{"gene":"PF3D7_0617800","run_date":"2026-09-08T12:51:26","timeline":{"discoveries":[{"year":1992,"finding":"The canonical histone H2A gene of Plasmodium falciparum (PF3D7_0617800) was identified and characterized at the sequence level.","method":"Molecular cloning and gene identification","journal":"Molecular and biochemical parasitology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single gene identification paper, no functional mechanistic follow-up described in abstract","pmids":["1518525"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1997,"finding":"Canonical H2A protein was purified from P. falciparum infected erythrocytes and culture supernatant; N-terminal sequence analysis confirmed its identity as a core histone and antibodies localized the protein to schizont nuclei by immunofluorescence.","method":"Acid extraction/purification, N-terminal sequencing, immunofluorescence","journal":"Parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct protein purification and localization by two orthogonal methods (sequencing + immunofluorescence), single lab","pmids":["9149412"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1999,"finding":"H2A transcript is absent in ring stage parasites but present at elevated levels in trophozoites, schizonts, and gametocytes of P. falciparum, indicating developmental stage-specific transcription of the canonical H2A gene.","method":"Transcription profiling across developmental stages (RT-based detection)","journal":"International journal for parasitology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single method (transcript detection), no mechanistic follow-up","pmids":["10579431"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2006,"finding":"Mass spectrometry confirmed synthesis of canonical H2A protein in P. falciparum erythrocytic stages; real-time RT-PCR and immunoblotting showed a dramatic increase in canonical H2A gene expression during late trophozoite stages, consistent with replication-related nucleosome assembly.","method":"Mass spectrometry, real-time RT-PCR, immunoblotting","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (MS, RT-PCR, western blot) in a single study confirming protein synthesis and expression dynamics","pmids":["16410041"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"finding":"Recombinant PfPRMT1 (a type I protein arginine methyltransferase) methylates histone H2A in vitro, establishing H2A as a substrate for arginine methylation by PfPRMT1 in P. falciparum.","method":"In vitro methyltransferase assay with recombinant PfPRMT1 and histone substrates","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct in vitro enzymatic assay with recombinant proteins, single lab, no site mapping reported for H2A specifically","pmids":["19344311"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"finding":"Global mass spectrometry analysis of P. falciparum histones identified and mapped post-translational modifications on canonical H2A protein, placing it in a comprehensive histone modification map of the parasite.","method":"Acid extraction, SDS-PAGE, LC-MS/MS (Q-TOF and LTQ-FT mass spectrometry)","journal":"Journal of proteome research","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — high mass accuracy MS with multiple instrument types, single lab but rigorous methodology","pmids":["19351122"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"PfNapS (nucleosome assembly protein) interacts with core histones including H2A in P. falciparum, as shown by fluorescence spectroscopy; the interaction site on PfNapS for core histones (H2A, H2B, H3, H4 tetramer and octamer) is distinct from its site for linker histone H1.","method":"Fluorescence spectroscopy binding assay, crystal structure of PfNapS","journal":"Malaria journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biophysical binding assay plus structural analysis, single lab","pmids":["20377878"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"finding":"P. falciparum H2A and H2B display decreased salt stability compared to human counterparts, and plasmodium nucleosomes overall show reduced stability (increased temperature-induced mobility, reduced binding affinity to GC-rich DNA), as determined by comparative biochemical analysis of human and parasite histones.","method":"In vitro nucleosome reconstitution, salt stability assay, thermal mobility assay, DNA binding affinity measurement","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with multiple orthogonal biochemical assays (salt stability, thermal mobility, DNA binding), single lab","pmids":["28033404"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"In P. falciparum, which lacks the H2A.X variant, the canonical H2A (PfH2A, PF3D7_0617800) is phosphorylated on serine 121 in response to DNA double-strand break-inducing damage. Phosphorylated PfH2A (γ-PfH2A) is recruited to foci of damaged chromatin, while non-phosphorylated PfH2A remains spread throughout the nucleoplasm. This phosphorylation is dynamic and is removed as the repair machinery is activated.","method":"Immunofluorescence with phospho-specific antibodies, live imaging, DNA damage assays with genotoxic agents","journal":"mSphere","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct phosphorylation site identification (S121), reciprocal localization studies with multiple DNA damage agents, functional linkage to DNA repair dynamics, single lab with multiple orthogonal approaches","pmids":["33441412"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"finding":"Canonical H2A (PfH2A) phosphorylation (γ-PfH2A) serves as a mark of DNA double-strand breaks in P. falciparum; PfMYST overexpression leads to high basal γ-PfH2A levels and PfMYST colocalizes with γ-PfH2A at DNA damage sites, indicating PfMYST is recruited to H2A phosphorylation foci during DNA damage response.","method":"Western blotting, immunofluorescence co-localization, overexpression and knockdown of PfMYST","journal":"mSphere","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional genetic manipulation (OE and KD) with direct co-localization, single lab","pmids":["38564734"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"In a bacterial two-hybrid screen, P. falciparum Tudor Staphylococcal Nuclease (PfTudor-SN) was found to interact with histone H2A, suggesting H2A participates in nuclear protein interactions involving PfTudor-SN.","method":"Bacterial two-hybrid screen","journal":"Gene","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single two-hybrid screen, no orthogonal validation of the H2A–PfTudor-SN interaction reported in abstract","pmids":["20713134"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"finding":"PfNPM (a nucleoplasmin isoform histone chaperone) interacts with assembled H2A/H2B dimers in P. falciparum with equimolar stoichiometry; the acidic tracts of PfNPM are necessary for these interactions. H3/H4 displays higher binding affinity for PfNPM than H2A/H2B, potentially due to stronger electrostatic interactions, and H3/H4 may displace H2A/H2B from the same binding site on the PfNPM distal face.","method":"Crystal structure determination, binding affinity measurements, mutagenesis of acidic tracts, size-exclusion chromatography","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus biophysical binding studies with mutagenesis, multiple orthogonal methods in a single rigorous study","pmids":["40049416"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"finding":"PfBDP1 bromodomain interacts with multi-acetylated H2A.Z (a H2A variant distinct from canonical H2A/PF3D7_0617800) in addition to its primary interaction with acetylated histone H3; no direct interaction of PfBDP1 with canonical H2A was reported.","method":"Solution NMR spectroscopy, ITC binding assays, crystal structure","journal":"International journal of biological macromolecules","confidence":"Low","confidence_rationale":"Tier 1 / Weak — this finding concerns H2A.Z (variant), not canonical H2A (PF3D7_0617800); included only to note canonical H2A was not identified as a PfBDP1 interactor","pmids":["36328269"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"Canonical P. falciparum H2A (PF3D7_0617800) is a core nucleosome component whose expression peaks in late trophozoite stages coinciding with DNA replication; its nucleosomes display reduced salt and thermal stability compared to human H2A-containing nucleosomes; it is a substrate for arginine methylation by PfPRMT1 in vitro; it interacts with the histone chaperones PfNapS and PfNPM (with H2A/H2B showing lower affinity for PfNPM than H3/H4); and critically, it functionally substitutes for the absent H2A.X variant by being phosphorylated on serine 121 in response to DNA double-strand breaks, with phospho-PfH2A (γ-PfH2A) recruited to damage foci and removed as repair proceeds, serving as a direct mark of DNA damage and repair in the parasite."},"narrative":{"mechanistic_narrative":"PF3D7_0617800 encodes the canonical core histone H2A of Plasmodium falciparum, a nucleosome-packaging protein whose expression is developmentally coupled to DNA replication, peaking in late trophozoite stages while being absent in rings [PMID:16410041, PMID:10579431]. Reconstituted nucleosomes containing parasite H2A display reduced salt and thermal stability and lower affinity for GC-rich DNA relative to their human counterparts, defining a biochemically distinct chromatin platform in P. falciparum [PMID:28033404]. H2A deposition is handled by dedicated histone chaperones: it binds PfNapS as part of the core histone assembly, and PfNPM engages assembled H2A/H2B dimers via its acidic tracts, with H3/H4 outcompeting H2A/H2B for the same chaperone surface [PMID:20377878, PMID:40049416]. Beyond its structural role, H2A functionally substitutes for the missing H2A.X variant in the DNA damage response: it is phosphorylated on serine 121 upon double-strand breaks, and this γ-PfH2A mark is recruited to damage foci and dynamically removed as repair proceeds, recruiting the acetyltransferase PfMYST to those sites [PMID:33441412, PMID:38564734]. H2A is additionally a substrate for arginine methylation by PfPRMT1 in vitro and carries a broader set of mapped post-translational modifications [PMID:19344311, PMID:19351122].","teleology":[{"year":1992,"claim":"Establishing the molecular identity of the parasite's canonical H2A gene was the necessary first step to studying its chromatin biology.","evidence":"Molecular cloning and sequence-level gene identification in P. falciparum","pmids":["1518525"],"confidence":"Low","gaps":["No functional or mechanistic characterization at this stage","Protein expression and localization not yet addressed"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1997,"claim":"Confirming that the encoded protein is a bona fide core histone localized to the nucleus grounded H2A as a genuine chromatin component rather than a predicted ORF.","evidence":"Acid extraction/purification, N-terminal sequencing, and immunofluorescence localization to schizont nuclei","pmids":["9149412"],"confidence":"Medium","gaps":["Stage-resolved expression not quantified","No interaction partners identified"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1999,"claim":"Defining stage-specific transcription linked H2A expression to the parasite's replicative program rather than constant chromatin turnover.","evidence":"Transcript profiling across developmental stages showing absence in rings and elevated levels in trophozoites, schizonts, and gametocytes","pmids":["10579431"],"confidence":"Low","gaps":["Transcript-level only, protein dynamics not measured","Mechanism coupling expression to replication unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2006,"claim":"Confirming protein-level synthesis and a late-trophozoite expression surge tied H2A abundance directly to replication-phase nucleosome assembly.","evidence":"Mass spectrometry, real-time RT-PCR, and immunoblotting across erythrocytic stages","pmids":["16410041"],"confidence":"Medium","gaps":["Causal role of the expression surge in replication not tested","Assembly machinery not identified here"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"claim":"Identifying H2A as a PfPRMT1 substrate and cataloging its post-translational modifications opened the question of how H2A marks regulate parasite chromatin.","evidence":"In vitro methyltransferase assay with recombinant PfPRMT1; global LC-MS/MS histone PTM mapping","pmids":["19344311","19351122"],"confidence":"Medium","gaps":["Arginine methylation site on H2A not mapped","In vivo relevance of the methylation not established","Functional readout of mapped PTMs unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"claim":"Mapping chaperone and nuclear-protein interactions began to define how H2A is handled during assembly and how it engages the nuclear proteome.","evidence":"Fluorescence spectroscopy binding with PfNapS plus PfNapS crystal structure; bacterial two-hybrid screen against PfTudor-SN","pmids":["20377878","20713134"],"confidence":"Medium","gaps":["PfTudor-SN interaction lacks orthogonal validation","Functional consequence of the PfNapS interaction not tested in vivo"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"claim":"Demonstrating that parasite H2A forms less stable nucleosomes than human H2A revealed an intrinsic biochemical distinctness of Plasmodium chromatin.","evidence":"In vitro nucleosome reconstitution with salt stability, thermal mobility, and GC-rich DNA binding assays comparing human and parasite histones","pmids":["28033404"],"confidence":"High","gaps":["Structural basis of reduced stability not resolved","In vivo consequence for genome accessibility not tested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"claim":"Showing that canonical H2A is phosphorylated on Ser121 and recruited to damage foci established that H2A functionally replaces the absent H2A.X variant in the parasite's DNA damage response.","evidence":"Phospho-specific immunofluorescence, live imaging, and DNA damage assays with genotoxic agents","pmids":["33441412"],"confidence":"High","gaps":["Kinase responsible for S121 phosphorylation not identified","Phosphatase removing the mark not defined","Downstream repair effectors reading γ-PfH2A not mapped"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"claim":"Linking PfMYST recruitment to γ-PfH2A foci placed H2A phosphorylation upstream of a specific chromatin-modifying effector in the damage response.","evidence":"Western blotting, immunofluorescence co-localization, and PfMYST overexpression/knockdown","pmids":["38564734"],"confidence":"Medium","gaps":["Direct physical interaction between PfMYST and γ-PfH2A not shown","Repair outcome dependence on PfMYST recruitment not quantified"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"claim":"Defining the stoichiometry and acidic-tract dependence of PfNPM binding to H2A/H2B refined how the parasite chaperone system stores and hands off core histones.","evidence":"Crystal structure, binding affinity measurements, acidic-tract mutagenesis, and size-exclusion chromatography","pmids":["40049416"],"confidence":"High","gaps":["In vivo role of PfNPM in H2A deposition not established","Competition with H3/H4 not tested in cells"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"The kinase/phosphatase circuit controlling S121 phosphorylation, the in vivo function of H2A arginine methylation, and the physiological consequences of the intrinsically unstable parasite nucleosome remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Enzymes writing and erasing γ-PfH2A not identified","Functional impact of reduced nucleosome stability on genome regulation untested","No loss-of-function genetics for PF3D7_0617800 itself in the corpus"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["Nucleosome (core histone octamer)"],"partners":["PFNAPS (NUCLEOSOME ASSEMBLY PROTEIN)","PFNPM (NUCLEOPLASMIN ISOFORM HISTONE CHAPERONE; H2A/H2B DIMER)","PFPRMT1 (ARGININE METHYLTRANSFERASE, IN VITRO)","PFTUDOR-SN (BACTERIAL TWO-HYBRID, UNVALIDATED)","PFMYST (CO-LOCALIZES AT DAMAGE FOCI)"],"other_free_text":["Functionally substitutes for absent H2A.X variant; phosphorylated on Ser121 (γ-PfH2A) as a dynamic DNA double-strand break mark [#8]","Expression peaks in late trophozoite stages, absent in rings [#2, #3]","Parasite H2A-containing nucleosomes show reduced salt/thermal stability vs human [#7]","PfBDP1 interacts with the H2A.Z variant, not with canonical H2A (PF3D7_0617800) [#12]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"21187892","id":"PMC_21187892","title":"H2A.Z demarcates intergenic regions of the plasmodium falciparum epigenome that are dynamically marked by H3K9ac and H3K4me3.","date":"2010","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/21187892","citation_count":180,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["H2A","histone H2A"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"16410041","id":"PMC_16410041","title":"The malaria parasite Plasmodium falciparum histones: organization, expression, and acetylation.","date":"2006","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/16410041","citation_count":155,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["H2A"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"19351122","id":"PMC_19351122","title":"Global 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reports","url":"https://pubmed.ncbi.nlm.nih.gov/41871101","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["PfH2A"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":16620,"output_tokens":3303,"usd":0.049702,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9060,"output_tokens":3801,"usd":0.070163,"stage2_stop_reason":"end_turn"},"total_usd":0.119865,"stage1_batch_id":"msgbatch_01DisAaTypwmC8QwdMBuePHo","stage2_batch_id":"msgbatch_0184zxZTqxiEfdYYfPMfkqjb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1992,\n      \"finding\": \"The canonical histone H2A gene of Plasmodium falciparum (PF3D7_0617800) was identified and characterized at the sequence level.\",\n      \"method\": \"Molecular cloning and gene identification\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single gene identification paper, no functional mechanistic follow-up described in abstract\",\n      \"pmids\": [\"1518525\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Canonical H2A protein was purified from P. falciparum infected erythrocytes and culture supernatant; N-terminal sequence analysis confirmed its identity as a core histone and antibodies localized the protein to schizont nuclei by immunofluorescence.\",\n      \"method\": \"Acid extraction/purification, N-terminal sequencing, immunofluorescence\",\n      \"journal\": \"Parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct protein purification and localization by two orthogonal methods (sequencing + immunofluorescence), single lab\",\n      \"pmids\": [\"9149412\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"H2A transcript is absent in ring stage parasites but present at elevated levels in trophozoites, schizonts, and gametocytes of P. falciparum, indicating developmental stage-specific transcription of the canonical H2A gene.\",\n      \"method\": \"Transcription profiling across developmental stages (RT-based detection)\",\n      \"journal\": \"International journal for parasitology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method (transcript detection), no mechanistic follow-up\",\n      \"pmids\": [\"10579431\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Mass spectrometry confirmed synthesis of canonical H2A protein in P. falciparum erythrocytic stages; real-time RT-PCR and immunoblotting showed a dramatic increase in canonical H2A gene expression during late trophozoite stages, consistent with replication-related nucleosome assembly.\",\n      \"method\": \"Mass spectrometry, real-time RT-PCR, immunoblotting\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (MS, RT-PCR, western blot) in a single study confirming protein synthesis and expression dynamics\",\n      \"pmids\": [\"16410041\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Recombinant PfPRMT1 (a type I protein arginine methyltransferase) methylates histone H2A in vitro, establishing H2A as a substrate for arginine methylation by PfPRMT1 in P. falciparum.\",\n      \"method\": \"In vitro methyltransferase assay with recombinant PfPRMT1 and histone substrates\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct in vitro enzymatic assay with recombinant proteins, single lab, no site mapping reported for H2A specifically\",\n      \"pmids\": [\"19344311\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Global mass spectrometry analysis of P. falciparum histones identified and mapped post-translational modifications on canonical H2A protein, placing it in a comprehensive histone modification map of the parasite.\",\n      \"method\": \"Acid extraction, SDS-PAGE, LC-MS/MS (Q-TOF and LTQ-FT mass spectrometry)\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high mass accuracy MS with multiple instrument types, single lab but rigorous methodology\",\n      \"pmids\": [\"19351122\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PfNapS (nucleosome assembly protein) interacts with core histones including H2A in P. falciparum, as shown by fluorescence spectroscopy; the interaction site on PfNapS for core histones (H2A, H2B, H3, H4 tetramer and octamer) is distinct from its site for linker histone H1.\",\n      \"method\": \"Fluorescence spectroscopy binding assay, crystal structure of PfNapS\",\n      \"journal\": \"Malaria journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biophysical binding assay plus structural analysis, single lab\",\n      \"pmids\": [\"20377878\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"P. falciparum H2A and H2B display decreased salt stability compared to human counterparts, and plasmodium nucleosomes overall show reduced stability (increased temperature-induced mobility, reduced binding affinity to GC-rich DNA), as determined by comparative biochemical analysis of human and parasite histones.\",\n      \"method\": \"In vitro nucleosome reconstitution, salt stability assay, thermal mobility assay, DNA binding affinity measurement\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with multiple orthogonal biochemical assays (salt stability, thermal mobility, DNA binding), single lab\",\n      \"pmids\": [\"28033404\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In P. falciparum, which lacks the H2A.X variant, the canonical H2A (PfH2A, PF3D7_0617800) is phosphorylated on serine 121 in response to DNA double-strand break-inducing damage. Phosphorylated PfH2A (γ-PfH2A) is recruited to foci of damaged chromatin, while non-phosphorylated PfH2A remains spread throughout the nucleoplasm. This phosphorylation is dynamic and is removed as the repair machinery is activated.\",\n      \"method\": \"Immunofluorescence with phospho-specific antibodies, live imaging, DNA damage assays with genotoxic agents\",\n      \"journal\": \"mSphere\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct phosphorylation site identification (S121), reciprocal localization studies with multiple DNA damage agents, functional linkage to DNA repair dynamics, single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"33441412\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Canonical H2A (PfH2A) phosphorylation (γ-PfH2A) serves as a mark of DNA double-strand breaks in P. falciparum; PfMYST overexpression leads to high basal γ-PfH2A levels and PfMYST colocalizes with γ-PfH2A at DNA damage sites, indicating PfMYST is recruited to H2A phosphorylation foci during DNA damage response.\",\n      \"method\": \"Western blotting, immunofluorescence co-localization, overexpression and knockdown of PfMYST\",\n      \"journal\": \"mSphere\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional genetic manipulation (OE and KD) with direct co-localization, single lab\",\n      \"pmids\": [\"38564734\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In a bacterial two-hybrid screen, P. falciparum Tudor Staphylococcal Nuclease (PfTudor-SN) was found to interact with histone H2A, suggesting H2A participates in nuclear protein interactions involving PfTudor-SN.\",\n      \"method\": \"Bacterial two-hybrid screen\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single two-hybrid screen, no orthogonal validation of the H2A–PfTudor-SN interaction reported in abstract\",\n      \"pmids\": [\"20713134\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PfNPM (a nucleoplasmin isoform histone chaperone) interacts with assembled H2A/H2B dimers in P. falciparum with equimolar stoichiometry; the acidic tracts of PfNPM are necessary for these interactions. H3/H4 displays higher binding affinity for PfNPM than H2A/H2B, potentially due to stronger electrostatic interactions, and H3/H4 may displace H2A/H2B from the same binding site on the PfNPM distal face.\",\n      \"method\": \"Crystal structure determination, binding affinity measurements, mutagenesis of acidic tracts, size-exclusion chromatography\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus biophysical binding studies with mutagenesis, multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"40049416\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PfBDP1 bromodomain interacts with multi-acetylated H2A.Z (a H2A variant distinct from canonical H2A/PF3D7_0617800) in addition to its primary interaction with acetylated histone H3; no direct interaction of PfBDP1 with canonical H2A was reported.\",\n      \"method\": \"Solution NMR spectroscopy, ITC binding assays, crystal structure\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 1 / Weak — this finding concerns H2A.Z (variant), not canonical H2A (PF3D7_0617800); included only to note canonical H2A was not identified as a PfBDP1 interactor\",\n      \"pmids\": [\"36328269\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"Canonical P. falciparum H2A (PF3D7_0617800) is a core nucleosome component whose expression peaks in late trophozoite stages coinciding with DNA replication; its nucleosomes display reduced salt and thermal stability compared to human H2A-containing nucleosomes; it is a substrate for arginine methylation by PfPRMT1 in vitro; it interacts with the histone chaperones PfNapS and PfNPM (with H2A/H2B showing lower affinity for PfNPM than H3/H4); and critically, it functionally substitutes for the absent H2A.X variant by being phosphorylated on serine 121 in response to DNA double-strand breaks, with phospho-PfH2A (γ-PfH2A) recruited to damage foci and removed as repair proceeds, serving as a direct mark of DNA damage and repair in the parasite.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PF3D7_0617800 encodes the canonical core histone H2A of Plasmodium falciparum, a nucleosome-packaging protein whose expression is developmentally coupled to DNA replication, peaking in late trophozoite stages while being absent in rings [#3, #2]. Reconstituted nucleosomes containing parasite H2A display reduced salt and thermal stability and lower affinity for GC-rich DNA relative to their human counterparts, defining a biochemically distinct chromatin platform in P. falciparum [#7]. H2A deposition is handled by dedicated histone chaperones: it binds PfNapS as part of the core histone assembly, and PfNPM engages assembled H2A/H2B dimers via its acidic tracts, with H3/H4 outcompeting H2A/H2B for the same chaperone surface [#6, #11]. Beyond its structural role, H2A functionally substitutes for the missing H2A.X variant in the DNA damage response: it is phosphorylated on serine 121 upon double-strand breaks, and this \\u03b3-PfH2A mark is recruited to damage foci and dynamically removed as repair proceeds, recruiting the acetyltransferase PfMYST to those sites [#8, #9]. H2A is additionally a substrate for arginine methylation by PfPRMT1 in vitro and carries a broader set of mapped post-translational modifications [#4, #5].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Establishing the molecular identity of the parasite's canonical H2A gene was the necessary first step to studying its chromatin biology.\",\n      \"evidence\": \"Molecular cloning and sequence-level gene identification in P. falciparum\",\n      \"pmids\": [\"1518525\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No functional or mechanistic characterization at this stage\", \"Protein expression and localization not yet addressed\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Confirming that the encoded protein is a bona fide core histone localized to the nucleus grounded H2A as a genuine chromatin component rather than a predicted ORF.\",\n      \"evidence\": \"Acid extraction/purification, N-terminal sequencing, and immunofluorescence localization to schizont nuclei\",\n      \"pmids\": [\"9149412\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stage-resolved expression not quantified\", \"No interaction partners identified\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defining stage-specific transcription linked H2A expression to the parasite's replicative program rather than constant chromatin turnover.\",\n      \"evidence\": \"Transcript profiling across developmental stages showing absence in rings and elevated levels in trophozoites, schizonts, and gametocytes\",\n      \"pmids\": [\"10579431\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Transcript-level only, protein dynamics not measured\", \"Mechanism coupling expression to replication unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Confirming protein-level synthesis and a late-trophozoite expression surge tied H2A abundance directly to replication-phase nucleosome assembly.\",\n      \"evidence\": \"Mass spectrometry, real-time RT-PCR, and immunoblotting across erythrocytic stages\",\n      \"pmids\": [\"16410041\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal role of the expression surge in replication not tested\", \"Assembly machinery not identified here\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying H2A as a PfPRMT1 substrate and cataloging its post-translational modifications opened the question of how H2A marks regulate parasite chromatin.\",\n      \"evidence\": \"In vitro methyltransferase assay with recombinant PfPRMT1; global LC-MS/MS histone PTM mapping\",\n      \"pmids\": [\"19344311\", \"19351122\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Arginine methylation site on H2A not mapped\", \"In vivo relevance of the methylation not established\", \"Functional readout of mapped PTMs unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Mapping chaperone and nuclear-protein interactions began to define how H2A is handled during assembly and how it engages the nuclear proteome.\",\n      \"evidence\": \"Fluorescence spectroscopy binding with PfNapS plus PfNapS crystal structure; bacterial two-hybrid screen against PfTudor-SN\",\n      \"pmids\": [\"20377878\", \"20713134\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"PfTudor-SN interaction lacks orthogonal validation\", \"Functional consequence of the PfNapS interaction not tested in vivo\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrating that parasite H2A forms less stable nucleosomes than human H2A revealed an intrinsic biochemical distinctness of Plasmodium chromatin.\",\n      \"evidence\": \"In vitro nucleosome reconstitution with salt stability, thermal mobility, and GC-rich DNA binding assays comparing human and parasite histones\",\n      \"pmids\": [\"28033404\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of reduced stability not resolved\", \"In vivo consequence for genome accessibility not tested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showing that canonical H2A is phosphorylated on Ser121 and recruited to damage foci established that H2A functionally replaces the absent H2A.X variant in the parasite's DNA damage response.\",\n      \"evidence\": \"Phospho-specific immunofluorescence, live imaging, and DNA damage assays with genotoxic agents\",\n      \"pmids\": [\"33441412\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase responsible for S121 phosphorylation not identified\", \"Phosphatase removing the mark not defined\", \"Downstream repair effectors reading \\u03b3-PfH2A not mapped\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linking PfMYST recruitment to \\u03b3-PfH2A foci placed H2A phosphorylation upstream of a specific chromatin-modifying effector in the damage response.\",\n      \"evidence\": \"Western blotting, immunofluorescence co-localization, and PfMYST overexpression/knockdown\",\n      \"pmids\": [\"38564734\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct physical interaction between PfMYST and \\u03b3-PfH2A not shown\", \"Repair outcome dependence on PfMYST recruitment not quantified\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defining the stoichiometry and acidic-tract dependence of PfNPM binding to H2A/H2B refined how the parasite chaperone system stores and hands off core histones.\",\n      \"evidence\": \"Crystal structure, binding affinity measurements, acidic-tract mutagenesis, and size-exclusion chromatography\",\n      \"pmids\": [\"40049416\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo role of PfNPM in H2A deposition not established\", \"Competition with H3/H4 not tested in cells\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The kinase/phosphatase circuit controlling S121 phosphorylation, the in vivo function of H2A arginine methylation, and the physiological consequences of the intrinsically unstable parasite nucleosome remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Enzymes writing and erasing \\u03b3-PfH2A not identified\", \"Functional impact of reduced nucleosome stability on genome regulation untested\", \"No loss-of-function genetics for PF3D7_0617800 itself in the corpus\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0030527\", \"supporting_discovery_ids\": [1, 7]},\n      {\"term_id\": \"GO:0046982\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0000786\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0035861\", \"supporting_discovery_ids\": [8, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006281\", \"supporting_discovery_ids\": [8, 9]},\n      {\"term_id\": \"GO:0006334\", \"supporting_discovery_ids\": [3, 6]},\n      {\"term_id\": \"GO:0006302\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"complexes\": [\n      \"Nucleosome (core histone octamer)\"\n    ],\n    \"partners\": [\n      \"PfNapS (nucleosome assembly protein)\",\n      \"PfNPM (nucleoplasmin isoform histone chaperone; H2A/H2B dimer)\",\n      \"PfPRMT1 (arginine methyltransferase, in vitro)\",\n      \"PfTudor-SN (bacterial two-hybrid, unvalidated)\",\n      \"PfMYST (co-localizes at damage foci)\"\n    ],\n    \"other_free_text\": [\n      \"Functionally substitutes for absent H2A.X variant; phosphorylated on Ser121 (\\u03b3-PfH2A) as a dynamic DNA double-strand break mark [#8]\",\n      \"Expression peaks in late trophozoite stages, absent in rings [#2, #3]\",\n      \"Parasite H2A-containing nucleosomes show reduced salt/thermal stability vs human [#7]\",\n      \"PfBDP1 interacts with the H2A.Z variant, not with canonical H2A (PF3D7_0617800) [#12]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_0617800","name":null,"product":"histone H2A","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_1117000","name":null,"product":"histone H2A, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_1132600","name":null,"product":"histone H2A, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"H2A","evaluation":null}