{"gene":"PF3D7_1362500","run_date":"2026-09-08T14:19:06","timeline":{"discoveries":[{"year":2024,"finding":"PF3D7_1362500 (EXO/PfExo) is an apicoplast-targeted exonuclease/FEN containing a [4Fe-4S] cluster and a long low-complexity region (LCR) insertion. It exhibits a uniquely broad substrate range: it hydrolyzes 5'-flaps, processes dsDNA as a 5'-3' exonuclease, and acts as a bipolar nuclease on ssDNA and RNA-DNA hybrids. The LCR insertion is responsible for its expanded substrate repertoire, as deletion of the insertion (PfExoΔins) restricts activity to a limited range due to compromised DNA binding, mirroring the behavior of the P. berghei ortholog PbExo which lacks the insertion. Conversely, introduction of the PfExo insertion into PbExo conferred gain of activities.","method":"In vitro nuclease activity assays with recombinant protein, insertion-deletion mutagenesis, interspecies domain-swap experiments, substrate-range characterization across ssDNA, dsDNA, RNA-DNA hybrids, and 5'-flap substrates","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted in vitro enzymatic assays combined with deletion and swap mutagenesis establishing structure-function relationship in a single rigorous study","pmids":["38888125"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":2024,"finding":"PfExo (PF3D7_1362500) physically interacts with PfPrex, the apicoplast multifunctional DNA polymerase, as detected by pull-down assay, suggesting EXO functions as the candidate flap-endonuclease and RNaseH required for lagging strand processing during apicoplast genome (plDNA) replication and maintenance.","method":"Pull-down assay with recombinant proteins; immunofluorescence/subcellular fractionation (apicoplast localization inferred from targeting sequence and interaction context)","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single pull-down assay from one lab establishing interaction with PfPrex; apicoplast localization inferred from targeting prediction and interaction data rather than direct live imaging","pmids":["38888125"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"finding":"Knockout of the P. berghei ortholog of PF3D7_1362500 (PbExo) demonstrated that the enzyme is essential for parasite survival, establishing that this apicoplast exonuclease is required for blood-stage viability.","method":"Gene knockout in P. berghei with assessment of parasite viability","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean KO with defined lethal phenotype, single study, single method","pmids":["38888125"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2016,"finding":"A non-synonymous SNP in EXO (PF3D7_1362500) encoding a Glu415Gly substitution (E415G) was identified by genome-wide association study to associate with raised piperaquine IC50s and significantly associates with parasite recrudescence following dihydroartemisinin-piperaquine treatment in Cambodia.","method":"Genome-wide association study (GWAS) of 11,630 exonic SNPs in 297 P. falciparum isolates; survival analysis of 133 patients","journal":"The Lancet. Infectious diseases","confidence":"Low","confidence_rationale":"Tier 4 / Strong — genetic marker association from population genomics; no in vitro mechanistic experiment directly on EXO protein; replicated across multiple subsequent studies but remains correlative","pmids":["27818095"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2020,"finding":"In vitro culture and piperaquine survival assays on Cambodian P. falciparum clinical isolates showed that the presence of the E415G-EXO mutation together with novel pfcrt mutations (T93S, H97Y, F145I, I218F) can confer piperaquine resistance in the absence of plasmepsin 2-3 amplification, indicating that the EXO E415G substitution contributes to the piperaquine-resistant phenotype.","method":"In vitro piperaquine survival assay on culture-adapted clinical isolates and cloned parasite lines; genotyping for E415G-EXO and pfcrt mutations; limiting dilution cloning","journal":"Malaria journal","confidence":"Low","confidence_rationale":"Tier 3 / Weak — phenotypic association in culture with multiple co-occurring mutations; E415G-EXO contribution is inferred by co-segregation, not by direct manipulation of EXO alone","pmids":["32711538"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"PF3D7_1362500 (EXO/PfExo) is an apicoplast-targeted, [4Fe-4S]-containing exonuclease/FEN that physically interacts with the apicoplast DNA polymerase PfPrex and displays an unusually broad substrate range—including 5'-flap hydrolysis, 5'-3' dsDNA exonuclease activity, and bipolar nuclease activity on ssDNA and RNA-DNA hybrids—attributable to a unique low-complexity region insertion that enhances DNA binding; its P. berghei ortholog is essential for blood-stage survival, and a Glu415Gly substitution in the gene associates with piperaquine resistance in field isolates."},"narrative":{"mechanistic_narrative":"PF3D7_1362500 (EXO) is an apicoplast-targeted 3'-5' exonuclease/flap-endonuclease implicated in replication and maintenance of the apicoplast genome in Plasmodium [PMID:38888125]. The recombinant enzyme carries a [4Fe-4S] cluster and displays an unusually broad substrate range for a nuclease of this class: it hydrolyzes 5'-flaps, degrades dsDNA as a 5'-3' exonuclease, and acts as a bipolar nuclease on ssDNA and RNA-DNA hybrids [PMID:38888125]. This expanded repertoire is conferred by a long low-complexity region (LCR) insertion that enhances DNA binding, since deleting the insertion (PfExoΔins) collapses activity to a restricted range—phenocopying the naturally insertion-less P. berghei ortholog PbExo—while transplanting the insertion into PbExo confers gain of the additional activities [PMID:38888125]. EXO physically interacts with the apicoplast multifunctional DNA polymerase PfPrex, consistent with a role as the flap-endonuclease/RNaseH activity required for lagging-strand processing during apicoplast (plDNA) replication [PMID:38888125]. The P. berghei ortholog is essential for blood-stage parasite viability [PMID:38888125]. An E415G substitution in EXO associates with raised piperaquine IC50 and recrudescence after dihydroartemisinin-piperaquine treatment in field isolates [PMID:27818095], and co-occurs with pfcrt mutations in piperaquine-resistant clinical parasites [PMID:32711538].","teleology":[{"year":2016,"claim":"Before any biochemical role was known, population genomics asked whether EXO variation tracked with drug response, revealing an E415G marker associated with piperaquine treatment failure.","evidence":"GWAS of 11,630 exonic SNPs across 297 P. falciparum isolates with survival analysis of 133 patients","pmids":["27818095"],"confidence":"Low","gaps":["Correlative association only; no direct manipulation of EXO to test causation","Does not establish how the E415G change alters EXO protein function","Molecular role of EXO in the parasite was unknown at this point"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2020,"claim":"To test whether the EXO marker contributes to resistance beyond the plasmepsin 2-3 amplification pathway, isolates were phenotyped in vitro, showing E415G-EXO can accompany piperaquine resistance in combination with novel pfcrt mutations.","evidence":"In vitro piperaquine survival assays on culture-adapted Cambodian clinical isolates and cloned lines with genotyping","pmids":["32711538"],"confidence":"Low","gaps":["E415G-EXO contribution inferred by co-segregation with pfcrt mutations, not by isolated manipulation of EXO","Does not identify the mechanistic basis by which EXO variation influences drug survival"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"claim":"The enzymatic identity of EXO was defined, establishing it as an apicoplast [4Fe-4S] exonuclease/FEN with an unusually broad substrate range, and pinpointing a low-complexity insertion as the determinant of that range.","evidence":"In vitro nuclease assays with recombinant protein, insertion-deletion mutagenesis, and interspecies domain-swap experiments across ssDNA, dsDNA, RNA-DNA hybrid, and flap substrates in P. falciparum and P. berghei orthologs","pmids":["38888125"],"confidence":"High","gaps":["No structural model of the enzyme or the LCR insertion","Activity characterized in vitro; substrate usage during in vivo replication not directly demonstrated","Whether E415G alters any of these catalytic or binding activities was not tested"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":2024,"claim":"To place EXO in a replication pathway, its physical partner was sought, identifying an interaction with the apicoplast polymerase PfPrex and framing EXO as the candidate lagging-strand flap/RNaseH nuclease.","evidence":"Pull-down assay with recombinant proteins, with apicoplast localization inferred from targeting sequence and interaction context","pmids":["38888125"],"confidence":"Medium","gaps":["Single pull-down without reciprocal validation","Apicoplast localization inferred rather than shown by direct live imaging","Functional coupling of EXO nuclease activity to PfPrex synthesis not reconstituted"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"claim":"The physiological importance of the enzyme was tested by knockout, demonstrating the P. berghei ortholog is essential for blood-stage survival.","evidence":"Gene knockout in P. berghei with viability assessment","pmids":["38888125"],"confidence":"Medium","gaps":["Single method, single study","Essentiality of the P. falciparum gene not directly demonstrated","Stage of the lethal defect and its link to apicoplast genome maintenance not resolved"],"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":null,"claim":"It remains unresolved how the E415G substitution mechanistically alters EXO function to influence piperaquine response, and whether EXO's nuclease activities are directly required for apicoplast genome replication in vivo.","evidence":"","pmids":[],"confidence":"Low","gaps":["No biochemical test of E415G on catalytic activity or DNA binding","No direct in vivo demonstration linking EXO nuclease activity to plDNA replication","No structural basis for the drug-resistance association"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":["PFPREX (APICOPLAST MULTIFUNCTIONAL DNA POLYMERASE) [#1]"],"other_free_text":["Contains a low-complexity region (LCR) insertion that enhances DNA binding and confers an expanded substrate range; deletion (PfExoΔins) restricts activity, and transplantation into P. berghei PbExo confers gain of activities [#0]","P. berghei ortholog PbExo lacks the insertion and is essential for blood-stage survival [#0, #2]","E415G substitution associates with piperaquine treatment failure and, with pfcrt mutations, with piperaquine resistance in clinical isolates [#3, #4]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"27818095","id":"PMC_27818095","title":"Genetic markers associated with dihydroartemisinin-piperaquine failure in Plasmodium falciparum malaria in Cambodia: a genotype-phenotype association study.","date":"2016","source":"The Lancet. Infectious diseases","url":"https://pubmed.ncbi.nlm.nih.gov/27818095","citation_count":306,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["EXO"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"32103124","id":"PMC_32103124","title":"Detection of mutations associated with artemisinin resistance at k13-propeller gene and a near complete return of chloroquine susceptible falciparum malaria in Southeast of Tanzania.","date":"2020","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/32103124","citation_count":91,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["EXO"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"12996740","id":"PMC_12996740","title":"Exo-erythrocytic stages of Plasmodium falciparum.","date":"1952","source":"The American journal of tropical medicine and hygiene","url":"https://pubmed.ncbi.nlm.nih.gov/12996740","citation_count":32,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["EXO"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"5485706","id":"PMC_5485706","title":"The chemotherapy of rodent malaria. IX. Causal prophylaxis. I. A method for demonstrating drug action on exo-erythrocytic stages.","date":"1970","source":"Annals of tropical medicine and parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/5485706","citation_count":32,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["EXO"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"32711538","id":"PMC_32711538","title":"Piperaquine resistant Cambodian Plasmodium falciparum clinical isolates: in vitro genotypic and phenotypic characterization.","date":"2020","source":"Malaria journal","url":"https://pubmed.ncbi.nlm.nih.gov/32711538","citation_count":31,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["EXO"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"31718631","id":"PMC_31718631","title":"A comprehensive analysis of drug resistance molecular markers and Plasmodium falciparum genetic diversity in two malaria endemic sites in Mali.","date":"2019","source":"Malaria journal","url":"https://pubmed.ncbi.nlm.nih.gov/31718631","citation_count":30,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["EXO"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"6067417","id":"PMC_6067417","title":"Direct hepatic inoculation of sporozoites for the study of the exo-erythrocytic stages of simian malarias.","date":"1967","source":"The Journal of parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/6067417","citation_count":21,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["EXO"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"4861312","id":"PMC_4861312","title":"The late primary exo-erythrocytic stages of Plasmodium malariae.","date":"1967","source":"Transactions of the Royal Society of Tropical Medicine and Hygiene","url":"https://pubmed.ncbi.nlm.nih.gov/4861312","citation_count":18,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["EXO"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"24670267","id":"PMC_24670267","title":"Generation of rodent malaria parasites with a high mutation rate by destructing proofreading activity of DNA polymerase δ.","date":"2014","source":"DNA research : an international journal for rapid publication of reports on genes and genomes","url":"https://pubmed.ncbi.nlm.nih.gov/24670267","citation_count":13,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["3'-5' exonuclease"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"41243319","id":"PMC_41243319","title":"Plasmodium mitochondrial exodeoxyribonucleases, Exomit1 and Exomit2, are conserved within alveolates with Exomit1 essential for the establishment of blood-stage infection.","date":"2025","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/41243319","citation_count":1,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["3'-5' exonuclease","EXO"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"39476461","id":"PMC_39476461","title":"Rapid detection of mutations in the suspected piperaquine resistance gene E415G-exo in Plasmodium falciparum exonuclease via AS‒PCR and RAA with CRISPR/Cas12a.","date":"2024","source":"International journal for parasitology. Drugs and drug resistance","url":"https://pubmed.ncbi.nlm.nih.gov/39476461","citation_count":4,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["EXO"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"38888125","id":"PMC_38888125","title":"A Plasmodium apicoplast-targeted unique exonuclease/FEN exhibits interspecies functional differences attributable to an insertion that alters DNA-binding.","date":"2024","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/38888125","citation_count":3,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["EXO"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8891,"output_tokens":1706,"usd":0.026131,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":6746,"output_tokens":2910,"usd":0.05324,"stage2_stop_reason":"end_turn"},"total_usd":0.079371,"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\": 2024,\n      \"finding\": \"PF3D7_1362500 (EXO/PfExo) is an apicoplast-targeted exonuclease/FEN containing a [4Fe-4S] cluster and a long low-complexity region (LCR) insertion. It exhibits a uniquely broad substrate range: it hydrolyzes 5'-flaps, processes dsDNA as a 5'-3' exonuclease, and acts as a bipolar nuclease on ssDNA and RNA-DNA hybrids. The LCR insertion is responsible for its expanded substrate repertoire, as deletion of the insertion (PfExoΔins) restricts activity to a limited range due to compromised DNA binding, mirroring the behavior of the P. berghei ortholog PbExo which lacks the insertion. Conversely, introduction of the PfExo insertion into PbExo conferred gain of activities.\",\n      \"method\": \"In vitro nuclease activity assays with recombinant protein, insertion-deletion mutagenesis, interspecies domain-swap experiments, substrate-range characterization across ssDNA, dsDNA, RNA-DNA hybrids, and 5'-flap substrates\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted in vitro enzymatic assays combined with deletion and swap mutagenesis establishing structure-function relationship in a single rigorous study\",\n      \"pmids\": [\"38888125\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"},\n        {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PfExo (PF3D7_1362500) physically interacts with PfPrex, the apicoplast multifunctional DNA polymerase, as detected by pull-down assay, suggesting EXO functions as the candidate flap-endonuclease and RNaseH required for lagging strand processing during apicoplast genome (plDNA) replication and maintenance.\",\n      \"method\": \"Pull-down assay with recombinant proteins; immunofluorescence/subcellular fractionation (apicoplast localization inferred from targeting sequence and interaction context)\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single pull-down assay from one lab establishing interaction with PfPrex; apicoplast localization inferred from targeting prediction and interaction data rather than direct live imaging\",\n      \"pmids\": [\"38888125\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Knockout of the P. berghei ortholog of PF3D7_1362500 (PbExo) demonstrated that the enzyme is essential for parasite survival, establishing that this apicoplast exonuclease is required for blood-stage viability.\",\n      \"method\": \"Gene knockout in P. berghei with assessment of parasite viability\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean KO with defined lethal phenotype, single study, single method\",\n      \"pmids\": [\"38888125\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"A non-synonymous SNP in EXO (PF3D7_1362500) encoding a Glu415Gly substitution (E415G) was identified by genome-wide association study to associate with raised piperaquine IC50s and significantly associates with parasite recrudescence following dihydroartemisinin-piperaquine treatment in Cambodia.\",\n      \"method\": \"Genome-wide association study (GWAS) of 11,630 exonic SNPs in 297 P. falciparum isolates; survival analysis of 133 patients\",\n      \"journal\": \"The Lancet. Infectious diseases\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Strong — genetic marker association from population genomics; no in vitro mechanistic experiment directly on EXO protein; replicated across multiple subsequent studies but remains correlative\",\n      \"pmids\": [\"27818095\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In vitro culture and piperaquine survival assays on Cambodian P. falciparum clinical isolates showed that the presence of the E415G-EXO mutation together with novel pfcrt mutations (T93S, H97Y, F145I, I218F) can confer piperaquine resistance in the absence of plasmepsin 2-3 amplification, indicating that the EXO E415G substitution contributes to the piperaquine-resistant phenotype.\",\n      \"method\": \"In vitro piperaquine survival assay on culture-adapted clinical isolates and cloned parasite lines; genotyping for E415G-EXO and pfcrt mutations; limiting dilution cloning\",\n      \"journal\": \"Malaria journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — phenotypic association in culture with multiple co-occurring mutations; E415G-EXO contribution is inferred by co-segregation, not by direct manipulation of EXO alone\",\n      \"pmids\": [\"32711538\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}\n      ]\n    }\n  ],\n  \"current_model\": \"PF3D7_1362500 (EXO/PfExo) is an apicoplast-targeted, [4Fe-4S]-containing exonuclease/FEN that physically interacts with the apicoplast DNA polymerase PfPrex and displays an unusually broad substrate range—including 5'-flap hydrolysis, 5'-3' dsDNA exonuclease activity, and bipolar nuclease activity on ssDNA and RNA-DNA hybrids—attributable to a unique low-complexity region insertion that enhances DNA binding; its P. berghei ortholog is essential for blood-stage survival, and a Glu415Gly substitution in the gene associates with piperaquine resistance in field isolates.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PF3D7_1362500 (EXO) is an apicoplast-targeted 3'-5' exonuclease/flap-endonuclease implicated in replication and maintenance of the apicoplast genome in Plasmodium [#0, #1]. The recombinant enzyme carries a [4Fe-4S] cluster and displays an unusually broad substrate range for a nuclease of this class: it hydrolyzes 5'-flaps, degrades dsDNA as a 5'-3' exonuclease, and acts as a bipolar nuclease on ssDNA and RNA-DNA hybrids [#0]. This expanded repertoire is conferred by a long low-complexity region (LCR) insertion that enhances DNA binding, since deleting the insertion (PfExoΔins) collapses activity to a restricted range—phenocopying the naturally insertion-less P. berghei ortholog PbExo—while transplanting the insertion into PbExo confers gain of the additional activities [#0]. EXO physically interacts with the apicoplast multifunctional DNA polymerase PfPrex, consistent with a role as the flap-endonuclease/RNaseH activity required for lagging-strand processing during apicoplast (plDNA) replication [#1]. The P. berghei ortholog is essential for blood-stage parasite viability [#2]. An E415G substitution in EXO associates with raised piperaquine IC50 and recrudescence after dihydroartemisinin-piperaquine treatment in field isolates [#3], and co-occurs with pfcrt mutations in piperaquine-resistant clinical parasites [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2016,\n      \"claim\": \"Before any biochemical role was known, population genomics asked whether EXO variation tracked with drug response, revealing an E415G marker associated with piperaquine treatment failure.\",\n      \"evidence\": \"GWAS of 11,630 exonic SNPs across 297 P. falciparum isolates with survival analysis of 133 patients\",\n      \"pmids\": [\"27818095\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Correlative association only; no direct manipulation of EXO to test causation\",\n        \"Does not establish how the E415G change alters EXO protein function\",\n        \"Molecular role of EXO in the parasite was unknown at this point\"\n      ],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"To test whether the EXO marker contributes to resistance beyond the plasmepsin 2-3 amplification pathway, isolates were phenotyped in vitro, showing E415G-EXO can accompany piperaquine resistance in combination with novel pfcrt mutations.\",\n      \"evidence\": \"In vitro piperaquine survival assays on culture-adapted Cambodian clinical isolates and cloned lines with genotyping\",\n      \"pmids\": [\"32711538\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"E415G-EXO contribution inferred by co-segregation with pfcrt mutations, not by isolated manipulation of EXO\",\n        \"Does not identify the mechanistic basis by which EXO variation influences drug survival\"\n      ],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The enzymatic identity of EXO was defined, establishing it as an apicoplast [4Fe-4S] exonuclease/FEN with an unusually broad substrate range, and pinpointing a low-complexity insertion as the determinant of that range.\",\n      \"evidence\": \"In vitro nuclease assays with recombinant protein, insertion-deletion mutagenesis, and interspecies domain-swap experiments across ssDNA, dsDNA, RNA-DNA hybrid, and flap substrates in P. falciparum and P. berghei orthologs\",\n      \"pmids\": [\"38888125\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No structural model of the enzyme or the LCR insertion\",\n        \"Activity characterized in vitro; substrate usage during in vivo replication not directly demonstrated\",\n        \"Whether E415G alters any of these catalytic or binding activities was not tested\"\n      ],\n      \"attribution\": [\n        {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"},\n        {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"To place EXO in a replication pathway, its physical partner was sought, identifying an interaction with the apicoplast polymerase PfPrex and framing EXO as the candidate lagging-strand flap/RNaseH nuclease.\",\n      \"evidence\": \"Pull-down assay with recombinant proteins, with apicoplast localization inferred from targeting sequence and interaction context\",\n      \"pmids\": [\"38888125\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single pull-down without reciprocal validation\",\n        \"Apicoplast localization inferred rather than shown by direct live imaging\",\n        \"Functional coupling of EXO nuclease activity to PfPrex synthesis not reconstituted\"\n      ],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The physiological importance of the enzyme was tested by knockout, demonstrating the P. berghei ortholog is essential for blood-stage survival.\",\n      \"evidence\": \"Gene knockout in P. berghei with viability assessment\",\n      \"pmids\": [\"38888125\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single method, single study\",\n        \"Essentiality of the P. falciparum gene not directly demonstrated\",\n        \"Stage of the lethal defect and its link to apicoplast genome maintenance not resolved\"\n      ],\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how the E415G substitution mechanistically alters EXO function to influence piperaquine response, and whether EXO's nuclease activities are directly required for apicoplast genome replication in vivo.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No biochemical test of E415G on catalytic activity or DNA binding\",\n        \"No direct in vivo demonstration linking EXO nuclease activity to plDNA replication\",\n        \"No structural basis for the drug-resistance association\"\n      ],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008409\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0048256\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0004523\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0051539\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0019899\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020011\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006260\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0006287\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"PfPrex (apicoplast multifunctional DNA polymerase) [#1]\"\n    ],\n    \"other_free_text\": [\n      \"Contains a low-complexity region (LCR) insertion that enhances DNA binding and confers an expanded substrate range; deletion (PfExoΔins) restricts activity, and transplantation into P. berghei PbExo confers gain of activities [#0]\",\n      \"P. berghei ortholog PbExo lacks the insertion and is essential for blood-stage survival [#0, #2]\",\n      \"E415G substitution associates with piperaquine treatment failure and, with pfcrt mutations, with piperaquine resistance in clinical isolates [#3, #4]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_1362500","name":null,"product":"3'-5' exonuclease, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_1138500","name":null,"product":"3'-5' exonuclease, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_1108800","name":null,"product":"3'-5' exonuclease, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"EXO","evaluation":null}