{"gene":"PF3D7_1360800","run_date":"2026-09-08T14:19:06","timeline":{"discoveries":[{"year":1999,"finding":"FLN (falcilysin) was purified from P. falciparum food vacuoles and identified as a metallopeptidase that cleaves peptide fragments of hemoglobin but cannot cleave intact hemoglobin or denatured globin, placing it downstream of plasmepsins I/II and falcipain in the hemoglobin proteolytic pathway. Cleavage site analysis showed preference for polar/charged residues (charged residues at P1 and/or P4' positions), in contrast to the hydrophobic preferences of plasmepsins and falcipain. The gene was cloned and found to encode an M16 family metallopeptidase with an 'inverted' HXXEH active-site motif.","method":"Enzyme purification from food vacuoles, peptide substrate cleavage assays, gene cloning, sequence analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical purification, in vitro activity assay with substrate mapping, gene cloning with active-site motif identification, all in a single rigorous study","pmids":["10542284"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2003,"finding":"Recombinant FLN is highly active at acidic pH consistent with its food vacuole role, but also robustly active at neutral pH with a substantially different substrate specificity. Imaging studies confirmed FLN localization in the food vacuole and revealed additional association with vesicular structures elsewhere in the parasite, suggesting FLN may function as two different proteases in its two subcellular locations.","method":"Random peptide substrate analysis of recombinant protein, fluorescence imaging","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro enzymatic assay with substrate profiling plus direct imaging, two orthogonal methods in a single study","pmids":["12876284"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2003,"finding":"FLN is an unprocessed food vacuole enzyme in P. falciparum (biochemical characterization of its processing state).","method":"Biochemical characterization (details inferred from title; abstract not provided)","journal":"Molecular and biochemical parasitology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — abstract not available; only title provides information, single study","pmids":["12798513"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2006,"finding":"FLN localizes to the apicoplast (in addition to the food vacuole), as demonstrated by a transgenic parasite expressing a chromosomally encoded FLN-GFP fusion. FLN cleaves in vitro the transit peptide from the apicoplast-resident acyl carrier protein, supporting a role in transit peptide degradation in the apicoplast. Attempts to truncate the chromosomal FLN open reading frame failed, suggesting FLN is essential for parasite development.","method":"Transgenic GFP fusion live imaging, in vitro transit peptide cleavage assay, gene truncation attempts","journal":"Molecular microbiology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — chromosomal GFP fusion for localization plus in vitro cleavage assay, two orthogonal methods, single lab","pmids":["17074076"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2018,"finding":"Piperazine-based hydroxamic acid inhibitors were developed against FLN, and parasiticidal activity against cultured P. falciparum correlated with potency against purified FLN, providing pharmacological evidence that FLN is essential for intraerythrocytic parasite development and is a druggable target.","method":"In vitro enzyme inhibition assay with purified FLN, cultured parasite growth inhibition assay, SAR optimization","journal":"Bioorganic & medicinal chemistry letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical enzyme assay correlated with cellular activity, two orthogonal methods, single lab","pmids":["29691139"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"finding":"X-ray crystallography revealed two binary complexes of FLN in a closed state bound to hemoglobin α- and β-chain peptide substrates: substrate recognition involves antiparallel β-sheet formation between substrate and enzyme, with sequence-independent contacts at P2 and P1 positions and preferential contacts favoring tyrosine/phenylalanine at the P1' position. Cryo-EM showed unbound FLN predominantly adopts an open conformation. MK-4815 (an investigational antimalarial) shifts ~two-thirds of FLN molecules to the closed state by binding an allosteric pocket adjacent to a hinge region, thereby blocking the open-to-closed dynamic transition required for the proteolytic cycle.","method":"X-ray crystallography of substrate-bound complexes, cryo-EM of unbound and inhibitor-bound FLN, structure-activity analysis","journal":"Communications biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — atomic-resolution structures (X-ray + cryo-EM) with functional validation of inhibitor mechanism, multiple orthogonal structural methods in a single rigorous study","pmids":["39217277"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"FLN (PF3D7_1360800) is an M16-family zinc metalloprotease that functions in at least two subcellular compartments of P. falciparum: in the acidic food vacuole it cleaves hemoglobin-derived peptide fragments (downstream of plasmepsins and falcipain, with preference for charged residues at P1/P4'), and in the apicoplast it degrades transit peptides after import of nuclear-encoded proteins; the enzyme interconverts between an open (substrate-accessible) and closed (catalytically competent) conformation, and MK-4815 inhibits it by binding an allosteric hinge pocket to trap the closed state, while gene-disruption failure and inhibitor-parasite correlation experiments indicate FLN is essential for intraerythrocytic parasite survival."},"narrative":{"mechanistic_narrative":"FLN (PF3D7_1360800) is an M16-family zinc metallopeptidase of Plasmodium falciparum that functions in intracellular peptide catabolism across two subcellular compartments [PMID:10542284, PMID:17074076]. In the acidic food vacuole it acts downstream of the plasmepsins and falcipain in the hemoglobin degradation pathway, cleaving hemoglobin-derived peptide fragments — but not intact hemoglobin or denatured globin — with a distinctive preference for polar/charged residues at P1/P4', contrasting with the hydrophobic preferences of the upstream proteases; the enzyme carries an 'inverted' HXXEH active-site motif characteristic of the M16 family [PMID:10542284]. Beyond the food vacuole, FLN localizes to the apicoplast, where it cleaves the transit peptide of the apicoplast acyl carrier protein, implicating it in degradation of transit peptides after protein import [PMID:17074076]; consistent with these dual roles, recombinant FLN is active at both acidic and neutral pH and displays markedly different substrate specificities at the two pH regimes [PMID:12876284]. Structurally, FLN cycles between an open, substrate-accessible conformation and a closed, catalytically competent state: substrate-bound crystal structures show recognition via antiparallel β-sheet formation with sequence-independent P2/P1 contacts and a preference for tyrosine/phenylalanine at P1', while the antimalarial MK-4815 traps the closed state by binding an allosteric pocket adjacent to a hinge region, blocking the dynamic transition required for the proteolytic cycle [PMID:39217277]. Failure to truncate the chromosomal locus and correlation between inhibitor potency against purified enzyme and parasite killing establish FLN as essential for intraerythrocytic parasite survival and a druggable target [PMID:17074076, PMID:29691139].","teleology":[{"year":1999,"claim":"Establishing where FLN acts in hemoglobin catabolism: it was unknown which protease processed hemoglobin peptide fragments after the primary endoproteases, and purification placed FLN downstream of plasmepsins and falcipain with a complementary charged-residue specificity.","evidence":"Enzyme purification from food vacuoles, peptide cleavage assays, and gene cloning revealing an M16 inverted HXXEH motif","pmids":["10542284"],"confidence":"High","gaps":["Full downstream fate of the resulting peptides not defined","No structural basis for the charged-residue preference at this stage"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2003,"claim":"Testing whether FLN is a single-role vacuolar enzyme: pH-dependent activity profiling and imaging showed robust activity and distinct specificity at neutral pH plus association with vesicular structures beyond the food vacuole, raising the possibility of two functional identities.","evidence":"Random peptide substrate profiling of recombinant enzyme plus fluorescence imaging","pmids":["12876284"],"confidence":"High","gaps":["Identity of the second, non-vacuolar compartment not resolved here","Physiological neutral-pH substrates not identified"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2003,"claim":"Characterizing FLN's processing state addressed whether the food vacuole enzyme is proteolytically matured; it was reported as an unprocessed food vacuole enzyme.","evidence":"Biochemical characterization (title-level; abstract unavailable)","pmids":["12798513"],"confidence":"Low","gaps":["Abstract not available; details of the processing analysis not confirmable","Not independently corroborated within the corpus"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2006,"claim":"Resolving FLN's second location and role: the non-vacuolar signal was assigned to the apicoplast, and FLN was shown to cleave an apicoplast transit peptide, defining a role in transit-peptide degradation and providing the first evidence for essentiality.","evidence":"Chromosomal FLN-GFP fusion live imaging, in vitro transit peptide cleavage assay, and failed gene truncation","pmids":["17074076"],"confidence":"High","gaps":["Failed truncation is indirect evidence of essentiality, not a conditional knockdown","How FLN is dually targeted to food vacuole and apicoplast unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2018,"claim":"Validating FLN as a drug target: it was unclear whether inhibiting FLN kills parasites, and correlation between hydroxamic acid inhibitor potency against purified enzyme and parasite growth inhibition provided pharmacological support for essentiality and druggability.","evidence":"In vitro enzyme inhibition with purified FLN correlated with cultured parasite growth inhibition and SAR optimization","pmids":["29691139"],"confidence":"Medium","gaps":["Correlation does not exclude off-target contributions to killing","Which of the two compartmental roles is the lethal one not distinguished"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"claim":"Defining the catalytic mechanism and inhibition mode: structures resolved how FLN recognizes substrate and cycles between open and closed states, and showed MK-4815 traps the closed state via an allosteric hinge pocket, explaining inhibition.","evidence":"X-ray crystallography of substrate-bound complexes and cryo-EM of unbound and inhibitor-bound FLN","pmids":["39217277"],"confidence":"High","gaps":["Structures address hemoglobin peptides, not apicoplast transit-peptide recognition","Allosteric inhibition validated structurally but not by resistance mapping in parasites"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"How FLN is selectively targeted to and functionally partitioned between the food vacuole and apicoplast, and which compartmental function underlies its essentiality, remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No conditional genetic separation of the two roles","Trafficking/targeting mechanism to two compartments uncharacterized","In vivo substrate repertoire in each compartment not fully defined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":[],"other_free_text":["M16-family zinc metallopeptidase with an inverted HXXEH active-site motif [#0]","Acts downstream of plasmepsins I/II and falcipain in hemoglobin degradation, cleaving peptide fragments with preference for charged residues at P1/P4' [#0]","Cannot cleave intact hemoglobin or denatured globin [#0]","Dual pH activity: active at acidic (food vacuole) and neutral pH with distinct substrate specificities [#1]","Cleaves the transit peptide of apicoplast acyl carrier protein, supporting a transit-peptide degradation role [#3]","Cycles between open (substrate-accessible) and closed (catalytically competent) conformations; substrate recognized via antiparallel β-sheet with P1' preference for Tyr/Phe [#5]","Inhibited by MK-4815, which traps the closed state via an allosteric hinge-adjacent pocket [#5]","Essential for intraerythrocytic development, based on failed gene truncation and inhibitor-parasite potency correlation [#3, #4]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"10542284","id":"PMC_10542284","title":"Identification and characterization of falcilysin, a metallopeptidase involved in hemoglobin catabolism within the malaria parasite Plasmodium falciparum.","date":"1999","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10542284","citation_count":196,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["falcilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"23471987","id":"PMC_23471987","title":"Protein complex directs hemoglobin-to-hemozoin formation in Plasmodium falciparum.","date":"2013","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/23471987","citation_count":131,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"12876284","id":"PMC_12876284","title":"Plasmodium falciparum falcilysin: a metalloprotease with dual specificity.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12876284","citation_count":67,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["falcilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"17074076","id":"PMC_17074076","title":"A role for falcilysin in transit peptide degradation in the Plasmodium falciparum apicoplast.","date":"2006","source":"Molecular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/17074076","citation_count":61,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["FLN","falcilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"21689375","id":"PMC_21689375","title":"Multi-targeted activity of maslinic acid as an antimalarial natural compound.","date":"2011","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/21689375","citation_count":39,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["falcilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"25156726","id":"PMC_25156726","title":"Damage to the blood-brain barrier during experimental cerebral malaria results from synergistic effects of CD8+ T cells with different specificities.","date":"2014","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/25156726","citation_count":36,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["bergheilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"12798513","id":"PMC_12798513","title":"Plasmodium falciparum falcilysin: an unprocessed food vacuole enzyme.","date":"2003","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/12798513","citation_count":23,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["falcilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"17241197","id":"PMC_17241197","title":"Subcellular multitasking - multiple destinations and roles for the Plasmodium falcilysin protease.","date":"2007","source":"Molecular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/17241197","citation_count":18,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["falcilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"29691139","id":"PMC_29691139","title":"Development of piperazine-based hydroxamic acid inhibitors against falcilysin, an essential malarial protease.","date":"2018","source":"Bioorganic & medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/29691139","citation_count":6,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["FLN","falcilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"39217277","id":"PMC_39217277","title":"Inhibition of falcilysin from Plasmodium falciparum by interference with its closed-to-open dynamic transition.","date":"2024","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/39217277","citation_count":5,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["falcilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"33227414","id":"PMC_33227414","title":"Structure guided development of potent piperazine-derived hydroxamic acid inhibitors targeting falcilysin.","date":"2020","source":"Bioorganic & medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/33227414","citation_count":4,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["FLN","falcilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"40442398","id":"PMC_40442398","title":"In vitro and in silico evaluation of fluorinated diphenylamine chalcone derivatives as potential antimalarial and anticancer agents.","date":"2025","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/40442398","citation_count":4,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["falcilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"34606998","id":"PMC_34606998","title":"Identification of Plasmodium falciparum falcilysin inhibitors by a virtual screen.","date":"2021","source":"Bioorganic & medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/34606998","citation_count":3,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["falcilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"41386433","id":"PMC_41386433","title":"Plasmodium falciparum falcilysin as an emerging potential drug target for antimalarial drug discovery.","date":"2025","source":"Drug discovery today","url":"https://pubmed.ncbi.nlm.nih.gov/41386433","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["FLN","falcilysin"],"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":["FLN","falcilysin"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8499,"output_tokens":1843,"usd":0.026571,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":7021,"output_tokens":3172,"usd":0.057203,"stage2_stop_reason":"end_turn"},"total_usd":0.083774,"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\": 1999,\n      \"finding\": \"FLN (falcilysin) was purified from P. falciparum food vacuoles and identified as a metallopeptidase that cleaves peptide fragments of hemoglobin but cannot cleave intact hemoglobin or denatured globin, placing it downstream of plasmepsins I/II and falcipain in the hemoglobin proteolytic pathway. Cleavage site analysis showed preference for polar/charged residues (charged residues at P1 and/or P4' positions), in contrast to the hydrophobic preferences of plasmepsins and falcipain. The gene was cloned and found to encode an M16 family metallopeptidase with an 'inverted' HXXEH active-site motif.\",\n      \"method\": \"Enzyme purification from food vacuoles, peptide substrate cleavage assays, gene cloning, sequence analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical purification, in vitro activity assay with substrate mapping, gene cloning with active-site motif identification, all in a single rigorous study\",\n      \"pmids\": [\"10542284\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Recombinant FLN is highly active at acidic pH consistent with its food vacuole role, but also robustly active at neutral pH with a substantially different substrate specificity. Imaging studies confirmed FLN localization in the food vacuole and revealed additional association with vesicular structures elsewhere in the parasite, suggesting FLN may function as two different proteases in its two subcellular locations.\",\n      \"method\": \"Random peptide substrate analysis of recombinant protein, fluorescence imaging\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro enzymatic assay with substrate profiling plus direct imaging, two orthogonal methods in a single study\",\n      \"pmids\": [\"12876284\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"FLN is an unprocessed food vacuole enzyme in P. falciparum (biochemical characterization of its processing state).\",\n      \"method\": \"Biochemical characterization (details inferred from title; abstract not provided)\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — abstract not available; only title provides information, single study\",\n      \"pmids\": [\"12798513\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"FLN localizes to the apicoplast (in addition to the food vacuole), as demonstrated by a transgenic parasite expressing a chromosomally encoded FLN-GFP fusion. FLN cleaves in vitro the transit peptide from the apicoplast-resident acyl carrier protein, supporting a role in transit peptide degradation in the apicoplast. Attempts to truncate the chromosomal FLN open reading frame failed, suggesting FLN is essential for parasite development.\",\n      \"method\": \"Transgenic GFP fusion live imaging, in vitro transit peptide cleavage assay, gene truncation attempts\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — chromosomal GFP fusion for localization plus in vitro cleavage assay, two orthogonal methods, single lab\",\n      \"pmids\": [\"17074076\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Piperazine-based hydroxamic acid inhibitors were developed against FLN, and parasiticidal activity against cultured P. falciparum correlated with potency against purified FLN, providing pharmacological evidence that FLN is essential for intraerythrocytic parasite development and is a druggable target.\",\n      \"method\": \"In vitro enzyme inhibition assay with purified FLN, cultured parasite growth inhibition assay, SAR optimization\",\n      \"journal\": \"Bioorganic & medicinal chemistry letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical enzyme assay correlated with cellular activity, two orthogonal methods, single lab\",\n      \"pmids\": [\"29691139\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"X-ray crystallography revealed two binary complexes of FLN in a closed state bound to hemoglobin α- and β-chain peptide substrates: substrate recognition involves antiparallel β-sheet formation between substrate and enzyme, with sequence-independent contacts at P2 and P1 positions and preferential contacts favoring tyrosine/phenylalanine at the P1' position. Cryo-EM showed unbound FLN predominantly adopts an open conformation. MK-4815 (an investigational antimalarial) shifts ~two-thirds of FLN molecules to the closed state by binding an allosteric pocket adjacent to a hinge region, thereby blocking the open-to-closed dynamic transition required for the proteolytic cycle.\",\n      \"method\": \"X-ray crystallography of substrate-bound complexes, cryo-EM of unbound and inhibitor-bound FLN, structure-activity analysis\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — atomic-resolution structures (X-ray + cryo-EM) with functional validation of inhibitor mechanism, multiple orthogonal structural methods in a single rigorous study\",\n      \"pmids\": [\"39217277\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"FLN (PF3D7_1360800) is an M16-family zinc metalloprotease that functions in at least two subcellular compartments of P. falciparum: in the acidic food vacuole it cleaves hemoglobin-derived peptide fragments (downstream of plasmepsins and falcipain, with preference for charged residues at P1/P4'), and in the apicoplast it degrades transit peptides after import of nuclear-encoded proteins; the enzyme interconverts between an open (substrate-accessible) and closed (catalytically competent) conformation, and MK-4815 inhibits it by binding an allosteric hinge pocket to trap the closed state, while gene-disruption failure and inhibitor-parasite correlation experiments indicate FLN is essential for intraerythrocytic parasite survival.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FLN (PF3D7_1360800) is an M16-family zinc metallopeptidase of Plasmodium falciparum that functions in intracellular peptide catabolism across two subcellular compartments [#0, #3]. In the acidic food vacuole it acts downstream of the plasmepsins and falcipain in the hemoglobin degradation pathway, cleaving hemoglobin-derived peptide fragments — but not intact hemoglobin or denatured globin — with a distinctive preference for polar/charged residues at P1/P4', contrasting with the hydrophobic preferences of the upstream proteases; the enzyme carries an 'inverted' HXXEH active-site motif characteristic of the M16 family [#0]. Beyond the food vacuole, FLN localizes to the apicoplast, where it cleaves the transit peptide of the apicoplast acyl carrier protein, implicating it in degradation of transit peptides after protein import [#3]; consistent with these dual roles, recombinant FLN is active at both acidic and neutral pH and displays markedly different substrate specificities at the two pH regimes [#1]. Structurally, FLN cycles between an open, substrate-accessible conformation and a closed, catalytically competent state: substrate-bound crystal structures show recognition via antiparallel β-sheet formation with sequence-independent P2/P1 contacts and a preference for tyrosine/phenylalanine at P1', while the antimalarial MK-4815 traps the closed state by binding an allosteric pocket adjacent to a hinge region, blocking the dynamic transition required for the proteolytic cycle [#5]. Failure to truncate the chromosomal locus and correlation between inhibitor potency against purified enzyme and parasite killing establish FLN as essential for intraerythrocytic parasite survival and a druggable target [#3, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Establishing where FLN acts in hemoglobin catabolism: it was unknown which protease processed hemoglobin peptide fragments after the primary endoproteases, and purification placed FLN downstream of plasmepsins and falcipain with a complementary charged-residue specificity.\",\n      \"evidence\": \"Enzyme purification from food vacuoles, peptide cleavage assays, and gene cloning revealing an M16 inverted HXXEH motif\",\n      \"pmids\": [\"10542284\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full downstream fate of the resulting peptides not defined\", \"No structural basis for the charged-residue preference at this stage\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Testing whether FLN is a single-role vacuolar enzyme: pH-dependent activity profiling and imaging showed robust activity and distinct specificity at neutral pH plus association with vesicular structures beyond the food vacuole, raising the possibility of two functional identities.\",\n      \"evidence\": \"Random peptide substrate profiling of recombinant enzyme plus fluorescence imaging\",\n      \"pmids\": [\"12876284\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the second, non-vacuolar compartment not resolved here\", \"Physiological neutral-pH substrates not identified\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Characterizing FLN's processing state addressed whether the food vacuole enzyme is proteolytically matured; it was reported as an unprocessed food vacuole enzyme.\",\n      \"evidence\": \"Biochemical characterization (title-level; abstract unavailable)\",\n      \"pmids\": [\"12798513\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Abstract not available; details of the processing analysis not confirmable\", \"Not independently corroborated within the corpus\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Resolving FLN's second location and role: the non-vacuolar signal was assigned to the apicoplast, and FLN was shown to cleave an apicoplast transit peptide, defining a role in transit-peptide degradation and providing the first evidence for essentiality.\",\n      \"evidence\": \"Chromosomal FLN-GFP fusion live imaging, in vitro transit peptide cleavage assay, and failed gene truncation\",\n      \"pmids\": [\"17074076\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Failed truncation is indirect evidence of essentiality, not a conditional knockdown\", \"How FLN is dually targeted to food vacuole and apicoplast unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Validating FLN as a drug target: it was unclear whether inhibiting FLN kills parasites, and correlation between hydroxamic acid inhibitor potency against purified enzyme and parasite growth inhibition provided pharmacological support for essentiality and druggability.\",\n      \"evidence\": \"In vitro enzyme inhibition with purified FLN correlated with cultured parasite growth inhibition and SAR optimization\",\n      \"pmids\": [\"29691139\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Correlation does not exclude off-target contributions to killing\", \"Which of the two compartmental roles is the lethal one not distinguished\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defining the catalytic mechanism and inhibition mode: structures resolved how FLN recognizes substrate and cycles between open and closed states, and showed MK-4815 traps the closed state via an allosteric hinge pocket, explaining inhibition.\",\n      \"evidence\": \"X-ray crystallography of substrate-bound complexes and cryo-EM of unbound and inhibitor-bound FLN\",\n      \"pmids\": [\"39217277\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structures address hemoglobin peptides, not apicoplast transit-peptide recognition\", \"Allosteric inhibition validated structurally but not by resistance mapping in parasites\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How FLN is selectively targeted to and functionally partitioned between the food vacuole and apicoplast, and which compartmental function underlies its essentiality, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No conditional genetic separation of the two roles\", \"Trafficking/targeting mechanism to two compartments uncharacterized\", \"In vivo substrate repertoire in each compartment not fully defined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0004222\", \"supporting_discovery_ids\": [0, 1, 3, 5]},\n      {\"term_id\": \"GO:0008270\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0008233\", \"supporting_discovery_ids\": [0, 1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020020\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"GO:0020011\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006508\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0043043\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": [\n      \"M16-family zinc metallopeptidase with an inverted HXXEH active-site motif [#0]\",\n      \"Acts downstream of plasmepsins I/II and falcipain in hemoglobin degradation, cleaving peptide fragments with preference for charged residues at P1/P4' [#0]\",\n      \"Cannot cleave intact hemoglobin or denatured globin [#0]\",\n      \"Dual pH activity: active at acidic (food vacuole) and neutral pH with distinct substrate specificities [#1]\",\n      \"Cleaves the transit peptide of apicoplast acyl carrier protein, supporting a transit-peptide degradation role [#3]\",\n      \"Cycles between open (substrate-accessible) and closed (catalytically competent) conformations; substrate recognized via antiparallel β-sheet with P1' preference for Tyr/Phe [#5]\",\n      \"Inhibited by MK-4815, which traps the closed state via an allosteric hinge-adjacent pocket [#5]\",\n      \"Essential for intraerythrocytic development, based on failed gene truncation and inhibitor-parasite potency correlation [#3, #4]\"\n    ]\n  }\n}\n```","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_1360800","name":null,"product":"falcilysin","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_1137000","name":null,"product":"bergheilysin","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_1110600","name":null,"product":"falcilysin, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"BLN","evaluation":null}