{"gene":"PF3D7_1311800","run_date":"2026-09-08T14:19:06","timeline":{"discoveries":[{"year":1998,"finding":"PF3D7_1311800 (M1AAP) is encoded by a single-copy gene in P. falciparum and contains the canonical HExxHx18E zinc-metallopeptidase active site signature (M1 family) at positions 467-490, a catalytic tyrosine at position 551, and the GAMEN aminopeptidase motif at positions 431-435; polyclonal antibody to a deduced peptide labeled schizont-stage proteins of 96 and 68 kDa that both displayed aminopeptidase activity.","method":"Gene cloning, sequence analysis, polyclonal antibody labeling, biochemical activity assay","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical activity assay combined with immunolabeling; single lab but two orthogonal methods","pmids":["9879894"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2002,"finding":"M1AAP (PfA-M1) is processed from a 120 kDa precursor into 96 kDa (p96) and 68 kDa (p68) isoforms; both processed forms contain the catalytic domain (N-terminal ends mapped between Gly-123 and Lys-163). The purified enzyme displays strict aminopeptidase activity with broad substrate spectrum, optimal at pH 7.4, and inhibition/reactivation profiles characteristic of zinc-metalloaminopeptidases. By immunofluorescence confocal microscopy, it localizes diffusely in the parasite cytoplasm with accumulations around the food vacuole in trophozoites, shifting to a vesicle-like then spot pattern in schizonts and released merozoites.","method":"Protease inhibitor treatment during harvest, N-terminal mapping, enzyme purification and kinetic assay, Western blot, indirect immunofluorescence confocal microscopy","journal":"Parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (biochemical characterization + localization), single lab","pmids":["12166515"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"finding":"Tagged M1AAP was found to localize to both the food vacuole and cytosol in intraerythrocytic P. falciparum; biochemical analysis of enriched food vacuoles confirmed its presence there. Loss-of-function (knockdown) established an apparent requirement for M1AAP for efficient parasite proliferation. Exogenous amino acids could not compensate for aminopeptidase inhibition by bestatin, indicating M1AAP activity is not simply required for amino acid supply from exogenous sources.","method":"Tagged-protein localization, food vacuole biochemical fractionation, parasite proliferation assay with bestatin inhibition, amino acid supplementation rescue experiment","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization with fractionation and functional proliferation assay; single lab, multiple orthogonal methods","pmids":["17895246"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"finding":"X-ray crystal structure of M1AAP (PfA-M1) was determined alone and in complex with bestatin and the phosphinate dipeptide inhibitor hPheP[CH2]Phe, revealing active-site features critical to aminopeptidase function and explaining how inhibitors engage the single catalytic zinc ion. The enzyme was validated as essential and shown to have broad substrate specificity for neutral amino acid residues.","method":"X-ray crystallography (apo and inhibitor-bound co-crystal structures), in vitro enzymatic assay, in vivo antimalarial activity","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple high-resolution crystal structures with functional validation; replicated by subsequent structural studies","pmids":["19196988"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"M1AAP (PfA-M1) exists as three forms: the high-molecular-weight p120 precursor (containing a hydrophobic transmembrane domain) is detected inside the parasite and in the parasitophorous vacuole (PV); the transient p96 form localizes at the border of the PV and within the parasite in a saponin-sensitive compartment; the processed p68 form is strictly soluble and cytoplasmic, with only marginal delivery to the food vacuole. Brefeldin A treatment blocks maturation and retains the enzyme near the nucleus, indicating trafficking through the ER/Golgi. GFP-fusion live imaging confirmed differential localization of the isoforms.","method":"Cellular and biochemical fractionation, mass spectrometry, immunofluorescence assay, GFP-fusion live imaging, brefeldin A treatment","journal":"Malaria journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (fractionation, MS, IFA, live GFP imaging, pharmacological perturbation) in one study","pmids":["20591164"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"finding":"Specific activity-based probes for M1AAP established that its inhibition causes swelling of the parasite digestive vacuole and prevents proteolysis of hemoglobin-derived oligopeptides, likely starving the parasite and causing death; this functionally distinguished M1AAP from the M17 leucine aminopeptidase (Pf-LAP), which has an essential role prior to hemoglobin degradation.","method":"Activity-based protein profiling with selective probes, peptidomic analysis, morphological assay (digestive vacuole swelling), parasite killing assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — selective activity-based probes with multiple orthogonal functional readouts; replicated mechanistic placement","pmids":["21844374"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"finding":"M1AAP (PfA-M1) is abundant in both the food vacuole and nucleus of intraerythrocytic P. falciparum. A unique N-terminal extension containing a signal peptide and putative alternate translation initiation sites contributes to dual targeting. The food-vacuole-localized form exists as a complex of 68- and 35-kDa fragments and is stable and catalytically active at the acidic pH of the food vacuole (5.0–5.5), though K(m) increases below pH 6.5. The nuclear form is the full-length 120 kDa species.","method":"Subcellular fractionation, Western blot, in vitro pH-dependent kinetic assays with aminoacyl-β-naphthylamide and dipeptide substrates, competitive inhibitor binding at varied pH","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — biochemical fractionation combined with detailed kinetic characterization at physiologically relevant pH; multiple orthogonal methods, single lab","pmids":["21659511"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"finding":"X-ray co-crystal structures of M1AAP (PfA-M1) with bestatin derivatives bearing extended aromatic P1 side chains revealed inhibitor-induced conformational rearrangement of the primary loop within the S1 pocket, demonstrating that the S1 subsite can adopt alternate conformations upon ligand binding.","method":"X-ray co-crystallography with bestatin derivative library","journal":"Journal of medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — crystal structures with multiple inhibitors, single lab","pmids":["21366301"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2012,"finding":"Using a 61-member fluorogenic substrate library, recombinant M1AAP (PfM1AAP) was shown to exhibit very broad substrate tolerance, efficiently hydrolyzing neutral and basic amino acid substrates, and was found to account for the majority of aminopeptidase activity in soluble P. falciparum cell lysates.","method":"Fluorogenic substrate library screening with recombinant enzyme and native parasite lysates, kinetic analysis","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstituted enzymatic assay with broad substrate library; single lab","pmids":["22359643"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"finding":"The S1 subsite residue Val-459 of M1AAP (PfA-M1) is a naturally variable position that modulates substrate specificity. Substitution V459P narrowed the S1 subsite specificity to only P1-Arg, -Lys, or -Met substrates; the crystal structure of V459P showed a local backbone conformational change narrowing the S1 subsite, mirroring the restricted specificity of human ERAP2 which has Pro at the equivalent position.","method":"Site-directed mutagenesis of 11 S1 residue variants, steady-state kinetics with dipeptide substrates, X-ray crystallography of V459P mutant","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis combined with crystal structure and kinetic characterization in one study; multiple orthogonal methods","pmids":["23897806"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"finding":"X-ray crystal structure of M1AAP (PfA-M1) in complex with Tosedostat showed that the inhibitor occupies the enzyme's putative product egress channel in addition to the substrate binding pocket, adopting a different binding pose compared to its binding to PfA-M17.","method":"X-ray co-crystallography","journal":"Proteins","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — crystal structure, single lab, no additional functional validation","pmids":["25645579"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"finding":"The cap residues E572 and M1034 at the top of the S1 subsite of M1AAP (PfA-M1) promote broad substrate specificity and enhance catalytic efficiency. E572 stabilizes basic P1 side chains via a salt bridge; M1034 is required for efficient hydrolysis of substrates with large, non-polar P1 side chains. Both residues contribute to competitive inhibitor (bestatin) binding.","method":"Site-directed mutagenesis (E572A, M1034A, double mutant, E572N/M1034Q), steady-state kinetic analysis with diverse dipeptide substrates, competitive inhibitor binding assay","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro mutagenesis with kinetic characterization; single lab, multiple substrates and mutants","pmids":["28811124"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"finding":"A selective inhibitor of M1AAP (PfA-M1) over PfA-M17 (amino-benzosuberone T5; Ki = 50 nM on PfA-M1, no inhibition of PfA-M17 up to 100 µM) blocked in vitro growth of P. falciparum strains 3D7 and FcB1 and reduced parasite burden in the P. chabaudi chabaudi murine model, establishing that M1AAP alone (without concurrent M17 inhibition) is sufficient to kill the parasite.","method":"Enzyme inhibition assay (Ki determination), in vitro parasite growth inhibition, in vivo 4-day Peters assay in P. chabaudi-infected mice","journal":"Malaria journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — selective inhibitor with defined kinetics tested both in vitro and in vivo; single lab","pmids":["28934959"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"},{"species":"Plasmodium falciparum","strain":"FcB1"},{"species":"Plasmodium chabaudi","strain":"chabaudi"}]},{"year":2018,"finding":"Steered molecular dynamics simulations and enzymatic mutagenesis of recombinant M1AAP (PfM1-AAP) identified a stepwise substrate/inhibitor passage through the C-terminal channel involving: ligand recognition at the channel opening, ionic translation to a 'water reservoir', reorientation in the 'water reservoir', and passage into the active site. Charge repulsion was identified as the driving force for product expulsion through the N-terminal channel. Specific channel residues controlling ligand migration were validated by mutagenesis and enzymatic analysis.","method":"Steered molecular dynamics, site-directed mutagenesis, recombinant enzyme activity assay","journal":"PLoS computational biology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — computational mechanism supported by mutagenesis and enzymatic analysis; single lab","pmids":["30379805"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"finding":"Hydroxamic acid inhibitors were co-crystallized with M1AAP (Pf-M1) from P. falciparum, revealing new binding modes including displacement of the catalytic zinc ion for bulky hydrophobic substituents. Potent inhibition was demonstrated across M1 enzymes from P. falciparum and P. vivax.","method":"X-ray co-crystallography, in vitro enzyme inhibition assay","journal":"Journal of medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — crystal structures with functional inhibition data; single lab, cross-species comparison","pmids":["30537832"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium vivax","strain":""}]},{"year":2021,"finding":"Cell fractionation and immunolocalization showed that M1AAP (PfM1AAP) is associated exclusively with the soluble cytosolic fraction of P. falciparum intraerythrocytic parasites, with no detectable presence in the digestive vacuole. Enzyme kinetic studies confirmed its optimal pH is 7.0–8.0 (with <20% activity at pH 5.0–5.5), consistent with a cytoplasmic rather than vacuolar function in degrading hemoglobin-derived peptides transported from the digestive vacuole.","method":"Cell fractionation, immunolocalization, enzyme kinetic assay across pH range","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (fractionation + immunolocalization + kinetics); single lab; partially contradicts earlier food-vacuole localization reports","pmids":["33536500"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"Overexpression of M1AAP (PfA-M1) without its signal peptide in the parasite cytosol caused a 2.5-fold increase in proteolytic activity toward alanyl-AMC substrate, decreased sensitivity to bestatin and other metalloaminopeptidase inhibitors, and was associated with decreased parasite growth (fewer merozoites per schizont, reduced iRBC area occupied at trophozoite and schizont stages), indicating a dosage-sensitive role in intraerythrocytic development.","method":"Stable transfection/overexpression, fluorogenic substrate assay, inhibitor sensitivity assay, parasite growth analysis","journal":"Pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct gain-of-function with functional phenotype and multiple inhibitor validations; single lab","pmids":["34832608"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"Substrate specificity profiling across Plasmodium species showed that M1AAP from P. falciparum displays the greatest diversity in P1 position specificity among Plasmodium M1 enzymes, with broad tolerance for neutral and basic residues, and a definitive preference for peptides with fewer negatively charged intrapeptide residues.","method":"Fluorogenic substrate library screening with recombinant enzymes from P. falciparum, P. vivax, and P. berghei; kinetic analysis","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstituted enzymatic assay; comparative cross-species characterization; single lab","pmids":["34133730"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium vivax","strain":""},{"species":"Plasmodium berghei","strain":""}]}],"current_model":"M1AAP (PF3D7_1311800, PfA-M1) is a monomeric zinc-metalloaminopeptidase of the M1 family that is synthesized as a 120 kDa precursor with a signal peptide-containing N-terminal extension, trafficked through the ER/Golgi to the parasitophorous vacuole, and processed into 96 kDa and 68 kDa isoforms; the processed forms localize primarily to the parasite cytosol (and to a lesser extent the food vacuole and nucleus), where the enzyme cleaves N-terminal residues from hemoglobin-derived peptides with broad substrate specificity governed by a cylindrical S1 subsite (with key residues Val-459, E572, and M1034), substrates and inhibitors enter through a C-terminal channel via a stepwise mechanism, and its activity is required for efficient parasite proliferation in the intraerythrocytic cycle."},"narrative":{"mechanistic_narrative":"M1AAP (PF3D7_1311800, PfA-M1) is a single-copy M1-family zinc-metalloaminopeptidase of P. falciparum that acts in the terminal steps of hemoglobin catabolism, cleaving N-terminal residues from hemoglobin-derived peptides and supporting efficient intraerythrocytic proliferation [PMID:9879894, PMID:19196988, PMID:21844374]. The enzyme carries the canonical M1 HExxHx18E active-site signature and GAMEN motif and is synthesized as a ~120 kDa precursor that is proteolytically matured into 96 kDa and 68 kDa catalytically active isoforms, both retaining the catalytic domain [PMID:9879894, PMID:12166515]. An N-terminal extension bearing a signal peptide and putative alternate translation start sites, together with trafficking through the ER/Golgi (blocked by brefeldin A), gives rise to differentially localized forms [PMID:20591164, PMID:21659511]; while the enzyme has been detected around and within the food vacuole and nucleus, kinetic and fractionation studies place the mature soluble form predominantly in the cytosol with a neutral-to-alkaline pH optimum, consistent with cytoplasmic degradation of peptides exported from the digestive vacuole [PMID:20591164, PMID:21659511, PMID:33536500]. High-resolution crystal structures define a single catalytic zinc engaged by inhibitors such as bestatin and phosphinate dipeptides, and a C-terminal substrate channel through which ligands enter the active site by a stepwise mechanism with charge repulsion driving product egress [PMID:19196988, PMID:25645579, PMID:30379805]. Broad substrate tolerance toward neutral and basic P1 residues is governed by S1 subsite architecture, with Val-459 modulating specificity and the cap residues E572 and M1034 promoting broad specificity and catalytic efficiency [PMID:22359643, PMID:23897806, PMID:28811124, PMID:34133730]. Chemical and genetic perturbation—selective activity-based probes, an M1-selective inhibitor active in vitro and in a murine model, and dosage-sensitive overexpression—establishes that M1AAP activity alone is sufficient to arrest and kill the parasite, distinguishing it functionally from the M17 leucine aminopeptidase [PMID:21844374, PMID:28934959, PMID:34832608].","teleology":[{"year":1998,"claim":"Establishing that PF3D7_1311800 encodes a bona fide M1 zinc-metalloaminopeptidase answered whether the parasite possesses this enzyme class and linked it to catalytically active schizont-stage proteins.","evidence":"Gene cloning, sequence analysis with active-site motif identification, and antibody-based labeling with activity assay","pmids":["9879894"],"confidence":"Medium","gaps":["Physiological substrates not defined","Subcellular localization not resolved","Relationship between the 96 and 68 kDa forms unclear"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2002,"claim":"Mapping precursor processing and biochemical properties established that both mature isoforms derive from a 120 kDa precursor and retain the catalytic domain, defining the enzyme's maturation pathway.","evidence":"N-terminal mapping, enzyme purification with kinetic assay, Western blot, and immunofluorescence confocal microscopy","pmids":["12166515"],"confidence":"Medium","gaps":["Physiological function untested","Protease responsible for processing not identified","Localization described only qualitatively"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"claim":"Loss-of-function and inhibitor experiments answered whether the enzyme is required for growth and whether its role is simply nutritional, showing an essential proliferation function not rescued by exogenous amino acids.","evidence":"Tagged-protein localization, food vacuole fractionation, and bestatin proliferation assay with amino acid supplementation","pmids":["17895246"],"confidence":"Medium","gaps":["Precise essential substrate not identified","Bestatin is not M1-selective","Food-vacuole versus cytosolic contribution unresolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"claim":"The crystal structures resolved how the single catalytic zinc and active site engage inhibitors, providing a structural basis for essentiality and broad neutral-residue specificity and enabling structure-guided inhibitor design.","evidence":"Apo and inhibitor-bound X-ray crystallography with in vitro and in vivo antimalarial validation","pmids":["19196988"],"confidence":"High","gaps":["Conformational dynamics of substrate entry not captured","In-cell substrate range not defined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"claim":"Resolving isoform-specific localization and trafficking answered where the different forms reside, showing the precursor traffics via ER/Golgi to the parasitophorous vacuole while the mature p68 is soluble and cytoplasmic.","evidence":"Fractionation, mass spectrometry, immunofluorescence, GFP-fusion live imaging, and brefeldin A perturbation","pmids":["20591164"],"confidence":"High","gaps":["Functional role of each localized form not dissected","Trafficking determinants beyond the hydrophobic domain unclear"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"claim":"Selective activity-based probes placed M1AAP downstream of hemoglobin degradation, showing its inhibition blocks oligopeptide proteolysis and swells the digestive vacuole, functionally distinct from M17 leucine aminopeptidase.","evidence":"Activity-based protein profiling, peptidomics, morphological and parasite-killing assays","pmids":["21844374"],"confidence":"High","gaps":["Exact peptide pool accumulating not fully enumerated","Mechanism of vacuole swelling not defined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"claim":"Dual food-vacuole/nuclear detection plus pH-dependent kinetics addressed whether the enzyme can function at acidic vacuolar pH and how alternate targeting arises via the N-terminal extension.","evidence":"Subcellular fractionation, Western blot, and pH-dependent kinetic assays with dipeptide and naphthylamide substrates","pmids":["21659511"],"confidence":"High","gaps":["Nuclear function of the 120 kDa form unknown","Later work contests strong food-vacuole localization"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"claim":"Mutagenesis and structure of the S1 residue Val-459 answered how a single naturally variable position tunes substrate specificity, drawing a mechanistic parallel to human ERAP2.","evidence":"Site-directed mutagenesis of S1 variants, steady-state kinetics, and X-ray crystallography of the V459P mutant","pmids":["23897806"],"confidence":"High","gaps":["In vivo consequence of natural variation not tested","Effect on preferred physiological peptides not shown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"claim":"Defining the cap residues E572 and M1034 explained the molecular basis of broad substrate tolerance and catalytic efficiency across neutral and basic P1 side chains.","evidence":"Site-directed mutagenesis with steady-state kinetics across diverse dipeptides and inhibitor binding assays","pmids":["28811124"],"confidence":"Medium","gaps":["Cellular impact of these substitutions untested","Coupling to the substrate channel not addressed"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"claim":"An M1-selective inhibitor that spares M17 established that inhibiting M1AAP alone is sufficient to kill parasites in vitro and reduce burden in vivo, validating it as an independent drug target.","evidence":"Ki determination, in vitro growth inhibition of 3D7 and FcB1, and a 4-day Peters assay in P. chabaudi-infected mice","pmids":["28934959"],"confidence":"Medium","gaps":["Resistance liability not evaluated","Cross-reactivity with human M1 enzymes not detailed here"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"},{"species":"Plasmodium falciparum","strain":"FcB1"},{"species":"Plasmodium chabaudi","strain":"chabaudi"}]},{"year":2018,"claim":"Steered molecular dynamics with mutagenesis proposed a stepwise ligand transit through the C-terminal channel and charge-driven product egress, mechanistically explaining how substrates reach the buried active site.","evidence":"Steered molecular dynamics simulations validated by site-directed mutagenesis and recombinant enzyme assays","pmids":["30379805"],"confidence":"Medium","gaps":["Channel transit not directly visualized experimentally","Kinetic contribution of each step not quantified"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"claim":"Hydroxamic acid co-crystal structures revealed binding modes including catalytic-zinc displacement, expanding the mechanistic repertoire for inhibitor engagement across Plasmodium M1 enzymes.","evidence":"X-ray co-crystallography and in vitro inhibition of P. falciparum and P. vivax M1 enzymes","pmids":["30537832"],"confidence":"Medium","gaps":["Cellular efficacy of zinc-displacing compounds not established here","Selectivity over host aminopeptidases not detailed"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium vivax","strain":""}]},{"year":2021,"claim":"Fractionation and pH-optimum kinetics revised localization, placing the mature enzyme exclusively in the neutral-pH cytosol and reframing its role as cytoplasmic degradation of peptides exported from the digestive vacuole.","evidence":"Cell fractionation, immunolocalization, and enzyme kinetics across a pH range","pmids":["33536500"],"confidence":"Medium","gaps":["Directly contradicts earlier food-vacuole localization reports","Mechanism of peptide export to cytosol not addressed"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"claim":"Overexpression of a cytosol-directed enzyme showed a dosage-sensitive growth defect, indicating that enzyme abundance must be tightly balanced for normal intraerythrocytic development.","evidence":"Stable overexpression without signal peptide, fluorogenic substrate and inhibitor sensitivity assays, and parasite growth analysis","pmids":["34832608"],"confidence":"Medium","gaps":["Mechanism linking excess activity to growth defect unclear","Whether defect reflects peptide pool depletion untested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"claim":"Comparative substrate profiling established that P. falciparum M1AAP has the broadest P1 diversity among Plasmodium M1 enzymes, with a preference for peptides bearing fewer negatively charged residues.","evidence":"Fluorogenic substrate library screening and kinetics of recombinant enzymes from P. falciparum, P. vivax, and P. berghei","pmids":["34133730"],"confidence":"Medium","gaps":["Physiological hemoglobin-peptide substrates not directly mapped","Functional consequence of species divergence not tested"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium vivax","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":null,"claim":"The definitive subcellular site(s) of physiologically essential M1AAP activity and the identity of its critical in-cell hemoglobin-derived peptide substrates remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Food-vacuole versus cytosolic function still debated across studies","No in-cell substrate map of essential peptides","Nuclear form's role unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["Food-vacuole-associated complex of 68- and 35-kDa fragments [#6]"],"partners":[],"other_free_text":["Synthesized as a 120 kDa precursor with an N-terminal extension (signal peptide plus putative alternate translation start sites) matured to 96 kDa and 68 kDa isoforms [#1, #4, #6].","Trafficking through ER/Golgi blocked by brefeldin A [#4].","S1 subsite specificity determinants: Val-459 (naturally variable), cap residues E572 and M1034 [#9, #11].","Substrates/inhibitors enter via a C-terminal channel by a stepwise mechanism; charge repulsion drives product egress through the N-terminal channel [#13].","Functionally distinct from the M17 leucine aminopeptidase (Pf-LAP); M1AAP inhibition alone is sufficient to kill parasites [#5, #12].","Dosage-sensitive: cytosolic overexpression impairs intraerythrocytic development [#16]."]}},"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":"19196988","id":"PMC_19196988","title":"Structural basis for the inhibition of the essential Plasmodium falciparum M1 neutral aminopeptidase.","date":"2009","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/19196988","citation_count":122,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"21844374","id":"PMC_21844374","title":"Bestatin-based chemical biology strategy reveals distinct roles for malaria M1- and M17-family aminopeptidases.","date":"2011","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/21844374","citation_count":109,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"19796954","id":"PMC_19796954","title":"Plasmodium falciparum neutral aminopeptidases: new targets for anti-malarials.","date":"2009","source":"Trends in biochemical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/19796954","citation_count":99,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["PfM1AAP"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"20133789","id":"PMC_20133789","title":"Structure of the Plasmodium falciparum M17 aminopeptidase and significance for the design of drugs targeting the neutral exopeptidases.","date":"2010","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/20133789","citation_count":82,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"12166515","id":"PMC_12166515","title":"Properties, stage-dependent expression and localization of Plasmodium falciparum M1 family zinc-aminopeptidase.","date":"2002","source":"Parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/12166515","citation_count":80,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"22359643","id":"PMC_22359643","title":"Fingerprinting the substrate specificity of M1 and M17 aminopeptidases of human malaria, Plasmodium falciparum.","date":"2012","source":"PloS 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biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23897806","citation_count":20,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"26406322","id":"PMC_26406322","title":"Identification and Validation of a Potent Dual Inhibitor of the P. falciparum M1 and M17 Aminopeptidases Using Virtual Screening.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26406322","citation_count":15,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"34133730","id":"PMC_34133730","title":"Mapping the substrate specificity of the Plasmodium M1 and M17 aminopeptidases.","date":"2021","source":"The Biochemical 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trophozoite stages.","date":"2025","source":"Malaria journal","url":"https://pubmed.ncbi.nlm.nih.gov/41286749","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["PfM1AAP"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":17463,"output_tokens":5341,"usd":0.066252,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12169,"output_tokens":5684,"usd":0.101472,"stage2_stop_reason":"end_turn"},"total_usd":0.167724,"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\": 1998,\n \"finding\": \"PF3D7_1311800 (M1AAP) is encoded by a single-copy gene in P. falciparum and contains the canonical HExxHx18E zinc-metallopeptidase active site signature (M1 family) at positions 467-490, a catalytic tyrosine at position 551, and the GAMEN aminopeptidase motif at positions 431-435; polyclonal antibody to a deduced peptide labeled schizont-stage proteins of 96 and 68 kDa that both displayed aminopeptidase activity.\",\n \"method\": \"Gene cloning, sequence analysis, polyclonal antibody labeling, biochemical activity assay\",\n \"journal\": \"Molecular and biochemical parasitology\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical activity assay combined with immunolabeling; single lab but two orthogonal methods\",\n \"pmids\": [\"9879894\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2002,\n \"finding\": \"M1AAP (PfA-M1) is processed from a 120 kDa precursor into 96 kDa (p96) and 68 kDa (p68) isoforms; both processed forms contain the catalytic domain (N-terminal ends mapped between Gly-123 and Lys-163). The purified enzyme displays strict aminopeptidase activity with broad substrate spectrum, optimal at pH 7.4, and inhibition/reactivation profiles characteristic of zinc-metalloaminopeptidases. By immunofluorescence confocal microscopy, it localizes diffusely in the parasite cytoplasm with accumulations around the food vacuole in trophozoites, shifting to a vesicle-like then spot pattern in schizonts and released merozoites.\",\n \"method\": \"Protease inhibitor treatment during harvest, N-terminal mapping, enzyme purification and kinetic assay, Western blot, indirect immunofluorescence confocal microscopy\",\n \"journal\": \"Parasitology\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (biochemical characterization + localization), single lab\",\n \"pmids\": [\"12166515\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2007,\n \"finding\": \"Tagged M1AAP was found to localize to both the food vacuole and cytosol in intraerythrocytic P. falciparum; biochemical analysis of enriched food vacuoles confirmed its presence there. Loss-of-function (knockdown) established an apparent requirement for M1AAP for efficient parasite proliferation. Exogenous amino acids could not compensate for aminopeptidase inhibition by bestatin, indicating M1AAP activity is not simply required for amino acid supply from exogenous sources.\",\n \"method\": \"Tagged-protein localization, food vacuole biochemical fractionation, parasite proliferation assay with bestatin inhibition, amino acid supplementation rescue experiment\",\n \"journal\": \"The Journal of biological chemistry\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 2 / Moderate — direct localization with fractionation and functional proliferation assay; single lab, multiple orthogonal methods\",\n \"pmids\": [\"17895246\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2009,\n \"finding\": \"X-ray crystal structure of M1AAP (PfA-M1) was determined alone and in complex with bestatin and the phosphinate dipeptide inhibitor hPheP[CH2]Phe, revealing active-site features critical to aminopeptidase function and explaining how inhibitors engage the single catalytic zinc ion. The enzyme was validated as essential and shown to have broad substrate specificity for neutral amino acid residues.\",\n \"method\": \"X-ray crystallography (apo and inhibitor-bound co-crystal structures), in vitro enzymatic assay, in vivo antimalarial activity\",\n \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 1 / Strong — multiple high-resolution crystal structures with functional validation; replicated by subsequent structural studies\",\n \"pmids\": [\"19196988\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2010,\n \"finding\": \"M1AAP (PfA-M1) exists as three forms: the high-molecular-weight p120 precursor (containing a hydrophobic transmembrane domain) is detected inside the parasite and in the parasitophorous vacuole (PV); the transient p96 form localizes at the border of the PV and within the parasite in a saponin-sensitive compartment; the processed p68 form is strictly soluble and cytoplasmic, with only marginal delivery to the food vacuole. Brefeldin A treatment blocks maturation and retains the enzyme near the nucleus, indicating trafficking through the ER/Golgi. GFP-fusion live imaging confirmed differential localization of the isoforms.\",\n \"method\": \"Cellular and biochemical fractionation, mass spectrometry, immunofluorescence assay, GFP-fusion live imaging, brefeldin A treatment\",\n \"journal\": \"Malaria journal\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (fractionation, MS, IFA, live GFP imaging, pharmacological perturbation) in one study\",\n \"pmids\": [\"20591164\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2011,\n \"finding\": \"Specific activity-based probes for M1AAP established that its inhibition causes swelling of the parasite digestive vacuole and prevents proteolysis of hemoglobin-derived oligopeptides, likely starving the parasite and causing death; this functionally distinguished M1AAP from the M17 leucine aminopeptidase (Pf-LAP), which has an essential role prior to hemoglobin degradation.\",\n \"method\": \"Activity-based protein profiling with selective probes, peptidomic analysis, morphological assay (digestive vacuole swelling), parasite killing assay\",\n \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 2 / Strong — selective activity-based probes with multiple orthogonal functional readouts; replicated mechanistic placement\",\n \"pmids\": [\"21844374\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2011,\n \"finding\": \"M1AAP (PfA-M1) is abundant in both the food vacuole and nucleus of intraerythrocytic P. falciparum. A unique N-terminal extension containing a signal peptide and putative alternate translation initiation sites contributes to dual targeting. The food-vacuole-localized form exists as a complex of 68- and 35-kDa fragments and is stable and catalytically active at the acidic pH of the food vacuole (5.0–5.5), though K(m) increases below pH 6.5. The nuclear form is the full-length 120 kDa species.\",\n \"method\": \"Subcellular fractionation, Western blot, in vitro pH-dependent kinetic assays with aminoacyl-β-naphthylamide and dipeptide substrates, competitive inhibitor binding at varied pH\",\n \"journal\": \"The Journal of biological chemistry\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 2 / Strong — biochemical fractionation combined with detailed kinetic characterization at physiologically relevant pH; multiple orthogonal methods, single lab\",\n \"pmids\": [\"21659511\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2011,\n \"finding\": \"X-ray co-crystal structures of M1AAP (PfA-M1) with bestatin derivatives bearing extended aromatic P1 side chains revealed inhibitor-induced conformational rearrangement of the primary loop within the S1 pocket, demonstrating that the S1 subsite can adopt alternate conformations upon ligand binding.\",\n \"method\": \"X-ray co-crystallography with bestatin derivative library\",\n \"journal\": \"Journal of medicinal chemistry\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 1 / Moderate — crystal structures with multiple inhibitors, single lab\",\n \"pmids\": [\"21366301\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2012,\n \"finding\": \"Using a 61-member fluorogenic substrate library, recombinant M1AAP (PfM1AAP) was shown to exhibit very broad substrate tolerance, efficiently hydrolyzing neutral and basic amino acid substrates, and was found to account for the majority of aminopeptidase activity in soluble P. falciparum cell lysates.\",\n \"method\": \"Fluorogenic substrate library screening with recombinant enzyme and native parasite lysates, kinetic analysis\",\n \"journal\": \"PloS one\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstituted enzymatic assay with broad substrate library; single lab\",\n \"pmids\": [\"22359643\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2013,\n \"finding\": \"The S1 subsite residue Val-459 of M1AAP (PfA-M1) is a naturally variable position that modulates substrate specificity. Substitution V459P narrowed the S1 subsite specificity to only P1-Arg, -Lys, or -Met substrates; the crystal structure of V459P showed a local backbone conformational change narrowing the S1 subsite, mirroring the restricted specificity of human ERAP2 which has Pro at the equivalent position.\",\n \"method\": \"Site-directed mutagenesis of 11 S1 residue variants, steady-state kinetics with dipeptide substrates, X-ray crystallography of V459P mutant\",\n \"journal\": \"The Journal of biological chemistry\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis combined with crystal structure and kinetic characterization in one study; multiple orthogonal methods\",\n \"pmids\": [\"23897806\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2015,\n \"finding\": \"X-ray crystal structure of M1AAP (PfA-M1) in complex with Tosedostat showed that the inhibitor occupies the enzyme's putative product egress channel in addition to the substrate binding pocket, adopting a different binding pose compared to its binding to PfA-M17.\",\n \"method\": \"X-ray co-crystallography\",\n \"journal\": \"Proteins\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure, single lab, no additional functional validation\",\n \"pmids\": [\"25645579\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2017,\n \"finding\": \"The cap residues E572 and M1034 at the top of the S1 subsite of M1AAP (PfA-M1) promote broad substrate specificity and enhance catalytic efficiency. E572 stabilizes basic P1 side chains via a salt bridge; M1034 is required for efficient hydrolysis of substrates with large, non-polar P1 side chains. Both residues contribute to competitive inhibitor (bestatin) binding.\",\n \"method\": \"Site-directed mutagenesis (E572A, M1034A, double mutant, E572N/M1034Q), steady-state kinetic analysis with diverse dipeptide substrates, competitive inhibitor binding assay\",\n \"journal\": \"Molecular and biochemical parasitology\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 1 / Moderate — in vitro mutagenesis with kinetic characterization; single lab, multiple substrates and mutants\",\n \"pmids\": [\"28811124\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2017,\n \"finding\": \"A selective inhibitor of M1AAP (PfA-M1) over PfA-M17 (amino-benzosuberone T5; Ki = 50 nM on PfA-M1, no inhibition of PfA-M17 up to 100 µM) blocked in vitro growth of P. falciparum strains 3D7 and FcB1 and reduced parasite burden in the P. chabaudi chabaudi murine model, establishing that M1AAP alone (without concurrent M17 inhibition) is sufficient to kill the parasite.\",\n \"method\": \"Enzyme inhibition assay (Ki determination), in vitro parasite growth inhibition, in vivo 4-day Peters assay in P. chabaudi-infected mice\",\n \"journal\": \"Malaria journal\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 2 / Moderate — selective inhibitor with defined kinetics tested both in vitro and in vivo; single lab\",\n \"pmids\": [\"28934959\"],\n \"is_preprint\": false,\n \"attribution\": [\n {\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"},\n {\"species\": \"Plasmodium falciparum\", \"strain\": \"FcB1\"},\n {\"species\": \"Plasmodium chabaudi\", \"strain\": \"chabaudi\"}\n ]\n },\n {\n \"year\": 2018,\n \"finding\": \"Steered molecular dynamics simulations and enzymatic mutagenesis of recombinant M1AAP (PfM1-AAP) identified a stepwise substrate/inhibitor passage through the C-terminal channel involving: ligand recognition at the channel opening, ionic translation to a 'water reservoir', reorientation in the 'water reservoir', and passage into the active site. Charge repulsion was identified as the driving force for product expulsion through the N-terminal channel. Specific channel residues controlling ligand migration were validated by mutagenesis and enzymatic analysis.\",\n \"method\": \"Steered molecular dynamics, site-directed mutagenesis, recombinant enzyme activity assay\",\n \"journal\": \"PLoS computational biology\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 1 / Moderate — computational mechanism supported by mutagenesis and enzymatic analysis; single lab\",\n \"pmids\": [\"30379805\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2019,\n \"finding\": \"Hydroxamic acid inhibitors were co-crystallized with M1AAP (Pf-M1) from P. falciparum, revealing new binding modes including displacement of the catalytic zinc ion for bulky hydrophobic substituents. Potent inhibition was demonstrated across M1 enzymes from P. falciparum and P. vivax.\",\n \"method\": \"X-ray co-crystallography, in vitro enzyme inhibition assay\",\n \"journal\": \"Journal of medicinal chemistry\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 1 / Moderate — crystal structures with functional inhibition data; single lab, cross-species comparison\",\n \"pmids\": [\"30537832\"],\n \"is_preprint\": false,\n \"attribution\": [\n {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"},\n {\"species\": \"Plasmodium vivax\", \"strain\": \"\"}\n ]\n },\n {\n \"year\": 2021,\n \"finding\": \"Cell fractionation and immunolocalization showed that M1AAP (PfM1AAP) is associated exclusively with the soluble cytosolic fraction of P. falciparum intraerythrocytic parasites, with no detectable presence in the digestive vacuole. Enzyme kinetic studies confirmed its optimal pH is 7.0–8.0 (with <20% activity at pH 5.0–5.5), consistent with a cytoplasmic rather than vacuolar function in degrading hemoglobin-derived peptides transported from the digestive vacuole.\",\n \"method\": \"Cell fractionation, immunolocalization, enzyme kinetic assay across pH range\",\n \"journal\": \"Scientific reports\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (fractionation + immunolocalization + kinetics); single lab; partially contradicts earlier food-vacuole localization reports\",\n \"pmids\": [\"33536500\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2021,\n \"finding\": \"Overexpression of M1AAP (PfA-M1) without its signal peptide in the parasite cytosol caused a 2.5-fold increase in proteolytic activity toward alanyl-AMC substrate, decreased sensitivity to bestatin and other metalloaminopeptidase inhibitors, and was associated with decreased parasite growth (fewer merozoites per schizont, reduced iRBC area occupied at trophozoite and schizont stages), indicating a dosage-sensitive role in intraerythrocytic development.\",\n \"method\": \"Stable transfection/overexpression, fluorogenic substrate assay, inhibitor sensitivity assay, parasite growth analysis\",\n \"journal\": \"Pathogens\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 2 / Moderate — direct gain-of-function with functional phenotype and multiple inhibitor validations; single lab\",\n \"pmids\": [\"34832608\"],\n \"is_preprint\": false,\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2021,\n \"finding\": \"Substrate specificity profiling across Plasmodium species showed that M1AAP from P. falciparum displays the greatest diversity in P1 position specificity among Plasmodium M1 enzymes, with broad tolerance for neutral and basic residues, and a definitive preference for peptides with fewer negatively charged intrapeptide residues.\",\n \"method\": \"Fluorogenic substrate library screening with recombinant enzymes from P. falciparum, P. vivax, and P. berghei; kinetic analysis\",\n \"journal\": \"The Biochemical journal\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstituted enzymatic assay; comparative cross-species characterization; single lab\",\n \"pmids\": [\"34133730\"],\n \"is_preprint\": false,\n \"attribution\": [\n {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"},\n {\"species\": \"Plasmodium vivax\", \"strain\": \"\"},\n {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}\n ]\n }\n ],\n \"current_model\": \"M1AAP (PF3D7_1311800, PfA-M1) is a monomeric zinc-metalloaminopeptidase of the M1 family that is synthesized as a 120 kDa precursor with a signal peptide-containing N-terminal extension, trafficked through the ER/Golgi to the parasitophorous vacuole, and processed into 96 kDa and 68 kDa isoforms; the processed forms localize primarily to the parasite cytosol (and to a lesser extent the food vacuole and nucleus), where the enzyme cleaves N-terminal residues from hemoglobin-derived peptides with broad substrate specificity governed by a cylindrical S1 subsite (with key residues Val-459, E572, and M1034), substrates and inhibitors enter through a C-terminal channel via a stepwise mechanism, and its activity is required for efficient parasite proliferation in the intraerythrocytic cycle.\"\n}\n```","stage2_raw":"{\n \"mechanistic_narrative\": \"M1AAP (PF3D7_1311800, PfA-M1) is a single-copy M1-family zinc-metalloaminopeptidase of P. falciparum that acts in the terminal steps of hemoglobin catabolism, cleaving N-terminal residues from hemoglobin-derived peptides and supporting efficient intraerythrocytic proliferation [#0, #3, #5]. The enzyme carries the canonical M1 HExxHx18E active-site signature and GAMEN motif and is synthesized as a ~120 kDa precursor that is proteolytically matured into 96 kDa and 68 kDa catalytically active isoforms, both retaining the catalytic domain [#0, #1]. An N-terminal extension bearing a signal peptide and putative alternate translation start sites, together with trafficking through the ER/Golgi (blocked by brefeldin A), gives rise to differentially localized forms [#4, #6]; while the enzyme has been detected around and within the food vacuole and nucleus, kinetic and fractionation studies place the mature soluble form predominantly in the cytosol with a neutral-to-alkaline pH optimum, consistent with cytoplasmic degradation of peptides exported from the digestive vacuole [#4, #6, #15]. High-resolution crystal structures define a single catalytic zinc engaged by inhibitors such as bestatin and phosphinate dipeptides, and a C-terminal substrate channel through which ligands enter the active site by a stepwise mechanism with charge repulsion driving product egress [#3, #10, #13]. Broad substrate tolerance toward neutral and basic P1 residues is governed by S1 subsite architecture, with Val-459 modulating specificity and the cap residues E572 and M1034 promoting broad specificity and catalytic efficiency [#8, #9, #11, #17]. Chemical and genetic perturbation—selective activity-based probes, an M1-selective inhibitor active in vitro and in a murine model, and dosage-sensitive overexpression—establishes that M1AAP activity alone is sufficient to arrest and kill the parasite, distinguishing it functionally from the M17 leucine aminopeptidase [#5, #12, #16].\",\n \"teleology\": [\n {\n \"year\": 1998,\n \"claim\": \"Establishing that PF3D7_1311800 encodes a bona fide M1 zinc-metalloaminopeptidase answered whether the parasite possesses this enzyme class and linked it to catalytically active schizont-stage proteins.\",\n \"evidence\": \"Gene cloning, sequence analysis with active-site motif identification, and antibody-based labeling with activity assay\",\n \"pmids\": [\"9879894\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Physiological substrates not defined\", \"Subcellular localization not resolved\", \"Relationship between the 96 and 68 kDa forms unclear\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2002,\n \"claim\": \"Mapping precursor processing and biochemical properties established that both mature isoforms derive from a 120 kDa precursor and retain the catalytic domain, defining the enzyme's maturation pathway.\",\n \"evidence\": \"N-terminal mapping, enzyme purification with kinetic assay, Western blot, and immunofluorescence confocal microscopy\",\n \"pmids\": [\"12166515\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Physiological function untested\", \"Protease responsible for processing not identified\", \"Localization described only qualitatively\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2007,\n \"claim\": \"Loss-of-function and inhibitor experiments answered whether the enzyme is required for growth and whether its role is simply nutritional, showing an essential proliferation function not rescued by exogenous amino acids.\",\n \"evidence\": \"Tagged-protein localization, food vacuole fractionation, and bestatin proliferation assay with amino acid supplementation\",\n \"pmids\": [\"17895246\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Precise essential substrate not identified\", \"Bestatin is not M1-selective\", \"Food-vacuole versus cytosolic contribution unresolved\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2009,\n \"claim\": \"The crystal structures resolved how the single catalytic zinc and active site engage inhibitors, providing a structural basis for essentiality and broad neutral-residue specificity and enabling structure-guided inhibitor design.\",\n \"evidence\": \"Apo and inhibitor-bound X-ray crystallography with in vitro and in vivo antimalarial validation\",\n \"pmids\": [\"19196988\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Conformational dynamics of substrate entry not captured\", \"In-cell substrate range not defined\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2010,\n \"claim\": \"Resolving isoform-specific localization and trafficking answered where the different forms reside, showing the precursor traffics via ER/Golgi to the parasitophorous vacuole while the mature p68 is soluble and cytoplasmic.\",\n \"evidence\": \"Fractionation, mass spectrometry, immunofluorescence, GFP-fusion live imaging, and brefeldin A perturbation\",\n \"pmids\": [\"20591164\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Functional role of each localized form not dissected\", \"Trafficking determinants beyond the hydrophobic domain unclear\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2011,\n \"claim\": \"Selective activity-based probes placed M1AAP downstream of hemoglobin degradation, showing its inhibition blocks oligopeptide proteolysis and swells the digestive vacuole, functionally distinct from M17 leucine aminopeptidase.\",\n \"evidence\": \"Activity-based protein profiling, peptidomics, morphological and parasite-killing assays\",\n \"pmids\": [\"21844374\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Exact peptide pool accumulating not fully enumerated\", \"Mechanism of vacuole swelling not defined\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2011,\n \"claim\": \"Dual food-vacuole/nuclear detection plus pH-dependent kinetics addressed whether the enzyme can function at acidic vacuolar pH and how alternate targeting arises via the N-terminal extension.\",\n \"evidence\": \"Subcellular fractionation, Western blot, and pH-dependent kinetic assays with dipeptide and naphthylamide substrates\",\n \"pmids\": [\"21659511\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Nuclear function of the 120 kDa form unknown\", \"Later work contests strong food-vacuole localization\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2013,\n \"claim\": \"Mutagenesis and structure of the S1 residue Val-459 answered how a single naturally variable position tunes substrate specificity, drawing a mechanistic parallel to human ERAP2.\",\n \"evidence\": \"Site-directed mutagenesis of S1 variants, steady-state kinetics, and X-ray crystallography of the V459P mutant\",\n \"pmids\": [\"23897806\"],\n \"confidence\": \"High\",\n \"gaps\": [\"In vivo consequence of natural variation not tested\", \"Effect on preferred physiological peptides not shown\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2017,\n \"claim\": \"Defining the cap residues E572 and M1034 explained the molecular basis of broad substrate tolerance and catalytic efficiency across neutral and basic P1 side chains.\",\n \"evidence\": \"Site-directed mutagenesis with steady-state kinetics across diverse dipeptides and inhibitor binding assays\",\n \"pmids\": [\"28811124\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Cellular impact of these substitutions untested\", \"Coupling to the substrate channel not addressed\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2017,\n \"claim\": \"An M1-selective inhibitor that spares M17 established that inhibiting M1AAP alone is sufficient to kill parasites in vitro and reduce burden in vivo, validating it as an independent drug target.\",\n \"evidence\": \"Ki determination, in vitro growth inhibition of 3D7 and FcB1, and a 4-day Peters assay in P. chabaudi-infected mice\",\n \"pmids\": [\"28934959\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Resistance liability not evaluated\", \"Cross-reactivity with human M1 enzymes not detailed here\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"FcB1\"}, {\"species\": \"Plasmodium chabaudi\", \"strain\": \"chabaudi\"}]\n },\n {\n \"year\": 2018,\n \"claim\": \"Steered molecular dynamics with mutagenesis proposed a stepwise ligand transit through the C-terminal channel and charge-driven product egress, mechanistically explaining how substrates reach the buried active site.\",\n \"evidence\": \"Steered molecular dynamics simulations validated by site-directed mutagenesis and recombinant enzyme assays\",\n \"pmids\": [\"30379805\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Channel transit not directly visualized experimentally\", \"Kinetic contribution of each step not quantified\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2019,\n \"claim\": \"Hydroxamic acid co-crystal structures revealed binding modes including catalytic-zinc displacement, expanding the mechanistic repertoire for inhibitor engagement across Plasmodium M1 enzymes.\",\n \"evidence\": \"X-ray co-crystallography and in vitro inhibition of P. falciparum and P. vivax M1 enzymes\",\n \"pmids\": [\"30537832\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Cellular efficacy of zinc-displacing compounds not established here\", \"Selectivity over host aminopeptidases not detailed\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium vivax\", \"strain\": \"\"}]\n },\n {\n \"year\": 2021,\n \"claim\": \"Fractionation and pH-optimum kinetics revised localization, placing the mature enzyme exclusively in the neutral-pH cytosol and reframing its role as cytoplasmic degradation of peptides exported from the digestive vacuole.\",\n \"evidence\": \"Cell fractionation, immunolocalization, and enzyme kinetics across a pH range\",\n \"pmids\": [\"33536500\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Directly contradicts earlier food-vacuole localization reports\", \"Mechanism of peptide export to cytosol not addressed\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2021,\n \"claim\": \"Overexpression of a cytosol-directed enzyme showed a dosage-sensitive growth defect, indicating that enzyme abundance must be tightly balanced for normal intraerythrocytic development.\",\n \"evidence\": \"Stable overexpression without signal peptide, fluorogenic substrate and inhibitor sensitivity assays, and parasite growth analysis\",\n \"pmids\": [\"34832608\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Mechanism linking excess activity to growth defect unclear\", \"Whether defect reflects peptide pool depletion untested\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n },\n {\n \"year\": 2021,\n \"claim\": \"Comparative substrate profiling established that P. falciparum M1AAP has the broadest P1 diversity among Plasmodium M1 enzymes, with a preference for peptides bearing fewer negatively charged residues.\",\n \"evidence\": \"Fluorogenic substrate library screening and kinetics of recombinant enzymes from P. falciparum, P. vivax, and P. berghei\",\n \"pmids\": [\"34133730\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Physiological hemoglobin-peptide substrates not directly mapped\", \"Functional consequence of species divergence not tested\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium vivax\", \"strain\": \"\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n },\n {\n \"year\": null,\n \"claim\": \"The definitive subcellular site(s) of physiologically essential M1AAP activity and the identity of its critical in-cell hemoglobin-derived peptide substrates remain unresolved.\",\n \"evidence\": \"\",\n \"pmids\": [],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Food-vacuole versus cytosolic function still debated across studies\", \"No in-cell substrate map of essential peptides\", \"Nuclear form's role unknown\"],\n \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n }\n ],\n \"mechanism_profile\": {\n \"molecular_activity\": [\n {\"term_id\": \"GO:0004177\", \"supporting_discovery_ids\": [0, 1, 2, 8, 12, 17]},\n {\"term_id\": \"GO:0008237\", \"supporting_discovery_ids\": [0, 1, 3]},\n {\"term_id\": \"GO:0008270\", \"supporting_discovery_ids\": [0, 3, 14]},\n {\"term_id\": \"GO:0070006\", \"supporting_discovery_ids\": [0, 3, 9, 11]}\n ],\n \"localization\": [\n {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1, 4, 15]},\n {\"term_id\": \"GO:0020020\", \"supporting_discovery_ids\": [2, 5, 6]},\n {\"term_id\": \"GO:0020003\", \"supporting_discovery_ids\": [4]},\n {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [6]},\n {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [4]}\n ],\n \"pathway\": [\n {\"term_id\": \"GO:0043171\", \"supporting_discovery_ids\": [5, 15]},\n {\"term_id\": \"GO:0006508\", \"supporting_discovery_ids\": [0, 5, 8]}\n ],\n \"complexes\": [\n \"Food-vacuole-associated complex of 68- and 35-kDa fragments [#6]\"\n ],\n \"partners\": [],\n \"other_free_text\": [\n \"Synthesized as a 120 kDa precursor with an N-terminal extension (signal peptide plus putative alternate translation start sites) matured to 96 kDa and 68 kDa isoforms [#1, #4, #6].\",\n \"Trafficking through ER/Golgi blocked by brefeldin A [#4].\",\n \"S1 subsite specificity determinants: Val-459 (naturally variable), cap residues E572 and M1034 [#9, #11].\",\n \"Substrates/inhibitors enter via a C-terminal channel by a stepwise mechanism; charge repulsion drives product egress through the N-terminal channel [#13].\",\n \"Functionally distinct from the M17 leucine aminopeptidase (Pf-LAP); M1AAP inhibition alone is sufficient to kill parasites [#5, #12].\",\n \"Dosage-sensitive: cytosolic overexpression impairs intraerythrocytic development [#16].\"\n ]\n }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_1311800","name":null,"product":"M1-family alanyl aminopeptidase","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_1410300","name":null,"product":"M1-family alanyl aminopeptidase, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_1412500","name":null,"product":"M1-family alanyl aminopeptidase, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"M1AAP","evaluation":null}