{"gene":"PF3D7_1446800","run_date":"2026-09-08T14:19:07","timeline":{"discoveries":[{"year":2008,"finding":"HDP (PF3D7_1446800) is extremely potent in converting heme into hemozoin (Hz) in vitro. The parasite traffics HDP via an 'Outbound-Inbound' route: HDP is initially secreted into the cytosol of the infected red blood cell, and a subsequent endocytosis of host cytosol (together with hemoglobin) delivers HDP to the food vacuole, the site of Hz formation. The HDP gene locus could not be disrupted, indicating essentiality.","method":"Hz formation assay, cellular fractionation/trafficking experiments, gene disruption attempts, functional conservation across Plasmodium species","journal":"PLoS Pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (in vitro Hz assay, localization, gene disruption), replicated across species, published in peer-reviewed journal","pmids":["18437218"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"finding":"HDP is a component of a ~200-kDa protein complex in the food vacuole that also contains falcipain 2/2', plasmepsin II, plasmepsin IV, and histo aspartic protease; this complex is required for hemoglobin degradation and Hz formation. Specifically, falcipain 2 and HDP associate with each other to efficiently convert hemoglobin to Hz in vitro.","method":"Co-immunoprecipitation followed by mass spectrometry, gel filtration co-elution, glycerol gradient cosedimentation, in vitro protein interaction analyses, in vitro Hz formation assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — four orthogonal biochemical methods (Co-IP/MS, gel filtration, gradient cosedimentation, in vitro reconstitution) in a single rigorous study","pmids":["23471987"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"finding":"Recombinant non-tagged HDP has two heme-binding sites and exhibits a spectrum typical of heme proteins; the His-tag interferes with the heme-binding properties of the recombinant protein, indicating that the N-terminal/tag region affects the active conformation.","method":"Recombinant protein expression and purification, UV-visible spectroscopy, heme-binding characterization","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro spectroscopic characterization with purified protein, single lab, single method set","pmids":["24025682"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"finding":"Histidine residues His122, His172, His175, and His197 are essential for HDP activity: substitution of each reduced Hz formation to ~50% of wild-type. His122 directly binds heme; His172 and His175 form part of a second heme-binding site. These histidines act as molecular tethers positioning two hemes for dimer formation, which seeds Hz crystal growth.","method":"Site-directed mutagenesis, in vitro Hz formation assay, UV-visible and resonance Raman spectroscopy of mutant proteins","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — active-site mutagenesis combined with spectroscopic characterization and Hz formation assay, single lab but multiple orthogonal methods","pmids":["25138161"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"finding":"HDP from Plasmodium vinckei (PvHDP) binds free heme (KD = 89 nM) and efficiently converts heme into hemozoin in a time- and concentration-dependent manner at acidic pH. Chemical modification of histidine residues with DEPC reduced heme binding and Hz formation, confirming that histidine residues are critical for heme binding and hemozoin production. PvHDP is cytosolic and expressed throughout intraerythrocytic stages, with higher expression in late trophozoite and schizont stages.","method":"Cloning, recombinant expression and purification, heme-binding assay, in vitro Hz formation assay, DEPC histidine modification, subcellular fractionation, western blot across stages","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple biochemical methods (binding assay, Hz assay, chemical modification, fractionation), single lab","pmids":["25891072"],"is_preprint":false,"attribution":[{"species":"Plasmodium vinckei","strain":""}]},{"year":2012,"finding":"Down-expression of HDP in Plasmodium yoelii is associated with resistance to artemisinin-based compounds. Resistant strains showed loss of hemozoin formation linked to reduced HDP expression, and detoxification shifted to an alternative glutathione-mediated pathway, suggesting that HDP-dependent hemozoin formation is part of the mechanism of action of artemisinins.","method":"In vivo drug pressure selection in murine model, measurement of hemozoin formation, HDP expression analysis, glutathione pathway assessment","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo genetic selection with phenotypic and molecular readouts, single lab, correlative but with functional drug-resistance phenotype","pmids":["22403683"],"is_preprint":false,"attribution":[{"species":"Plasmodium yoelii","strain":""}]},{"year":2017,"finding":"HDP has two heme-binding sites and a hemoglobin-binding site identified by in silico and biochemical approaches. A peptide corresponding to the hemoglobin-binding domain of HDP caused food vacuole abnormalities in P. falciparum 3D7 parasites similar to those induced by cysteine protease inhibitor E-64, functionally linking this domain to hemoglobin processing in the food vacuole.","method":"In silico structural modeling, biochemical binding assays, peptide competition experiment in live P. falciparum 3D7 culture with morphological readout, compound screening against modeled structure","journal":"Journal of medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — combines in silico modeling with biochemical assays and cell-based peptide inhibition experiment, single lab","pmids":["28949547"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2022,"finding":"HDP localizes to the parasitophorous vacuole, parasite food vacuole, and infected erythrocyte cytosol. Immunoprecipitation of PfHDP-GFP showed association of HDP with hemoglobin and with members of the PTEX translocon complex (including PfEXP-2). Knockdown of HDP using a GlmS ribozyme system significantly reduced hemoglobin uptake, caused food vacuole abnormalities, and produced a growth defect, establishing a role for HDP in hemoglobin uptake.","method":"GFP-trap immunoprecipitation, protein-protein interaction assays, immunolocalization, GlmS ribozyme conditional knockdown, hemoglobin uptake assay, morphological analysis","journal":"FASEB bioAdvances","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, conditional knockdown with defined functional readout (Hb uptake), immunolocalization, multiple orthogonal methods in single study","pmids":["36238365"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"finding":"HDP-mediated transformation of heme into hemozoin is not a single-step process and involves a transient intermediate, most likely a cyclic heme dimer. The N-terminal region of HDP is essential: a construct with a 44-residue N-terminal truncation (HDPpf-C10) retained heme-binding domains but exhibited no detectable heme-to-Hz transformation activity.","method":"Optimized pyridine hemochrome assay for kinetic studies, substrate and time kinetics, recombinant N-terminal truncation constructs","journal":"Biochimica et biophysica acta. Proteins and proteomics","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic kinetics with truncation mutant, single lab, two orthogonal approaches (kinetics + truncation mutagenesis)","pmids":["35934300","40759288"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2026,"finding":"Endogenous tagging reveals that HDP localizes to the mitochondrion, not the digestive vacuole. HDP inactivation (knockout) has no effect on heme biomineralization (hemozoin formation) but causes mitochondrial depolarization, proguanil hypersensitivity, and developmental arrest; this developmental arrest is rescued by bypassing respiratory-chain-dependent pyrimidine biosynthesis. HDP knockout abolishes mitochondrial electron flow due to loss of complexes III and IV, consistent with impaired mitochondrial protein synthesis. Structural modelling integrated with quantitative proteomics places HDP within the mitoribosomal large subunit.","method":"Endogenous protein tagging, live fluorescence microscopy, genetic knockout, bioenergetic assays (mitochondrial membrane potential), drug sensitivity assays, quantitative proteomics, structural modelling of mitoribosome","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — endogenous tagging localization, genetic KO with multiple orthogonal phenotypic readouts (bioenergetics, drug sensitivity, proteomics, genetic rescue), single rigorous study with multiple methods","pmids":["42567866"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"HDP (PF3D7_1446800) localizes to the mitochondrion (not the digestive vacuole as previously believed) where it is essential for mitochondrial protein synthesis as a component of the mitoribosomal large subunit; its knockout abolishes mitochondrial electron flow through complexes III and IV, causes developmental arrest rescued by bypassing respiratory-chain-dependent pyrimidine biosynthesis, and has no detectable effect on hemozoin formation — contradicting earlier work (based on non-endogenously-tagged or heterologously-expressed protein) that placed HDP in the food vacuole as the primary driver of heme-to-hemozoin conversion, and indicating that those prior mechanistic assignments require re-evaluation in light of the more rigorous endogenous-tagging and knockout study."},"narrative":{"mechanistic_narrative":"PF3D7_1446800 (HDP) is an essential Plasmodium protein whose function has been the subject of two divergent mechanistic models built on different experimental foundations [PMID:18437218, PMID:42567866]. In vitro and heterologous/non-endogenous-tagging studies characterized HDP as a highly potent heme detoxification protein that converts free heme into hemozoin: recombinant protein possesses two heme-binding sites with a heme-protein spectrum [PMID:24025682], and histidine residues His122, His172, His175, and His197 act as molecular tethers that position two hemes for dimer formation seeding hemozoin crystal growth [PMID:25138161], with heme-to-hemozoin conversion proceeding through a transient cyclic heme-dimer intermediate and depending on the N-terminal region [PMID:35934300, PMID:40759288]. In this model HDP reaches the food vacuole via an 'Outbound-Inbound' trafficking route through the infected-erythrocyte cytosol [PMID:18437218], associates with a food-vacuole protease complex containing falcipain 2/2', plasmepsins II and IV, and histo-aspartic protease to couple hemoglobin degradation to hemozoin formation [PMID:23471987], and contributes to hemoglobin uptake through interactions with hemoglobin and PTEX translocon components including PfEXP-2 [PMID:36238365]. A subsequent study using endogenous tagging and genetic knockout instead localizes HDP to the mitochondrion and places it within the mitoribosomal large subunit, where its loss abolishes mitochondrial electron flow through complexes III and IV and causes developmental arrest rescued by bypassing respiratory-chain-dependent pyrimidine biosynthesis, while having no detectable effect on hemozoin formation [PMID:42567866]. The prior food-vacuole/heme-detoxification assignments therefore require re-evaluation against this endogenous-tagging and knockout evidence [PMID:42567866].","teleology":[{"year":2008,"claim":"Establishing whether a dedicated parasite factor drives heme-to-hemozoin conversion, this work identified HDP as a potent heme-detoxifying protein trafficked to the food vacuole and showed the locus is essential.","evidence":"In vitro hemozoin formation assay, cellular fractionation/trafficking, and failed gene-disruption in P. falciparum","pmids":["18437218"],"confidence":"High","gaps":["Essentiality inferred from failed disruption, not conditional depletion","Trafficking route inferred rather than directly imaged for endogenous protein","In vitro activity does not establish the physiological site of action"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2012,"claim":"To connect HDP to antimalarial action, reduced HDP expression was linked to loss of hemozoin formation and artemisinin resistance, implying hemozoin production is part of the artemisinin mechanism.","evidence":"In vivo drug-pressure selection in P. yoelii with hemozoin, HDP expression, and glutathione-pathway readouts","pmids":["22403683"],"confidence":"Medium","gaps":["Correlative expression change rather than defined genetic lesion","Does not exclude other adaptive changes in resistant strains","Rodent-parasite model of unclear translation to human parasites"],"attribution":[{"species":"Plasmodium yoelii","strain":""}]},{"year":2013,"claim":"To define the biochemical context of heme processing, HDP was shown to form part of a food-vacuole protease complex and to cooperate with falcipain 2 in converting hemoglobin to hemozoin, and separately to possess two intrinsic heme-binding sites.","evidence":"Co-IP/MS, gel filtration, glycerol gradient cosedimentation and in vitro reconstitution [#1]; recombinant protein UV-visible spectroscopy [#2] in P. falciparum","pmids":["23471987","24025682"],"confidence":"High","gaps":["Complex composition from co-fractionation does not establish direct binary contacts for all members","His-tag altered heme-binding, complicating interpretation of recombinant spectra","Physiological necessity of the complex for hemozoin formation not tested by depletion"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"claim":"To resolve the catalytic chemistry, specific histidines were shown to tether and position two hemes for dimer formation that seeds hemozoin crystallization.","evidence":"Site-directed mutagenesis of His122/His172/His175/His197 with hemozoin assay and UV-visible/resonance Raman spectroscopy in P. falciparum","pmids":["25138161"],"confidence":"High","gaps":["Each mutation only halved activity, leaving residual mechanism unexplained","No crystal structure of the heme-bound protein","Assays performed in vitro with recombinant protein"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"claim":"Cross-species conservation of the heme-detoxification model was tested by characterizing the P. vinckei ortholog's high-affinity heme binding and histidine-dependent hemozoin formation.","evidence":"Recombinant PvHDP heme-binding and hemozoin assays, DEPC histidine modification, subcellular fractionation and stage western blots in P. vinckei","pmids":["25891072"],"confidence":"Medium","gaps":["Cytosolic localization from fractionation not corroborated by imaging","Ortholog behavior may not fully mirror P. falciparum protein","No genetic test of function"],"attribution":[{"species":"Plasmodium vinckei","strain":""}]},{"year":2017,"claim":"To link HDP function to hemoglobin processing in cells, a hemoglobin-binding domain was mapped and a peptide against it phenocopied cysteine-protease-inhibitor food-vacuole defects.","evidence":"In silico modeling, biochemical binding assays, and peptide competition in live P. falciparum 3D7 with morphological readout","pmids":["28949547"],"confidence":"Medium","gaps":["Peptide phenotype does not prove the endogenous domain acts in the food vacuole","Binding-site assignment partly in silico","No direct depletion of HDP"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2022,"claim":"Conditional depletion and reciprocal interaction studies extended HDP's proposed role to hemoglobin uptake via PTEX-associated partners, and kinetic/truncation work refined the heme-to-hemozoin reaction as multi-step and N-terminus-dependent.","evidence":"GFP-trap Co-IP, GlmS knockdown with hemoglobin-uptake and morphology readouts [#7]; pyridine hemochrome kinetics and N-terminal truncation constructs [#8] in P. falciparum","pmids":["36238365","35934300","40759288"],"confidence":"High","gaps":["Localization by antibody/IP overlaps compartments not resolved to a single site","Interaction with PTEX components not shown to be direct","Kinetic intermediate identity inferred, not structurally captured"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2026,"claim":"Endogenous tagging and knockout overturned the food-vacuole/heme-detoxification model, placing HDP in the mitochondrion as a mitoribosomal large-subunit component essential for mitochondrial protein synthesis and respiration.","evidence":"Endogenous tagging with live imaging, genetic knockout, bioenergetic assays, drug-sensitivity, quantitative proteomics and mitoribosome structural modeling in P. falciparum","pmids":["42567866"],"confidence":"High","gaps":["Direct structural placement in the mitoribosome rests on modeling plus proteomics","Reconciliation with prior in vitro heme-binding and complex data not experimentally addressed here","Whether any residual food-vacuole pool exists is not resolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"It remains unresolved how the earlier heme-binding, histidine-catalysis, and food-vacuole-complex observations relate to the mitochondrial/mitoribosomal function established by endogenous tagging and knockout.","evidence":"","pmids":[],"confidence":"High","gaps":["No study directly reconciles the in vitro hemozoin activity with the knockout phenotype showing no effect on hemozoin","No structure of endogenous HDP in either proposed context","Species divergence (P. vinckei, P. yoelii) not re-examined with endogenous methods"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["~200-kDa food-vacuole protease complex with falcipain 2/2', plasmepsin II, plasmepsin IV, and histo-aspartic protease [#1]","Mitoribosomal large subunit [#9]"],"partners":["FALCIPAIN 2/2' [#1]","PLASMEPSIN II [#1]","PLASMEPSIN IV [#1]","HISTO-ASPARTIC PROTEASE [#1]","HEMOGLOBIN [#7]","PTEX TRANSLOCON COMPONENTS INCLUDING PFEXP-2 [#7]"],"other_free_text":["Two proposed heme-binding sites; His122 binds heme directly, His172/His175 form a second site, and His197 contributes to activity [#2, #3].","Heme-to-hemozoin conversion is multi-step, involving a transient cyclic heme-dimer intermediate, and requires the N-terminal region [#8].","Down-expression correlated with artemisinin resistance and loss of hemozoin in P. yoelii [#5].","Endogenous tagging/knockout places HDP in the mitochondrion with no detectable effect on hemozoin formation, contradicting the food-vacuole heme-detoxification model [#9]."]}},"prefetch_data":{},"corpus_meta":[{"pmid":"18437218","id":"PMC_18437218","title":"HDP-a novel heme detoxification protein from the malaria parasite.","date":"2008","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/18437218","citation_count":132,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HDP","heme detoxification 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detoxification protein (HDP).","date":"2008","source":"Infection, genetics and evolution : journal of molecular epidemiology and evolutionary genetics in infectious diseases","url":"https://pubmed.ncbi.nlm.nih.gov/19135554","citation_count":8,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HDP","heme detoxification protein"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"35724244","id":"PMC_35724244","title":"Limited genetic diversity and expression profile of Plasmodium falciparum haem detoxification protein: a possible diagnostic target.","date":"2022","source":"Transactions of the Royal Society of Tropical Medicine and Hygiene","url":"https://pubmed.ncbi.nlm.nih.gov/35724244","citation_count":7,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HDP"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"35934300","id":"PMC_35934300","title":"An assay procedure to investigate the transformation of toxic heme into inert hemozoin via plasmodial heme detoxification protein.","date":"2022","source":"Biochimica et biophysica acta. Proteins and proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/35934300","citation_count":4,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HDP","heme detoxification protein"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"38197419","id":"PMC_38197419","title":"A computational strategy for systematic virtual screening of plasmodium falciparum heme detoxification protein inhibitors from the Drugbank database.","date":"2024","source":"Journal of biomolecular structure & dynamics","url":"https://pubmed.ncbi.nlm.nih.gov/38197419","citation_count":3,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HDP","heme detoxification protein"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"42567866","id":"PMC_42567866","title":"The Plasmodium heme detoxification protein functions in mitochondrial protein synthesis.","date":"2026","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/42567866","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HDP","heme detoxification protein"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"41091754","id":"PMC_41091754","title":"Evaluation of GDH and HDP as novel serological biomarkers for Plasmodium falciparum malaria diagnosis across varying parasitemia and transmission settings in India.","date":"2025","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/41091754","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HDP"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"39269102","id":"PMC_39269102","title":"Potential of Enzymatically Synthesized Hemozoin Analog as Th1 Cell Adjuvant.","date":"2024","source":"Nanomaterials (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/39269102","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HDP","heme detoxification protein"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"40759288","id":"PMC_40759288","title":"Recombinant expression and purification of Plasmodium heme detoxification protein in E. coli: Challenges and discoveries.","date":"2025","source":"Protein expression and purification","url":"https://pubmed.ncbi.nlm.nih.gov/40759288","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HDP","heme detoxification protein"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"41713229","id":"PMC_41713229","title":"Atomistic simulations identify the Tetrandrine as potent anti-malarial drug candidate against Plasmodium falciparum targeting Heme Detoxification Protein (HDP).","date":"2026","source":"Journal of molecular graphics & modelling","url":"https://pubmed.ncbi.nlm.nih.gov/41713229","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HDP","heme detoxification protein"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"40945876","id":"PMC_40945876","title":"Characterization of genes involved in hemoglobin degradation in Plasmodium vivax isolates from Chennai, India, and species of non-human primate malaria.","date":"2025","source":"Infection, genetics and evolution : journal of molecular epidemiology and evolutionary genetics in infectious diseases","url":"https://pubmed.ncbi.nlm.nih.gov/40945876","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HDP","heme detoxification protein"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":14719,"output_tokens":3092,"usd":0.045269,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8867,"output_tokens":4170,"usd":0.074292,"stage2_stop_reason":"end_turn"},"total_usd":0.119561,"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\": 2008,\n      \"finding\": \"HDP (PF3D7_1446800) is extremely potent in converting heme into hemozoin (Hz) in vitro. The parasite traffics HDP via an 'Outbound-Inbound' route: HDP is initially secreted into the cytosol of the infected red blood cell, and a subsequent endocytosis of host cytosol (together with hemoglobin) delivers HDP to the food vacuole, the site of Hz formation. The HDP gene locus could not be disrupted, indicating essentiality.\",\n      \"method\": \"Hz formation assay, cellular fractionation/trafficking experiments, gene disruption attempts, functional conservation across Plasmodium species\",\n      \"journal\": \"PLoS Pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (in vitro Hz assay, localization, gene disruption), replicated across species, published in peer-reviewed journal\",\n      \"pmids\": [\"18437218\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"HDP is a component of a ~200-kDa protein complex in the food vacuole that also contains falcipain 2/2', plasmepsin II, plasmepsin IV, and histo aspartic protease; this complex is required for hemoglobin degradation and Hz formation. Specifically, falcipain 2 and HDP associate with each other to efficiently convert hemoglobin to Hz in vitro.\",\n      \"method\": \"Co-immunoprecipitation followed by mass spectrometry, gel filtration co-elution, glycerol gradient cosedimentation, in vitro protein interaction analyses, in vitro Hz formation assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — four orthogonal biochemical methods (Co-IP/MS, gel filtration, gradient cosedimentation, in vitro reconstitution) in a single rigorous study\",\n      \"pmids\": [\"23471987\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Recombinant non-tagged HDP has two heme-binding sites and exhibits a spectrum typical of heme proteins; the His-tag interferes with the heme-binding properties of the recombinant protein, indicating that the N-terminal/tag region affects the active conformation.\",\n      \"method\": \"Recombinant protein expression and purification, UV-visible spectroscopy, heme-binding characterization\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro spectroscopic characterization with purified protein, single lab, single method set\",\n      \"pmids\": [\"24025682\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Histidine residues His122, His172, His175, and His197 are essential for HDP activity: substitution of each reduced Hz formation to ~50% of wild-type. His122 directly binds heme; His172 and His175 form part of a second heme-binding site. These histidines act as molecular tethers positioning two hemes for dimer formation, which seeds Hz crystal growth.\",\n      \"method\": \"Site-directed mutagenesis, in vitro Hz formation assay, UV-visible and resonance Raman spectroscopy of mutant proteins\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — active-site mutagenesis combined with spectroscopic characterization and Hz formation assay, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"25138161\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"HDP from Plasmodium vinckei (PvHDP) binds free heme (KD = 89 nM) and efficiently converts heme into hemozoin in a time- and concentration-dependent manner at acidic pH. Chemical modification of histidine residues with DEPC reduced heme binding and Hz formation, confirming that histidine residues are critical for heme binding and hemozoin production. PvHDP is cytosolic and expressed throughout intraerythrocytic stages, with higher expression in late trophozoite and schizont stages.\",\n      \"method\": \"Cloning, recombinant expression and purification, heme-binding assay, in vitro Hz formation assay, DEPC histidine modification, subcellular fractionation, western blot across stages\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple biochemical methods (binding assay, Hz assay, chemical modification, fractionation), single lab\",\n      \"pmids\": [\"25891072\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium vinckei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Down-expression of HDP in Plasmodium yoelii is associated with resistance to artemisinin-based compounds. Resistant strains showed loss of hemozoin formation linked to reduced HDP expression, and detoxification shifted to an alternative glutathione-mediated pathway, suggesting that HDP-dependent hemozoin formation is part of the mechanism of action of artemisinins.\",\n      \"method\": \"In vivo drug pressure selection in murine model, measurement of hemozoin formation, HDP expression analysis, glutathione pathway assessment\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo genetic selection with phenotypic and molecular readouts, single lab, correlative but with functional drug-resistance phenotype\",\n      \"pmids\": [\"22403683\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium yoelii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"HDP has two heme-binding sites and a hemoglobin-binding site identified by in silico and biochemical approaches. A peptide corresponding to the hemoglobin-binding domain of HDP caused food vacuole abnormalities in P. falciparum 3D7 parasites similar to those induced by cysteine protease inhibitor E-64, functionally linking this domain to hemoglobin processing in the food vacuole.\",\n      \"method\": \"In silico structural modeling, biochemical binding assays, peptide competition experiment in live P. falciparum 3D7 culture with morphological readout, compound screening against modeled structure\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — combines in silico modeling with biochemical assays and cell-based peptide inhibition experiment, single lab\",\n      \"pmids\": [\"28949547\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"HDP localizes to the parasitophorous vacuole, parasite food vacuole, and infected erythrocyte cytosol. Immunoprecipitation of PfHDP-GFP showed association of HDP with hemoglobin and with members of the PTEX translocon complex (including PfEXP-2). Knockdown of HDP using a GlmS ribozyme system significantly reduced hemoglobin uptake, caused food vacuole abnormalities, and produced a growth defect, establishing a role for HDP in hemoglobin uptake.\",\n      \"method\": \"GFP-trap immunoprecipitation, protein-protein interaction assays, immunolocalization, GlmS ribozyme conditional knockdown, hemoglobin uptake assay, morphological analysis\",\n      \"journal\": \"FASEB bioAdvances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, conditional knockdown with defined functional readout (Hb uptake), immunolocalization, multiple orthogonal methods in single study\",\n      \"pmids\": [\"36238365\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"HDP-mediated transformation of heme into hemozoin is not a single-step process and involves a transient intermediate, most likely a cyclic heme dimer. The N-terminal region of HDP is essential: a construct with a 44-residue N-terminal truncation (HDPpf-C10) retained heme-binding domains but exhibited no detectable heme-to-Hz transformation activity.\",\n      \"method\": \"Optimized pyridine hemochrome assay for kinetic studies, substrate and time kinetics, recombinant N-terminal truncation constructs\",\n      \"journal\": \"Biochimica et biophysica acta. Proteins and proteomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic kinetics with truncation mutant, single lab, two orthogonal approaches (kinetics + truncation mutagenesis)\",\n      \"pmids\": [\"35934300\", \"40759288\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Endogenous tagging reveals that HDP localizes to the mitochondrion, not the digestive vacuole. HDP inactivation (knockout) has no effect on heme biomineralization (hemozoin formation) but causes mitochondrial depolarization, proguanil hypersensitivity, and developmental arrest; this developmental arrest is rescued by bypassing respiratory-chain-dependent pyrimidine biosynthesis. HDP knockout abolishes mitochondrial electron flow due to loss of complexes III and IV, consistent with impaired mitochondrial protein synthesis. Structural modelling integrated with quantitative proteomics places HDP within the mitoribosomal large subunit.\",\n      \"method\": \"Endogenous protein tagging, live fluorescence microscopy, genetic knockout, bioenergetic assays (mitochondrial membrane potential), drug sensitivity assays, quantitative proteomics, structural modelling of mitoribosome\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — endogenous tagging localization, genetic KO with multiple orthogonal phenotypic readouts (bioenergetics, drug sensitivity, proteomics, genetic rescue), single rigorous study with multiple methods\",\n      \"pmids\": [\"42567866\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"HDP (PF3D7_1446800) localizes to the mitochondrion (not the digestive vacuole as previously believed) where it is essential for mitochondrial protein synthesis as a component of the mitoribosomal large subunit; its knockout abolishes mitochondrial electron flow through complexes III and IV, causes developmental arrest rescued by bypassing respiratory-chain-dependent pyrimidine biosynthesis, and has no detectable effect on hemozoin formation — contradicting earlier work (based on non-endogenously-tagged or heterologously-expressed protein) that placed HDP in the food vacuole as the primary driver of heme-to-hemozoin conversion, and indicating that those prior mechanistic assignments require re-evaluation in light of the more rigorous endogenous-tagging and knockout study.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PF3D7_1446800 (HDP) is an essential Plasmodium protein whose function has been the subject of two divergent mechanistic models built on different experimental foundations [#0, #9]. In vitro and heterologous/non-endogenous-tagging studies characterized HDP as a highly potent heme detoxification protein that converts free heme into hemozoin: recombinant protein possesses two heme-binding sites with a heme-protein spectrum [#2], and histidine residues His122, His172, His175, and His197 act as molecular tethers that position two hemes for dimer formation seeding hemozoin crystal growth [#3], with heme-to-hemozoin conversion proceeding through a transient cyclic heme-dimer intermediate and depending on the N-terminal region [#8]. In this model HDP reaches the food vacuole via an 'Outbound-Inbound' trafficking route through the infected-erythrocyte cytosol [#0], associates with a food-vacuole protease complex containing falcipain 2/2', plasmepsins II and IV, and histo-aspartic protease to couple hemoglobin degradation to hemozoin formation [#1], and contributes to hemoglobin uptake through interactions with hemoglobin and PTEX translocon components including PfEXP-2 [#7]. A subsequent study using endogenous tagging and genetic knockout instead localizes HDP to the mitochondrion and places it within the mitoribosomal large subunit, where its loss abolishes mitochondrial electron flow through complexes III and IV and causes developmental arrest rescued by bypassing respiratory-chain-dependent pyrimidine biosynthesis, while having no detectable effect on hemozoin formation [#9]. The prior food-vacuole/heme-detoxification assignments therefore require re-evaluation against this endogenous-tagging and knockout evidence [#9].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Establishing whether a dedicated parasite factor drives heme-to-hemozoin conversion, this work identified HDP as a potent heme-detoxifying protein trafficked to the food vacuole and showed the locus is essential.\",\n      \"evidence\": \"In vitro hemozoin formation assay, cellular fractionation/trafficking, and failed gene-disruption in P. falciparum\",\n      \"pmids\": [\"18437218\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Essentiality inferred from failed disruption, not conditional depletion\", \"Trafficking route inferred rather than directly imaged for endogenous protein\", \"In vitro activity does not establish the physiological site of action\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"To connect HDP to antimalarial action, reduced HDP expression was linked to loss of hemozoin formation and artemisinin resistance, implying hemozoin production is part of the artemisinin mechanism.\",\n      \"evidence\": \"In vivo drug-pressure selection in P. yoelii with hemozoin, HDP expression, and glutathione-pathway readouts\",\n      \"pmids\": [\"22403683\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Correlative expression change rather than defined genetic lesion\", \"Does not exclude other adaptive changes in resistant strains\", \"Rodent-parasite model of unclear translation to human parasites\"],\n      \"attribution\": [{\"species\": \"Plasmodium yoelii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"To define the biochemical context of heme processing, HDP was shown to form part of a food-vacuole protease complex and to cooperate with falcipain 2 in converting hemoglobin to hemozoin, and separately to possess two intrinsic heme-binding sites.\",\n      \"evidence\": \"Co-IP/MS, gel filtration, glycerol gradient cosedimentation and in vitro reconstitution [#1]; recombinant protein UV-visible spectroscopy [#2] in P. falciparum\",\n      \"pmids\": [\"23471987\", \"24025682\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Complex composition from co-fractionation does not establish direct binary contacts for all members\", \"His-tag altered heme-binding, complicating interpretation of recombinant spectra\", \"Physiological necessity of the complex for hemozoin formation not tested by depletion\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"To resolve the catalytic chemistry, specific histidines were shown to tether and position two hemes for dimer formation that seeds hemozoin crystallization.\",\n      \"evidence\": \"Site-directed mutagenesis of His122/His172/His175/His197 with hemozoin assay and UV-visible/resonance Raman spectroscopy in P. falciparum\",\n      \"pmids\": [\"25138161\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Each mutation only halved activity, leaving residual mechanism unexplained\", \"No crystal structure of the heme-bound protein\", \"Assays performed in vitro with recombinant protein\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Cross-species conservation of the heme-detoxification model was tested by characterizing the P. vinckei ortholog's high-affinity heme binding and histidine-dependent hemozoin formation.\",\n      \"evidence\": \"Recombinant PvHDP heme-binding and hemozoin assays, DEPC histidine modification, subcellular fractionation and stage western blots in P. vinckei\",\n      \"pmids\": [\"25891072\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cytosolic localization from fractionation not corroborated by imaging\", \"Ortholog behavior may not fully mirror P. falciparum protein\", \"No genetic test of function\"],\n      \"attribution\": [{\"species\": \"Plasmodium vinckei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"To link HDP function to hemoglobin processing in cells, a hemoglobin-binding domain was mapped and a peptide against it phenocopied cysteine-protease-inhibitor food-vacuole defects.\",\n      \"evidence\": \"In silico modeling, biochemical binding assays, and peptide competition in live P. falciparum 3D7 with morphological readout\",\n      \"pmids\": [\"28949547\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Peptide phenotype does not prove the endogenous domain acts in the food vacuole\", \"Binding-site assignment partly in silico\", \"No direct depletion of HDP\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Conditional depletion and reciprocal interaction studies extended HDP's proposed role to hemoglobin uptake via PTEX-associated partners, and kinetic/truncation work refined the heme-to-hemozoin reaction as multi-step and N-terminus-dependent.\",\n      \"evidence\": \"GFP-trap Co-IP, GlmS knockdown with hemoglobin-uptake and morphology readouts [#7]; pyridine hemochrome kinetics and N-terminal truncation constructs [#8] in P. falciparum\",\n      \"pmids\": [\"36238365\", \"35934300\", \"40759288\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Localization by antibody/IP overlaps compartments not resolved to a single site\", \"Interaction with PTEX components not shown to be direct\", \"Kinetic intermediate identity inferred, not structurally captured\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Endogenous tagging and knockout overturned the food-vacuole/heme-detoxification model, placing HDP in the mitochondrion as a mitoribosomal large-subunit component essential for mitochondrial protein synthesis and respiration.\",\n      \"evidence\": \"Endogenous tagging with live imaging, genetic knockout, bioenergetic assays, drug-sensitivity, quantitative proteomics and mitoribosome structural modeling in P. falciparum\",\n      \"pmids\": [\"42567866\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct structural placement in the mitoribosome rests on modeling plus proteomics\", \"Reconciliation with prior in vitro heme-binding and complex data not experimentally addressed here\", \"Whether any residual food-vacuole pool exists is not resolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how the earlier heme-binding, histidine-catalysis, and food-vacuole-complex observations relate to the mitochondrial/mitoribosomal function established by endogenous tagging and knockout.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No study directly reconciles the in vitro hemozoin activity with the knockout phenotype showing no effect on hemozoin\", \"No structure of endogenous HDP in either proposed context\", \"Species divergence (P. vinckei, P. yoelii) not re-examined with endogenous methods\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0020037\", \"supporting_discovery_ids\": [2, 3, 4]},\n      {\"term_id\": \"GO:0004392\", \"supporting_discovery_ids\": [0, 3, 8]},\n      {\"term_id\": \"GO:0003735\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020020\", \"supporting_discovery_ids\": [0, 1, 6]},\n      {\"term_id\": \"GO:0020005\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0005762\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0042541\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0032543\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0006119\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0044205\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"complexes\": [\n      \"~200-kDa food-vacuole protease complex with falcipain 2/2', plasmepsin II, plasmepsin IV, and histo-aspartic protease [#1]\",\n      \"Mitoribosomal large subunit [#9]\"\n    ],\n    \"partners\": [\n      \"Falcipain 2/2' [#1]\",\n      \"Plasmepsin II [#1]\",\n      \"Plasmepsin IV [#1]\",\n      \"Histo-aspartic protease [#1]\",\n      \"Hemoglobin [#7]\",\n      \"PTEX translocon components including PfEXP-2 [#7]\"\n    ],\n    \"other_free_text\": [\n      \"Two proposed heme-binding sites; His122 binds heme directly, His172/His175 form a second site, and His197 contributes to activity [#2, #3].\",\n      \"Heme-to-hemozoin conversion is multi-step, involving a transient cyclic heme-dimer intermediate, and requires the N-terminal region [#8].\",\n      \"Down-expression correlated with artemisinin resistance and loss of hemozoin in P. yoelii [#5].\",\n      \"Endogenous tagging/knockout places HDP in the mitochondrion with no detectable effect on hemozoin formation, contradicting the food-vacuole heme-detoxification model [#9].\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_1446800","name":null,"product":"heme detoxification protein","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_1310600","name":null,"product":"heme detoxification protein, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_1235400","name":null,"product":"heme detoxification protein, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"HDP","evaluation":null}