance and NMR; mutagenesis of conserved carboxylate-clamp residues abolished Hsp90 MEEVD binding, establishing the molecular basis of PfFKBP35–PfHsp90 interaction.","method":"X-ray crystallography, surface plasmon resonance, NMR spectroscopy, site-directed mutagenesis","journal":"Protein science","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with SPR, NMR, and mutagenesis in single study; multiple orthogonal methods rigorously validate interaction","pmids":["19691130"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2012,"finding":"Introducing the human or P. falciparum charged linker sequences into yeast Hsp90 showed that linker sequence (not just length) modulates ATPase activity, cochaperone interaction, and conformation, establishing that the extended charged linker unique to PfHsp90 is functionally significant.","method":"Chimeric Hsp90 construction in yeast, in vitro ATPase assay, biophysical characterization","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro ATPase plus in vivo yeast assay, Plasmodium linker used as a tool reagent; functional attribution to PfHsp90's linker specifically is indirect","pmids":["22315411"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2012,"finding":"Site-directed mutagenesis of Arg98 in PfHsp90 abolished selective binding of the harmine alkaloid, identifying Arg98 as critical for the species-selective binding of harmine to PfHsp90's ATP-binding domain.","method":"Site-directed mutagenesis, surface plasmon resonance","journal":"Antimicrobial agents and chemotherapy","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — mutagenesis plus SPR binding in single lab; functional consequence (species selectivity) directly linked to residue","pmids":["22615284"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"finding":"The ATP-binding pocket of PfHsp90 has a Plasmodium-specific structural extension that differs in tertiary structure and dynamics (not sequence) from human Hsp90; exploiting this dynamic difference enabled discovery of 7-azaindole compounds that exclusively bind recombinant PfHsp90 N-terminal domain but not human Hsp90, and preferentially inhibit yeast complemented with PfHsp90.","method":"Structural/dynamics analysis, in vitro binding assays with recombinant domains, yeast complementation growth assay","journal":"Journal of medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — combined structural, biochemical, and genetic complementation evidence; single lab","pmids":["24580531"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"finding":"LC-MS/MS of PfHsp90 interactors identified the P. falciparum chloroquine resistance transporter (PfCRT) as a direct or indirect interactor of PfHsp90; the PfHsp90 inhibitor PU-H71 synergizes with chloroquine in vitro and in the P. berghei mouse model, suggesting PfHsp90 chaperones PfCRT.","method":"LC-MS/MS interactomics of PfHsp90 pulldown, surface plasmon resonance (PU-H71 affinity), ATPase assay, in vitro drug synergy, P. berghei mouse model","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MS-identified interaction with functional pharmacological follow-up; interactome data supports but does not prove direct binding of PfCRT to PfHsp90","pmids":["24098696"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":2019,"finding":"PfHsp90 inhibition (by SNX-0723 and other inhibitors) kills P. falciparum at both liver and blood stages; expression analysis and time-course inhibition studies support a role for PfHsp90 in late liver-stage parasite development. PfHsp90 inhibitor SNX-0723 combined with PIK-75 synergistically reduces liver-stage parasite load.","method":"Cell-based liver- and blood-stage parasite assays, time-course inhibition, expression analysis, drug combination studies","journal":"Antimicrobial agents and chemotherapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based assays in two life cycle stages with time-course and combination readouts; liver-stage role inferred, not genetically validated","pmids":["29339390"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"PfAP2-HS transcription factor activates transcription of hsp90 (and hsp70-1) at elevated febrile temperatures; parasites lacking PfAP2-HS show reduced heat-shock survival and severe growth defects, establishing that hsp90 upregulation at fever temperatures is under PfAP2-HS control.","method":"Conditional/engineered gene knockout, transcriptional analysis, ChIP (promoter binding), heat-shock survival assay","journal":"Nature microbiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with defined phenotype, ChIP-confirmed promoter binding, transcriptional and growth readouts, single rigorous study","pmids":["34400833"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"PfHsp90 acts as a transcriptional repressor of PfSIR2A and PfSIR2B by occupying their promoter-proximal regions and recruiting H3K9me3, inducing a heterochromatic state; this repression is reversed by GA or radicicol (PfHsp90 inhibitors), leading to de-repression of var genes at sub-telomeric regions.","method":"ChIP (chromatin immunoprecipitation for PfHsp90 at promoters and H3K9me3), drug treatment with PfHsp90 inhibitors, transcriptional analysis","journal":"Molecular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP establishes PfHsp90 promoter occupancy and histone modification linkage; pharmacological validation; single lab","pmids":["33538363"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2024,"finding":"Thermal proteome profiling following selective PfHsp90 inhibition (using Tropane 1 and XL888 derivatives) identified the 26S proteasome as enriched among proteins with perturbed stability; biochemical and cellular studies showed that PfHsp90 directly promotes proteasome hydrolytic activity by chaperoning the active 26S complex.","method":"Thermal proteome profiling, biochemical proteasome activity assays, cellular imaging/analysis, selective PfHsp90 inhibitor treatment","journal":"Cell chemical biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — thermal proteome profiling combined with biochemical and cellular validation of proteasome chaperoning; rigorous multi-method study, single lab","pmids":["38492573"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2023,"finding":"HSP90 is present on the surface of Plasmodium female gametes; anti-Hsp90 antibodies inhibit fertilization, and peptide competition experiments established that female gamete surface HSP90 is required for gamete fertilization in the mosquito.","method":"Phage peptide display screening, antibody binding assays, fertilization inhibition assay","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct antibody blocking of fertilization with Hsp90 identification; species not fully specified but Plasmodium gamete experiments directly conducted","pmids":["38131664"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"finding":"Recombinant PfHsp90 behaves as an elongated, flexible homodimer in solution (sub-micromolar dissociation constant); its C-terminal domain is required for dimerization. PfHsp90 and PfHsp90NMD interact with adenosine nucleotides via the NTD, and Mg2+ is critical for strong nucleotide binding.","method":"Small-angle X-ray scattering (SAXS), size exclusion chromatography, isothermal titration calorimetry","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — SAXS and solution biophysics with domain constructs; dimerization and nucleotide binding characterized, single lab","pmids":["32679196"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"finding":"Isothermal titration calorimetry showed that PfHsp90 has distinct thermodynamic signatures for ADP vs. ATP binding: ADP interaction is enthalpy-driven but entropy-opposed, while ATP interaction is driven by both enthalpy and entropy, indicating state-dependent conformational properties of PfHsp90.","method":"Isothermal titration calorimetry, comparative thermodynamic analysis","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — rigorous thermodynamic measurement with recombinant protein; single lab comparative study","pmids":["30797004"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2026,"finding":"In vitro selection experiments identified 10 distinct resistance mutations to geldanamycin in PfHsp90 conferring up to 22-fold resistance; AUY-922 (binding same ATP site) yielded only one mutation (A41S) with 2-fold resistance. The A41S mutation paradoxically increased AUY-922 binding affinity via additional hydrogen bonding yet conferred resistance; conditional PfHsp90 knockdown increased geldanamycin sensitivity but not AUY-922 activity, suggesting different target dependencies.","method":"In vitro drug selection, whole-genome sequencing of resistant parasites, conditional knockdown, binding affinity measurement, yeast complementation","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple selection experiments, genetic knockdown, binding assays, and yeast epistasis all in one rigorous study","pmids":["42406593"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"finding":"In vitro experiments demonstrated that PfHsp90 has a cryptic C-terminal nucleotide-binding site: an ATP-reactive lysine-reactive probe and an ATP resin specifically interacted with PfHsp90 C-terminal truncation; limited proteolysis showed association with ATP, dATP, and ADP but not AMP or GTP; mutagenesis defined molecular determinants of this interaction.","method":"Affinity chromatography (ATP resin), lysine-reactive nucleotide analog labeling, limited proteolysis, site-directed mutagenesis, in silico analysis","journal":"Bioorganic & medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical assays with domain constructs plus mutagenesis; single lab, novel finding without independent replication","pmids":["40907219"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"PfHsp90 (PF3D7_0708400) is an essential cytosolic molecular chaperone in P. falciparum with the highest known ATPase activity among Hsp90 orthologs; it forms ~300 kDa hetero-oligomeric complexes with PfHsp70, PfPP5, tubulin, and co-chaperones (PfHop, Pfp23, PfAha1, PfFKBP35), whose assembly is regulated by acetylation and co-chaperone binding; it is required for Ring-to-trophozoite progression and for chaperoning the active 26S proteasome; its transcription at febrile temperatures is activated by the PfAP2-HS transcription factor; it additionally functions as a transcriptional repressor by occupying the PfSIR2A/B promoters and recruiting H3K9me3; surface HSP90 on female gametes is required for fertilization; and its N-terminal ATP-binding domain and a cryptic C-terminal nucleotide-binding site are both druggable, with geldanamycin resistance mutations mapping throughout the binding pocket while AUY-922 resistance is restricted to a single residue near the ATP site."},"narrative":{"mechanistic_narrative":"PfHsp90 (PF3D7_0708400) is an essential cytosolic molecular chaperone of Plasmodium falciparum that drives intraerythrocytic development, with geldanamycin inhibition arresting the Ring-to-trophozoite transition [PMID:12584193, PMID:15339915]. It assembles into ~300 kDa, 11S hetero-oligomeric multi-chaperone complexes containing PfHsp70, the TPR-phosphatase PfPP5, and tubulin, whose integrity is required for heat-shock-dependent cytoprotection and developmental progression [PMID:12584193, PMID:15339915, PMID:11737864]. As an elongated, C-terminally dimerizing ATPase, PfHsp90 possesses the highest ATPase activity of any known Hsp90 ortholog, and its cycle is tuned by a suite of co-chaperones — the p23 orthologue Pfp23 suppresses ATPase activity while PfAha1 stimulates it, with the two competing for binding, and the TPR co-chaperones PfHop, PfFKBP35, and PfPP5 docking onto the C-terminal MEEVD motif [PMID:20837488, PMID:22005844, PMID:20140477, PMID:22100910, PMID:19691130, PMID:32679196]. Complex assembly is further modulated by an acetylation site overlapping the Aha1/p23 interface [PMID:20837488]. Beyond canonical client folding — where it stabilizes calcineurin, chaperones the active 26S proteasome, and interacts with the drug-resistance transporter PfCRT [PMID:15811524, PMID:24098696, PMID:38492573] — PfHsp90 has a nuclear function as a transcriptional repressor, occupying the PfSIR2A/B promoters and recruiting H3K9me3 to enforce heterochromatin [PMID:33538363], while its own febrile-temperature induction is driven by the PfAP2-HS transcription factor [PMID:34400833]. Surface HSP90 on female gametes is required for fertilization in the mosquito stage [PMID:38131664]. Its N-terminal ATP-binding pocket carries a Plasmodium-specific structural extension that confers pharmacological divergence from human Hsp90 and enables species-selective inhibitors, and a cryptic C-terminal nucleotide-binding site provides a second druggable pocket [PMID:20635416, PMID:24580531, PMID:42406593, PMID:40907219].","teleology":[{"year":2001,"claim":"Establishing that PfHsp90 physically associates with a parasite TPR phosphatase addressed whether the chaperone recruits regulatory partners in P. falciparum.","evidence":"Co-immunoprecipitation of native PfPP5 with PfHsp90 from parasite extract","pmids":["11737864"],"confidence":"Medium","gaps":["Single co-IP without reciprocal validation","Functional consequence of the PfPP5-PfHsp90 interaction not defined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2003,"claim":"The unknown essentiality and complex context of PfHsp90 was resolved by showing it forms ~300 kDa Hsp70-containing complexes and that its inhibition arrests development, establishing it as a bona fide drug target.","evidence":"Sedimentation/SEC complex analysis, geldanamycin growth inhibition, and phosphorylation assays; recombinant ATP-binding and GA-inhibition assays","pmids":["12584193","14514358"],"confidence":"High","gaps":["Stage-specific mechanism of the Ring-to-trophozoite arrest not defined","Full complex composition not yet enumerated"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium falciparum","strain":"3D7"},{"species":"Plasmodium falciparum","strain":"W2"}]},{"year":2005,"claim":"Defining the composition and clientele of the PfHsp90 complex addressed which parasite factors depend on the chaperone, expanding it from PfHsp70/PfPP5/tubulin to FKBP35 and calcineurin.","evidence":"Co-immunoprecipitation and GA/CsA pharmacological dissection plus GA-ascomycin synergy in cultured parasites","pmids":["15339915","15850699","15811524"],"confidence":"Medium","gaps":["Direct vs. indirect binding of calcineurin not distinguished","Client-folding mechanism not reconstituted"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"claim":"Biochemical and structural reconstitution answered how PfHsp90's catalytic cycle is regulated, revealing record-high ATPase activity, acetylation-dependent assembly, and a solved N-terminal drug-binding pocket.","evidence":"In vitro ATPase assays, mass spectrometry of PTM sites, HDAC inhibitor complex analysis, Pfp23 ATPase-suppression mutagenesis, and X-ray crystallography of the NTD","pmids":["20837488","20140477","20635416"],"confidence":"High","gaps":["Physiological trigger for acetylation in vivo unknown","Full-length conformational cycle not captured crystallographically"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"claim":"Mapping the co-chaperone interfaces resolved how the ATPase cycle is bidirectionally controlled, showing PfAha1 stimulates and Pfp23 suppresses activity while PfHop and PfFKBP35 bridge to PfHsp70 via the MEEVD motif.","evidence":"Split-ubiquitin, GST pull-down, ATPase assays, interface mutagenesis, gel filtration/co-IP, and crystallography plus SPR/NMR of the FKBP35 TPR-MEEVD interaction","pmids":["22100910","22005844","19691130"],"confidence":"High","gaps":["Temporal ordering of co-chaperone exchange on the cycle not resolved","In vivo stoichiometry of the assembled complex unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"claim":"The question of whether PfHsp90 can be selectively targeted over human Hsp90 was addressed by identifying a Plasmodium-specific structural/dynamic extension in the ATP pocket and linker that confers pharmacological divergence.","evidence":"Yeast complementation drug-sensitivity comparisons, chimeric-linker biophysics, SPR-mapped residue Arg98 for harmine selectivity, and 7-azaindole selective binding studies","pmids":["19320098","22315411","22615284","24580531"],"confidence":"Medium","gaps":["Selectivity demonstrated largely in surrogate/recombinant systems","In-parasite efficacy of selective scaffolds not established here"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"claim":"Solution biophysics and life-cycle profiling extended the mechanistic picture by defining PfHsp90 as a C-terminally dimerizing, elongated homodimer with state-dependent nucleotide thermodynamics and roles beyond blood stage.","evidence":"SAXS, SEC, ITC of ADP vs ATP binding, and liver/blood-stage inhibitor killing with time-course and combination studies","pmids":["32679196","30797004","29339390"],"confidence":"Medium","gaps":["Liver-stage role inferred pharmacologically, not genetically validated","Client repertoire in liver stage undefined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"claim":"Discovery of nuclear and transcriptional functions redefined PfHsp90 beyond cytosolic folding, showing it both is induced by PfAP2-HS at fever temperatures and itself represses PfSIR2A/B via H3K9me3-directed heterochromatin.","evidence":"PfAP2-HS knockout with ChIP and heat-shock survival assays; ChIP of PfHsp90 and H3K9me3 at SIR2 promoters with inhibitor-reversal transcriptional analysis","pmids":["34400833","33538363"],"confidence":"High","gaps":["Mechanism recruiting PfHsp90 to specific promoters unknown","Link between chaperone activity and repressor function not established"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2023,"claim":"Identifying surface HSP90 on female gametes addressed whether the chaperone has a role in transmission, showing it is required for fertilization in the mosquito.","evidence":"Phage peptide display, antibody binding, and fertilization-inhibition/peptide-competition assays","pmids":["38131664"],"confidence":"Medium","gaps":["Mechanism by which a cytosolic chaperone reaches the gamete surface unresolved","Fertilization partner/receptor on the gamete surface unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"claim":"Unbiased target-engagement profiling identified the 26S proteasome as a PfHsp90 client, establishing that the chaperone directly sustains proteasomal hydrolytic activity.","evidence":"Thermal proteome profiling under selective inhibition with biochemical proteasome-activity and cellular validation","pmids":["38492573"],"confidence":"High","gaps":["Which proteasome subunit(s) PfHsp90 engages not defined","Structural basis of proteasome chaperoning unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2026,"claim":"Resistance selection and a newly mapped cryptic C-terminal site clarified the druggable landscape, showing distinct binding-pocket mutation profiles for geldanamycin versus AUY-922 and a second nucleotide-binding pocket.","evidence":"In vitro drug selection with whole-genome sequencing, conditional knockdown, binding-affinity and yeast complementation; ATP-resin/lysine-reactive probe labeling, limited proteolysis, and mutagenesis of the C-terminal site","pmids":["42406593","40907219"],"confidence":"High","gaps":["Physiological function of the cryptic C-terminal nucleotide site unknown","Mechanism of the A41S resistance paradox not fully resolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"How PfHsp90's cytosolic chaperone cycle is coordinated with its distinct nuclear-repressor, gamete-surface, and proteasome-chaperoning roles, and how its clientele shifts across life-cycle stages, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking chaperone ATPase cycle to transcriptional repression","Stage-specific client repertoire not mapped","Trafficking to gamete surface unexplained"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["~300 kDa / 11S PfHsp90 multi-chaperone complex containing PfHsp70, PfPP5, and tubulin","PfHsp90-PfHop-PfHsp70 ternary complex","PfHsp90-active 26S proteasome complex"],"partners":["PFHSP70","PFPP5","TUBULIN","PFHOP","PFP23","PFAHA1","PFFKBP35","PLASMODIAL CALCINEURIN (PFCN)","PFCRT","26S PROTEASOME"],"other_free_text":["Highest ATPase activity of any known Hsp90 ortholog (~6-fold above human Hsp90); GA inhibits PfHsp90 ATPase more robustly than human [#6].","Acetylation site overlapping the Aha1/p23 binding domain modulates multichaperone assembly [#6].","Elongated flexible homodimer requiring the C-terminal domain for dimerization; Mg2+ critical for nucleotide binding [#22].","N-terminal ATP-binding domain crystallized in apo and ADP-bound states; harbors a Plasmodium-specific structural/dynamic extension enabling species-selective inhibitors [#7, #15].","Cryptic C-terminal nucleotide-binding site reactive with ATP/dATP/ADP but not AMP or GTP [#25].","hsp90 transcription activated at febrile temperatures by PfAP2-HS [#18].","Geldanamycin resistance maps to multiple binding-pocket residues; AUY-922 resistance restricted to A41S with distinct target dependency [#24]."]}},"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 chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12584193","citation_count":190,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HSP90","heat shock protein 90","PfHSP90"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"20837488","id":"PMC_20837488","title":"Heat shock protein 90 as 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selectively inhibits PfHsp90 phosphorylation, and disrupts the PfHsp90 multi-chaperone complex, establishing PfHsp90 as essential for intraerythrocytic development.\",\n      \"method\": \"Sedimentation analysis, size exclusion chromatography, homology modeling of GA-binding pocket, drug inhibition assays, metabolic labeling/phosphorylation analysis, flow cytometry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal biochemical methods (sedimentation, SEC, phosphorylation assay, growth inhibition), single lab but convergent results\",\n      \"pmids\": [\"12584193\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Recombinant PfHsp90 binds ATP in vitro, and this ATP-binding activity is specifically inhibited by geldanamycin; PfHsp90 mRNA is predominantly expressed in ring and trophozoite stages while the protein is present in all asexual blood stages.\",\n      \"method\": \"Recombinant protein expression, ATP-binding assay, drug inhibition assay, stage-specific protein/mRNA analysis\",\n      \"journal\": \"Malaria journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vitro ATP binding and specific GA inhibition demonstrated in single lab with single method per finding\",\n      \"pmids\": [\"14514358\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"W2\"}]\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The PfHsp90 multi-chaperone complex, which includes PfHsp70, PfPP5, and tubulin, mediates heat shock-dependent cytoprotection and promotes Ring-to-trophozoite progression; GA disrupts this complex and blocks temperature-dependent developmental promotion.\",\n      \"method\": \"Flow cytometry, geldanamycin-based complex disruption, co-immunoprecipitation/complex isolation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — complex composition determined by co-immunoprecipitation + functional rescue by heat shock abrogated by GA, single lab\",\n      \"pmids\": [\"15339915\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PfPP5 (a tetratricopeptide repeat serine/threonine phosphatase) co-immunoprecipitates with PfHsp90 in P. falciparum, establishing a direct interaction between these two proteins in the parasite.\",\n      \"method\": \"Co-immunoprecipitation of native proteins\",\n      \"journal\": \"BMC microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single co-IP experiment, single lab\",\n      \"pmids\": [\"11737864\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PfFKBP35 associates with PfHsp90 via its TPR domain in vivo; geldanamycin and ascomycin (a FK506 derivative) act synergistically to inhibit P. falciparum erythrocytic growth, consistent with functional coupling of FKBP35 and Hsp90.\",\n      \"method\": \"Co-immunoprecipitation, drug synergy assay in cultured parasites\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP established interaction; functional synergy of inhibitors corroborates coupling, single lab\",\n      \"pmids\": [\"15850699\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Plasmodial calcineurin (PfCN) associates with PfHsp90 in vivo; GA disrupts this PfHsp90–calcineurin association but cyclosporin A does not, demonstrating that PfHsp90 is required for stabilizing the calcineurin complex in the parasite.\",\n      \"method\": \"Co-immunoprecipitation with native parasite extracts, GA and CsA treatment\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP combined with pharmacological dissection in parasite culture, single lab\",\n      \"pmids\": [\"15811524\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Full-length recombinant PfHsp90 exhibits the highest ATPase activity among known Hsp90 orthologs (6-fold higher than human Hsp90); GA inhibits PfHsp90 ATPase activity more robustly than human Hsp90. Mass spectrometry identified an acetylation site on PfHsp90 that overlaps with the Aha1 and p23 co-chaperone binding domain; treatment with a histone deacetylase inhibitor partially dissociates the PfHsp90 complex, suggesting acetylation modulates multichaperone assembly.\",\n      \"method\": \"In vitro ATPase assay with purified recombinant protein, mass spectrometry, HDAC inhibitor treatment and complex analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic reconstitution with recombinant protein, MS-identified PTM site, functional dissection with inhibitors, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"20837488\"],\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 was solved in apo and ADP-bound states at 2.3 Å resolution, revealing high structural similarity to human Hsp90 in the drug-binding pocket and confirming the same mode of geldanamycin binding.\",\n      \"method\": \"X-ray crystallography\",\n      \"journal\": \"Proteins\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure at 2.3 Å resolution, apo and ligand-bound forms, single lab\",\n      \"pmids\": [\"20635416\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PfHsp90 expressed in yeast (replacing endogenous yeast Hsp90) confers differential sensitivity to geldanamycin vs. radicicol relative to human Hsp90, demonstrating intrinsic pharmacological differences between PfHsp90 and its human ortholog in a living cellular context.\",\n      \"method\": \"Yeast complementation assay with isogenic strains, drug sensitivity comparison\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic complementation in isogenic yeast strains with drug sensitivity readout, single lab\",\n      \"pmids\": [\"19320098\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PfHop co-localizes with PfHsp70 and PfHsp90 in trophozoite-stage parasites and forms a complex with both chaperones as demonstrated by gel filtration and co-immunoprecipitation, suggesting PfHop mediates the functional interaction between PfHsp70 and PfHsp90.\",\n      \"method\": \"Immunofluorescence microscopy (co-localization), gel filtration chromatography, co-immunoprecipitation\",\n      \"journal\": \"Cell stress & chaperones\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP and gel filtration establish ternary complex; direct localization, single lab\",\n      \"pmids\": [\"22005844\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Recombinant Pfp23 (P. falciparum p23 co-chaperone) directly interacts with PfHsp90 and suppresses its ATPase activity; site-directed mutagenesis identified residues K91, H93, W94, and K96 in Pfp23 as critical for PfHsp90 binding.\",\n      \"method\": \"In vitro ATPase assay, recombinant protein interaction studies, site-directed mutagenesis, citrate synthase aggregation suppression assay\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay (ATPase suppression), mutagenesis of binding interface, 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 (P. falciparum Aha1 co-chaperone) interacts with PfHsp90 in an ATP- and MgCl2-dependent manner, as established by split-ubiquitin assay and GST pull-down; the interaction is competed by Pfp23. Residue N108 of PfAha1 is essential for PfHsp90 binding by site-directed mutagenesis. PfAha1 stimulates PfHsp90 ATPase activity.\",\n      \"method\": \"Split-ubiquitin yeast assay, GST pull-down, site-directed mutagenesis, ATPase activity assay\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro ATPase reconstitution, mutagenesis of interface residue, multiple orthogonal binding assays, single lab\",\n      \"pmids\": [\"22100910\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The TPR domain of PfFKBP35 was crystallized and its interaction with the PfHsp90 C-terminal MEEVD pentapeptide was demonstrated by surface plasmon resonance and NMR; mutagenesis of conserved carboxylate-clamp residues abolished Hsp90 MEEVD binding, establishing the molecular basis of PfFKBP35–PfHsp90 interaction.\",\n      \"method\": \"X-ray crystallography, surface plasmon resonance, NMR spectroscopy, site-directed mutagenesis\",\n      \"journal\": \"Protein science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with SPR, NMR, and mutagenesis in single study; multiple orthogonal methods rigorously validate interaction\",\n      \"pmids\": [\"19691130\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Introducing the human or P. falciparum charged linker sequences into yeast Hsp90 showed that linker sequence (not just length) modulates ATPase activity, cochaperone interaction, and conformation, establishing that the extended charged linker unique to PfHsp90 is functionally significant.\",\n      \"method\": \"Chimeric Hsp90 construction in yeast, in vitro ATPase assay, biophysical characterization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro ATPase plus in vivo yeast assay, Plasmodium linker used as a tool reagent; functional attribution to PfHsp90's linker specifically is indirect\",\n      \"pmids\": [\"22315411\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Site-directed mutagenesis of Arg98 in PfHsp90 abolished selective binding of the harmine alkaloid, identifying Arg98 as critical for the species-selective binding of harmine to PfHsp90's ATP-binding domain.\",\n      \"method\": \"Site-directed mutagenesis, surface plasmon resonance\",\n      \"journal\": \"Antimicrobial agents and chemotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis plus SPR binding in single lab; functional consequence (species selectivity) directly linked to residue\",\n      \"pmids\": [\"22615284\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The ATP-binding pocket of PfHsp90 has a Plasmodium-specific structural extension that differs in tertiary structure and dynamics (not sequence) from human Hsp90; exploiting this dynamic difference enabled discovery of 7-azaindole compounds that exclusively bind recombinant PfHsp90 N-terminal domain but not human Hsp90, and preferentially inhibit yeast complemented with PfHsp90.\",\n      \"method\": \"Structural/dynamics analysis, in vitro binding assays with recombinant domains, yeast complementation growth assay\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — combined structural, biochemical, and genetic complementation evidence; single lab\",\n      \"pmids\": [\"24580531\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"LC-MS/MS of PfHsp90 interactors identified the P. falciparum chloroquine resistance transporter (PfCRT) as a direct or indirect interactor of PfHsp90; the PfHsp90 inhibitor PU-H71 synergizes with chloroquine in vitro and in the P. berghei mouse model, suggesting PfHsp90 chaperones PfCRT.\",\n      \"method\": \"LC-MS/MS interactomics of PfHsp90 pulldown, surface plasmon resonance (PU-H71 affinity), ATPase assay, in vitro drug synergy, P. berghei mouse model\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS-identified interaction with functional pharmacological follow-up; interactome data supports but does not prove direct binding of PfCRT to PfHsp90\",\n      \"pmids\": [\"24098696\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PfHsp90 inhibition (by SNX-0723 and other inhibitors) kills P. falciparum at both liver and blood stages; expression analysis and time-course inhibition studies support a role for PfHsp90 in late liver-stage parasite development. PfHsp90 inhibitor SNX-0723 combined with PIK-75 synergistically reduces liver-stage parasite load.\",\n      \"method\": \"Cell-based liver- and blood-stage parasite assays, time-course inhibition, expression analysis, drug combination studies\",\n      \"journal\": \"Antimicrobial agents and chemotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based assays in two life cycle stages with time-course and combination readouts; liver-stage role inferred, not genetically validated\",\n      \"pmids\": [\"29339390\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PfAP2-HS transcription factor activates transcription of hsp90 (and hsp70-1) at elevated febrile temperatures; parasites lacking PfAP2-HS show reduced heat-shock survival and severe growth defects, establishing that hsp90 upregulation at fever temperatures is under PfAP2-HS control.\",\n      \"method\": \"Conditional/engineered gene knockout, transcriptional analysis, ChIP (promoter binding), heat-shock survival assay\",\n      \"journal\": \"Nature microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with defined phenotype, ChIP-confirmed promoter binding, transcriptional and growth readouts, single rigorous study\",\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 by occupying their promoter-proximal regions and recruiting H3K9me3, inducing a heterochromatic state; this repression is reversed by GA or radicicol (PfHsp90 inhibitors), leading to de-repression of var genes at sub-telomeric regions.\",\n      \"method\": \"ChIP (chromatin immunoprecipitation for PfHsp90 at promoters and H3K9me3), drug treatment with PfHsp90 inhibitors, transcriptional analysis\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP establishes PfHsp90 promoter occupancy and histone modification linkage; pharmacological validation; single lab\",\n      \"pmids\": [\"33538363\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Thermal proteome profiling following selective PfHsp90 inhibition (using Tropane 1 and XL888 derivatives) identified the 26S proteasome as enriched among proteins with perturbed stability; biochemical and cellular studies showed that PfHsp90 directly promotes proteasome hydrolytic activity by chaperoning the active 26S complex.\",\n      \"method\": \"Thermal proteome profiling, biochemical proteasome activity assays, cellular imaging/analysis, selective PfHsp90 inhibitor treatment\",\n      \"journal\": \"Cell chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — thermal proteome profiling combined with biochemical and cellular validation of proteasome chaperoning; rigorous multi-method study, single lab\",\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; anti-Hsp90 antibodies inhibit fertilization, and peptide competition experiments established that female gamete surface HSP90 is required for gamete fertilization in the mosquito.\",\n      \"method\": \"Phage peptide display screening, antibody binding assays, fertilization inhibition assay\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct antibody blocking of fertilization with Hsp90 identification; species not fully specified but Plasmodium gamete experiments directly conducted\",\n      \"pmids\": [\"38131664\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Recombinant PfHsp90 behaves as an elongated, flexible homodimer in solution (sub-micromolar dissociation constant); its C-terminal domain is required for dimerization. PfHsp90 and PfHsp90NMD interact with adenosine nucleotides via the NTD, and Mg2+ is critical for strong nucleotide binding.\",\n      \"method\": \"Small-angle X-ray scattering (SAXS), size exclusion chromatography, isothermal titration calorimetry\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — SAXS and solution biophysics with domain constructs; dimerization and nucleotide binding characterized, single lab\",\n      \"pmids\": [\"32679196\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Isothermal titration calorimetry showed that PfHsp90 has distinct thermodynamic signatures for ADP vs. ATP binding: ADP interaction is enthalpy-driven but entropy-opposed, while ATP interaction is driven by both enthalpy and entropy, indicating state-dependent conformational properties of PfHsp90.\",\n      \"method\": \"Isothermal titration calorimetry, comparative thermodynamic analysis\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — rigorous thermodynamic measurement with recombinant protein; single lab comparative study\",\n      \"pmids\": [\"30797004\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In vitro selection experiments identified 10 distinct resistance mutations to geldanamycin in PfHsp90 conferring up to 22-fold resistance; AUY-922 (binding same ATP site) yielded only one mutation (A41S) with 2-fold resistance. The A41S mutation paradoxically increased AUY-922 binding affinity via additional hydrogen bonding yet conferred resistance; conditional PfHsp90 knockdown increased geldanamycin sensitivity but not AUY-922 activity, suggesting different target dependencies.\",\n      \"method\": \"In vitro drug selection, whole-genome sequencing of resistant parasites, conditional knockdown, binding affinity measurement, yeast complementation\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple selection experiments, genetic knockdown, binding assays, and yeast epistasis all in one rigorous study\",\n      \"pmids\": [\"42406593\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In vitro experiments demonstrated that PfHsp90 has a cryptic C-terminal nucleotide-binding site: an ATP-reactive lysine-reactive probe and an ATP resin specifically interacted with PfHsp90 C-terminal truncation; limited proteolysis showed association with ATP, dATP, and ADP but not AMP or GTP; mutagenesis defined molecular determinants of this interaction.\",\n      \"method\": \"Affinity chromatography (ATP resin), lysine-reactive nucleotide analog labeling, limited proteolysis, site-directed mutagenesis, in silico analysis\",\n      \"journal\": \"Bioorganic & medicinal chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical assays with domain constructs plus mutagenesis; single lab, novel finding without independent replication\",\n      \"pmids\": [\"40907219\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"PfHsp90 (PF3D7_0708400) is an essential cytosolic molecular chaperone in P. falciparum with the highest known ATPase activity among Hsp90 orthologs; it forms ~300 kDa hetero-oligomeric complexes with PfHsp70, PfPP5, tubulin, and co-chaperones (PfHop, Pfp23, PfAha1, PfFKBP35), whose assembly is regulated by acetylation and co-chaperone binding; it is required for Ring-to-trophozoite progression and for chaperoning the active 26S proteasome; its transcription at febrile temperatures is activated by the PfAP2-HS transcription factor; it additionally functions as a transcriptional repressor by occupying the PfSIR2A/B promoters and recruiting H3K9me3; surface HSP90 on female gametes is required for fertilization; and its N-terminal ATP-binding domain and a cryptic C-terminal nucleotide-binding site are both druggable, with geldanamycin resistance mutations mapping throughout the binding pocket while AUY-922 resistance is restricted to a single residue near the ATP site.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PfHsp90 (PF3D7_0708400) is an essential cytosolic molecular chaperone of Plasmodium falciparum that drives intraerythrocytic development, with geldanamycin inhibition arresting the Ring-to-trophozoite transition [#0, #2]. It assembles into ~300 kDa, 11S hetero-oligomeric multi-chaperone complexes containing PfHsp70, the TPR-phosphatase PfPP5, and tubulin, whose integrity is required for heat-shock-dependent cytoprotection and developmental progression [#0, #2, #3]. As an elongated, C-terminally dimerizing ATPase, PfHsp90 possesses the highest ATPase activity of any known Hsp90 ortholog, and its cycle is tuned by a suite of co-chaperones — the p23 orthologue Pfp23 suppresses ATPase activity while PfAha1 stimulates it, with the two competing for binding, and the TPR co-chaperones PfHop, PfFKBP35, and PfPP5 docking onto the C-terminal MEEVD motif [#6, #9, #10, #11, #12, #22]. Complex assembly is further modulated by an acetylation site overlapping the Aha1/p23 interface [#6]. Beyond canonical client folding — where it stabilizes calcineurin, chaperones the active 26S proteasome, and interacts with the drug-resistance transporter PfCRT [#5, #16, #20] — PfHsp90 has a nuclear function as a transcriptional repressor, occupying the PfSIR2A/B promoters and recruiting H3K9me3 to enforce heterochromatin [#19], while its own febrile-temperature induction is driven by the PfAP2-HS transcription factor [#18]. Surface HSP90 on female gametes is required for fertilization in the mosquito stage [#21]. Its N-terminal ATP-binding pocket carries a Plasmodium-specific structural extension that confers pharmacological divergence from human Hsp90 and enables species-selective inhibitors, and a cryptic C-terminal nucleotide-binding site provides a second druggable pocket [#7, #15, #24, #25].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing that PfHsp90 physically associates with a parasite TPR phosphatase addressed whether the chaperone recruits regulatory partners in P. falciparum.\",\n      \"evidence\": \"Co-immunoprecipitation of native PfPP5 with PfHsp90 from parasite extract\",\n      \"pmids\": [\"11737864\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Single co-IP without reciprocal validation\", \"Functional consequence of the PfPP5-PfHsp90 interaction not defined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The unknown essentiality and complex context of PfHsp90 was resolved by showing it forms ~300 kDa Hsp70-containing complexes and that its inhibition arrests development, establishing it as a bona fide drug target.\",\n      \"evidence\": \"Sedimentation/SEC complex analysis, geldanamycin growth inhibition, and phosphorylation assays; recombinant ATP-binding and GA-inhibition assays\",\n      \"pmids\": [\"12584193\", \"14514358\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Stage-specific mechanism of the Ring-to-trophozoite arrest not defined\", \"Full complex composition not yet enumerated\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"W2\"}]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defining the composition and clientele of the PfHsp90 complex addressed which parasite factors depend on the chaperone, expanding it from PfHsp70/PfPP5/tubulin to FKBP35 and calcineurin.\",\n      \"evidence\": \"Co-immunoprecipitation and GA/CsA pharmacological dissection plus GA-ascomycin synergy in cultured parasites\",\n      \"pmids\": [\"15339915\", \"15850699\", \"15811524\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct vs. indirect binding of calcineurin not distinguished\", \"Client-folding mechanism not reconstituted\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Biochemical and structural reconstitution answered how PfHsp90's catalytic cycle is regulated, revealing record-high ATPase activity, acetylation-dependent assembly, and a solved N-terminal drug-binding pocket.\",\n      \"evidence\": \"In vitro ATPase assays, mass spectrometry of PTM sites, HDAC inhibitor complex analysis, Pfp23 ATPase-suppression mutagenesis, and X-ray crystallography of the NTD\",\n      \"pmids\": [\"20837488\", \"20140477\", \"20635416\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Physiological trigger for acetylation in vivo unknown\", \"Full-length conformational cycle not captured crystallographically\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Mapping the co-chaperone interfaces resolved how the ATPase cycle is bidirectionally controlled, showing PfAha1 stimulates and Pfp23 suppresses activity while PfHop and PfFKBP35 bridge to PfHsp70 via the MEEVD motif.\",\n      \"evidence\": \"Split-ubiquitin, GST pull-down, ATPase assays, interface mutagenesis, gel filtration/co-IP, and crystallography plus SPR/NMR of the FKBP35 TPR-MEEVD interaction\",\n      \"pmids\": [\"22100910\", \"22005844\", \"19691130\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Temporal ordering of co-chaperone exchange on the cycle not resolved\", \"In vivo stoichiometry of the assembled complex unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"The question of whether PfHsp90 can be selectively targeted over human Hsp90 was addressed by identifying a Plasmodium-specific structural/dynamic extension in the ATP pocket and linker that confers pharmacological divergence.\",\n      \"evidence\": \"Yeast complementation drug-sensitivity comparisons, chimeric-linker biophysics, SPR-mapped residue Arg98 for harmine selectivity, and 7-azaindole selective binding studies\",\n      \"pmids\": [\"19320098\", \"22315411\", \"22615284\", \"24580531\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Selectivity demonstrated largely in surrogate/recombinant systems\", \"In-parasite efficacy of selective scaffolds not established here\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Solution biophysics and life-cycle profiling extended the mechanistic picture by defining PfHsp90 as a C-terminally dimerizing, elongated homodimer with state-dependent nucleotide thermodynamics and roles beyond blood stage.\",\n      \"evidence\": \"SAXS, SEC, ITC of ADP vs ATP binding, and liver/blood-stage inhibitor killing with time-course and combination studies\",\n      \"pmids\": [\"32679196\", \"30797004\", \"29339390\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Liver-stage role inferred pharmacologically, not genetically validated\", \"Client repertoire in liver stage undefined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery of nuclear and transcriptional functions redefined PfHsp90 beyond cytosolic folding, showing it both is induced by PfAP2-HS at fever temperatures and itself represses PfSIR2A/B via H3K9me3-directed heterochromatin.\",\n      \"evidence\": \"PfAP2-HS knockout with ChIP and heat-shock survival assays; ChIP of PfHsp90 and H3K9me3 at SIR2 promoters with inhibitor-reversal transcriptional analysis\",\n      \"pmids\": [\"34400833\", \"33538363\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Mechanism recruiting PfHsp90 to specific promoters unknown\", \"Link between chaperone activity and repressor function not established\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identifying surface HSP90 on female gametes addressed whether the chaperone has a role in transmission, showing it is required for fertilization in the mosquito.\",\n      \"evidence\": \"Phage peptide display, antibody binding, and fertilization-inhibition/peptide-competition assays\",\n      \"pmids\": [\"38131664\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Mechanism by which a cytosolic chaperone reaches the gamete surface unresolved\", \"Fertilization partner/receptor on the gamete surface unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Unbiased target-engagement profiling identified the 26S proteasome as a PfHsp90 client, establishing that the chaperone directly sustains proteasomal hydrolytic activity.\",\n      \"evidence\": \"Thermal proteome profiling under selective inhibition with biochemical proteasome-activity and cellular validation\",\n      \"pmids\": [\"38492573\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Which proteasome subunit(s) PfHsp90 engages not defined\", \"Structural basis of proteasome chaperoning unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Resistance selection and a newly mapped cryptic C-terminal site clarified the druggable landscape, showing distinct binding-pocket mutation profiles for geldanamycin versus AUY-922 and a second nucleotide-binding pocket.\",\n      \"evidence\": \"In vitro drug selection with whole-genome sequencing, conditional knockdown, binding-affinity and yeast complementation; ATP-resin/lysine-reactive probe labeling, limited proteolysis, and mutagenesis of the C-terminal site\",\n      \"pmids\": [\"42406593\", \"40907219\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Physiological function of the cryptic C-terminal nucleotide site unknown\", \"Mechanism of the A41S resistance paradox not fully resolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PfHsp90's cytosolic chaperone cycle is coordinated with its distinct nuclear-repressor, gamete-surface, and proteasome-chaperoning roles, and how its clientele shifts across life-cycle stages, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No unified model linking chaperone ATPase cycle to transcriptional repression\", \"Stage-specific client repertoire not mapped\", \"Trafficking to gamete surface unexplained\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140662\", \"supporting_discovery_ids\": [6, 10, 11, 22, 23]},\n      {\"term_id\": \"GO:0005524\", \"supporting_discovery_ids\": [1, 7, 22, 25]},\n      {\"term_id\": \"GO:0051082\", \"supporting_discovery_ids\": [0, 2, 5, 16, 20]},\n      {\"term_id\": \"GO:0051087\", \"supporting_discovery_ids\": [9, 10, 11, 12]},\n      {\"term_id\": \"GO:0003714\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"GO:0042803\", \"supporting_discovery_ids\": [22]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 2, 9]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"GO:0009986\", \"supporting_discovery_ids\": [21]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006457\", \"supporting_discovery_ids\": [0, 2, 5, 20]},\n      {\"term_id\": \"GO:0034605\", \"supporting_discovery_ids\": [2, 18]},\n      {\"term_id\": \"GO:0006338\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"GO:0009566\", \"supporting_discovery_ids\": [21]}\n    ],\n    \"complexes\": [\n      \"~300 kDa / 11S PfHsp90 multi-chaperone complex containing PfHsp70, PfPP5, and tubulin\",\n      \"PfHsp90-PfHop-PfHsp70 ternary complex\",\n      \"PfHsp90-active 26S proteasome complex\"\n    ],\n    \"partners\": [\n      \"PfHsp70\",\n      \"PfPP5\",\n      \"tubulin\",\n      \"PfHop\",\n      \"Pfp23\",\n      \"PfAha1\",\n      \"PfFKBP35\",\n      \"plasmodial calcineurin (PfCN)\",\n      \"PfCRT\",\n      \"26S proteasome\"\n    ],\n    \"other_free_text\": [\n      \"Highest ATPase activity of any known Hsp90 ortholog (~6-fold above human Hsp90); GA inhibits PfHsp90 ATPase more robustly than human [#6].\",\n      \"Acetylation site overlapping the Aha1/p23 binding domain modulates multichaperone assembly [#6].\",\n      \"Elongated flexible homodimer requiring the C-terminal domain for dimerization; Mg2+ critical for nucleotide binding [#22].\",\n      \"N-terminal ATP-binding domain crystallized in apo and ADP-bound states; harbors a Plasmodium-specific structural/dynamic extension enabling species-selective inhibitors [#7, #15].\",\n      \"Cryptic C-terminal nucleotide-binding site reactive with ATP/dATP/ADP but not AMP or GTP [#25].\",\n      \"hsp90 transcription activated at febrile temperatures by PfAP2-HS [#18].\",\n      \"Geldanamycin resistance maps to multiple binding-pocket residues; AUY-922 resistance restricted to A41S with distinct target dependency [#24].\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_0708400","name":null,"product":"heat shock protein 90","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_0805700","name":null,"product":"heat shock protein 90, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_0107000","name":null,"product":"heat shock protein 90, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"HSP90","evaluation":null}