{"gene":"PF3D7_1318100","run_date":"2026-09-08T14:19:06","timeline":{"discoveries":[{"year":2000,"finding":"P. falciparum FD (PF3D7_1318100) was cloned and shown to encode a [2Fe-2S] ferredoxin with an N-terminal bipartite transit peptide directing it to the apicoplast; recombinant protein was obtained in active form, establishing apicoplast localization and activity.","method":"Molecular cloning, bipartite transit peptide analysis, recombinant protein expression and activity assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct cloning, transit peptide characterization, and recombinant protein activity; single lab, two orthogonal methods","pmids":["11056177"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"finding":"P. falciparum FD forms a stable protein complex with LytB (the [4Fe-4S] enzyme catalyzing the last step of the DOXP/MEP isoprenoid pathway) and, together with ferredoxin-NADP+ reductase (FNR) and NADPH, reconstitutes catalytic activity of LytB in vitro, identifying FD as the physiological electron donor for LytB in the apicoplast.","method":"In vitro reconstitution of electron transfer, co-purification/stable complex formation assay","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution of full electron transfer pathway, stable complex formation demonstrated, mechanistic conclusion directly supported","pmids":["16289098"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"finding":"X-ray crystallography of recombinant P. falciparum FD revealed that its backbone structure closely resembles plant ferredoxins; its redox potential is considerably more positive than leaf-type and root-type plant Fds, consistent with electron flow from NADPH to Fd in the apicoplast (rather than from photosystem I). P. falciparum FNR selectively transfers electrons to P. falciparum FD in a reconstituted NADPH-dependent cytochrome c reduction system.","method":"X-ray crystallography, redox potential measurement, reconstituted electron transfer assay","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus functional reconstitution plus redox potential measurement; multiple orthogonal methods in single study","pmids":["17251200"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"finding":"NMR chemical shift perturbation mapping of P. falciparum FD surface identified two acidic interaction regions for FNR binding: one including Asp26, Glu29, and Glu34, and another including Asp65 and Glu66. Site-directed mutagenesis confirmed that Glu29 is the most important residue; these acidic patches mediate electrostatic interaction with P. falciparum FNR.","method":"NMR chemical shift perturbation, site-directed mutagenesis, electron transfer activity assay, affinity chromatography","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR mapping combined with mutagenesis and functional assays; multiple orthogonal methods","pmids":["17938142"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"finding":"P. falciparum FD participates in FNR-catalyzed single-electron reduction of quinones: reduced PfFd provides an additional reduction pathway that stimulates quinone- and nitro-reductase reactions of PfFNR, demonstrating FD's role in reductive activation of redox-cycling compounds in P. falciparum.","method":"In vitro enzymatic kinetics with purified recombinant PfFNR and PfFd, single-electron reduction rate measurements","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro reconstitution with kinetic analysis; single lab but two independent assay formats","pmids":["19523113"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2018,"finding":"Basic amino acid residues on the FAD-binding surface of PfFNR, including Plasmodium-specific residues in an insertion region, are required for high-affinity and specific interaction with P. falciparum FD. Site-directed mutagenesis of these basic residues on FNR reduces electron transfer to PfFd and physical binding, showing that the interaction mode between FD and FNR is Plasmodium-specific.","method":"Site-directed mutagenesis of PfFNR, electron transfer kinetics with PfFd, affinity binding assay, thermodynamic binding measurements","journal":"Journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis plus kinetics plus binding thermodynamics; single lab","pmids":["29688515"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2020,"finding":"The C-terminal aromatic residues of P. falciparum FD (positions 96 and 97) contribute to tighter and more specific interaction with PfFNR. Substitution of the C-terminal three residues between plant Fd and PfFd, and site-directed mutagenesis, revealed that aromatic residues at positions 96 and 97 lower the Km for PfFNR; the D97Y mutation (associated with artemisinin resistance) increases affinity for PfFNR.","method":"Site-directed mutagenesis, kinetic analysis of electron transfer, fluorescence binding assay, isothermal titration calorimetry","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis combined with kinetics, fluorescence titration, and calorimetry; multiple orthogonal methods in one study","pmids":["32470136"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"The D97Y mutation in P. falciparum FD (associated with artemisinin resistance) increases affinity with PfFNR as measured by dissociation constant (Kd) via tryptophan fluorescence titration and Michaelis constant (Km) in kinetic analysis. D97Y PfFd inhibits diaphorase activity of PfFNR at lower concentration than wild-type PfFd. D97Y PfFd shows lower ascorbate radical scavenging activity and lower electron transfer to a heterologous Fd-dependent enzyme than wild-type, suggesting that tighter binding to FNR sequesters FNR and suppresses downstream electron flow.","method":"Site-directed mutagenesis, tryptophan fluorescence titration (Kd measurement), enzyme kinetics (Km), diaphorase activity assay, ascorbate radical scavenging assay, heterologous electron transfer assay","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal biochemical assays on defined mutant; mechanistic conclusion well supported","pmids":["34415329"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"finding":"Genetic deletion of P. falciparum FD in a parasite line with an apicoplast metabolic bypass (PfMev) showed that FD is essential for blood-stage parasite survival but is not required for apicoplast maintenance. Iron-sulfur (FeS) transfer proteins SufA and NfuApi act redundantly to deliver FeS clusters to FD (double deletion is synthetically lethal, while individual deletions are viable).","method":"Genetic deletion (CRISPR/conditional KO in PfMev bypass line), parasite growth/viability assay, apicoplast morphology assessment, double-deletion synthetic lethality","journal":"mBio","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with defined viability phenotype, apicoplast maintenance readout, and synthetic lethality epistasis; multiple orthogonal approaches","pmids":["35164549"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"finding":"Dihydroartemisinin (DHA) partially inhibits FNR diaphorase activity by decreasing FNR's affinity for NADPH, but does not significantly affect electron transfer activity from FNR to wild-type or D97Y mutant FD in vitro, indicating that FD is not a direct molecular target of artemisinin.","method":"In vitro reconstituted NADPH/FNR/ferredoxin electron transfer assay, diaphorase activity assay with DHA, in silico docking","journal":"Antioxidants (Basel, Switzerland)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro reconstitution with defined substrate/inhibitor; single lab; finding is negative for direct FD targeting but mechanistically informative","pmids":["35204156"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"Point mutation editing of the ferredoxin D193Y variant (corresponding to a background mutation associated with artemisinin resistance in field isolates) into P. falciparum parasites had no impact on ART susceptibility or parasite fitness in vitro.","method":"Gene editing (point mutation introduction), in vitro ring-stage survival assay (RSA), parasite fitness assay","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean gene editing with defined phenotypic readout; this is a negative result for ART resistance contribution of the fd D193Y allele","pmids":["34279219"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"finding":"A reconstituted E. coli system in which the endogenous flavodoxin and ispH were replaced by P. falciparum ptFd (FD), ptFNR, and IspH restored bacterial growth dependent on the MEP isoprenoid pathway, demonstrating that P. falciparum FD can functionally substitute for the bacterial flavodoxin electron carrier in the terminal IspH reaction. Point mutations in ptFd that abolished function were confirmed to deplete MEP metabolites by LC-MS, and selected FD mutants failed to complement a conditional T. gondii Fd KO strain.","method":"Functional complementation in E. coli double mutant, LC-MS metabolite analysis, conditional KO complementation in T. gondii","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — functional reconstitution in heterologous system, metabolite readout by LC-MS, and in vivo complementation; multiple orthogonal methods","pmids":["40967433"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"P. falciparum FD (PF3D7_1318100) is a [2Fe-2S] plant-type ferredoxin that localizes to the apicoplast via an N-terminal bipartite transit peptide, where it acts as the central electron carrier in the NADPH→FNR→FD redox cascade, donating electrons to essential downstream iron-sulfur cluster-containing enzymes including LytB (the terminal MEP/isoprenoid pathway enzyme); FD is essential for blood-stage parasite survival but not for apicoplast maintenance, receives its FeS cofactor from redundant SufA/NfuApi transfer proteins, interacts with FNR through specific acidic surface patches (particularly Glu29, Asp65, Glu66) and a C-terminal aromatic residue (positions 96/97), and the resistance-associated D97Y mutation tightens FD–FNR binding without making FD a direct artemisinin target."},"narrative":{"mechanistic_narrative":"PF3D7_1318100 (FD) is a [2Fe-2S] plant-type ferredoxin of P. falciparum that functions as the central soluble electron carrier of the apicoplast, where it is delivered by an N-terminal bipartite transit peptide [PMID:11056177]. Within the apicoplast, FD operates in an NADPH→FNR→FD redox relay: FNR selectively reduces FD, and FD in turn donates electrons to downstream iron-sulfur enzymes, most directly to the terminal MEP/DOXP isoprenoid pathway enzyme LytB/IspH, whose catalytic activity FD reconstitutes together with FNR and NADPH in vitro [PMID:16289098, PMID:17251200]; heterologous reconstitution in E. coli confirms FD can substitute for a bacterial flavodoxin to drive the terminal IspH reaction and sustain MEP-dependent growth [PMID:40967433]. FD binds FNR through a Plasmodium-specific electrostatic interface involving acidic surface patches (notably Glu29, and residues Asp65/Glu66) and C-terminal aromatic residues at positions 96/97 [PMID:17938142, PMID:32470136]. Genetic deletion establishes that FD is essential for blood-stage survival but dispensable for apicoplast maintenance, and that it receives its FeS cofactor redundantly from SufA and NfuApi [PMID:35164549]. The artemisinin-resistance-associated D97Y substitution tightens FD–FNR binding and thereby sequesters FNR and suppresses downstream electron flow, but FD itself is not a direct molecular target of artemisinin, and editing the related D193Y variant confers no change in artemisinin susceptibility or fitness [PMID:34415329, PMID:35204156, PMID:34279219].","teleology":[{"year":2000,"claim":"Establishing that the parasite encodes a bona fide apicoplast-targeted ferredoxin answered whether Plasmodium possesses a plant-type FeS electron carrier and where it acts.","evidence":"Molecular cloning, bipartite transit peptide analysis, and recombinant expression of active [2Fe-2S] protein in P. falciparum","pmids":["11056177"],"confidence":"Medium","gaps":["Downstream electron acceptors not yet identified","In vivo localization inferred from transit peptide rather than directly imaged"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"claim":"Identifying LytB as an FD electron acceptor answered what physiological process FD powers, linking the ferredoxin to the essential MEP isoprenoid pathway.","evidence":"In vitro reconstitution of NADPH/FNR/FD-dependent LytB activity and stable FD–LytB complex formation in P. falciparum","pmids":["16289098"],"confidence":"High","gaps":["Whether LytB is the only downstream acceptor not established","Complex not resolved structurally"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"claim":"Structural and redox characterization answered the directionality of electron flow, showing FD receives rather than donates electrons to a photosystem, consistent with an NADPH→FNR→FD cascade.","evidence":"X-ray crystallography, redox potential measurement, and reconstituted NADPH-dependent electron transfer with P. falciparum FNR and FD","pmids":["17251200"],"confidence":"High","gaps":["Structure of the FD–FNR complex not solved","In-cell redox state not measured"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"claim":"Mapping the FD surface answered which residues mediate FNR docking, defining the electrostatic recognition interface.","evidence":"NMR chemical shift perturbation with site-directed mutagenesis and electron transfer assays on P. falciparum FD","pmids":["17938142"],"confidence":"High","gaps":["Reciprocal contacts on FNR not yet defined here","Contribution of non-acidic contacts unresolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"claim":"Demonstrating FD-stimulated single-electron quinone/nitro reduction answered whether the FD–FNR system contributes to reductive activation of redox-cycling compounds.","evidence":"In vitro kinetics with purified recombinant P. falciparum FNR and FD","pmids":["19523113"],"confidence":"Medium","gaps":["Physiological relevance in the parasite not established","Endogenous substrates of this activity unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2018,"claim":"Identifying basic FNR surface residues answered why FD–FNR recognition is Plasmodium-specific, defining the complementary side of the interaction interface.","evidence":"Site-directed mutagenesis of P. falciparum FNR with electron transfer kinetics and thermodynamic binding measurements against FD","pmids":["29688515"],"confidence":"Medium","gaps":["Structural model of the assembled complex still absent","Whether specificity extends to other FD partners untested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2020,"claim":"Defining the role of FD C-terminal aromatic residues answered how binding affinity is tuned and provided the first mechanistic link to the artemisinin-resistance D97Y allele.","evidence":"Chimeric substitution and site-directed mutagenesis with kinetics, fluorescence binding, and isothermal titration calorimetry on P. falciparum FD","pmids":["32470136"],"confidence":"High","gaps":["Consequences of tighter binding for parasite physiology not tested here","In vivo relevance of D97Y not yet addressed"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"claim":"Characterizing D97Y biochemistry answered how the resistance-associated mutation alters function, showing tighter FNR binding sequesters FNR and suppresses downstream electron flow.","evidence":"Site-directed mutagenesis with fluorescence titration, kinetics, diaphorase, ascorbate radical scavenging, and heterologous electron transfer assays on P. falciparum FD","pmids":["34415329"],"confidence":"High","gaps":["Whether sequestration occurs at physiological FNR/FD ratios in vivo untested","Link to a resistance mechanism in parasites not demonstrated"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"claim":"Editing the FD D193Y variant into parasites answered whether this field-associated allele contributes to artemisinin resistance, and it does not.","evidence":"Point-mutation gene editing with ring-stage survival and fitness assays in P. falciparum","pmids":["34279219"],"confidence":"Medium","gaps":["Negative result for a single background allele","Does not address D97Y in vivo"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"claim":"Genetic deletion answered whether FD is essential and how its cofactor is supplied, showing FD is required for blood-stage survival independent of apicoplast maintenance and receives FeS redundantly from SufA and NfuApi.","evidence":"CRISPR/conditional deletion in the PfMev bypass line with viability, apicoplast morphology, and synthetic-lethality epistasis in P. falciparum","pmids":["35164549"],"confidence":"High","gaps":["Precise essential downstream process not pinpointed genetically","Direct FeS handoff mechanism from SufA/NfuApi to FD not resolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"claim":"Testing dihydroartemisinin against the FD–FNR system answered whether FD is a direct drug target, showing artemisinin acts on FNR–NADPH affinity rather than on FD-directed electron transfer.","evidence":"In vitro reconstituted NADPH/FNR/FD electron transfer and diaphorase assays with DHA plus in silico docking in P. falciparum","pmids":["35204156"],"confidence":"Medium","gaps":["In-cell drug interaction not tested","Negative result for direct FD targeting"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"claim":"Heterologous reconstitution answered whether FD is functionally sufficient to drive the terminal IspH/MEP reaction, confirming it can replace a bacterial flavodoxin and that function-abolishing FD mutations deplete MEP metabolites.","evidence":"Functional complementation in an E. coli double mutant with LC-MS metabolite analysis and conditional T. gondii Fd KO complementation, using P. falciparum FD, FNR, and IspH","pmids":["40967433"],"confidence":"High","gaps":["Native apicoplast partner network beyond IspH not fully mapped","Quantitative flux control by FD in vivo not established"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"It remains unresolved how FeS clusters are physically handed from SufA/NfuApi to FD and whether the tighter D97Y FD–FNR interaction has any measurable consequence for parasite physiology or drug response in vivo.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of the FD–FNR complex","Cofactor delivery mechanism uncharacterized at the molecular level","In vivo phenotype of D97Y not established"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["FD–LytB(IspH) complex","FD–FNR redox pair"],"partners":["FNR (FERREDOXIN-NADP+ REDUCTASE)","LYTB / ISPH","SUFA","NFUAPI"],"other_free_text":["N-terminal bipartite transit peptide directs FD to the apicoplast [#0]","Redox potential more positive than plant leaf/root ferredoxins, consistent with NADPH→FNR→FD electron flow [#2]","FNR-binding interface on FD: acidic patches (Glu29 most critical; Asp26/Glu34; Asp65/Glu66) and C-terminal aromatic residues at positions 96/97 [#3, #6]","Essential for blood-stage survival but dispensable for apicoplast maintenance; FeS cofactor supplied redundantly by SufA and NfuApi [#8]","D97Y resistance-associated mutation increases FD–FNR affinity and suppresses downstream electron flow via FNR sequestration [#6, #7]","FD is not a direct target of artemisinin; DHA acts on FNR–NADPH affinity, and the D193Y FD variant does not alter artemisinin susceptibility or fitness [#9, #10]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"25599401","id":"PMC_25599401","title":"Genetic architecture of artemisinin-resistant Plasmodium 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microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/35463632","citation_count":3,"is_preprint":false,"source_species":["Pf"],"role":"citation_expansion","match_terms":["fwd_cite"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":25253,"output_tokens":3509,"usd":0.064197,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9413,"output_tokens":4495,"usd":0.07972,"stage2_stop_reason":"end_turn"},"total_usd":0.143917,"stage1_batch_id":"msgbatch_011BPjN2BL33F8cJXD1r7V7T","stage2_batch_id":"msgbatch_01Qwg6vP7qxkpL6Gsc7tajsb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"P. falciparum FD (PF3D7_1318100) was cloned and shown to encode a [2Fe-2S] ferredoxin with an N-terminal bipartite transit peptide directing it to the apicoplast; recombinant protein was obtained in active form, establishing apicoplast localization and activity.\",\n      \"method\": \"Molecular cloning, bipartite transit peptide analysis, recombinant protein expression and activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct cloning, transit peptide characterization, and recombinant protein activity; single lab, two orthogonal methods\",\n      \"pmids\": [\"11056177\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"P. falciparum FD forms a stable protein complex with LytB (the [4Fe-4S] enzyme catalyzing the last step of the DOXP/MEP isoprenoid pathway) and, together with ferredoxin-NADP+ reductase (FNR) and NADPH, reconstitutes catalytic activity of LytB in vitro, identifying FD as the physiological electron donor for LytB in the apicoplast.\",\n      \"method\": \"In vitro reconstitution of electron transfer, co-purification/stable complex formation assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution of full electron transfer pathway, stable complex formation demonstrated, mechanistic conclusion directly supported\",\n      \"pmids\": [\"16289098\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"X-ray crystallography of recombinant P. falciparum FD revealed that its backbone structure closely resembles plant ferredoxins; its redox potential is considerably more positive than leaf-type and root-type plant Fds, consistent with electron flow from NADPH to Fd in the apicoplast (rather than from photosystem I). P. falciparum FNR selectively transfers electrons to P. falciparum FD in a reconstituted NADPH-dependent cytochrome c reduction system.\",\n      \"method\": \"X-ray crystallography, redox potential measurement, reconstituted electron transfer assay\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus functional reconstitution plus redox potential measurement; multiple orthogonal methods in single study\",\n      \"pmids\": [\"17251200\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"NMR chemical shift perturbation mapping of P. falciparum FD surface identified two acidic interaction regions for FNR binding: one including Asp26, Glu29, and Glu34, and another including Asp65 and Glu66. Site-directed mutagenesis confirmed that Glu29 is the most important residue; these acidic patches mediate electrostatic interaction with P. falciparum FNR.\",\n      \"method\": \"NMR chemical shift perturbation, site-directed mutagenesis, electron transfer activity assay, affinity chromatography\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR mapping combined with mutagenesis and functional assays; multiple orthogonal methods\",\n      \"pmids\": [\"17938142\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"P. falciparum FD participates in FNR-catalyzed single-electron reduction of quinones: reduced PfFd provides an additional reduction pathway that stimulates quinone- and nitro-reductase reactions of PfFNR, demonstrating FD's role in reductive activation of redox-cycling compounds in P. falciparum.\",\n      \"method\": \"In vitro enzymatic kinetics with purified recombinant PfFNR and PfFd, single-electron reduction rate measurements\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro reconstitution with kinetic analysis; single lab but two independent assay formats\",\n      \"pmids\": [\"19523113\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Basic amino acid residues on the FAD-binding surface of PfFNR, including Plasmodium-specific residues in an insertion region, are required for high-affinity and specific interaction with P. falciparum FD. Site-directed mutagenesis of these basic residues on FNR reduces electron transfer to PfFd and physical binding, showing that the interaction mode between FD and FNR is Plasmodium-specific.\",\n      \"method\": \"Site-directed mutagenesis of PfFNR, electron transfer kinetics with PfFd, affinity binding assay, thermodynamic binding measurements\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis plus kinetics plus binding thermodynamics; single lab\",\n      \"pmids\": [\"29688515\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The C-terminal aromatic residues of P. falciparum FD (positions 96 and 97) contribute to tighter and more specific interaction with PfFNR. Substitution of the C-terminal three residues between plant Fd and PfFd, and site-directed mutagenesis, revealed that aromatic residues at positions 96 and 97 lower the Km for PfFNR; the D97Y mutation (associated with artemisinin resistance) increases affinity for PfFNR.\",\n      \"method\": \"Site-directed mutagenesis, kinetic analysis of electron transfer, fluorescence binding assay, isothermal titration calorimetry\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis combined with kinetics, fluorescence titration, and calorimetry; multiple orthogonal methods in one study\",\n      \"pmids\": [\"32470136\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The D97Y mutation in P. falciparum FD (associated with artemisinin resistance) increases affinity with PfFNR as measured by dissociation constant (Kd) via tryptophan fluorescence titration and Michaelis constant (Km) in kinetic analysis. D97Y PfFd inhibits diaphorase activity of PfFNR at lower concentration than wild-type PfFd. D97Y PfFd shows lower ascorbate radical scavenging activity and lower electron transfer to a heterologous Fd-dependent enzyme than wild-type, suggesting that tighter binding to FNR sequesters FNR and suppresses downstream electron flow.\",\n      \"method\": \"Site-directed mutagenesis, tryptophan fluorescence titration (Kd measurement), enzyme kinetics (Km), diaphorase activity assay, ascorbate radical scavenging assay, heterologous electron transfer assay\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal biochemical assays on defined mutant; mechanistic conclusion well supported\",\n      \"pmids\": [\"34415329\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Genetic deletion of P. falciparum FD in a parasite line with an apicoplast metabolic bypass (PfMev) showed that FD is essential for blood-stage parasite survival but is not required for apicoplast maintenance. Iron-sulfur (FeS) transfer proteins SufA and NfuApi act redundantly to deliver FeS clusters to FD (double deletion is synthetically lethal, while individual deletions are viable).\",\n      \"method\": \"Genetic deletion (CRISPR/conditional KO in PfMev bypass line), parasite growth/viability assay, apicoplast morphology assessment, double-deletion synthetic lethality\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with defined viability phenotype, apicoplast maintenance readout, and synthetic lethality epistasis; multiple orthogonal approaches\",\n      \"pmids\": [\"35164549\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Dihydroartemisinin (DHA) partially inhibits FNR diaphorase activity by decreasing FNR's affinity for NADPH, but does not significantly affect electron transfer activity from FNR to wild-type or D97Y mutant FD in vitro, indicating that FD is not a direct molecular target of artemisinin.\",\n      \"method\": \"In vitro reconstituted NADPH/FNR/ferredoxin electron transfer assay, diaphorase activity assay with DHA, in silico docking\",\n      \"journal\": \"Antioxidants (Basel, Switzerland)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro reconstitution with defined substrate/inhibitor; single lab; finding is negative for direct FD targeting but mechanistically informative\",\n      \"pmids\": [\"35204156\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Point mutation editing of the ferredoxin D193Y variant (corresponding to a background mutation associated with artemisinin resistance in field isolates) into P. falciparum parasites had no impact on ART susceptibility or parasite fitness in vitro.\",\n      \"method\": \"Gene editing (point mutation introduction), in vitro ring-stage survival assay (RSA), parasite fitness assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean gene editing with defined phenotypic readout; this is a negative result for ART resistance contribution of the fd D193Y allele\",\n      \"pmids\": [\"34279219\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A reconstituted E. coli system in which the endogenous flavodoxin and ispH were replaced by P. falciparum ptFd (FD), ptFNR, and IspH restored bacterial growth dependent on the MEP isoprenoid pathway, demonstrating that P. falciparum FD can functionally substitute for the bacterial flavodoxin electron carrier in the terminal IspH reaction. Point mutations in ptFd that abolished function were confirmed to deplete MEP metabolites by LC-MS, and selected FD mutants failed to complement a conditional T. gondii Fd KO strain.\",\n      \"method\": \"Functional complementation in E. coli double mutant, LC-MS metabolite analysis, conditional KO complementation in T. gondii\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — functional reconstitution in heterologous system, metabolite readout by LC-MS, and in vivo complementation; multiple orthogonal methods\",\n      \"pmids\": [\"40967433\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"P. falciparum FD (PF3D7_1318100) is a [2Fe-2S] plant-type ferredoxin that localizes to the apicoplast via an N-terminal bipartite transit peptide, where it acts as the central electron carrier in the NADPH→FNR→FD redox cascade, donating electrons to essential downstream iron-sulfur cluster-containing enzymes including LytB (the terminal MEP/isoprenoid pathway enzyme); FD is essential for blood-stage parasite survival but not for apicoplast maintenance, receives its FeS cofactor from redundant SufA/NfuApi transfer proteins, interacts with FNR through specific acidic surface patches (particularly Glu29, Asp65, Glu66) and a C-terminal aromatic residue (positions 96/97), and the resistance-associated D97Y mutation tightens FD–FNR binding without making FD a direct artemisinin target.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PF3D7_1318100 (FD) is a [2Fe-2S] plant-type ferredoxin of P. falciparum that functions as the central soluble electron carrier of the apicoplast, where it is delivered by an N-terminal bipartite transit peptide [#0]. Within the apicoplast, FD operates in an NADPH→FNR→FD redox relay: FNR selectively reduces FD, and FD in turn donates electrons to downstream iron-sulfur enzymes, most directly to the terminal MEP/DOXP isoprenoid pathway enzyme LytB/IspH, whose catalytic activity FD reconstitutes together with FNR and NADPH in vitro [#1, #2]; heterologous reconstitution in E. coli confirms FD can substitute for a bacterial flavodoxin to drive the terminal IspH reaction and sustain MEP-dependent growth [#11]. FD binds FNR through a Plasmodium-specific electrostatic interface involving acidic surface patches (notably Glu29, and residues Asp65/Glu66) and C-terminal aromatic residues at positions 96/97 [#3, #6]. Genetic deletion establishes that FD is essential for blood-stage survival but dispensable for apicoplast maintenance, and that it receives its FeS cofactor redundantly from SufA and NfuApi [#8]. The artemisinin-resistance-associated D97Y substitution tightens FD–FNR binding and thereby sequesters FNR and suppresses downstream electron flow, but FD itself is not a direct molecular target of artemisinin, and editing the related D193Y variant confers no change in artemisinin susceptibility or fitness [#7, #9, #10].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing that the parasite encodes a bona fide apicoplast-targeted ferredoxin answered whether Plasmodium possesses a plant-type FeS electron carrier and where it acts.\",\n      \"evidence\": \"Molecular cloning, bipartite transit peptide analysis, and recombinant expression of active [2Fe-2S] protein in P. falciparum\",\n      \"pmids\": [\"11056177\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Downstream electron acceptors not yet identified\", \"In vivo localization inferred from transit peptide rather than directly imaged\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identifying LytB as an FD electron acceptor answered what physiological process FD powers, linking the ferredoxin to the essential MEP isoprenoid pathway.\",\n      \"evidence\": \"In vitro reconstitution of NADPH/FNR/FD-dependent LytB activity and stable FD–LytB complex formation in P. falciparum\",\n      \"pmids\": [\"16289098\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether LytB is the only downstream acceptor not established\", \"Complex not resolved structurally\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Structural and redox characterization answered the directionality of electron flow, showing FD receives rather than donates electrons to a photosystem, consistent with an NADPH→FNR→FD cascade.\",\n      \"evidence\": \"X-ray crystallography, redox potential measurement, and reconstituted NADPH-dependent electron transfer with P. falciparum FNR and FD\",\n      \"pmids\": [\"17251200\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the FD–FNR complex not solved\", \"In-cell redox state not measured\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Mapping the FD surface answered which residues mediate FNR docking, defining the electrostatic recognition interface.\",\n      \"evidence\": \"NMR chemical shift perturbation with site-directed mutagenesis and electron transfer assays on P. falciparum FD\",\n      \"pmids\": [\"17938142\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reciprocal contacts on FNR not yet defined here\", \"Contribution of non-acidic contacts unresolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrating FD-stimulated single-electron quinone/nitro reduction answered whether the FD–FNR system contributes to reductive activation of redox-cycling compounds.\",\n      \"evidence\": \"In vitro kinetics with purified recombinant P. falciparum FNR and FD\",\n      \"pmids\": [\"19523113\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological relevance in the parasite not established\", \"Endogenous substrates of this activity unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identifying basic FNR surface residues answered why FD–FNR recognition is Plasmodium-specific, defining the complementary side of the interaction interface.\",\n      \"evidence\": \"Site-directed mutagenesis of P. falciparum FNR with electron transfer kinetics and thermodynamic binding measurements against FD\",\n      \"pmids\": [\"29688515\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural model of the assembled complex still absent\", \"Whether specificity extends to other FD partners untested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defining the role of FD C-terminal aromatic residues answered how binding affinity is tuned and provided the first mechanistic link to the artemisinin-resistance D97Y allele.\",\n      \"evidence\": \"Chimeric substitution and site-directed mutagenesis with kinetics, fluorescence binding, and isothermal titration calorimetry on P. falciparum FD\",\n      \"pmids\": [\"32470136\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Consequences of tighter binding for parasite physiology not tested here\", \"In vivo relevance of D97Y not yet addressed\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Characterizing D97Y biochemistry answered how the resistance-associated mutation alters function, showing tighter FNR binding sequesters FNR and suppresses downstream electron flow.\",\n      \"evidence\": \"Site-directed mutagenesis with fluorescence titration, kinetics, diaphorase, ascorbate radical scavenging, and heterologous electron transfer assays on P. falciparum FD\",\n      \"pmids\": [\"34415329\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether sequestration occurs at physiological FNR/FD ratios in vivo untested\", \"Link to a resistance mechanism in parasites not demonstrated\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Editing the FD D193Y variant into parasites answered whether this field-associated allele contributes to artemisinin resistance, and it does not.\",\n      \"evidence\": \"Point-mutation gene editing with ring-stage survival and fitness assays in P. falciparum\",\n      \"pmids\": [\"34279219\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Negative result for a single background allele\", \"Does not address D97Y in vivo\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Genetic deletion answered whether FD is essential and how its cofactor is supplied, showing FD is required for blood-stage survival independent of apicoplast maintenance and receives FeS redundantly from SufA and NfuApi.\",\n      \"evidence\": \"CRISPR/conditional deletion in the PfMev bypass line with viability, apicoplast morphology, and synthetic-lethality epistasis in P. falciparum\",\n      \"pmids\": [\"35164549\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise essential downstream process not pinpointed genetically\", \"Direct FeS handoff mechanism from SufA/NfuApi to FD not resolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Testing dihydroartemisinin against the FD–FNR system answered whether FD is a direct drug target, showing artemisinin acts on FNR–NADPH affinity rather than on FD-directed electron transfer.\",\n      \"evidence\": \"In vitro reconstituted NADPH/FNR/FD electron transfer and diaphorase assays with DHA plus in silico docking in P. falciparum\",\n      \"pmids\": [\"35204156\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In-cell drug interaction not tested\", \"Negative result for direct FD targeting\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Heterologous reconstitution answered whether FD is functionally sufficient to drive the terminal IspH/MEP reaction, confirming it can replace a bacterial flavodoxin and that function-abolishing FD mutations deplete MEP metabolites.\",\n      \"evidence\": \"Functional complementation in an E. coli double mutant with LC-MS metabolite analysis and conditional T. gondii Fd KO complementation, using P. falciparum FD, FNR, and IspH\",\n      \"pmids\": [\"40967433\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Native apicoplast partner network beyond IspH not fully mapped\", \"Quantitative flux control by FD in vivo not established\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how FeS clusters are physically handed from SufA/NfuApi to FD and whether the tighter D97Y FD–FNR interaction has any measurable consequence for parasite physiology or drug response in vivo.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of the FD–FNR complex\", \"Cofactor delivery mechanism uncharacterized at the molecular level\", \"In vivo phenotype of D97Y not established\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0009055\", \"supporting_discovery_ids\": [0, 1, 2, 3, 11]},\n      {\"term_id\": \"GO:0051537\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0016730\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0009507\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0019288\", \"supporting_discovery_ids\": [1, 11]},\n      {\"term_id\": \"GO:0008299\", \"supporting_discovery_ids\": [1, 11]}\n    ],\n    \"complexes\": [\n      \"FD–LytB(IspH) complex\",\n      \"FD–FNR redox pair\"\n    ],\n    \"partners\": [\n      \"FNR (ferredoxin-NADP+ reductase)\",\n      \"LytB / IspH\",\n      \"SufA\",\n      \"NfuApi\"\n    ],\n    \"other_free_text\": [\n      \"N-terminal bipartite transit peptide directs FD to the apicoplast [#0]\",\n      \"Redox potential more positive than plant leaf/root ferredoxins, consistent with NADPH→FNR→FD electron flow [#2]\",\n      \"FNR-binding interface on FD: acidic patches (Glu29 most critical; Asp26/Glu34; Asp65/Glu66) and C-terminal aromatic residues at positions 96/97 [#3, #6]\",\n      \"Essential for blood-stage survival but dispensable for apicoplast maintenance; FeS cofactor supplied redundantly by SufA and NfuApi [#8]\",\n      \"D97Y resistance-associated mutation increases FD–FNR affinity and suppresses downstream electron flow via FNR sequestration [#6, #7]\",\n      \"FD is not a direct target of artemisinin; DHA acts on FNR–NADPH affinity, and the D193Y FD variant does not alter artemisinin susceptibility or fitness [#9, #10]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_1318100","name":null,"product":"ferredoxin","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_1416600","name":null,"product":"ferredoxin, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_1418800","name":null,"product":"ferredoxin, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"FD","evaluation":null}