{"gene":"TG_274000","gene_symbol":"SFI1","run_date":"2026-09-08T14:08:30","timeline":{"discoveries":[{"year":2015,"finding":"TgSfi1 localizes to the outer core of the bipartite Toxoplasma gondii centrosome, where it forms a complex with TgCentrin1, TgSas-6 (cartwheel protein), and a novel Aurora-related kinase. This outer core is spatially distinct from the inner core (which contains CEP250/C-Nap orthologs) and functions primarily in cytokinesis. Temperature-sensitive inhibition of TgSfi1 caused loss of outer cores and a severe block to budding, while the inner core and spindle pole continued to amplify, demonstrating that TgSfi1 is required for daughter parasite formation (cytokinesis) but not karyokinesis.","method":"Genetic analysis of temperature-sensitive mutant (ts-TgSfi1), fluorescence microscopy localization, immunofluorescence co-localization of centrosome components","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — temperature-sensitive loss-of-function with specific cellular phenotype (budding block), co-localization with multiple partners, genetic dissection of inner vs. outer core functions in a single rigorous study","pmids":["25734885"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2015,"finding":"The outer centrosome core containing TgSfi1 duplicates before the inner core during the cell cycle (outer core first, inner core second) as parasites transition into S phase, ensuring each daughter inherits one copy of each core type.","method":"Time-resolved fluorescence microscopy of centrosome duplication during the cell cycle","journal":"PLoS biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct imaging of sequential duplication in a single study, no independent replication reported","pmids":["25734885"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2022,"finding":"TgCentrin1 (TgCEN1) directly binds to synthetic peptides derived from distinct SFI1-repeat motifs of TgSFI1. The binding modes differ appreciably across repeats in terms of affinity, Ca2+ sensitivity, and which lobe (N- or C-terminal domain) of TgCEN1 engages each repeat, indicating conformational plasticity of TgCEN1 in its interaction with TgSFI1 that is regulated by Ca2+ sensing.","method":"Isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR), circular dichroism, and fluorescence spectroscopy using synthetic TgSFI1-repeat peptides and recombinant TgCEN1 domains","journal":"Biomolecules","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal biophysical methods (ITC, NMR, CD, fluorescence) in a single study establishing direct binding properties; no independent replication","pmids":["36009009"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"TgSFI1 is a large centrosomal scaffold protein that localizes to the outer core of the bipartite Toxoplasma gondii centrosome, where it partners with TgCentrin1 (via Ca2+-regulated, repeat-specific binding interactions), TgSas-6, and an Aurora-related kinase; this outer core duplicates first during S phase and is required specifically for cytokinesis (daughter budding), while the functionally distinct inner core independently drives karyokinesis."},"narrative":{"mechanistic_narrative":"SFI1 (TgSFI1) is a centrosomal scaffold protein that localizes to the outer core of the bipartite Toxoplasma gondii centrosome, where it is specifically required for cytokinesis (daughter parasite budding) but dispensable for karyokinesis [PMID:25734885]. At the outer core it forms a complex with TgCentrin1, the cartwheel protein TgSas-6, and a novel Aurora-related kinase, a compartment spatially and functionally distinct from the CEP250/C-Nap-containing inner core that independently drives nuclear division [PMID:25734885]. Temperature-sensitive inactivation of TgSFI1 abolishes outer cores and blocks budding while the inner core and spindle pole continue to amplify, establishing its selective role in daughter formation [PMID:25734885]. The outer core duplicates ahead of the inner core as parasites enter S phase, ensuring each daughter inherits one copy of each core type [PMID:25734885]. TgSFI1 engages TgCentrin1 through multiple distinct SFI1-repeat motifs, with each repeat differing in affinity, Ca2+ sensitivity, and which lobe of TgCentrin1 it binds — a repeat-specific, Ca2+-regulated interaction that endows the complex with conformational plasticity [PMID:36009009].","teleology":[{"year":2015,"claim":"It was unknown which centrosomal component coordinates daughter parasite budding in Toxoplasma; localizing TgSFI1 to a discrete outer core and inactivating it established that this core drives cytokinesis independently of karyokinesis.","evidence":"Temperature-sensitive loss-of-function mutant, fluorescence localization, and co-localization of centrosome components in Toxoplasma gondii","pmids":["25734885"],"confidence":"High","gaps":["The molecular activity of TgSFI1 within the complex (scaffolding vs. regulatory) is not defined","How TgSFI1 loss mechanistically prevents budding is not resolved","Roles of the associated Aurora-related kinase and TgSas-6 relative to TgSFI1 are not dissected"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2015,"claim":"How each daughter inherits both centrosome core types was unclear; time-resolved imaging showed the outer core duplicates before the inner core at S-phase entry, defining the temporal logic of bipartite centrosome inheritance.","evidence":"Time-resolved fluorescence microscopy of centrosome duplication across the cell cycle in Toxoplasma gondii","pmids":["25734885"],"confidence":"Medium","gaps":["The trigger coupling outer-core duplication to S-phase entry is unknown","No independent replication of the sequential-duplication timing reported"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2022,"claim":"The physical basis of the TgSFI1–TgCentrin1 partnership was uncharacterized; biophysical dissection of individual repeat peptides showed each SFI1 repeat binds TgCentrin1 with distinct affinity, Ca2+ sensitivity, and lobe engagement, establishing a repeat-specific, Ca2+-regulated interaction.","evidence":"ITC, NMR, circular dichroism, and fluorescence spectroscopy with synthetic TgSFI1-repeat peptides and recombinant TgCentrin1 domains","pmids":["36009009"],"confidence":"High","gaps":["Binding was measured with isolated synthetic repeat peptides, not full-length TgSFI1 in situ","The functional consequence of Ca2+-regulated repeat binding for cytokinesis is not tested","Stoichiometry of the assembled TgSFI1–TgCentrin1 array is not determined"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"How the TgSFI1 scaffold mechanistically licenses daughter budding, and how the Aurora-related kinase and Ca2+ signaling regulate its assembly and duplication, remains open.","evidence":"","pmids":[],"confidence":"Low","gaps":["No mechanism connecting outer-core assembly to the budding machinery","Regulatory inputs to outer-core duplication timing are undefined","Role of the Aurora-related kinase relative to TgSFI1 function is uncharacterized"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["Outer-core centrosomal complex: TgSFI1, TgCentrin1, TgSas-6, and an Aurora-related kinase"],"partners":["TGCENTRIN1 (TGCEN1) — DIRECT, REPEAT-SPECIFIC, CA2+-REGULATED BINDING","TGSAS-6 (CARTWHEEL PROTEIN)","AURORA-RELATED KINASE"],"other_free_text":["Outer core is spatially and functionally distinct from the inner core (CEP250/C-Nap orthologs), which drives karyokinesis","TgSFI1 is required for cytokinesis/daughter budding but not karyokinesis","Outer core duplicates before the inner core at S-phase entry"]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"25734885","id":"PMC_25734885","title":"A novel bipartite centrosome coordinates the apicomplexan cell cycle.","date":"2015","source":"PLoS biology","url":"https://pubmed.ncbi.nlm.nih.gov/25734885","citation_count":112,"is_preprint":false},{"pmid":"36009009","id":"PMC_36009009","title":"Conformational Plasticity of Centrin 1 from Toxoplasma gondii in Binding to the Centrosomal Protein SFI1.","date":"2022","source":"Biomolecules","url":"https://pubmed.ncbi.nlm.nih.gov/36009009","citation_count":8,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":3485,"output_tokens":1031,"usd":0.01296,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":5916,"output_tokens":2359,"usd":0.044277,"stage2_stop_reason":"end_turn"},"total_usd":0.057237,"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\": \"TgSfi1 localizes to the outer core of the bipartite Toxoplasma gondii centrosome, where it forms a complex with TgCentrin1, TgSas-6 (cartwheel protein), and a novel Aurora-related kinase. This outer core is spatially distinct from the inner core (which contains CEP250/C-Nap orthologs) and functions primarily in cytokinesis. Temperature-sensitive inhibition of TgSfi1 caused loss of outer cores and a severe block to budding, while the inner core and spindle pole continued to amplify, demonstrating that TgSfi1 is required for daughter parasite formation (cytokinesis) but not karyokinesis.\",\n      \"method\": \"Genetic analysis of temperature-sensitive mutant (ts-TgSfi1), fluorescence microscopy localization, immunofluorescence co-localization of centrosome components\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — temperature-sensitive loss-of-function with specific cellular phenotype (budding block), co-localization with multiple partners, genetic dissection of inner vs. outer core functions in a single rigorous study\",\n      \"pmids\": [\"25734885\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The outer centrosome core containing TgSfi1 duplicates before the inner core during the cell cycle (outer core first, inner core second) as parasites transition into S phase, ensuring each daughter inherits one copy of each core type.\",\n      \"method\": \"Time-resolved fluorescence microscopy of centrosome duplication during the cell cycle\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct imaging of sequential duplication in a single study, no independent replication reported\",\n      \"pmids\": [\"25734885\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"TgCentrin1 (TgCEN1) directly binds to synthetic peptides derived from distinct SFI1-repeat motifs of TgSFI1. The binding modes differ appreciably across repeats in terms of affinity, Ca2+ sensitivity, and which lobe (N- or C-terminal domain) of TgCEN1 engages each repeat, indicating conformational plasticity of TgCEN1 in its interaction with TgSFI1 that is regulated by Ca2+ sensing.\",\n      \"method\": \"Isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR), circular dichroism, and fluorescence spectroscopy using synthetic TgSFI1-repeat peptides and recombinant TgCEN1 domains\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal biophysical methods (ITC, NMR, CD, fluorescence) in a single study establishing direct binding properties; no independent replication\",\n      \"pmids\": [\"36009009\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    }\n  ],\n  \"current_model\": \"TgSFI1 is a large centrosomal scaffold protein that localizes to the outer core of the bipartite Toxoplasma gondii centrosome, where it partners with TgCentrin1 (via Ca2+-regulated, repeat-specific binding interactions), TgSas-6, and an Aurora-related kinase; this outer core duplicates first during S phase and is required specifically for cytokinesis (daughter budding), while the functionally distinct inner core independently drives karyokinesis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SFI1 (TgSFI1) is a centrosomal scaffold protein that localizes to the outer core of the bipartite Toxoplasma gondii centrosome, where it is specifically required for cytokinesis (daughter parasite budding) but dispensable for karyokinesis [#0]. At the outer core it forms a complex with TgCentrin1, the cartwheel protein TgSas-6, and a novel Aurora-related kinase, a compartment spatially and functionally distinct from the CEP250/C-Nap-containing inner core that independently drives nuclear division [#0]. Temperature-sensitive inactivation of TgSFI1 abolishes outer cores and blocks budding while the inner core and spindle pole continue to amplify, establishing its selective role in daughter formation [#0]. The outer core duplicates ahead of the inner core as parasites enter S phase, ensuring each daughter inherits one copy of each core type [#1]. TgSFI1 engages TgCentrin1 through multiple distinct SFI1-repeat motifs, with each repeat differing in affinity, Ca2+ sensitivity, and which lobe of TgCentrin1 it binds — a repeat-specific, Ca2+-regulated interaction that endows the complex with conformational plasticity [#2].\",\n  \"teleology\": [\n    {\n      \"year\": 2015,\n      \"claim\": \"It was unknown which centrosomal component coordinates daughter parasite budding in Toxoplasma; localizing TgSFI1 to a discrete outer core and inactivating it established that this core drives cytokinesis independently of karyokinesis.\",\n      \"evidence\": \"Temperature-sensitive loss-of-function mutant, fluorescence localization, and co-localization of centrosome components in Toxoplasma gondii\",\n      \"pmids\": [\"25734885\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The molecular activity of TgSFI1 within the complex (scaffolding vs. regulatory) is not defined\",\n        \"How TgSFI1 loss mechanistically prevents budding is not resolved\",\n        \"Roles of the associated Aurora-related kinase and TgSas-6 relative to TgSFI1 are not dissected\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"How each daughter inherits both centrosome core types was unclear; time-resolved imaging showed the outer core duplicates before the inner core at S-phase entry, defining the temporal logic of bipartite centrosome inheritance.\",\n      \"evidence\": \"Time-resolved fluorescence microscopy of centrosome duplication across the cell cycle in Toxoplasma gondii\",\n      \"pmids\": [\"25734885\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The trigger coupling outer-core duplication to S-phase entry is unknown\",\n        \"No independent replication of the sequential-duplication timing reported\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The physical basis of the TgSFI1–TgCentrin1 partnership was uncharacterized; biophysical dissection of individual repeat peptides showed each SFI1 repeat binds TgCentrin1 with distinct affinity, Ca2+ sensitivity, and lobe engagement, establishing a repeat-specific, Ca2+-regulated interaction.\",\n      \"evidence\": \"ITC, NMR, circular dichroism, and fluorescence spectroscopy with synthetic TgSFI1-repeat peptides and recombinant TgCentrin1 domains\",\n      \"pmids\": [\"36009009\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Binding was measured with isolated synthetic repeat peptides, not full-length TgSFI1 in situ\",\n        \"The functional consequence of Ca2+-regulated repeat binding for cytokinesis is not tested\",\n        \"Stoichiometry of the assembled TgSFI1–TgCentrin1 array is not determined\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the TgSFI1 scaffold mechanistically licenses daughter budding, and how the Aurora-related kinase and Ca2+ signaling regulate its assembly and duplication, remains open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No mechanism connecting outer-core assembly to the budding machinery\",\n        \"Regulatory inputs to outer-core duplication timing are undefined\",\n        \"Role of the Aurora-related kinase relative to TgSFI1 function is uncharacterized\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0048306\", \"supporting_discovery_ids\": [2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005813\", \"supporting_discovery_ids\": [0, 1], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0000910\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0051298\", \"supporting_discovery_ids\": [1], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [\n      \"Outer-core centrosomal complex: TgSFI1, TgCentrin1, TgSas-6, and an Aurora-related kinase\"\n    ],\n    \"partners\": [\n      \"TgCentrin1 (TgCEN1) — direct, repeat-specific, Ca2+-regulated binding\",\n      \"TgSas-6 (cartwheel protein)\",\n      \"Aurora-related kinase\"\n    ],\n    \"other_free_text\": [\n      \"Outer core is spatially and functionally distinct from the inner core (CEP250/C-Nap orthologs), which drives karyokinesis\",\n      \"TgSFI1 is required for cytokinesis/daughter budding but not karyokinesis\",\n      \"Outer core duplicates before the inner core at S-phase entry\"\n    ]\n  },\n  \"strain_conflicts\": []\n}\n```","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_274000","name":"SFI1","product":"centrin-binding protein SFI1","uniprot_acc":"S8F258","chromosome":"TGME49_chrVIII","start_pos":3104107},{"strain":"GT1","gene_id":"TGGT1_274000","name":null,"product":"hypothetical protein","uniprot_acc":null,"chromosome":"TGGT1_chrVIII","start_pos":3101950},{"strain":"RH88","gene_id":"TGRH88_078040","name":null,"product":"unspecified product","uniprot_acc":null,"chromosome":"CM023089","start_pos":8213299},{"strain":"VEG","gene_id":"TGVEG_274000","name":null,"product":"hypothetical protein","uniprot_acc":"A0A0F7V4J6","chromosome":"TGVEG_chrVIII","start_pos":3114746}]}