{"gene":"TG_209800","gene_symbol":"FNT1","run_date":"2026-09-08T11:06:21","timeline":{"discoveries":[{"year":2021,"finding":"TgFNT1 localizes to the T. gondii plasma membrane and mediates L-lactate transport across it, making the primary contribution to L-lactate export during the tachyzoite lytic cycle. Direct transport measurements were obtained using the Xenopus oocyte heterologous expression system.","method":"Xenopus oocyte expression system (direct transport assay), fluorescence localization, genetic knockouts","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct functional transport assay in Xenopus oocytes plus plasma membrane localization and genetic disruption in a single focused study with multiple orthogonal methods","pmids":["33762657"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2021,"finding":"All three tgfnt genes (including tgfnt1) can be individually and jointly disrupted without affecting parasite proliferation under standard in vitro culture conditions, indicating TgFNTs are not required for the lytic cycle in vitro and are unlikely drug targets.","method":"Genetic knockout (triple tgfnt knockout), in vitro plaque/proliferation assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean genetic knockout with defined phenotypic readout, single lab, single study","pmids":["33762657"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2022,"finding":"Auxin-induced conditional knockdown and knockout of FNT1 (and FNT2) reduced lactate and pyruvate release by parasites and diminished acidification of the parasitophorous vacuole (PV), linking FNT1-mediated monocarboxylate export to PV acidification prior to egress.","method":"Auxin-inducible degron (AID) conditional knockdown, genetic knockout, ratiometric pHluorin live-imaging pH measurement, lactate/pyruvate secretion assays","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genetic perturbation with orthogonal functional readouts (pH measurement, metabolite secretion), single lab, single study","pmids":["35512005"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":"RH"}]},{"year":2026,"finding":"TgFNT1 (together with TgFNT2) functions as a principal monocarboxylate (lactate and pyruvate) importer across the parasite plasma membrane; genetic ablation of TgFNT1 and TgFNT2 together impairs lactate- and pyruvate-driven mitochondrial respiratory responses, extracellular survival, and virulence in mice.","method":"Genetic knockout (TgFNT1-3 disruption, hexokinase knockout background), oxygen consumption assays, mitochondrial membrane potential measurements, ATP quantification, mouse virulence assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean genetic knockouts with multiple functional readouts (respiration, membrane potential, ATP, virulence), single lab, preprint not yet peer-reviewed","pmids":["42124602"],"is_preprint":true,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"TgFNT1 is a plasma membrane formate-nitrite/monocarboxylate transporter that serves as the primary conduit for L-lactate export in tachyzoites and, together with TgFNT2, mediates import of host-derived lactate and pyruvate to sustain mitochondrial respiration and virulence; it also contributes to parasitophorous vacuole acidification during egress via monocarboxylate secretion, but is dispensable for in vitro lytic-cycle proliferation under standard culture conditions."},"narrative":{"mechanistic_narrative":"TgFNT1 is a plasma membrane formate-nitrite/monocarboxylate transporter that governs bidirectional monocarboxylate (L-lactate and pyruvate) flux in Toxoplasma gondii tachyzoites [PMID:33762657, PMID:42124602]. Direct transport assays in Xenopus oocytes established it as a plasma membrane L-lactate carrier that makes the primary contribution to lactate export during the lytic cycle [PMID:33762657], and monocarboxylate secretion through TgFNT1 acidifies the parasitophorous vacuole prior to egress [PMID:35512005]. Acting together with TgFNT2, it also imports host-derived lactate and pyruvate to sustain mitochondrial respiration, extracellular survival, and virulence in mice [PMID:42124602]. Despite these roles, individual and combined disruption of all three tgfnt genes does not affect parasite proliferation under standard in vitro culture, indicating TgFNTs are dispensable for the in vitro lytic cycle and unlikely drug targets [PMID:33762657]. No structural model or residue-level transport mechanism for TgFNT1 has been characterized in the available corpus.","teleology":[{"year":2021,"claim":"Establishing whether TgFNT1 is a genuine transporter and what it moves: direct assay identified it as the plasma membrane conduit for parasite L-lactate export.","evidence":"Xenopus oocyte heterologous transport assay, fluorescence localization, and genetic knockout in T. gondii","pmids":["33762657"],"confidence":"High","gaps":["No structural or residue-level mechanism of substrate selectivity","Directionality (export vs import) under physiological gradients not resolved by this study"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2021,"claim":"Testing whether TgFNTs are essential and druggable: triple knockout showed they are dispensable for in vitro proliferation.","evidence":"Triple tgfnt genetic knockout with plaque/proliferation assays","pmids":["33762657"],"confidence":"Medium","gaps":["Does not address in vivo or stress-condition requirements","Single lab, single study"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2022,"claim":"Connecting transport activity to a cellular process: FNT1-mediated monocarboxylate export drives acidification of the parasitophorous vacuole before egress.","evidence":"Auxin-inducible degron knockdown and knockout with ratiometric pHluorin pH imaging and lactate/pyruvate secretion assays in RH strain","pmids":["35512005"],"confidence":"Medium","gaps":["Mechanistic link between vacuolar acidification and egress timing not fully defined","Shown only in RH strain"],"attribution":[{"species":"Toxoplasma gondii","strain":"RH"}]},{"year":2026,"claim":"Defining the import role and physiological consequence: TgFNT1/TgFNT2 import host lactate and pyruvate to fuel mitochondrial respiration, extracellular survival, and virulence.","evidence":"Genetic knockout in hexokinase-null background with oxygen consumption, mitochondrial membrane potential, ATP quantification, and mouse virulence assays (preprint)","pmids":["42124602"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Relative contribution of TgFNT1 vs TgFNT2 to import not separated","In vivo relevance beyond mouse virulence model unaddressed"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"The structural basis of substrate recognition and the mechanism controlling directional (import vs export) flux through TgFNT1 remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of TgFNT1","Determinants of import vs export switching unknown","Individual contribution of TgFNT1 separated from TgFNT2/3 in import not established"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":["TGFNT2"],"other_free_text":["Makes the primary contribution to L-lactate export during the tachyzoite lytic cycle [#0].","Monocarboxylate export via TgFNT1 contributes to parasitophorous vacuole acidification prior to egress [#2].","Together with TgFNT2, imports host-derived lactate and pyruvate to sustain mitochondrial respiration, extracellular survival, and mouse virulence [#3].","All three tgfnt genes are individually and jointly dispensable for in vitro proliferation, indicating they are unlikely drug targets [#1]."]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"33762657","id":"PMC_33762657","title":"Identifying the major lactate transporter of Toxoplasma gondii tachyzoites.","date":"2021","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/33762657","citation_count":17,"is_preprint":false},{"pmid":"35512005","id":"PMC_35512005","title":"Toxoplasma gondii excretion of glycolytic products is associated with acidification of the parasitophorous vacuole during parasite egress.","date":"2022","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/35512005","citation_count":10,"is_preprint":false},{"pmid":"42124602","id":"PMC_42124602","title":"A two-membrane gateway for monocarboxylates couples host glycolysis to Toxoplasma mitochondrial fitness and virulence.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/42124602","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":4021,"output_tokens":1137,"usd":0.014559,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":6093,"output_tokens":2199,"usd":0.04272,"stage2_stop_reason":"end_turn"},"total_usd":0.057279,"stage1_batch_id":"msgbatch_01WokvBYTB6JLnYrpD4rXnyV","stage2_batch_id":"msgbatch_01M7hsQDvz6AqVC9DLVjQzzc","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2021,\n      \"finding\": \"TgFNT1 localizes to the T. gondii plasma membrane and mediates L-lactate transport across it, making the primary contribution to L-lactate export during the tachyzoite lytic cycle. Direct transport measurements were obtained using the Xenopus oocyte heterologous expression system.\",\n      \"method\": \"Xenopus oocyte expression system (direct transport assay), fluorescence localization, genetic knockouts\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct functional transport assay in Xenopus oocytes plus plasma membrane localization and genetic disruption in a single focused study with multiple orthogonal methods\",\n      \"pmids\": [\"33762657\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"All three tgfnt genes (including tgfnt1) can be individually and jointly disrupted without affecting parasite proliferation under standard in vitro culture conditions, indicating TgFNTs are not required for the lytic cycle in vitro and are unlikely drug targets.\",\n      \"method\": \"Genetic knockout (triple tgfnt knockout), in vitro plaque/proliferation assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean genetic knockout with defined phenotypic readout, single lab, single study\",\n      \"pmids\": [\"33762657\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Auxin-induced conditional knockdown and knockout of FNT1 (and FNT2) reduced lactate and pyruvate release by parasites and diminished acidification of the parasitophorous vacuole (PV), linking FNT1-mediated monocarboxylate export to PV acidification prior to egress.\",\n      \"method\": \"Auxin-inducible degron (AID) conditional knockdown, genetic knockout, ratiometric pHluorin live-imaging pH measurement, lactate/pyruvate secretion assays\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genetic perturbation with orthogonal functional readouts (pH measurement, metabolite secretion), single lab, single study\",\n      \"pmids\": [\"35512005\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"RH\"}]\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TgFNT1 (together with TgFNT2) functions as a principal monocarboxylate (lactate and pyruvate) importer across the parasite plasma membrane; genetic ablation of TgFNT1 and TgFNT2 together impairs lactate- and pyruvate-driven mitochondrial respiratory responses, extracellular survival, and virulence in mice.\",\n      \"method\": \"Genetic knockout (TgFNT1-3 disruption, hexokinase knockout background), oxygen consumption assays, mitochondrial membrane potential measurements, ATP quantification, mouse virulence assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean genetic knockouts with multiple functional readouts (respiration, membrane potential, ATP, virulence), single lab, preprint not yet peer-reviewed\",\n      \"pmids\": [\"42124602\"],\n      \"is_preprint\": true,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"TgFNT1 is a plasma membrane formate-nitrite/monocarboxylate transporter that serves as the primary conduit for L-lactate export in tachyzoites and, together with TgFNT2, mediates import of host-derived lactate and pyruvate to sustain mitochondrial respiration and virulence; it also contributes to parasitophorous vacuole acidification during egress via monocarboxylate secretion, but is dispensable for in vitro lytic-cycle proliferation under standard culture conditions.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TgFNT1 is a plasma membrane formate-nitrite/monocarboxylate transporter that governs bidirectional monocarboxylate (L-lactate and pyruvate) flux in Toxoplasma gondii tachyzoites [#0, #3]. Direct transport assays in Xenopus oocytes established it as a plasma membrane L-lactate carrier that makes the primary contribution to lactate export during the lytic cycle [#0], and monocarboxylate secretion through TgFNT1 acidifies the parasitophorous vacuole prior to egress [#2]. Acting together with TgFNT2, it also imports host-derived lactate and pyruvate to sustain mitochondrial respiration, extracellular survival, and virulence in mice [#3]. Despite these roles, individual and combined disruption of all three tgfnt genes does not affect parasite proliferation under standard in vitro culture, indicating TgFNTs are dispensable for the in vitro lytic cycle and unlikely drug targets [#1]. No structural model or residue-level transport mechanism for TgFNT1 has been characterized in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2021,\n      \"claim\": \"Establishing whether TgFNT1 is a genuine transporter and what it moves: direct assay identified it as the plasma membrane conduit for parasite L-lactate export.\",\n      \"evidence\": \"Xenopus oocyte heterologous transport assay, fluorescence localization, and genetic knockout in T. gondii\",\n      \"pmids\": [\"33762657\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural or residue-level mechanism of substrate selectivity\", \"Directionality (export vs import) under physiological gradients not resolved by this study\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Testing whether TgFNTs are essential and druggable: triple knockout showed they are dispensable for in vitro proliferation.\",\n      \"evidence\": \"Triple tgfnt genetic knockout with plaque/proliferation assays\",\n      \"pmids\": [\"33762657\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not address in vivo or stress-condition requirements\", \"Single lab, single study\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connecting transport activity to a cellular process: FNT1-mediated monocarboxylate export drives acidification of the parasitophorous vacuole before egress.\",\n      \"evidence\": \"Auxin-inducible degron knockdown and knockout with ratiometric pHluorin pH imaging and lactate/pyruvate secretion assays in RH strain\",\n      \"pmids\": [\"35512005\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link between vacuolar acidification and egress timing not fully defined\", \"Shown only in RH strain\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"RH\"}]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defining the import role and physiological consequence: TgFNT1/TgFNT2 import host lactate and pyruvate to fuel mitochondrial respiration, extracellular survival, and virulence.\",\n      \"evidence\": \"Genetic knockout in hexokinase-null background with oxygen consumption, mitochondrial membrane potential, ATP quantification, and mouse virulence assays (preprint)\",\n      \"pmids\": [\"42124602\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Relative contribution of TgFNT1 vs TgFNT2 to import not separated\", \"In vivo relevance beyond mouse virulence model unaddressed\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis of substrate recognition and the mechanism controlling directional (import vs export) flux through TgFNT1 remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of TgFNT1\", \"Determinants of import vs export switching unknown\", \"Individual contribution of TgFNT1 separated from TgFNT2/3 in import not established\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0015129\", \"supporting_discovery_ids\": [0, 2, 3], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0015355\", \"supporting_discovery_ids\": [3], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006090\", \"supporting_discovery_ids\": [3], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0045454\", \"supporting_discovery_ids\": [2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"RH\"}]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"TgFNT2\"],\n    \"other_free_text\": [\n      \"Makes the primary contribution to L-lactate export during the tachyzoite lytic cycle [#0].\",\n      \"Monocarboxylate export via TgFNT1 contributes to parasitophorous vacuole acidification prior to egress [#2].\",\n      \"Together with TgFNT2, imports host-derived lactate and pyruvate to sustain mitochondrial respiration, extracellular survival, and mouse virulence [#3].\",\n      \"All three tgfnt genes are individually and jointly dispensable for in vitro proliferation, indicating they are unlikely drug targets [#1].\"\n    ]\n  },\n  \"strain_conflicts\": []\n}","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_209800","name":"FNT1","product":"formate/nitrite transporter FNT1","uniprot_acc":"A0A125YSC7","chromosome":"TGME49_chrIb","start_pos":1460334},{"strain":"GT1","gene_id":"TGGT1_209800","name":null,"product":"formate/nitrite transporter protein","uniprot_acc":null,"chromosome":"TGGT1_chrIb","start_pos":1476667},{"strain":"RH88","gene_id":"TGRH88_021380","name":null,"product":"formate/nitrite transporter protein","uniprot_acc":null,"chromosome":"CM023082","start_pos":549663},{"strain":"VEG","gene_id":"TGVEG_209800","name":null,"product":"formate/nitrite transporter protein","uniprot_acc":"A0A0F7UUK6","chromosome":"TGVEG_chrIb","start_pos":1462885}]}