{"gene":"TG_253360","gene_symbol":"STX20","run_date":"2026-09-08T12:58:25","timeline":{"discoveries":[{"year":2023,"finding":"An unconventional SNARE complex comprising TgStx1, TgStx20, and TgStx21 mediates vesicular fusion at the plasma membrane and at the apical annuli in Toxoplasma gondii, replacing the canonical Stx1/SNAP25 mechanism used in mammalian cells. This complex is essential for exocytosis of surface proteins.","method":"Genetic and cell biological characterization of SNARE complex components; functional analysis of vesicular fusion at the plasma membrane and apical annuli","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — single lab, complex membership established with functional phenotype readout (exocytosis of surface proteins), but abstract does not detail Co-IP/reconstitution methods explicitly","pmids":["36972314"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2024,"finding":"SNARE proteins including TgStx20 localize specifically to apical annuli (IMC-embedded structures), which are the sites of dense granule vesicle fusion and exocytosis after host cell invasion. Perturbation of secretion at these sites strongly impairs parasite growth.","method":"Localization of integral membrane SNARE proteins to apical annuli by direct imaging; loss-of-function analysis linking apical annuli to dense granule cargo secretion and parasite growth","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment with functional consequence (dense granule secretion, parasite growth impairment), single lab, multiple orthogonal readouts","pmids":["38270431"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"TgSTX20 is a component of an unconventional trimeric SNARE complex (with TgStx1 and TgStx21) that localizes to apical annuli—IMC-embedded structures distinct from the apical complex—where it mediates vesicular fusion and exocytosis of dense granule cargo proteins following host cell invasion, a process essential for parasite growth."},"narrative":{"mechanistic_narrative":"In Toxoplasma gondii, TgStx20 is a component of an unconventional trimeric SNARE complex, together with TgStx1 and TgStx21, that mediates vesicular fusion at the plasma membrane and at the apical annuli, replacing the canonical Stx1/SNAP25 fusion machinery used in mammalian cells [PMID:36972314]. This SNARE complex is essential for exocytosis of surface proteins [PMID:36972314]. TgStx20 localizes specifically to the apical annuli, IMC-embedded structures that serve as sites of dense granule vesicle fusion and exocytosis following host cell invasion, and disruption of secretion at these sites strongly impairs parasite growth [PMID:38270431]. Beyond its membership in this fusion complex and its apical annuli localization, no further mechanistic detail on TgStx20 has been characterized in the available corpus.","teleology":[{"year":2023,"claim":"It was unknown how Toxoplasma mediates vesicular fusion for surface protein exocytosis given the absence of the canonical mammalian machinery; identifying TgStx20 as part of an unconventional trimeric SNARE complex established the molecular basis for fusion at the plasma membrane and apical annuli.","evidence":"Genetic and cell biological characterization of SNARE complex components with functional exocytosis readout in T. gondii","pmids":["36972314"],"confidence":"Medium","gaps":["Co-IP and in vitro reconstitution of the trimeric complex not detailed","Stoichiometry and direct binding among TgStx1, TgStx20, and TgStx21 not resolved","Whether TgStx20 acts as a Qa/Qb/Qc or R-SNARE not established"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2024,"claim":"It was unclear which cellular site the SNARE-mediated fusion serves; localizing TgStx20 to apical annuli and linking these structures to dense granule cargo secretion established the functional destination of the complex and its relevance to parasite growth.","evidence":"Direct imaging of integral membrane SNARE localization plus loss-of-function analysis of dense granule secretion and growth in T. gondii","pmids":["38270431"],"confidence":"Medium","gaps":["Identity of the cognate vesicular SNARE partner at apical annuli not defined","Mechanism recruiting TgStx20 to IMC-embedded apical annuli unknown","Which specific dense granule cargoes depend on this fusion step not fully cataloged"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"The direct binding topology, stoichiometry, and regulatory partners of the TgStx1/TgStx20/TgStx21 complex, and the trafficking route delivering it to apical annuli, remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural or reconstitution data for the trimeric complex","No identified regulators (e.g. Sec1/Munc18-type proteins) in the corpus","Vesicle SNARE partner and Ca2+/signaling triggers for fusion undefined"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["Unconventional trimeric SNARE complex (TgStx1 / TgStx20 / TgStx21)"],"partners":["TGSTX1","TGSTX21"],"other_free_text":["Localizes to apical annuli, IMC-embedded structures distinct from the apical complex.","Mediates exocytosis of dense granule cargo proteins following host cell invasion.","Function is essential for T. gondii growth; perturbation of apical annuli secretion strongly impairs proliferation."]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"36972314","id":"PMC_36972314","title":"An unconventional SNARE complex mediates exocytosis at the plasma membrane and vesicular fusion at the apical annuli in Toxoplasma gondii.","date":"2023","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/36972314","citation_count":11,"is_preprint":false},{"pmid":"38270431","id":"PMC_38270431","title":"Apical annuli are specialised sites of post-invasion secretion of dense granules in Toxoplasma.","date":"2024","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/38270431","citation_count":10,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":3301,"output_tokens":631,"usd":0.009684,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":5357,"output_tokens":1769,"usd":0.035505,"stage2_stop_reason":"end_turn"},"total_usd":0.045189,"stage1_batch_id":"msgbatch_01TEPNZ4MCzJ7xtsNwosiDRk","stage2_batch_id":"msgbatch_01FQShM7n1sfCr4pWTDShmki","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2023,\n      \"finding\": \"An unconventional SNARE complex comprising TgStx1, TgStx20, and TgStx21 mediates vesicular fusion at the plasma membrane and at the apical annuli in Toxoplasma gondii, replacing the canonical Stx1/SNAP25 mechanism used in mammalian cells. This complex is essential for exocytosis of surface proteins.\",\n      \"method\": \"Genetic and cell biological characterization of SNARE complex components; functional analysis of vesicular fusion at the plasma membrane and apical annuli\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — single lab, complex membership established with functional phenotype readout (exocytosis of surface proteins), but abstract does not detail Co-IP/reconstitution methods explicitly\",\n      \"pmids\": [\"36972314\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SNARE proteins including TgStx20 localize specifically to apical annuli (IMC-embedded structures), which are the sites of dense granule vesicle fusion and exocytosis after host cell invasion. Perturbation of secretion at these sites strongly impairs parasite growth.\",\n      \"method\": \"Localization of integral membrane SNARE proteins to apical annuli by direct imaging; loss-of-function analysis linking apical annuli to dense granule cargo secretion and parasite growth\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment with functional consequence (dense granule secretion, parasite growth impairment), single lab, multiple orthogonal readouts\",\n      \"pmids\": [\"38270431\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    }\n  ],\n  \"current_model\": \"TgSTX20 is a component of an unconventional trimeric SNARE complex (with TgStx1 and TgStx21) that localizes to apical annuli—IMC-embedded structures distinct from the apical complex—where it mediates vesicular fusion and exocytosis of dense granule cargo proteins following host cell invasion, a process essential for parasite growth.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"In Toxoplasma gondii, TgStx20 is a component of an unconventional trimeric SNARE complex, together with TgStx1 and TgStx21, that mediates vesicular fusion at the plasma membrane and at the apical annuli, replacing the canonical Stx1/SNAP25 fusion machinery used in mammalian cells [#0]. This SNARE complex is essential for exocytosis of surface proteins [#0]. TgStx20 localizes specifically to the apical annuli, IMC-embedded structures that serve as sites of dense granule vesicle fusion and exocytosis following host cell invasion, and disruption of secretion at these sites strongly impairs parasite growth [#1]. Beyond its membership in this fusion complex and its apical annuli localization, no further mechanistic detail on TgStx20 has been characterized in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2023,\n      \"claim\": \"It was unknown how Toxoplasma mediates vesicular fusion for surface protein exocytosis given the absence of the canonical mammalian machinery; identifying TgStx20 as part of an unconventional trimeric SNARE complex established the molecular basis for fusion at the plasma membrane and apical annuli.\",\n      \"evidence\": \"Genetic and cell biological characterization of SNARE complex components with functional exocytosis readout in T. gondii\",\n      \"pmids\": [\"36972314\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Co-IP and in vitro reconstitution of the trimeric complex not detailed\",\n        \"Stoichiometry and direct binding among TgStx1, TgStx20, and TgStx21 not resolved\",\n        \"Whether TgStx20 acts as a Qa/Qb/Qc or R-SNARE not established\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"It was unclear which cellular site the SNARE-mediated fusion serves; localizing TgStx20 to apical annuli and linking these structures to dense granule cargo secretion established the functional destination of the complex and its relevance to parasite growth.\",\n      \"evidence\": \"Direct imaging of integral membrane SNARE localization plus loss-of-function analysis of dense granule secretion and growth in T. gondii\",\n      \"pmids\": [\"38270431\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Identity of the cognate vesicular SNARE partner at apical annuli not defined\",\n        \"Mechanism recruiting TgStx20 to IMC-embedded apical annuli unknown\",\n        \"Which specific dense granule cargoes depend on this fusion step not fully cataloged\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The direct binding topology, stoichiometry, and regulatory partners of the TgStx1/TgStx20/TgStx21 complex, and the trafficking route delivering it to apical annuli, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No structural or reconstitution data for the trimeric complex\",\n        \"No identified regulators (e.g. Sec1/Munc18-type proteins) in the corpus\",\n        \"Vesicle SNARE partner and Ca2+/signaling triggers for fusion undefined\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0000149\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0006906\", \"supporting_discovery_ids\": [0, 1], \"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:0006887\", \"supporting_discovery_ids\": [0, 1], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [\n      \"Unconventional trimeric SNARE complex (TgStx1 / TgStx20 / TgStx21)\"\n    ],\n    \"partners\": [\n      \"TgStx1\",\n      \"TgStx21\"\n    ],\n    \"other_free_text\": [\n      \"Localizes to apical annuli, IMC-embedded structures distinct from the apical complex.\",\n      \"Mediates exocytosis of dense granule cargo proteins following host cell invasion.\",\n      \"Function is essential for T. gondii growth; perturbation of apical annuli secretion strongly impairs proliferation.\"\n    ]\n  },\n  \"strain_conflicts\": []\n}","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_253360","name":"STX20","product":"SNARE protein STX20","uniprot_acc":"S8GJ01","chromosome":"TGME49_chrIII","start_pos":871335},{"strain":"GT1","gene_id":"TGGT1_253360","name":null,"product":"hypothetical protein","uniprot_acc":null,"chromosome":"TGGT1_chrIII","start_pos":852946},{"strain":"RH88","gene_id":"TGRH88_004960","name":null,"product":"unspecified product","uniprot_acc":null,"chromosome":"CM023084","start_pos":1730706},{"strain":"VEG","gene_id":"TGVEG_253360","name":null,"product":"putative transmembrane protein","uniprot_acc":"B9QIW1","chromosome":"TGVEG_chrIII","start_pos":880355}]}