{"gene":"TG_289100","gene_symbol":"HOOK","run_date":"2026-09-08T14:08:30","timeline":{"discoveries":[{"year":2023,"finding":"TgHOOK forms a complex with an FTS homolog and two parasite-specific proteins (TGGT1_306920 and TGGT1_316650), representing a partially conserved FHF (HOOK-FTS-FHIP) complex in T. gondii; TgHOOK colocalizes with TgFTS and TgHIP at the parasite apical tip and displays an apically enriched vesicular pattern.","method":"Co-immunoprecipitation/complex characterization, fluorescence colocalization imaging","journal":"eLife / mBio","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal complex characterization and colocalization confirmed independently by two separate labs (Chan et al. and Dubois et al.) using orthogonal methods","pmids":["37933960","37093045"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2023,"finding":"HOOK is phosphorylated in a CDPK1-dependent manner, identifying it as a downstream substrate of the Ca2+-dependent protein kinase CDPK1; CDPK1 kinase activity is required for rapid apical trafficking of micronemes.","method":"Sub-minute resolution phosphoproteomics and bio-orthogonal labeling of kinase substrates","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — phosphoproteomic identification combined with bio-orthogonal kinase substrate labeling in a single rigorous study, replicated in preprint","pmids":["37933960","36712004"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2023,"finding":"Loss of HOOK or FTS impairs rapid apical trafficking of micronemes and microneme protein secretion, leading to a block in host cell invasion, establishing HOOK as required for microneme exocytosis and invasion.","method":"Genetic knockout/conditional depletion of HOOK and FTS with secretion assays and invasion assays","journal":"eLife / mBio","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean loss-of-function with defined cellular phenotypes (microneme secretion, invasion) independently replicated by two labs","pmids":["37933960","37093045"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2023,"finding":"Conditional depletion of TgFTS or TgHIP (the coccidian-specific HOOK interacting partner) phenocopies HOOK depletion but leads to more severe defects in egress, motility, host cell attachment, and invasion, indicating that the full HOOK-FTS-HIP complex is required for optimal microneme apical positioning and exocytosis.","method":"Conditional depletion (auxin-inducible degron or equivalent) with motility, egress, attachment, and invasion assays","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined phenotypic readouts across multiple processes, single lab, multiple orthogonal functional assays","pmids":["37093045"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"In Toxoplasma gondii, HOOK forms an FHF-like complex with an FTS homolog and parasite-specific partners (including HIP/TGGT1_306920/TGGT1_316650) that localizes apically and is required for dynein-mediated apical trafficking, docking, and Ca2+-regulated exocytosis of micronemes; HOOK is itself a substrate of CDPK1, placing it downstream of the Ca2+ signaling cascade that triggers microneme secretion, motility, and host cell invasion."},"narrative":{"mechanistic_narrative":"In Toxoplasma gondii, HOOK is a component of a parasite-adapted FHF-like adaptor complex that couples dynein-based transport to the Ca2+-triggered secretory events driving host cell invasion [PMID:37933960, PMID:37093045]. HOOK assembles with an FTS homolog and two parasite-specific partners (the coccidian-specific interactor HIP/TGGT1_306920 and TGGT1_316650) into a partially conserved HOOK-FTS-FHIP complex that localizes to the parasite apical tip in an apically enriched vesicular pattern [PMID:37933960, PMID:37093045]. Loss of HOOK or FTS impairs the rapid apical trafficking of micronemes and blocks microneme protein secretion and host cell invasion, and depletion of FTS or HIP phenocopies and exacerbates these defects across egress, motility, and attachment, establishing the intact complex as required for apical microneme positioning and exocytosis [PMID:37933960, PMID:37093045]. HOOK is itself phosphorylated in a CDPK1-dependent manner, placing it downstream of the Ca2+-dependent kinase cascade that governs microneme secretion [PMID:37933960, PMID:36712004].","teleology":[{"year":2023,"claim":"Whether Toxoplasma possesses a HOOK-based transport adaptor and which partners it uses was unknown; identifying an FHF-like complex established the molecular architecture linking HOOK to the parasite apical secretory machinery.","evidence":"Co-immunoprecipitation/complex characterization and fluorescence colocalization imaging in T. gondii","pmids":["37933960","37093045"],"confidence":"High","gaps":["Role of dynein engagement in complex function not directly demonstrated in the timeline","Function of the two parasite-specific partners at the biochemical level not resolved","Stoichiometry and structural basis of complex assembly not defined"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2023,"claim":"How HOOK connects to the Ca2+ signaling that triggers secretion was unknown; showing it is a CDPK1-dependent phosphosubstrate placed HOOK downstream of the master Ca2+ kinase controlling microneme trafficking.","evidence":"Sub-minute phosphoproteomics and bio-orthogonal kinase substrate labeling in T. gondii","pmids":["37933960","36712004"],"confidence":"High","gaps":["Functional consequence of specific phosphosites on HOOK activity not defined","Whether phosphorylation controls complex assembly or dynein coupling not established"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2023,"claim":"Whether HOOK and FTS are functionally required for invasion was untested; loss-of-function established them as essential for rapid apical microneme trafficking, secretion, and invasion.","evidence":"Genetic knockout/conditional depletion of HOOK and FTS with secretion and invasion assays in T. gondii","pmids":["37933960","37093045"],"confidence":"High","gaps":["Molecular step at which trafficking fails not pinpointed","Direct link between HOOK phosphorylation and the trafficking phenotype not established"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2023,"claim":"Whether the full complex or HOOK alone drives the phenotype was unresolved; depletion of FTS or the coccidian-specific HIP phenocopied and worsened HOOK loss, establishing the intact HOOK-FTS-HIP complex as required for optimal microneme positioning and exocytosis.","evidence":"Conditional depletion with motility, egress, attachment, and invasion assays in T. gondii","pmids":["37093045"],"confidence":"Medium","gaps":["Basis for the more severe HIP/FTS phenotype relative to HOOK not explained","Contribution of each subunit to dynein recruitment not dissected"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"How CDPK1 phosphorylation of HOOK is mechanistically coupled to dynein-driven apical microneme transport and Ca2+-regulated exocytosis remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the parasite FHF complex","Direct demonstration of dynein-motor coupling absent","Functional role of individual HOOK phosphosites undefined"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["HOOK-FTS-FHIP (FHF-like) complex, comprising TgHOOK, TgFTS, TgHIP (TGGT1_306920) and TGGT1_316650"],"partners":["TGFTS","TGHIP / TGGT1_306920","TGGT1_316650","CDPK1 (UPSTREAM KINASE)"],"other_free_text":["HOOK is a CDPK1-dependent phosphosubstrate, placing it downstream of Ca2+-dependent signaling that triggers microneme secretion.","Loss of HOOK, FTS, or HIP impairs rapid apical trafficking and exocytosis of micronemes; HIP/FTS depletion produces more severe egress, motility, and attachment defects than HOOK depletion alone."]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"37933960","id":"PMC_37933960","title":"Analysis of CDPK1 targets identifies a trafficking adaptor complex that regulates microneme exocytosis in Toxoplasma.","date":"2023","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/37933960","citation_count":13,"is_preprint":false},{"pmid":"37093045","id":"PMC_37093045","title":"Toxoplasma gondii HOOK-FTS-HIP Complex is Critical for Secretory Organelle Discharge during Motility, Invasion, and Egress.","date":"2023","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/37093045","citation_count":6,"is_preprint":false},{"pmid":"36712004","id":"PMC_36712004","title":"Analysis of CDPK1 targets identifies a trafficking adaptor complex that regulates microneme exocytosis in Toxoplasma.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/36712004","citation_count":4,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":4119,"output_tokens":1139,"usd":0.014721,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":6058,"output_tokens":2523,"usd":0.046683,"stage2_stop_reason":"end_turn"},"total_usd":0.061404,"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\": 2023,\n      \"finding\": \"TgHOOK forms a complex with an FTS homolog and two parasite-specific proteins (TGGT1_306920 and TGGT1_316650), representing a partially conserved FHF (HOOK-FTS-FHIP) complex in T. gondii; TgHOOK colocalizes with TgFTS and TgHIP at the parasite apical tip and displays an apically enriched vesicular pattern.\",\n      \"method\": \"Co-immunoprecipitation/complex characterization, fluorescence colocalization imaging\",\n      \"journal\": \"eLife / mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal complex characterization and colocalization confirmed independently by two separate labs (Chan et al. and Dubois et al.) using orthogonal methods\",\n      \"pmids\": [\"37933960\", \"37093045\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HOOK is phosphorylated in a CDPK1-dependent manner, identifying it as a downstream substrate of the Ca2+-dependent protein kinase CDPK1; CDPK1 kinase activity is required for rapid apical trafficking of micronemes.\",\n      \"method\": \"Sub-minute resolution phosphoproteomics and bio-orthogonal labeling of kinase substrates\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — phosphoproteomic identification combined with bio-orthogonal kinase substrate labeling in a single rigorous study, replicated in preprint\",\n      \"pmids\": [\"37933960\", \"36712004\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Loss of HOOK or FTS impairs rapid apical trafficking of micronemes and microneme protein secretion, leading to a block in host cell invasion, establishing HOOK as required for microneme exocytosis and invasion.\",\n      \"method\": \"Genetic knockout/conditional depletion of HOOK and FTS with secretion assays and invasion assays\",\n      \"journal\": \"eLife / mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean loss-of-function with defined cellular phenotypes (microneme secretion, invasion) independently replicated by two labs\",\n      \"pmids\": [\"37933960\", \"37093045\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Conditional depletion of TgFTS or TgHIP (the coccidian-specific HOOK interacting partner) phenocopies HOOK depletion but leads to more severe defects in egress, motility, host cell attachment, and invasion, indicating that the full HOOK-FTS-HIP complex is required for optimal microneme apical positioning and exocytosis.\",\n      \"method\": \"Conditional depletion (auxin-inducible degron or equivalent) with motility, egress, attachment, and invasion assays\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined phenotypic readouts across multiple processes, single lab, multiple orthogonal functional assays\",\n      \"pmids\": [\"37093045\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    }\n  ],\n  \"current_model\": \"In Toxoplasma gondii, HOOK forms an FHF-like complex with an FTS homolog and parasite-specific partners (including HIP/TGGT1_306920/TGGT1_316650) that localizes apically and is required for dynein-mediated apical trafficking, docking, and Ca2+-regulated exocytosis of micronemes; HOOK is itself a substrate of CDPK1, placing it downstream of the Ca2+ signaling cascade that triggers microneme secretion, motility, and host cell invasion.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"In Toxoplasma gondii, HOOK is a component of a parasite-adapted FHF-like adaptor complex that couples dynein-based transport to the Ca2+-triggered secretory events driving host cell invasion [#0, #2]. HOOK assembles with an FTS homolog and two parasite-specific partners (the coccidian-specific interactor HIP/TGGT1_306920 and TGGT1_316650) into a partially conserved HOOK-FTS-FHIP complex that localizes to the parasite apical tip in an apically enriched vesicular pattern [#0]. Loss of HOOK or FTS impairs the rapid apical trafficking of micronemes and blocks microneme protein secretion and host cell invasion, and depletion of FTS or HIP phenocopies and exacerbates these defects across egress, motility, and attachment, establishing the intact complex as required for apical microneme positioning and exocytosis [#2, #3]. HOOK is itself phosphorylated in a CDPK1-dependent manner, placing it downstream of the Ca2+-dependent kinase cascade that governs microneme secretion [#1].\",\n  \"teleology\": [\n    {\n      \"year\": 2023,\n      \"claim\": \"Whether Toxoplasma possesses a HOOK-based transport adaptor and which partners it uses was unknown; identifying an FHF-like complex established the molecular architecture linking HOOK to the parasite apical secretory machinery.\",\n      \"evidence\": \"Co-immunoprecipitation/complex characterization and fluorescence colocalization imaging in T. gondii\",\n      \"pmids\": [\"37933960\", \"37093045\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Role of dynein engagement in complex function not directly demonstrated in the timeline\", \"Function of the two parasite-specific partners at the biochemical level not resolved\", \"Stoichiometry and structural basis of complex assembly not defined\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"How HOOK connects to the Ca2+ signaling that triggers secretion was unknown; showing it is a CDPK1-dependent phosphosubstrate placed HOOK downstream of the master Ca2+ kinase controlling microneme trafficking.\",\n      \"evidence\": \"Sub-minute phosphoproteomics and bio-orthogonal kinase substrate labeling in T. gondii\",\n      \"pmids\": [\"37933960\", \"36712004\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of specific phosphosites on HOOK activity not defined\", \"Whether phosphorylation controls complex assembly or dynein coupling not established\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Whether HOOK and FTS are functionally required for invasion was untested; loss-of-function established them as essential for rapid apical microneme trafficking, secretion, and invasion.\",\n      \"evidence\": \"Genetic knockout/conditional depletion of HOOK and FTS with secretion and invasion assays in T. gondii\",\n      \"pmids\": [\"37933960\", \"37093045\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular step at which trafficking fails not pinpointed\", \"Direct link between HOOK phosphorylation and the trafficking phenotype not established\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Whether the full complex or HOOK alone drives the phenotype was unresolved; depletion of FTS or the coccidian-specific HIP phenocopied and worsened HOOK loss, establishing the intact HOOK-FTS-HIP complex as required for optimal microneme positioning and exocytosis.\",\n      \"evidence\": \"Conditional depletion with motility, egress, attachment, and invasion assays in T. gondii\",\n      \"pmids\": [\"37093045\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Basis for the more severe HIP/FTS phenotype relative to HOOK not explained\", \"Contribution of each subunit to dynein recruitment not dissected\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CDPK1 phosphorylation of HOOK is mechanistically coupled to dynein-driven apical microneme transport and Ca2+-regulated exocytosis remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the parasite FHF complex\", \"Direct demonstration of dynein-motor coupling absent\", \"Functional role of individual HOOK phosphosites undefined\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0030674\", \"supporting_discovery_ids\": [0, 2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0019904\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020009\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006887\", \"supporting_discovery_ids\": [2, 3], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0046718\", \"supporting_discovery_ids\": [2, 3], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0047496\", \"supporting_discovery_ids\": [2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [\"HOOK-FTS-FHIP (FHF-like) complex, comprising TgHOOK, TgFTS, TgHIP (TGGT1_306920) and TGGT1_316650\"],\n    \"partners\": [\"TgFTS\", \"TgHIP / TGGT1_306920\", \"TGGT1_316650\", \"CDPK1 (upstream kinase)\"],\n    \"other_free_text\": [\n      \"HOOK is a CDPK1-dependent phosphosubstrate, placing it downstream of Ca2+-dependent signaling that triggers microneme secretion.\",\n      \"Loss of HOOK, FTS, or HIP impairs rapid apical trafficking and exocytosis of micronemes; HIP/FTS depletion produces more severe egress, motility, and attachment defects than HOOK depletion alone.\"\n    ]\n  },\n  \"strain_conflicts\": []\n}\n```","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_289100","name":"HOOK","product":"protein hook","uniprot_acc":"S8EWU3","chromosome":"TGME49_chrIX","start_pos":2983587},{"strain":"GT1","gene_id":"TGGT1_289100","name":null,"product":"hypothetical protein","uniprot_acc":null,"chromosome":"TGGT1_chrIX","start_pos":2793313},{"strain":"RH88","gene_id":"TGRH88_013920","name":null,"product":"unspecified product","uniprot_acc":null,"chromosome":"CM023090","start_pos":3048893},{"strain":"VEG","gene_id":"TGVEG_289100","name":null,"product":"hook protein","uniprot_acc":"V4Z0C7","chromosome":"TGVEG_chrIX","start_pos":3019447}]}