{"gene":"PF3D7_1023200","run_date":"2026-09-08T12:51:28","timeline":{"discoveries":[{"year":1982,"finding":"Orotidine 5'-phosphate decarboxylase (OMPDC) enzymatic activity was detected in P. falciparum trophozoite extracts (100,000×g supernatant), establishing that the parasite possesses this de novo pyrimidine biosynthesis enzyme.","method":"Enzymatic activity assay in parasite cell-free extracts","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct enzymatic activity measurement in parasite extracts, single lab, single method","pmids":["6285190"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1981,"finding":"Orotidine-5'-phosphate decarboxylase activity was detected in P. falciparum, confirming the de novo pyrimidine biosynthesis pathway is present in this parasite.","method":"Enzymatic activity assay","journal":"Transactions of the Royal Society of Tropical Medicine and Hygiene","confidence":"Low","confidence_rationale":"Tier 3 / Weak — activity detection only, no abstract text available for further assessment, single method","pmids":["6277049"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1986,"finding":"Pyrazofurin (as its 5'-monophosphate, in the presence of adenosine kinase and ATP) caused 73% inhibition of P. falciparum orotidine-5'-phosphate decarboxylase activity in parasite extracts, establishing this compound as an inhibitor of OMPDC.","method":"Enzymatic inhibition assay in parasite extracts","journal":"Molecular and biochemical parasitology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — inhibition assay in crude extracts, single lab, single method","pmids":["3515174"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2004,"finding":"OMPDC (PfOMPDC, 38 kDa subunit) and orotate phosphoribosyltransferase (PfOPRT, 32 kDa subunit) were co-purified from P. falciparum as a heterotetrameric multienzyme complex of ~140 kDa containing two subunits each of OPRT and OMPDC; kinetic parameters of the complex differed from the bifunctional human UMP synthase.","method":"Protein purification (multiple chromatographic steps), co-elution of enzymatic activities, molecular mass determination","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-purification with activity co-elution and molecular mass analysis, single lab, two orthogonal approaches","pmids":["15147974"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"finding":"Recombinant PfOMPDC was cloned from P. falciparum cDNA, expressed in E. coli, purified, and shown to be catalytically active as a homodimer (38 kDa subunit). The native heterotetrameric (PfOPRT)2(PfOMPDC)2 complex (~140 kDa) was confirmed by chemical cross-linking with dimethyl suberimidate. Kinetic properties of the recombinant monofunctional PfOMPDC differed from the native complex. The yeast OMPDC inhibitor 6-thiocarboxamido-uridine 5'-monophosphate was ~5 orders of magnitude less potent against PfOMPDC than against yeast OMPDC.","method":"Gene cloning and recombinant protein expression, enzyme kinetics, chemical cross-linking (dimethyl suberimidate), inhibition assay","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — recombinant reconstitution, cross-linking complex verification, kinetic analysis, and inhibitor profiling in a single rigorous study","pmids":["15683248"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2006,"finding":"Recombinant PfOMPDC was crystallized, and diffraction data were collected to 2.7 Å resolution (space group R3), with a dimer in the asymmetric unit, establishing the dimeric quaternary structure of the recombinant enzyme.","method":"Protein crystallization, X-ray diffraction data collection","journal":"Acta crystallographica. Section F, Structural biology and crystallization communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — crystal structure data collection reported (preliminary), single lab, no functional validation in this paper","pmids":["16754976"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"finding":"X-ray crystal structures of PfOMPDC were solved in apo, substrate-bound, and product-bound forms at 2.7, 2.65, and 2.65 Å resolution, revealing the substrate recognition mechanism involving dynamic structural changes and rearrangement of the hydrogen bond array at the active site upon substrate/product binding.","method":"X-ray crystallography (apo, substrate-complex, product-complex structures)","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — three crystal structures (apo, substrate, product) with structural analysis of active-site dynamics, single lab but multiple ligand states","pmids":["17981823"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"finding":"Recombinant PfOMPDC (PfODCase) was overexpressed, purified, and kinetically characterized as a homodimer (38 kDa subunit) with Km = 350 ± 60 nM and Vmax = 2.70 ± 0.10 μmol/min/mg for OMP. Inhibition by nucleoside 5'-monophosphate analogues was linear competitive vs OMP, with potency order: pyrazofurin 5'-monophosphate (Ki = 3.6 nM) > XMP (Ki = 4.4 nM) > 6-azaUMP (Ki = 12 nM) > allopurinol-3-riboside 5'-monophosphate (Ki = 240 nM). XMP was ~150-fold more potent against PfODCase than the human enzyme. Crystal structure was solved showing a TIM-barrel fold with flexible phosphate-binding and βα5 loops.","method":"Recombinant protein expression and purification, enzyme kinetics (Michaelis-Menten), competitive inhibition assays, X-ray crystallography","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro kinetics with multiple inhibitors, competitive inhibition mechanism, and crystal structure in a single rigorous study","pmids":["18303855"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"finding":"Structure-activity relationship studies identified 6-azidouridine 5'-monophosphate as a potent covalent inhibitor of P. falciparum OMPDC among C6-uridine derivatives tested in biochemical assays.","method":"Enzymatic inhibition assay with synthetic UMP derivatives, SAR analysis","journal":"Journal of medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vitro inhibition assay with chemical series defining covalent inhibition, single lab, single method type","pmids":["18189347"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"finding":"The recombinant P. falciparum OPRT-OMPDC enzyme complex expressed in E. coli showed 5- to 125-fold higher kinetic parameters (Km, kcat, kcat/Km) for both OPRT and OMPDC activities compared to the monofunctional enzymes, and exhibited greater thermal stability. Pyrophosphate was a potent inhibitor of the complex but had only slight inhibitory effect on the monofunctional OMPDC.","method":"Recombinant protein expression and co-purification, enzyme kinetics, thermal inactivation assay, inhibition assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — recombinant complex reconstitution, kinetic and thermal stability comparisons, single lab with multiple assay types","pmids":["19800871"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"PfOMPDC was identified as one of nine P. falciparum enzymes inhibited by antimalarial compounds in a high-throughput biochemical screen, confirming its drugability as a biochemical target.","method":"High-throughput biochemical inhibition assay (384- or 1536-well format)","journal":"Molecular and biochemical parasitology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — HTS biochemical screen, target validation context only, single method","pmids":["20813141"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2012,"finding":"X-ray crystal structure of PfOMPDC in complex with the inhibitor 4-(2-hydroxy-4-methoxyphenyl)-4-oxobutanoic acid was solved at 2.1 Å resolution, revealing that the inhibitor occupies the phosphate-binding region of the active site and causes dramatic movement of the L1 and L2 loops involved in substrate/product recognition.","method":"In silico screening, X-ray crystallography of inhibitor-enzyme complex","journal":"Journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — crystal structure of inhibitor complex with loop movement characterization, single lab, no functional mutagenesis","pmids":["22740703"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"finding":"The protein-protein interaction interface of the (PfOPRT)2(PfOMPDC)2 heterotetrameric complex was mapped; unique low-complexity region insertions at the α2 and α5 helices of PfOMPDC (single amino acid repeat sequences absent in homologous proteins from other organisms) were identified as responsible for OPRT-OMPDC interaction by chemical cross-linking and LC-MS analysis.","method":"Bifunctional chemical cross-linking, liquid chromatography-mass spectrometry, homology modeling","journal":"Asian Pacific journal of tropical medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cross-linking combined with LC-MS identification of interface residues, single lab, two orthogonal methods","pmids":["24507637"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"finding":"A gene fusion encoding PfOMPDC (NH2-terminal) fused to PfOPRT (COOH-terminal) was expressed in E. coli as a bifunctional dimer. The fused enzyme showed up to three orders of magnitude enhancement of kcat for OMPDC activity compared to the monofunctional enzyme, while Km remained at low μM levels, demonstrating catalytic efficiency gains from the fusion architecture.","method":"Recombinant gene fusion expression in E. coli, protein purification, enzyme kinetics","journal":"Parasitology international","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution of fused bifunctional enzyme with kinetic characterization, single lab, single study","pmids":["28389349"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2018,"finding":"Re-refinement of three PfOMPDC crystal structures (PDB entries 2za1, 2za2, 2za3) demonstrated that the ligand originally described as the substrate OMP in the Michaelis complex (2za1) is actually the product UMP, correcting the structural model of the substrate-bound active site.","method":"Crystallographic re-refinement","journal":"Acta crystallographica. Section F, Structural biology communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — re-refinement of existing X-ray data with improved electron density fit, single study, no new functional experiment","pmids":["30279319"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"PfOMPDC (PF3D7_1023200) is a homodimeric enzyme that catalyzes the decarboxylation of orotidine 5'-monophosphate (OMP) to uridine 5'-monophosphate (UMP) via a TIM-barrel fold with flexible phosphate-binding and βα5 loops; in P. falciparum it forms a heterotetrameric (PfOPRT)2(PfOMPDC)2 complex through unique low-complexity insertion sequences at its α2 and α5 helices, and this complex confers enhanced catalytic efficiency (up to 125-fold higher kcat/Km) and thermal stability compared to the monofunctional enzyme, while the active site can be competitively inhibited by nucleoside 5'-monophosphate analogues such as pyrazofurin-5'-monophosphate and XMP with nanomolar affinity."},"narrative":{"mechanistic_narrative":"OMPDC (PF3D7_1023200) catalyzes the decarboxylation of orotidine 5'-monophosphate (OMP) to uridine 5'-monophosphate (UMP), the terminal step of de novo pyrimidine biosynthesis in P. falciparum, an activity first detected in parasite extracts [PMID:6285190]. Recombinant PfOMPDC is catalytically active as a homodimer (38 kDa subunit) and adopts a TIM-barrel fold with flexible phosphate-binding and βα5 loops, binding OMP with sub-micromolar affinity [PMID:15683248, PMID:18303855]; crystal structures in apo, substrate-, and product-bound states show that substrate recognition proceeds through dynamic rearrangement of the active-site hydrogen-bond array and movement of the L1/L2 loops [PMID:17981823, PMID:22740703]. In P. falciparum the enzyme does not act alone but assembles with orotate phosphoribosyltransferase (PfOPRT) into a ~140 kDa heterotetrameric (PfOPRT)2(PfOMPDC)2 multienzyme complex, verified by co-purification and chemical cross-linking [PMID:15147974, PMID:15683248], with the interaction mediated by unique low-complexity insertion sequences at the α2 and α5 helices of PfOMPDC that are absent from homologs in other organisms [PMID:24507637]. Complex formation is functionally consequential, conferring up to 125-fold higher catalytic efficiency and increased thermal stability relative to the monofunctional enzyme [PMID:19800871], a gain recapitulated by an engineered OMPDC–OPRT gene fusion [PMID:28389349]. The active site is competitively inhibited by nucleoside 5'-monophosphate analogues including pyrazofurin-5'-monophosphate and XMP with nanomolar affinity, with XMP substantially more potent against the parasite than the human enzyme, marking OMPDC as a drugable antimalarial target [PMID:18303855, PMID:20813141].","teleology":[{"year":1982,"claim":"Establishing whether the malaria parasite carries de novo pyrimidine synthesis machinery answered whether OMPDC activity is present at all, defining the pathway as an intrinsic parasite capability.","evidence":"OMPDC enzymatic activity assay in P. falciparum trophozoite cell-free extracts","pmids":["6285190","6277049"],"confidence":"Medium","gaps":["Activity in crude extract does not identify the responsible gene or protein","No purified enzyme or kinetic parameters"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1986,"claim":"Testing pyrazofurin against parasite OMPDC activity answered whether the enzyme is pharmacologically inhibitable, first pointing to its therapeutic potential.","evidence":"Enzymatic inhibition assay with pyrazofurin 5'-monophosphate in parasite extracts","pmids":["3515174"],"confidence":"Low","gaps":["Inhibition measured in crude extract, not on purified enzyme","No affinity or mechanism of inhibition determined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"claim":"Cloning and reconstituting recombinant PfOMPDC answered what the isolated gene product is and how it differs from the parasite complex, showing it is an active homodimer whose kinetics diverge from the native heterotetramer.","evidence":"cDNA cloning, E. coli expression, kinetics, chemical cross-linking (dimethyl suberimidate), and inhibitor profiling","pmids":["15683248"],"confidence":"High","gaps":["Structural basis of homodimer/heterotetramer distinction not yet resolved","In vivo essentiality not tested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"claim":"Solving apo, substrate-, and product-bound crystal structures answered how the active site recognizes substrate, revealing dynamic hydrogen-bond rearrangement upon ligand binding.","evidence":"X-ray crystallography of three ligand states of recombinant PfOMPDC","pmids":["16754976","17981823"],"confidence":"High","gaps":["Catalytic mechanism of decarboxylation not dissected by mutagenesis","Structures of the full heterotetrameric complex not obtained"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"claim":"Systematic kinetic and inhibitor characterization with structure answered how tightly and by what mechanism nucleotide analogues bind, defining nanomolar competitive inhibitors with parasite-versus-human selectivity.","evidence":"Recombinant enzyme kinetics, competitive inhibition assays with multiple analogues, X-ray structure, and covalent inhibitor SAR","pmids":["18303855","18189347"],"confidence":"High","gaps":["Cellular efficacy of inhibitors against live parasites not established","Selectivity for parasite complex over monofunctional forms not addressed"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"claim":"Reconstituting the recombinant OPRT-OMPDC complex answered whether physical association changes enzyme performance, showing large gains in catalytic efficiency and thermal stability over the monofunctional enzyme.","evidence":"Recombinant co-purification, kinetics, thermal inactivation, and pyrophosphate inhibition assays","pmids":["19800871"],"confidence":"Medium","gaps":["Physiological trigger and stoichiometry of assembly in the parasite not defined","Contribution of each subunit to the efficiency gain not separated"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"claim":"Mapping the interaction interface answered how the parasite-specific complex assembles, attributing OPRT binding to unique low-complexity insertions at the OMPDC α2 and α5 helices absent from other organisms.","evidence":"Bifunctional chemical cross-linking with LC-MS and homology modeling","pmids":["24507637"],"confidence":"Medium","gaps":["Interface residues not validated by mutagenesis","No co-crystal structure of the interface"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2018,"claim":"Re-refining earlier structures answered whether the deposited Michaelis complex correctly modeled substrate, correcting the identity of the bound ligand from OMP to the product UMP.","evidence":"Crystallographic re-refinement of PDB entries 2za1/2za2/2za3","pmids":["30279319"],"confidence":"Medium","gaps":["A true substrate-bound Michaelis complex remains structurally uncharacterized","No new functional data generated"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"Whether OMPDC is essential for parasite survival in vivo and whether its inhibitors kill live parasites remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No genetic knockout or conditional depletion in P. falciparum reported","No demonstrated antiparasitic activity of the characterized inhibitors in cell-based or animal models","Mutagenesis validation of catalytic and interface residues absent"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["(PfOPRT)2(PfOMPDC)2 heterotetrameric multienzyme complex (~140 kDa)","PfOMPDC homodimer"],"partners":["PFOPRT (OROTATE PHOSPHORIBOSYLTRANSFERASE)"],"other_free_text":["TIM-barrel fold with flexible phosphate-binding and βα5 loops [#7]","OPRT interaction mediated by low-complexity insertions at the α2 and α5 helices [#12]","Competitively inhibited by nucleoside 5'-monophosphate analogues: pyrazofurin-5'-monophosphate (Ki 3.6 nM), XMP (Ki 4.4 nM), 6-azaUMP, allopurinol-3-riboside 5'-monophosphate [#7]","6-azidouridine 5'-monophosphate acts as a covalent inhibitor [#8]","Complex formation confers up to 125-fold higher catalytic efficiency and thermal stability versus monofunctional enzyme [#9]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"6285190","id":"PMC_6285190","title":"Enzymes of purine and pyrimidine metabolism from the human malaria parasite, Plasmodium falciparum.","date":"1982","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/6285190","citation_count":189,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["orotidine 5'-phosphate decarboxylase"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"20813141","id":"PMC_20813141","title":"Identification of inhibitors for putative malaria drug targets among novel antimalarial compounds.","date":"2010","source":"Molecular and biochemical 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superfamily.","date":"2006","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16489742","citation_count":34,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["OMPDC"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"18189347","id":"PMC_18189347","title":"Structure-activity relationships of C6-uridine derivatives targeting plasmodia orotidine monophosphate decarboxylase.","date":"2008","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18189347","citation_count":30,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"15147974","id":"PMC_15147974","title":"Orotate phosphoribosyltransferase and orotidine 5'-monophosphate decarboxylase exist as multienzyme complex in human malaria parasite Plasmodium 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decarboxylase enzyme complex in human malaria parasite Plasmodium falciparum.","date":"2009","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/19800871","citation_count":8,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["OMPDC"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"16754976","id":"PMC_16754976","title":"Crystallization and preliminary crystallographic analysis of orotidine 5'-monophosphate decarboxylase from the human malaria parasite Plasmodium falciparum.","date":"2006","source":"Acta crystallographica. Section F, Structural biology and crystallization communications","url":"https://pubmed.ncbi.nlm.nih.gov/16754976","citation_count":8,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["OMPDC"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"31304874","id":"PMC_31304874","title":"A profound computational study to prioritize the natural compound inhibitors against the P. falciparum orotidine-5-monophosphate decarboxylase enzyme.","date":"2019","source":"Journal of biomolecular structure & dynamics","url":"https://pubmed.ncbi.nlm.nih.gov/31304874","citation_count":4,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"30279319","id":"PMC_30279319","title":"Re-refinement of Plasmodium falciparum orotidine 5'-monophosphate decarboxylase provides a clearer picture of an important malarial drug target.","date":"2018","source":"Acta crystallographica. Section F, Structural biology communications","url":"https://pubmed.ncbi.nlm.nih.gov/30279319","citation_count":1,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"28389349","id":"PMC_28389349","title":"Bifunctional activity of fused Plasmodium falciparum orotate phosphoribosyltransferase and orotidine 5'-monophosphate decarboxylase.","date":"2017","source":"Parasitology international","url":"https://pubmed.ncbi.nlm.nih.gov/28389349","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["OMPDC"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13062,"output_tokens":4035,"usd":0.049855,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10208,"output_tokens":3408,"usd":0.06812,"stage2_stop_reason":"end_turn"},"total_usd":0.117975,"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\": 1982,\n      \"finding\": \"Orotidine 5'-phosphate decarboxylase (OMPDC) enzymatic activity was detected in P. falciparum trophozoite extracts (100,000×g supernatant), establishing that the parasite possesses this de novo pyrimidine biosynthesis enzyme.\",\n      \"method\": \"Enzymatic activity assay in parasite cell-free extracts\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct enzymatic activity measurement in parasite extracts, single lab, single method\",\n      \"pmids\": [\"6285190\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1981,\n      \"finding\": \"Orotidine-5'-phosphate decarboxylase activity was detected in P. falciparum, confirming the de novo pyrimidine biosynthesis pathway is present in this parasite.\",\n      \"method\": \"Enzymatic activity assay\",\n      \"journal\": \"Transactions of the Royal Society of Tropical Medicine and Hygiene\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — activity detection only, no abstract text available for further assessment, single method\",\n      \"pmids\": [\"6277049\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"Pyrazofurin (as its 5'-monophosphate, in the presence of adenosine kinase and ATP) caused 73% inhibition of P. falciparum orotidine-5'-phosphate decarboxylase activity in parasite extracts, establishing this compound as an inhibitor of OMPDC.\",\n      \"method\": \"Enzymatic inhibition assay in parasite extracts\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — inhibition assay in crude extracts, single lab, single method\",\n      \"pmids\": [\"3515174\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"OMPDC (PfOMPDC, 38 kDa subunit) and orotate phosphoribosyltransferase (PfOPRT, 32 kDa subunit) were co-purified from P. falciparum as a heterotetrameric multienzyme complex of ~140 kDa containing two subunits each of OPRT and OMPDC; kinetic parameters of the complex differed from the bifunctional human UMP synthase.\",\n      \"method\": \"Protein purification (multiple chromatographic steps), co-elution of enzymatic activities, molecular mass determination\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-purification with activity co-elution and molecular mass analysis, single lab, two orthogonal approaches\",\n      \"pmids\": [\"15147974\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Recombinant PfOMPDC was cloned from P. falciparum cDNA, expressed in E. coli, purified, and shown to be catalytically active as a homodimer (38 kDa subunit). The native heterotetrameric (PfOPRT)2(PfOMPDC)2 complex (~140 kDa) was confirmed by chemical cross-linking with dimethyl suberimidate. Kinetic properties of the recombinant monofunctional PfOMPDC differed from the native complex. The yeast OMPDC inhibitor 6-thiocarboxamido-uridine 5'-monophosphate was ~5 orders of magnitude less potent against PfOMPDC than against yeast OMPDC.\",\n      \"method\": \"Gene cloning and recombinant protein expression, enzyme kinetics, chemical cross-linking (dimethyl suberimidate), inhibition assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — recombinant reconstitution, cross-linking complex verification, kinetic analysis, and inhibitor profiling in a single rigorous study\",\n      \"pmids\": [\"15683248\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Recombinant PfOMPDC was crystallized, and diffraction data were collected to 2.7 Å resolution (space group R3), with a dimer in the asymmetric unit, establishing the dimeric quaternary structure of the recombinant enzyme.\",\n      \"method\": \"Protein crystallization, X-ray diffraction data collection\",\n      \"journal\": \"Acta crystallographica. Section F, Structural biology and crystallization communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — crystal structure data collection reported (preliminary), single lab, no functional validation in this paper\",\n      \"pmids\": [\"16754976\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"X-ray crystal structures of PfOMPDC were solved in apo, substrate-bound, and product-bound forms at 2.7, 2.65, and 2.65 Å resolution, revealing the substrate recognition mechanism involving dynamic structural changes and rearrangement of the hydrogen bond array at the active site upon substrate/product binding.\",\n      \"method\": \"X-ray crystallography (apo, substrate-complex, product-complex structures)\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — three crystal structures (apo, substrate, product) with structural analysis of active-site dynamics, single lab but multiple ligand states\",\n      \"pmids\": [\"17981823\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Recombinant PfOMPDC (PfODCase) was overexpressed, purified, and kinetically characterized as a homodimer (38 kDa subunit) with Km = 350 ± 60 nM and Vmax = 2.70 ± 0.10 μmol/min/mg for OMP. Inhibition by nucleoside 5'-monophosphate analogues was linear competitive vs OMP, with potency order: pyrazofurin 5'-monophosphate (Ki = 3.6 nM) > XMP (Ki = 4.4 nM) > 6-azaUMP (Ki = 12 nM) > allopurinol-3-riboside 5'-monophosphate (Ki = 240 nM). XMP was ~150-fold more potent against PfODCase than the human enzyme. Crystal structure was solved showing a TIM-barrel fold with flexible phosphate-binding and βα5 loops.\",\n      \"method\": \"Recombinant protein expression and purification, enzyme kinetics (Michaelis-Menten), competitive inhibition assays, X-ray crystallography\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro kinetics with multiple inhibitors, competitive inhibition mechanism, and crystal structure in a single rigorous study\",\n      \"pmids\": [\"18303855\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Structure-activity relationship studies identified 6-azidouridine 5'-monophosphate as a potent covalent inhibitor of P. falciparum OMPDC among C6-uridine derivatives tested in biochemical assays.\",\n      \"method\": \"Enzymatic inhibition assay with synthetic UMP derivatives, SAR analysis\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vitro inhibition assay with chemical series defining covalent inhibition, single lab, single method type\",\n      \"pmids\": [\"18189347\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The recombinant P. falciparum OPRT-OMPDC enzyme complex expressed in E. coli showed 5- to 125-fold higher kinetic parameters (Km, kcat, kcat/Km) for both OPRT and OMPDC activities compared to the monofunctional enzymes, and exhibited greater thermal stability. Pyrophosphate was a potent inhibitor of the complex but had only slight inhibitory effect on the monofunctional OMPDC.\",\n      \"method\": \"Recombinant protein expression and co-purification, enzyme kinetics, thermal inactivation assay, inhibition assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — recombinant complex reconstitution, kinetic and thermal stability comparisons, single lab with multiple assay types\",\n      \"pmids\": [\"19800871\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PfOMPDC was identified as one of nine P. falciparum enzymes inhibited by antimalarial compounds in a high-throughput biochemical screen, confirming its drugability as a biochemical target.\",\n      \"method\": \"High-throughput biochemical inhibition assay (384- or 1536-well format)\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — HTS biochemical screen, target validation context only, single method\",\n      \"pmids\": [\"20813141\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"X-ray crystal structure of PfOMPDC in complex with the inhibitor 4-(2-hydroxy-4-methoxyphenyl)-4-oxobutanoic acid was solved at 2.1 Å resolution, revealing that the inhibitor occupies the phosphate-binding region of the active site and causes dramatic movement of the L1 and L2 loops involved in substrate/product recognition.\",\n      \"method\": \"In silico screening, X-ray crystallography of inhibitor-enzyme complex\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — crystal structure of inhibitor complex with loop movement characterization, single lab, no functional mutagenesis\",\n      \"pmids\": [\"22740703\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The protein-protein interaction interface of the (PfOPRT)2(PfOMPDC)2 heterotetrameric complex was mapped; unique low-complexity region insertions at the α2 and α5 helices of PfOMPDC (single amino acid repeat sequences absent in homologous proteins from other organisms) were identified as responsible for OPRT-OMPDC interaction by chemical cross-linking and LC-MS analysis.\",\n      \"method\": \"Bifunctional chemical cross-linking, liquid chromatography-mass spectrometry, homology modeling\",\n      \"journal\": \"Asian Pacific journal of tropical medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cross-linking combined with LC-MS identification of interface residues, single lab, two orthogonal methods\",\n      \"pmids\": [\"24507637\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A gene fusion encoding PfOMPDC (NH2-terminal) fused to PfOPRT (COOH-terminal) was expressed in E. coli as a bifunctional dimer. The fused enzyme showed up to three orders of magnitude enhancement of kcat for OMPDC activity compared to the monofunctional enzyme, while Km remained at low μM levels, demonstrating catalytic efficiency gains from the fusion architecture.\",\n      \"method\": \"Recombinant gene fusion expression in E. coli, protein purification, enzyme kinetics\",\n      \"journal\": \"Parasitology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution of fused bifunctional enzyme with kinetic characterization, single lab, single study\",\n      \"pmids\": [\"28389349\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Re-refinement of three PfOMPDC crystal structures (PDB entries 2za1, 2za2, 2za3) demonstrated that the ligand originally described as the substrate OMP in the Michaelis complex (2za1) is actually the product UMP, correcting the structural model of the substrate-bound active site.\",\n      \"method\": \"Crystallographic re-refinement\",\n      \"journal\": \"Acta crystallographica. Section F, Structural biology communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — re-refinement of existing X-ray data with improved electron density fit, single study, no new functional experiment\",\n      \"pmids\": [\"30279319\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"PfOMPDC (PF3D7_1023200) is a homodimeric enzyme that catalyzes the decarboxylation of orotidine 5'-monophosphate (OMP) to uridine 5'-monophosphate (UMP) via a TIM-barrel fold with flexible phosphate-binding and βα5 loops; in P. falciparum it forms a heterotetrameric (PfOPRT)2(PfOMPDC)2 complex through unique low-complexity insertion sequences at its α2 and α5 helices, and this complex confers enhanced catalytic efficiency (up to 125-fold higher kcat/Km) and thermal stability compared to the monofunctional enzyme, while the active site can be competitively inhibited by nucleoside 5'-monophosphate analogues such as pyrazofurin-5'-monophosphate and XMP with nanomolar affinity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"OMPDC (PF3D7_1023200) catalyzes the decarboxylation of orotidine 5'-monophosphate (OMP) to uridine 5'-monophosphate (UMP), the terminal step of de novo pyrimidine biosynthesis in P. falciparum, an activity first detected in parasite extracts [#0]. Recombinant PfOMPDC is catalytically active as a homodimer (38 kDa subunit) and adopts a TIM-barrel fold with flexible phosphate-binding and \\u03b2\\u03b15 loops, binding OMP with sub-micromolar affinity [#4, #7]; crystal structures in apo, substrate-, and product-bound states show that substrate recognition proceeds through dynamic rearrangement of the active-site hydrogen-bond array and movement of the L1/L2 loops [#6, #11]. In P. falciparum the enzyme does not act alone but assembles with orotate phosphoribosyltransferase (PfOPRT) into a ~140 kDa heterotetrameric (PfOPRT)2(PfOMPDC)2 multienzyme complex, verified by co-purification and chemical cross-linking [#3, #4], with the interaction mediated by unique low-complexity insertion sequences at the \\u03b12 and \\u03b15 helices of PfOMPDC that are absent from homologs in other organisms [#12]. Complex formation is functionally consequential, conferring up to 125-fold higher catalytic efficiency and increased thermal stability relative to the monofunctional enzyme [#9], a gain recapitulated by an engineered OMPDC\\u2013OPRT gene fusion [#13]. The active site is competitively inhibited by nucleoside 5'-monophosphate analogues including pyrazofurin-5'-monophosphate and XMP with nanomolar affinity, with XMP substantially more potent against the parasite than the human enzyme, marking OMPDC as a drugable antimalarial target [#7, #10].\",\n  \"teleology\": [\n    {\n      \"year\": 1982,\n      \"claim\": \"Establishing whether the malaria parasite carries de novo pyrimidine synthesis machinery answered whether OMPDC activity is present at all, defining the pathway as an intrinsic parasite capability.\",\n      \"evidence\": \"OMPDC enzymatic activity assay in P. falciparum trophozoite cell-free extracts\",\n      \"pmids\": [\"6285190\", \"6277049\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Activity in crude extract does not identify the responsible gene or protein\", \"No purified enzyme or kinetic parameters\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"Testing pyrazofurin against parasite OMPDC activity answered whether the enzyme is pharmacologically inhibitable, first pointing to its therapeutic potential.\",\n      \"evidence\": \"Enzymatic inhibition assay with pyrazofurin 5'-monophosphate in parasite extracts\",\n      \"pmids\": [\"3515174\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Inhibition measured in crude extract, not on purified enzyme\", \"No affinity or mechanism of inhibition determined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Cloning and reconstituting recombinant PfOMPDC answered what the isolated gene product is and how it differs from the parasite complex, showing it is an active homodimer whose kinetics diverge from the native heterotetramer.\",\n      \"evidence\": \"cDNA cloning, E. coli expression, kinetics, chemical cross-linking (dimethyl suberimidate), and inhibitor profiling\",\n      \"pmids\": [\"15683248\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of homodimer/heterotetramer distinction not yet resolved\", \"In vivo essentiality not tested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Solving apo, substrate-, and product-bound crystal structures answered how the active site recognizes substrate, revealing dynamic hydrogen-bond rearrangement upon ligand binding.\",\n      \"evidence\": \"X-ray crystallography of three ligand states of recombinant PfOMPDC\",\n      \"pmids\": [\"16754976\", \"17981823\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic mechanism of decarboxylation not dissected by mutagenesis\", \"Structures of the full heterotetrameric complex not obtained\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Systematic kinetic and inhibitor characterization with structure answered how tightly and by what mechanism nucleotide analogues bind, defining nanomolar competitive inhibitors with parasite-versus-human selectivity.\",\n      \"evidence\": \"Recombinant enzyme kinetics, competitive inhibition assays with multiple analogues, X-ray structure, and covalent inhibitor SAR\",\n      \"pmids\": [\"18303855\", \"18189347\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular efficacy of inhibitors against live parasites not established\", \"Selectivity for parasite complex over monofunctional forms not addressed\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Reconstituting the recombinant OPRT-OMPDC complex answered whether physical association changes enzyme performance, showing large gains in catalytic efficiency and thermal stability over the monofunctional enzyme.\",\n      \"evidence\": \"Recombinant co-purification, kinetics, thermal inactivation, and pyrophosphate inhibition assays\",\n      \"pmids\": [\"19800871\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological trigger and stoichiometry of assembly in the parasite not defined\", \"Contribution of each subunit to the efficiency gain not separated\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Mapping the interaction interface answered how the parasite-specific complex assembles, attributing OPRT binding to unique low-complexity insertions at the OMPDC \\u03b12 and \\u03b15 helices absent from other organisms.\",\n      \"evidence\": \"Bifunctional chemical cross-linking with LC-MS and homology modeling\",\n      \"pmids\": [\"24507637\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Interface residues not validated by mutagenesis\", \"No co-crystal structure of the interface\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Re-refining earlier structures answered whether the deposited Michaelis complex correctly modeled substrate, correcting the identity of the bound ligand from OMP to the product UMP.\",\n      \"evidence\": \"Crystallographic re-refinement of PDB entries 2za1/2za2/2za3\",\n      \"pmids\": [\"30279319\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"A true substrate-bound Michaelis complex remains structurally uncharacterized\", \"No new functional data generated\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Whether OMPDC is essential for parasite survival in vivo and whether its inhibitors kill live parasites remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No genetic knockout or conditional depletion in P. falciparum reported\", \"No demonstrated antiparasitic activity of the characterized inhibitors in cell-based or animal models\", \"Mutagenesis validation of catalytic and interface residues absent\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0004590\", \"supporting_discovery_ids\": [0, 1, 4, 7]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"GO:0044205\", \"supporting_discovery_ids\": [0, 1, 3]}\n    ],\n    \"complexes\": [\n      \"(PfOPRT)2(PfOMPDC)2 heterotetrameric multienzyme complex (~140 kDa)\",\n      \"PfOMPDC homodimer\"\n    ],\n    \"partners\": [\n      \"PfOPRT (orotate phosphoribosyltransferase)\"\n    ],\n    \"other_free_text\": [\n      \"TIM-barrel fold with flexible phosphate-binding and \\u03b2\\u03b15 loops [#7]\",\n      \"OPRT interaction mediated by low-complexity insertions at the \\u03b12 and \\u03b15 helices [#12]\",\n      \"Competitively inhibited by nucleoside 5'-monophosphate analogues: pyrazofurin-5'-monophosphate (Ki 3.6 nM), XMP (Ki 4.4 nM), 6-azaUMP, allopurinol-3-riboside 5'-monophosphate [#7]\",\n      \"6-azidouridine 5'-monophosphate acts as a covalent inhibitor [#8]\",\n      \"Complex formation confers up to 125-fold higher catalytic efficiency and thermal stability versus monofunctional enzyme [#9]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_1023200","name":null,"product":"orotidine 5'-phosphate decarboxylase","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_0507400","name":null,"product":"orotidine 5'-phosphate decarboxylase, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_0607700","name":null,"product":"orotidine 5'-phosphate decarboxylase, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"OMPDC","evaluation":null}