{"gene":"TG_272420","gene_symbol":"LCAT","run_date":"2026-09-08T14:08:30","timeline":{"discoveries":[{"year":2015,"finding":"TgLCAT contains a serine lipase motif 'AHSLG' and a catalytic triad (serine, aspartate, histidine); it is secreted from a subpopulation of dense granule organelles and localizes to the parasitophorous vacuole (PV) and parasite plasma membrane following secretion.","method":"Sequence analysis of catalytic motifs; subcellular fractionation and localization imaging of dense granules and PV","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment with organelle identification and functional context, single lab with multiple methods","pmids":["26694607"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2015,"finding":"TgLCAT is cleaved into two proteolytic fragments that each carry part of the catalytic triad residues and must be reassembled to reconstitute enzymatic activity, unlike other LCAT enzymes.","method":"Biochemical characterization; in vitro enzymatic reconstitution assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of enzymatic activity from proteolytic fragments, single lab with direct biochemical evidence","pmids":["26694607"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2015,"finding":"TgLCAT uses phosphatidylcholine as substrate to produce lysophosphatidylcholine (which can disrupt membranes) and transfers the released fatty acid to cholesterol, but with lower transesterification activity than mammalian LCAT.","method":"In vitro lipid substrate assay measuring product formation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro enzymatic assay with defined substrates and products, single lab","pmids":["26694607"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2015,"finding":"LCAT-null parasites show impaired growth in vitro, reduced virulence in animals, and delayed egress from host cells; parasites overexpressing LCAT display increased virulence and faster egress, demonstrating TgLCAT facilitates replication and egress.","method":"Genetic knockout and overexpression; in vitro growth assay; in vivo virulence assay; egress assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function and gain-of-function experiments with multiple phenotypic readouts, single lab","pmids":["26694607"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2018,"finding":"Catalytic activity of TgLCAT is required for its role in parasite egress, as shown by genetic complementation with a catalytically inactive mutant failing to rescue the egress defect of LCAT-deficient parasites.","method":"Genetic complementation with catalytic mutant; egress assay across multiple independent mutant parasite lines","journal":"mSphere","confidence":"High","confidence_rationale":"Tier 1 / Strong — active-site mutagenesis with genetic complementation confirming catalytic requirement, replicated in multiple independent mutant lines","pmids":["29507893"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2018,"finding":"LCAT-deficient tachyzoites are unable to efficiently egress from infected host cell monolayers, confirming LCAT's primary contribution is to egress; no defects in intracellular growth or virulence were detected in this study.","method":"Multiple independent LCAT-deficient parasite lines; egress assay; growth assay; virulence assay","journal":"mSphere","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined phenotypic readout replicated in multiple lines, single lab; negative growth/virulence results noted","pmids":["29507893"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"TgLCAT is a secreted phospholipase stored in dense granules that localizes to the parasitophorous vacuole and parasite plasma membrane; it is cleaved into two fragments requiring reassembly for activity, uses phosphatidylcholine to generate lysophosphatidylcholine and transfer fatty acids to cholesterol, and its catalytic activity is essential for efficient tachyzoite egress from host cells."},"narrative":{"mechanistic_narrative":"TgLCAT is a secreted phospholipase of Toxoplasma gondii that is stored in a subpopulation of dense granule organelles and, upon secretion, localizes to the parasitophorous vacuole and the parasite plasma membrane, where it acts on host- and parasite-derived membranes to promote tachyzoite egress [PMID:26694607]. The enzyme carries a serine lipase motif ('AHSLG') and a Ser-Asp-His catalytic triad, but unlike other LCAT enzymes it is cleaved into two proteolytic fragments that each retain part of the triad and must reassemble to reconstitute activity [PMID:26694607]. Catalytically, TgLCAT hydrolyzes phosphatidylcholine to generate membrane-disruptive lysophosphatidylcholine and transesterifies the released fatty acid onto cholesterol, though with lower transesterification activity than mammalian LCAT [PMID:26694607]. This catalytic activity is required for its biological role: a catalytically inactive mutant fails to rescue the egress defect of LCAT-deficient parasites, and loss of LCAT delays or blocks efficient egress from host cells [PMID:29507893].","teleology":[{"year":2015,"claim":"Establishing where TgLCAT resides and what enzymatic machinery it carries defined it as a secreted dense-granule phospholipase acting at the host-parasite interface.","evidence":"Catalytic-motif sequence analysis plus organelle fractionation and localization imaging in T. gondii","pmids":["26694607"],"confidence":"Medium","gaps":["Mechanism of dense-granule sorting and secretion timing not defined","Precise membrane targets at the PV versus plasma membrane not resolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2015,"claim":"Reconstituting activity from two proteolytic fragments revealed an unusual maturation mechanism distinguishing TgLCAT from canonical LCAT enzymes.","evidence":"In vitro enzymatic reconstitution assay from proteolytic fragments in T. gondii","pmids":["26694607"],"confidence":"High","gaps":["Identity of the protease responsible for cleavage unknown","Structural basis of fragment reassembly not determined"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2015,"claim":"Defining the substrate and products showed TgLCAT generates membrane-disruptive lysophosphatidylcholine while transferring fatty acid to cholesterol, linking its biochemistry to membrane perturbation.","evidence":"In vitro lipid substrate assay measuring product formation in T. gondii","pmids":["26694607"],"confidence":"High","gaps":["Physiological membrane substrate in vivo not identified","Functional significance of lower transesterification activity versus mammalian LCAT unclear"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2015,"claim":"Loss- and gain-of-function genetics tied TgLCAT to replication, virulence, and egress, positioning it as a facilitator of the intracellular lytic cycle.","evidence":"Genetic knockout and overexpression with growth, in vivo virulence, and egress assays in T. gondii","pmids":["26694607"],"confidence":"Medium","gaps":["Whether growth/virulence defects are direct or secondary to egress defect not resolved in this study","Molecular events downstream of egress not defined"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2018,"claim":"Active-site mutagenesis with complementation established that TgLCAT's catalytic activity is specifically required for egress, isolating egress as its primary function.","evidence":"Genetic complementation with catalytically inactive mutant and egress assay across multiple independent LCAT-deficient lines in T. gondii","pmids":["29507893"],"confidence":"High","gaps":["The absence of growth/virulence defects here versus the 2015 study not reconciled","Direct in situ demonstration of membrane lysis during egress lacking"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"How TgLCAT-generated lysophosphatidylcholine drives membrane rupture during egress at the molecular level remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the reassembled active enzyme","Protease and regulation of fragment maturation unknown","In situ demonstration linking lipid products to egress membrane disruption absent"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":[],"other_free_text":["Stored in a subpopulation of dense granule organelles and secreted [#0].","Cleaved into two proteolytic fragments that must reassemble to reconstitute catalytic activity [#1].","Catalytic activity is required for efficient tachyzoite egress from host cells [#4, #5]."]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"26694607","id":"PMC_26694607","title":"A Lipolytic Lecithin:Cholesterol Acyltransferase Secreted by Toxoplasma Facilitates Parasite Replication and Egress.","date":"2015","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/26694607","citation_count":45,"is_preprint":false},{"pmid":"29507893","id":"PMC_29507893","title":"Toxoplasma gondii LCAT Primarily Contributes to Tachyzoite Egress.","date":"2018","source":"mSphere","url":"https://pubmed.ncbi.nlm.nih.gov/29507893","citation_count":13,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":3556,"output_tokens":1408,"usd":0.015894,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":6503,"output_tokens":2264,"usd":0.044557,"stage2_stop_reason":"end_turn"},"total_usd":0.060451,"stage1_batch_id":"msgbatch_015xmQKDRqnTh9anE4m7LiD6","stage2_batch_id":"msgbatch_01JLpkFTVhoQBNgqHCKFrVVU","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2015,\n      \"finding\": \"TgLCAT contains a serine lipase motif 'AHSLG' and a catalytic triad (serine, aspartate, histidine); it is secreted from a subpopulation of dense granule organelles and localizes to the parasitophorous vacuole (PV) and parasite plasma membrane following secretion.\",\n      \"method\": \"Sequence analysis of catalytic motifs; subcellular fractionation and localization imaging of dense granules and PV\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment with organelle identification and functional context, single lab with multiple methods\",\n      \"pmids\": [\"26694607\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"TgLCAT is cleaved into two proteolytic fragments that each carry part of the catalytic triad residues and must be reassembled to reconstitute enzymatic activity, unlike other LCAT enzymes.\",\n      \"method\": \"Biochemical characterization; in vitro enzymatic reconstitution assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of enzymatic activity from proteolytic fragments, single lab with direct biochemical evidence\",\n      \"pmids\": [\"26694607\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"TgLCAT uses phosphatidylcholine as substrate to produce lysophosphatidylcholine (which can disrupt membranes) and transfers the released fatty acid to cholesterol, but with lower transesterification activity than mammalian LCAT.\",\n      \"method\": \"In vitro lipid substrate assay measuring product formation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro enzymatic assay with defined substrates and products, single lab\",\n      \"pmids\": [\"26694607\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"LCAT-null parasites show impaired growth in vitro, reduced virulence in animals, and delayed egress from host cells; parasites overexpressing LCAT display increased virulence and faster egress, demonstrating TgLCAT facilitates replication and egress.\",\n      \"method\": \"Genetic knockout and overexpression; in vitro growth assay; in vivo virulence assay; egress assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function and gain-of-function experiments with multiple phenotypic readouts, single lab\",\n      \"pmids\": [\"26694607\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Catalytic activity of TgLCAT is required for its role in parasite egress, as shown by genetic complementation with a catalytically inactive mutant failing to rescue the egress defect of LCAT-deficient parasites.\",\n      \"method\": \"Genetic complementation with catalytic mutant; egress assay across multiple independent mutant parasite lines\",\n      \"journal\": \"mSphere\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — active-site mutagenesis with genetic complementation confirming catalytic requirement, replicated in multiple independent mutant lines\",\n      \"pmids\": [\"29507893\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"LCAT-deficient tachyzoites are unable to efficiently egress from infected host cell monolayers, confirming LCAT's primary contribution is to egress; no defects in intracellular growth or virulence were detected in this study.\",\n      \"method\": \"Multiple independent LCAT-deficient parasite lines; egress assay; growth assay; virulence assay\",\n      \"journal\": \"mSphere\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined phenotypic readout replicated in multiple lines, single lab; negative growth/virulence results noted\",\n      \"pmids\": [\"29507893\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"TgLCAT is a secreted phospholipase stored in dense granules that localizes to the parasitophorous vacuole and parasite plasma membrane; it is cleaved into two fragments requiring reassembly for activity, uses phosphatidylcholine to generate lysophosphatidylcholine and transfer fatty acids to cholesterol, and its catalytic activity is essential for efficient tachyzoite egress from host cells.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TgLCAT is a secreted phospholipase of Toxoplasma gondii that is stored in a subpopulation of dense granule organelles and, upon secretion, localizes to the parasitophorous vacuole and the parasite plasma membrane, where it acts on host- and parasite-derived membranes to promote tachyzoite egress [#0, #3]. The enzyme carries a serine lipase motif ('AHSLG') and a Ser-Asp-His catalytic triad, but unlike other LCAT enzymes it is cleaved into two proteolytic fragments that each retain part of the triad and must reassemble to reconstitute activity [#0, #1]. Catalytically, TgLCAT hydrolyzes phosphatidylcholine to generate membrane-disruptive lysophosphatidylcholine and transesterifies the released fatty acid onto cholesterol, though with lower transesterification activity than mammalian LCAT [#2]. This catalytic activity is required for its biological role: a catalytically inactive mutant fails to rescue the egress defect of LCAT-deficient parasites, and loss of LCAT delays or blocks efficient egress from host cells [#4, #5].\",\n  \"teleology\": [\n    {\n      \"year\": 2015,\n      \"claim\": \"Establishing where TgLCAT resides and what enzymatic machinery it carries defined it as a secreted dense-granule phospholipase acting at the host-parasite interface.\",\n      \"evidence\": \"Catalytic-motif sequence analysis plus organelle fractionation and localization imaging in T. gondii\",\n      \"pmids\": [\"26694607\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of dense-granule sorting and secretion timing not defined\", \"Precise membrane targets at the PV versus plasma membrane not resolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Reconstituting activity from two proteolytic fragments revealed an unusual maturation mechanism distinguishing TgLCAT from canonical LCAT enzymes.\",\n      \"evidence\": \"In vitro enzymatic reconstitution assay from proteolytic fragments in T. gondii\",\n      \"pmids\": [\"26694607\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the protease responsible for cleavage unknown\", \"Structural basis of fragment reassembly not determined\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defining the substrate and products showed TgLCAT generates membrane-disruptive lysophosphatidylcholine while transferring fatty acid to cholesterol, linking its biochemistry to membrane perturbation.\",\n      \"evidence\": \"In vitro lipid substrate assay measuring product formation in T. gondii\",\n      \"pmids\": [\"26694607\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological membrane substrate in vivo not identified\", \"Functional significance of lower transesterification activity versus mammalian LCAT unclear\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Loss- and gain-of-function genetics tied TgLCAT to replication, virulence, and egress, positioning it as a facilitator of the intracellular lytic cycle.\",\n      \"evidence\": \"Genetic knockout and overexpression with growth, in vivo virulence, and egress assays in T. gondii\",\n      \"pmids\": [\"26694607\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether growth/virulence defects are direct or secondary to egress defect not resolved in this study\", \"Molecular events downstream of egress not defined\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Active-site mutagenesis with complementation established that TgLCAT's catalytic activity is specifically required for egress, isolating egress as its primary function.\",\n      \"evidence\": \"Genetic complementation with catalytically inactive mutant and egress assay across multiple independent LCAT-deficient lines in T. gondii\",\n      \"pmids\": [\"29507893\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The absence of growth/virulence defects here versus the 2015 study not reconciled\", \"Direct in situ demonstration of membrane lysis during egress lacking\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How TgLCAT-generated lysophosphatidylcholine drives membrane rupture during egress at the molecular level remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the reassembled active enzyme\", \"Protease and regulation of fragment maturation unknown\", \"In situ demonstration linking lipid products to egress membrane disruption absent\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0004607\", \"supporting_discovery_ids\": [0, 1, 2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0004622\", \"supporting_discovery_ids\": [2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020003\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0020020\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": [\n      \"Stored in a subpopulation of dense granule organelles and secreted [#0].\",\n      \"Cleaved into two proteolytic fragments that must reassemble to reconstitute catalytic activity [#1].\",\n      \"Catalytic activity is required for efficient tachyzoite egress from host cells [#4, #5].\"\n    ]\n  },\n  \"strain_conflicts\": []\n}","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_272420","name":"LCAT","product":"phosphatidylcholine-sterol acyltransferase","uniprot_acc":"S8GJB1","chromosome":"TGME49_chrVIII","start_pos":3979523},{"strain":"GT1","gene_id":"TGGT1_272420","name":null,"product":"putative phosphatidylcholine-sterol O-acyltransferase","uniprot_acc":null,"chromosome":"TGGT1_chrVIII","start_pos":3977483},{"strain":"RH88","gene_id":"TGRH88_079290","name":null,"product":"putative phosphatidylcholine-sterol O-acyltransferase","uniprot_acc":null,"chromosome":"CM023089","start_pos":9088980},{"strain":"VEG","gene_id":"TGVEG_272420","name":null,"product":"putative phosphatidylcholine-sterol O-acyltransferase","uniprot_acc":"B9Q3X1","chromosome":"TGVEG_chrVIII","start_pos":3989519}]}