{"gene":"PF3D7_0932300","run_date":"2026-09-08T12:51:27","timeline":{"discoveries":[{"year":2007,"finding":"M18AAP (PfM18AAP) is expressed in the cytosol of intra-erythrocytic P. falciparum parasites, but immunoblotting also detected the enzyme in the parasitophorous vacuole, indicating trafficking out of the parasite. Antisense-mediated knockdown of M18AAP produced a lethal phenotype with significant intracellular damage.","method":"Immunocytochemistry of transgenic P. falciparum expressing tagged protein; immunoblotting of fractionated parasites; antisense RNA knockdown with phenotypic readout","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization by two orthogonal methods (IHC + immunoblot fractionation) in a single lab, knockdown with defined lethal phenotype","pmids":["17720817"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"finding":"Recombinant and native M18AAP (PfM18AAP) forms 560-kDa octamers, exhibits optimal activity at neutral pH, requires metal ions for enzymatic activity and stability, and displays strict exopeptidase specificity exclusively for N-terminal acidic amino acids (glutamate and aspartate).","method":"Recombinant protein expression and purification; size-exclusion chromatography/native gel electrophoresis; in vitro aminopeptidase activity assays with defined substrates; metal ion dependence assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro biochemical reconstitution with multiple orthogonal methods (activity assay, native PAGE sizing, metal dependence), replicated by independent structural study (PMID:22709581)","pmids":["17720817"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"finding":"Two food vacuole aminopeptidases (distinct from M18AAP) were localized to the food vacuole, while M18AAP was found in the cytosol; biochemical analysis of enriched food vacuoles supported amino acid-generating pathways in both compartments. Three of four aminopeptidases tested (including M18AAP) were required for efficient parasite proliferation.","method":"Localization of epitope-tagged aminopeptidases by fluorescence microscopy; biochemical fractionation of food vacuoles; parasite growth assays with aminopeptidase inhibitor bestatin; amino acid supplementation experiments","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization with tagged protein plus biochemical fractionation and growth assay, single lab","pmids":["17895246"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"finding":"Recombinant M18AAP (PfM18AAP) binds in vitro to human erythrocyte spectrin, protein 4.1, protein 4.2, actin, and glyceraldehyde 3-phosphate dehydrogenase; the spectrin-binding region of PfM18AAP is absent in human, yeast, and other Plasmodium species homologs. The enzyme cleaves N-terminal aspartate from a tripeptide substrate with maximal activity at pH 7.5 and 37°C.","method":"Blot overlay assays of recombinant PfM18AAP against erythrocyte membrane proteins; coupled enzyme assay for aminopeptidase activity; two-dimensional gel electrophoresis; Ferguson plot analysis for oligomer size","journal":"Malaria journal","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — blot overlay (single method for binding) and in vitro activity assay; binding to spectrin confirmed by two methods (phage display prior work + blot overlay here), single lab","pmids":["18721457"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2012,"finding":"The X-ray crystal structure of M18AAP (PfM18AAP) reveals a dodecameric assembly arranged via dimer and trimer units forming a large tetrahedral shape that completely encloses 12 active sites within a central cavity; four entry points to the catalytic lumen are guarded by 12 large flexible loops that may control substrate entry. Substrate specificity assays confirmed exclusive activity toward N-terminal Glu or Asp residues. Significant structural differences around the active site compared to mammalian/human homologs were identified.","method":"X-ray crystallography; fluorogenic substrate specificity profiling with positional scanning substrate combinatorial library","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — X-ray crystal structure at atomic resolution combined with substrate specificity profiling; structural findings replicate and extend the biochemical octamer/activity data from PMID:17720817","pmids":["22709581"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"finding":"Two structurally related compounds (CID 6852389 and CID 23724194) inhibit recombinant M18AAP (PfM18AAP) with micromolar potency via a noncompetitive mechanism (Ki assay), and both show antiplasmodial activity in parasite growth assays (IC50 ~4 µM and ~1.3 µM, respectively).","method":"High-throughput fluorescence enzymatic assay with recombinant PfM18AAP and fluorogenic substrate H-Glu-NHMec; Ki determination; counter-screen with cathepsin L1; parasite growth inhibition assay","journal":"Journal of biomolecular screening","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro kinetic mechanism (noncompetitive Ki) established with recombinant enzyme plus cellular phenotypic confirmation, single lab","pmids":["24619116"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"finding":"6-phenyl-2(H)-1,2,4-triazin-5-one oxime, a compound identified from Balanites aegyptiaca seed extract, inhibits recombinant M18AAP (PfM18AAP) in vitro with a Ki of 2.35 µg/µL in the crude extract context; depletion of this compound reduced inhibition, confirming its contribution.","method":"GC-MS identification of inhibitor in plant extract; in vitro coupled enzyme assay with recombinant PfM18AAP; depletion experiment","journal":"Journal of parasitology research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, inhibition measured in crude extract context with indirect depletion, no pure compound kinetics","pmids":["21687598"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"NF54"}]}],"current_model":"M18AAP (PfM18AAP) is a metallo-exopeptidase that assembles as a dodecamer (crystal structure confirmed) with 12 active sites enclosed in a central tetrahedral cavity; it exclusively cleaves N-terminal glutamate or aspartate residues, localizes primarily to the parasite cytosol (with some trafficking into the parasitophorous vacuole), binds erythrocyte membrane proteins including spectrin in vitro, is essential for intra-erythrocytic parasite proliferation (antisense knockdown is lethal), and is proposed to function alongside neutral cytosolic aminopeptidases in the terminal degradation of hemoglobin-derived peptides."},"narrative":{"mechanistic_narrative":"M18AAP (PF3D7_0932300) is a metal-dependent aspartyl aminoexopeptidase of intra-erythrocytic P. falciparum that is required for parasite proliferation and is implicated in the terminal degradation of peptides in the parasite cytosol [PMID:17720817]. The enzyme displays strict exopeptidase specificity, cleaving only N-terminal acidic residues (glutamate or aspartate), operates optimally at neutral pH, and depends on metal ions for both activity and stability [PMID:17720817, PMID:22709581]. Biochemical sizing indicated a ~560-kDa oligomer, and X-ray crystallography resolved a dodecameric tetrahedral assembly that encloses 12 active sites within a central catalytic cavity accessed through four entry points guarded by flexible loops, with active-site features distinct from mammalian homologs [PMID:17720817, PMID:22709581]. M18AAP localizes predominantly to the parasite cytosol but is also detected in the parasitophorous vacuole, indicating trafficking out of the parasite, and antisense knockdown is lethal [PMID:17720817]. Recombinant M18AAP binds several human erythrocyte membrane and cytoskeletal proteins including spectrin in vitro, and its spectrin-binding region is absent in human, yeast, and other Plasmodium homologs [PMID:18721457]. The enzyme is inhibitable by small molecules with associated antiplasmodial activity, supporting it as a candidate antimalarial target [PMID:24619116].","teleology":[{"year":2007,"claim":"Establishing where the enzyme acts and whether it matters was the first question; localization plus knockdown defined M18AAP as an essential cytosolic (and partly PV-trafficked) enzyme of blood-stage parasites.","evidence":"Immunocytochemistry and immunoblot fractionation of transgenic parasites with antisense RNA knockdown in P. falciparum","pmids":["17720817"],"confidence":"Medium","gaps":["Mechanism of trafficking to the parasitophorous vacuole unresolved","Precise cause of lethality (which pathway fails) not defined","Endogenous physiological substrates not identified"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"claim":"Defining the catalytic identity of the enzyme was needed; biochemical reconstitution showed strict N-terminal acidic-residue specificity, neutral pH optimum, metal dependence, and an oligomeric assembly.","evidence":"Recombinant expression, native PAGE/size-exclusion sizing, defined-substrate activity and metal-dependence assays for P. falciparum M18AAP","pmids":["17720817"],"confidence":"High","gaps":["Identity of the required metal ion not resolved","Relationship of the biochemical oligomer to a cellular assembly unclear at this stage"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"claim":"Placing M18AAP within compartmentalized amino-acid generation showed it acts in the cytosol distinct from food-vacuole aminopeptidases while contributing to efficient proliferation.","evidence":"Localization of epitope-tagged aminopeptidases, food-vacuole fractionation, bestatin growth inhibition and amino-acid supplementation in P. falciparum","pmids":["17895246"],"confidence":"Medium","gaps":["Direct demonstration that M18AAP acts on hemoglobin-derived peptides in vivo is lacking","Functional interplay with the food-vacuole enzymes not resolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"claim":"Testing a possible host-interaction role revealed the enzyme binds erythrocyte membrane/cytoskeletal proteins, with a spectrin-binding region unique among homologs.","evidence":"Blot overlay of recombinant P. falciparum M18AAP against erythrocyte membrane proteins plus coupled activity assays","pmids":["18721457"],"confidence":"Medium","gaps":["Binding shown only in vitro by a single method (blot overlay)","Functional consequence of erythrocyte-protein binding in vivo unknown","No reciprocal validation of the interactions"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2012,"claim":"The architectural basis of catalysis was unresolved until crystallography revealed a dodecameric tetrahedral cage enclosing 12 active sites accessed through gated entry points, with distinct active-site features versus mammalian homologs.","evidence":"X-ray crystallography and positional-scanning fluorogenic substrate profiling of P. falciparum M18AAP","pmids":["22709581"],"confidence":"High","gaps":["How the flexible gating loops select substrates mechanistically not established","Structural basis of erythrocyte-protein binding not resolved","No structure with a physiological substrate or inhibitor bound"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"claim":"Establishing druggability, small-molecule inhibitors of recombinant enzyme with antiplasmodial activity supported M18AAP as an antimalarial target and defined a noncompetitive inhibition mode.","evidence":"High-throughput fluorescence enzymatic assay with Ki determination, cathepsin L1 counter-screen, and parasite growth inhibition in P. falciparum","pmids":["24619116"],"confidence":"Medium","gaps":["On-target mechanism of killing in parasites not directly demonstrated","Micromolar potency leaves selectivity/potency unoptimized","Binding site of the noncompetitive inhibitors not mapped"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"claim":"A natural-product screen identified a plant-derived triazinone oxime as an in vitro inhibitor of the enzyme.","evidence":"GC-MS identification, coupled enzyme assay, and depletion experiment with recombinant P. falciparum M18AAP (crude extract context)","pmids":["21687598"],"confidence":"Low","gaps":["Inhibition measured in crude extract with indirect depletion, not with purified compound kinetics","No cellular antiplasmodial confirmation for the isolated compound","Not independently replicated"],"attribution":[{"species":"Plasmodium falciparum","strain":"NF54"}]},{"year":null,"claim":"The endogenous in vivo substrates and the precise metabolic role of M18AAP in hemoglobin-derived peptide catabolism remain to be directly demonstrated.","evidence":"","pmids":[],"confidence":"Low","gaps":["No in vivo substrate identified","Contribution to cytosolic peptide degradation inferred but not directly measured","Physiological relevance of erythrocyte-protein binding unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["Homo-oligomeric assembly: ~560-kDa oligomer / dodecameric tetrahedral cage enclosing 12 active sites [#1, #4]"],"partners":["HUMAN ERYTHROCYTE SPECTRIN (IN VITRO) [#3]","HUMAN ERYTHROCYTE PROTEIN 4.1 (IN VITRO) [#3]","HUMAN ERYTHROCYTE PROTEIN 4.2 (IN VITRO) [#3]","ACTIN (IN VITRO) [#3]","GLYCERALDEHYDE 3-PHOSPHATE DEHYDROGENASE (IN VITRO) [#3]"],"other_free_text":["Strict specificity for N-terminal glutamate/aspartate; neutral pH optimum (~7.5), 37°C [#1, #3, #4]","Essential for intra-erythrocytic proliferation; antisense knockdown lethal [#0]","Inhibited by CID 6852389 and CID 23724194 (noncompetitive, micromolar) with antiplasmodial activity [#5]","Inhibited by a Balanites aegyptiaca-derived triazinone oxime in vitro [#6]","Spectrin-binding region absent in human, yeast, and other Plasmodium homologs; active-site divergence from mammalian homologs [#3, #4]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"17895246","id":"PMC_17895246","title":"Roles for two aminopeptidases in vacuolar hemoglobin catabolism in Plasmodium falciparum.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17895246","citation_count":125,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"17720817","id":"PMC_17720817","title":"The M18 aspartyl aminopeptidase of the human malaria parasite Plasmodium falciparum.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17720817","citation_count":47,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["M18 aspartyl aminopeptidase","M18","PfM18AAP"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"25700165","id":"PMC_25700165","title":"Screening the Medicines for Malaria Venture \"Malaria Box\" against the Plasmodium falciparum aminopeptidases, M1, M17 and M18.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/25700165","citation_count":32,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["M18","PfM18","PfM18AAP"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"22709581","id":"PMC_22709581","title":"X-ray crystal structure and specificity of the Plasmodium falciparum malaria aminopeptidase PfM18AAP.","date":"2012","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/22709581","citation_count":30,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["M18AAP","PfM18AAP"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"21687598","id":"PMC_21687598","title":"In Vitro and In Vivo Antimalarial Activity Assays of Seeds from Balanites aegyptiaca: Compounds of the Extract Show Growth Inhibition and Activity against Plasmodial Aminopeptidase.","date":"2011","source":"Journal of parasitology research","url":"https://pubmed.ncbi.nlm.nih.gov/21687598","citation_count":23,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["M18 aspartyl aminopeptidase","M18"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"27534744","id":"PMC_27534744","title":"3D QSAR, pharmacophore and molecular docking studies of known inhibitors and designing of novel inhibitors for M18 aspartyl aminopeptidase of Plasmodium falciparum.","date":"2016","source":"BMC structural biology","url":"https://pubmed.ncbi.nlm.nih.gov/27534744","citation_count":21,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["M18 aspartyl aminopeptidase","M18AAP","M18","PfM18AAP"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"18721457","id":"PMC_18721457","title":"The M18 aspartyl aminopeptidase of Plasmodium falciparum binds to human erythrocyte spectrin in vitro.","date":"2008","source":"Malaria journal","url":"https://pubmed.ncbi.nlm.nih.gov/18721457","citation_count":21,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["M18 aspartyl aminopeptidase","M18","PfM18AAP"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"24619116","id":"PMC_24619116","title":"Identification of Potent and Selective Inhibitors of the Plasmodium falciparum M18 Aspartyl Aminopeptidase (PfM18AAP) of Human Malaria via High-Throughput Screening.","date":"2014","source":"Journal of biomolecular screening","url":"https://pubmed.ncbi.nlm.nih.gov/24619116","citation_count":15,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["M18 aspartyl aminopeptidase","M18","PfM18","PfM18AAP"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"30929948","id":"PMC_30929948","title":"In silico study of M18 aspartyl amino peptidase (M18AAP) of Plasmodium vivax as an antimalarial drug target.","date":"2019","source":"Bioorganic & medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/30929948","citation_count":11,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["M18AAP","M18","PvM18AAP"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"36825701","id":"PMC_36825701","title":"Parasite Metalo-aminopeptidases as Targets in Human Infectious Diseases.","date":"2023","source":"Current drug targets","url":"https://pubmed.ncbi.nlm.nih.gov/36825701","citation_count":4,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["M18"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"25869318","id":"PMC_25869318","title":"In silico prediction of anti-malarial hit molecules based on machine learning methods.","date":"2015","source":"International journal of computational biology and drug design","url":"https://pubmed.ncbi.nlm.nih.gov/25869318","citation_count":3,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["M18AAP"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8794,"output_tokens":2202,"usd":0.029706,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":7570,"output_tokens":3399,"usd":0.061413,"stage2_stop_reason":"end_turn"},"total_usd":0.091119,"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\": 2007,\n      \"finding\": \"M18AAP (PfM18AAP) is expressed in the cytosol of intra-erythrocytic P. falciparum parasites, but immunoblotting also detected the enzyme in the parasitophorous vacuole, indicating trafficking out of the parasite. Antisense-mediated knockdown of M18AAP produced a lethal phenotype with significant intracellular damage.\",\n      \"method\": \"Immunocytochemistry of transgenic P. falciparum expressing tagged protein; immunoblotting of fractionated parasites; antisense RNA knockdown with phenotypic readout\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization by two orthogonal methods (IHC + immunoblot fractionation) in a single lab, knockdown with defined lethal phenotype\",\n      \"pmids\": [\"17720817\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Recombinant and native M18AAP (PfM18AAP) forms 560-kDa octamers, exhibits optimal activity at neutral pH, requires metal ions for enzymatic activity and stability, and displays strict exopeptidase specificity exclusively for N-terminal acidic amino acids (glutamate and aspartate).\",\n      \"method\": \"Recombinant protein expression and purification; size-exclusion chromatography/native gel electrophoresis; in vitro aminopeptidase activity assays with defined substrates; metal ion dependence assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro biochemical reconstitution with multiple orthogonal methods (activity assay, native PAGE sizing, metal dependence), replicated by independent structural study (PMID:22709581)\",\n      \"pmids\": [\"17720817\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Two food vacuole aminopeptidases (distinct from M18AAP) were localized to the food vacuole, while M18AAP was found in the cytosol; biochemical analysis of enriched food vacuoles supported amino acid-generating pathways in both compartments. Three of four aminopeptidases tested (including M18AAP) were required for efficient parasite proliferation.\",\n      \"method\": \"Localization of epitope-tagged aminopeptidases by fluorescence microscopy; biochemical fractionation of food vacuoles; parasite growth assays with aminopeptidase inhibitor bestatin; amino acid supplementation experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization with tagged protein plus biochemical fractionation and growth assay, single lab\",\n      \"pmids\": [\"17895246\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Recombinant M18AAP (PfM18AAP) binds in vitro to human erythrocyte spectrin, protein 4.1, protein 4.2, actin, and glyceraldehyde 3-phosphate dehydrogenase; the spectrin-binding region of PfM18AAP is absent in human, yeast, and other Plasmodium species homologs. The enzyme cleaves N-terminal aspartate from a tripeptide substrate with maximal activity at pH 7.5 and 37°C.\",\n      \"method\": \"Blot overlay assays of recombinant PfM18AAP against erythrocyte membrane proteins; coupled enzyme assay for aminopeptidase activity; two-dimensional gel electrophoresis; Ferguson plot analysis for oligomer size\",\n      \"journal\": \"Malaria journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — blot overlay (single method for binding) and in vitro activity assay; binding to spectrin confirmed by two methods (phage display prior work + blot overlay here), single lab\",\n      \"pmids\": [\"18721457\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The X-ray crystal structure of M18AAP (PfM18AAP) reveals a dodecameric assembly arranged via dimer and trimer units forming a large tetrahedral shape that completely encloses 12 active sites within a central cavity; four entry points to the catalytic lumen are guarded by 12 large flexible loops that may control substrate entry. Substrate specificity assays confirmed exclusive activity toward N-terminal Glu or Asp residues. Significant structural differences around the active site compared to mammalian/human homologs were identified.\",\n      \"method\": \"X-ray crystallography; fluorogenic substrate specificity profiling with positional scanning substrate combinatorial library\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — X-ray crystal structure at atomic resolution combined with substrate specificity profiling; structural findings replicate and extend the biochemical octamer/activity data from PMID:17720817\",\n      \"pmids\": [\"22709581\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Two structurally related compounds (CID 6852389 and CID 23724194) inhibit recombinant M18AAP (PfM18AAP) with micromolar potency via a noncompetitive mechanism (Ki assay), and both show antiplasmodial activity in parasite growth assays (IC50 ~4 µM and ~1.3 µM, respectively).\",\n      \"method\": \"High-throughput fluorescence enzymatic assay with recombinant PfM18AAP and fluorogenic substrate H-Glu-NHMec; Ki determination; counter-screen with cathepsin L1; parasite growth inhibition assay\",\n      \"journal\": \"Journal of biomolecular screening\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinetic mechanism (noncompetitive Ki) established with recombinant enzyme plus cellular phenotypic confirmation, single lab\",\n      \"pmids\": [\"24619116\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"6-phenyl-2(H)-1,2,4-triazin-5-one oxime, a compound identified from Balanites aegyptiaca seed extract, inhibits recombinant M18AAP (PfM18AAP) in vitro with a Ki of 2.35 µg/µL in the crude extract context; depletion of this compound reduced inhibition, confirming its contribution.\",\n      \"method\": \"GC-MS identification of inhibitor in plant extract; in vitro coupled enzyme assay with recombinant PfM18AAP; depletion experiment\",\n      \"journal\": \"Journal of parasitology research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, inhibition measured in crude extract context with indirect depletion, no pure compound kinetics\",\n      \"pmids\": [\"21687598\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"NF54\"}]\n    }\n  ],\n  \"current_model\": \"M18AAP (PfM18AAP) is a metallo-exopeptidase that assembles as a dodecamer (crystal structure confirmed) with 12 active sites enclosed in a central tetrahedral cavity; it exclusively cleaves N-terminal glutamate or aspartate residues, localizes primarily to the parasite cytosol (with some trafficking into the parasitophorous vacuole), binds erythrocyte membrane proteins including spectrin in vitro, is essential for intra-erythrocytic parasite proliferation (antisense knockdown is lethal), and is proposed to function alongside neutral cytosolic aminopeptidases in the terminal degradation of hemoglobin-derived peptides.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"M18AAP (PF3D7_0932300) is a metal-dependent aspartyl aminoexopeptidase of intra-erythrocytic P. falciparum that is required for parasite proliferation and is implicated in the terminal degradation of peptides in the parasite cytosol [#0, #1]. The enzyme displays strict exopeptidase specificity, cleaving only N-terminal acidic residues (glutamate or aspartate), operates optimally at neutral pH, and depends on metal ions for both activity and stability [#1, #4]. Biochemical sizing indicated a ~560-kDa oligomer, and X-ray crystallography resolved a dodecameric tetrahedral assembly that encloses 12 active sites within a central catalytic cavity accessed through four entry points guarded by flexible loops, with active-site features distinct from mammalian homologs [#1, #4]. M18AAP localizes predominantly to the parasite cytosol but is also detected in the parasitophorous vacuole, indicating trafficking out of the parasite, and antisense knockdown is lethal [#0]. Recombinant M18AAP binds several human erythrocyte membrane and cytoskeletal proteins including spectrin in vitro, and its spectrin-binding region is absent in human, yeast, and other Plasmodium homologs [#3]. The enzyme is inhibitable by small molecules with associated antiplasmodial activity, supporting it as a candidate antimalarial target [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Establishing where the enzyme acts and whether it matters was the first question; localization plus knockdown defined M18AAP as an essential cytosolic (and partly PV-trafficked) enzyme of blood-stage parasites.\",\n      \"evidence\": \"Immunocytochemistry and immunoblot fractionation of transgenic parasites with antisense RNA knockdown in P. falciparum\",\n      \"pmids\": [\"17720817\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of trafficking to the parasitophorous vacuole unresolved\", \"Precise cause of lethality (which pathway fails) not defined\", \"Endogenous physiological substrates not identified\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defining the catalytic identity of the enzyme was needed; biochemical reconstitution showed strict N-terminal acidic-residue specificity, neutral pH optimum, metal dependence, and an oligomeric assembly.\",\n      \"evidence\": \"Recombinant expression, native PAGE/size-exclusion sizing, defined-substrate activity and metal-dependence assays for P. falciparum M18AAP\",\n      \"pmids\": [\"17720817\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the required metal ion not resolved\", \"Relationship of the biochemical oligomer to a cellular assembly unclear at this stage\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Placing M18AAP within compartmentalized amino-acid generation showed it acts in the cytosol distinct from food-vacuole aminopeptidases while contributing to efficient proliferation.\",\n      \"evidence\": \"Localization of epitope-tagged aminopeptidases, food-vacuole fractionation, bestatin growth inhibition and amino-acid supplementation in P. falciparum\",\n      \"pmids\": [\"17895246\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct demonstration that M18AAP acts on hemoglobin-derived peptides in vivo is lacking\", \"Functional interplay with the food-vacuole enzymes not resolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Testing a possible host-interaction role revealed the enzyme binds erythrocyte membrane/cytoskeletal proteins, with a spectrin-binding region unique among homologs.\",\n      \"evidence\": \"Blot overlay of recombinant P. falciparum M18AAP against erythrocyte membrane proteins plus coupled activity assays\",\n      \"pmids\": [\"18721457\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding shown only in vitro by a single method (blot overlay)\", \"Functional consequence of erythrocyte-protein binding in vivo unknown\", \"No reciprocal validation of the interactions\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The architectural basis of catalysis was unresolved until crystallography revealed a dodecameric tetrahedral cage enclosing 12 active sites accessed through gated entry points, with distinct active-site features versus mammalian homologs.\",\n      \"evidence\": \"X-ray crystallography and positional-scanning fluorogenic substrate profiling of P. falciparum M18AAP\",\n      \"pmids\": [\"22709581\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the flexible gating loops select substrates mechanistically not established\", \"Structural basis of erythrocyte-protein binding not resolved\", \"No structure with a physiological substrate or inhibitor bound\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Establishing druggability, small-molecule inhibitors of recombinant enzyme with antiplasmodial activity supported M18AAP as an antimalarial target and defined a noncompetitive inhibition mode.\",\n      \"evidence\": \"High-throughput fluorescence enzymatic assay with Ki determination, cathepsin L1 counter-screen, and parasite growth inhibition in P. falciparum\",\n      \"pmids\": [\"24619116\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"On-target mechanism of killing in parasites not directly demonstrated\", \"Micromolar potency leaves selectivity/potency unoptimized\", \"Binding site of the noncompetitive inhibitors not mapped\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"A natural-product screen identified a plant-derived triazinone oxime as an in vitro inhibitor of the enzyme.\",\n      \"evidence\": \"GC-MS identification, coupled enzyme assay, and depletion experiment with recombinant P. falciparum M18AAP (crude extract context)\",\n      \"pmids\": [\"21687598\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Inhibition measured in crude extract with indirect depletion, not with purified compound kinetics\", \"No cellular antiplasmodial confirmation for the isolated compound\", \"Not independently replicated\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"NF54\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The endogenous in vivo substrates and the precise metabolic role of M18AAP in hemoglobin-derived peptide catabolism remain to be directly demonstrated.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No in vivo substrate identified\", \"Contribution to cytosolic peptide degradation inferred but not directly measured\", \"Physiological relevance of erythrocyte-protein binding unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0004177\", \"supporting_discovery_ids\": [1, 3, 4]},\n      {\"term_id\": \"GO:0008270\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0008233\", \"supporting_discovery_ids\": [1, 4, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0020020\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0043171\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"complexes\": [\n      \"Homo-oligomeric assembly: ~560-kDa oligomer / dodecameric tetrahedral cage enclosing 12 active sites [#1, #4]\"\n    ],\n    \"partners\": [\n      \"Human erythrocyte spectrin (in vitro) [#3]\",\n      \"Human erythrocyte protein 4.1 (in vitro) [#3]\",\n      \"Human erythrocyte protein 4.2 (in vitro) [#3]\",\n      \"Actin (in vitro) [#3]\",\n      \"Glyceraldehyde 3-phosphate dehydrogenase (in vitro) [#3]\"\n    ],\n    \"other_free_text\": [\n      \"Strict specificity for N-terminal glutamate/aspartate; neutral pH optimum (~7.5), 37\\u00b0C [#1, #3, #4]\",\n      \"Essential for intra-erythrocytic proliferation; antisense knockdown lethal [#0]\",\n      \"Inhibited by CID 6852389 and CID 23724194 (noncompetitive, micromolar) with antiplasmodial activity [#5]\",\n      \"Inhibited by a Balanites aegyptiaca-derived triazinone oxime in vitro [#6]\",\n      \"Spectrin-binding region absent in human, yeast, and other Plasmodium homologs; active-site divergence from mammalian homologs [#3, #4]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_0932300","name":null,"product":"M18 aspartyl aminopeptidase","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_0833100","name":null,"product":"M18 aspartyl aminopeptidase, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_0731000","name":null,"product":"M18 aspartyl aminopeptidase, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"M18AAP","evaluation":null}