{"gene":"TG_268210","gene_symbol":"SPARK","run_date":"2026-09-08T14:08:29","timeline":{"discoveries":[{"year":2022,"finding":"SPARK (Store Potentiating/Activating Regulatory Kinase) is a previously unstudied protein kinase in Toxoplasma gondii that regulates invasion and egress, and impacts intracellular Ca2+ stores. Despite homology to mammalian PDK1, SPARK lacks a lipid-binding domain, suggesting rewiring of the pathway in parasites.","method":"High-throughput auxin-inducible degron tagging (HiT screen), pooled and arrayed clone fitness screening, phenotypic assays for invasion and egress, Ca2+ store measurements","journal":"Nature microbiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional depletion with specific cellular phenotypes (invasion, egress, Ca2+ stores) using multiple orthogonal methods (HiT tagging, pooled screening, arrayed phenotyping) in a single rigorous study","pmids":["35484233"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2024,"finding":"SPARK complexes with an elongin-like protein to regulate the stability of PKA and PKG in Toxoplasma gondii. Defects attributed to SPARK depletion (including invasion/egress defects) occur downstream of and after PKG and PKA are down-regulated, placing SPARK upstream of both kinases in the AGC signaling hierarchy.","method":"Conditional genetics (auxin-inducible degron), unbiased quantitative proteomics, Co-immunoprecipitation/complex identification","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional depletion combined with unbiased proteomics and epistasis analysis (phenotypes develop after PKG/PKA down-regulation) in a single rigorous study with multiple orthogonal methods","pmids":["39136687"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2024,"finding":"Loss of SPARK causes Toxoplasma gondii to differentiate into the chronic (bradyzoite) form of infection, a phenotype that may arise from reduced activity of a coccidian-specific PKA ortholog downstream of SPARK.","method":"Conditional genetics (SPARK depletion), differentiation assays","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — conditional depletion with specific differentiation phenotype established in single lab; mechanistic link to coccidian-specific PKA is inferred from proteomics/epistasis but not fully reconstituted","pmids":["39136687"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"SPARK is a PDK1-like AGC kinase in Toxoplasma gondii that lacks a lipid-binding domain and acts upstream of PKG and PKA by complexing with an elongin-like protein to stabilize these kinases, thereby controlling Ca2+-dependent invasion, egress, and the transition between replicative (tachyzoite) and chronic (bradyzoite) life stages."},"narrative":{"mechanistic_narrative":"SPARK is a PDK1-like AGC kinase in Toxoplasma gondii that sits at the top of an AGC-kinase signaling hierarchy controlling the parasite's lytic cycle and life-stage transitions [PMID:35484233, PMID:39136687]. Despite homology to mammalian PDK1, SPARK lacks the lipid-binding domain of its mammalian counterpart, indicating a rewired pathway in the parasite [PMID:35484233]. Conditional depletion impairs host-cell invasion and egress and perturbs intracellular Ca2+ stores [PMID:35484233]. Mechanistically, SPARK complexes with an elongin-like protein to maintain the stability of the downstream kinases PKA and PKG, and the invasion/egress defects of SPARK-depleted parasites develop only after PKG and PKA are down-regulated, placing SPARK upstream of both [PMID:39136687]. Loss of SPARK also drives differentiation from the replicative tachyzoite into the chronic bradyzoite form, a phenotype linked to reduced activity of a coccidian-specific PKA ortholog acting downstream of SPARK [PMID:39136687].","teleology":[{"year":2022,"claim":"Establishing that SPARK is a functional kinase required for the lytic cycle answered whether this uncharacterized PDK1-homolog contributes to parasite biology, revealing a role in invasion, egress, and Ca2+ store homeostasis.","evidence":"High-throughput auxin-inducible degron (HiT) tagging with pooled/arrayed fitness screening and phenotypic invasion/egress and Ca2+ assays in Toxoplasma gondii","pmids":["35484233"],"confidence":"High","gaps":["Direct kinase substrates of SPARK not identified","How SPARK regulates Ca2+ stores mechanistically is unresolved","Absence of a lipid-binding domain implies an unknown mode of activation"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2024,"claim":"Placing SPARK within the AGC signaling hierarchy answered how its phenotypes arise, showing it complexes with an elongin-like protein to stabilize PKA and PKG and thereby acts upstream of both kinases.","evidence":"Conditional depletion, unbiased quantitative proteomics, and Co-IP/complex identification with epistasis analysis in Toxoplasma gondii","pmids":["39136687"],"confidence":"High","gaps":["Whether SPARK directly phosphorylates PKA/PKG or acts only through stabilization is not distinguished","The identity and role of the elongin-like partner in the complex is not fully defined","Structural basis of the SPARK-elongin complex unknown"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2024,"claim":"Testing SPARK's role in life-stage transition answered whether the kinase governs chronic-form conversion, showing its loss triggers bradyzoite differentiation likely via reduced coccidian-specific PKA activity.","evidence":"Conditional SPARK depletion and differentiation assays in Toxoplasma gondii","pmids":["39136687"],"confidence":"Medium","gaps":["Mechanistic link to the coccidian-specific PKA ortholog is inferred from proteomics/epistasis and not reconstituted","Whether differentiation is a direct consequence of PKA loss or a secondary stress response is unclear"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"The direct catalytic substrates of SPARK and the biochemical mechanism by which it activates or stabilizes PKA/PKG in the absence of a lipid-binding domain remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No direct phosphorylation substrate mapped","No structural or biochemical reconstitution of SPARK activity","Mode of SPARK activation without a lipid-binding domain unknown"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["SPARK-elongin-like protein complex"],"partners":["ELONGIN-LIKE PROTEIN","PKA (PROTEIN KINASE A)","PKG (PROTEIN KINASE G)","COCCIDIAN-SPECIFIC PKA ORTHOLOG"],"other_free_text":["PDK1-like AGC kinase in Toxoplasma gondii lacking a lipid-binding domain, indicating pathway rewiring relative to mammalian PDK1 [#0]","Regulates host-cell invasion, egress, and intracellular Ca2+ stores [#0]","Acts upstream of PKA and PKG by stabilizing them [#1]","Controls tachyzoite-to-bradyzoite (chronic form) differentiation [#2]"]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"35484233","id":"PMC_35484233","title":"Screening the Toxoplasma kinome with high-throughput tagging identifies a regulator of invasion and egress.","date":"2022","source":"Nature microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/35484233","citation_count":43,"is_preprint":false},{"pmid":"39136687","id":"PMC_39136687","title":"SPARK regulates AGC kinases central to the Toxoplasma gondii asexual cycle.","date":"2024","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/39136687","citation_count":5,"is_preprint":false},{"pmid":"37961644","id":"PMC_37961644","title":"SPARK regulates AGC kinases central to the Toxoplasma gondii asexual cycle.","date":"2024","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/37961644","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":3523,"output_tokens":892,"usd":0.011975,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":5768,"output_tokens":2145,"usd":0.041232,"stage2_stop_reason":"end_turn"},"total_usd":0.053207,"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\": 2022,\n      \"finding\": \"SPARK (Store Potentiating/Activating Regulatory Kinase) is a previously unstudied protein kinase in Toxoplasma gondii that regulates invasion and egress, and impacts intracellular Ca2+ stores. Despite homology to mammalian PDK1, SPARK lacks a lipid-binding domain, suggesting rewiring of the pathway in parasites.\",\n      \"method\": \"High-throughput auxin-inducible degron tagging (HiT screen), pooled and arrayed clone fitness screening, phenotypic assays for invasion and egress, Ca2+ store measurements\",\n      \"journal\": \"Nature microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional depletion with specific cellular phenotypes (invasion, egress, Ca2+ stores) using multiple orthogonal methods (HiT tagging, pooled screening, arrayed phenotyping) in a single rigorous study\",\n      \"pmids\": [\"35484233\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SPARK complexes with an elongin-like protein to regulate the stability of PKA and PKG in Toxoplasma gondii. Defects attributed to SPARK depletion (including invasion/egress defects) occur downstream of and after PKG and PKA are down-regulated, placing SPARK upstream of both kinases in the AGC signaling hierarchy.\",\n      \"method\": \"Conditional genetics (auxin-inducible degron), unbiased quantitative proteomics, Co-immunoprecipitation/complex identification\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional depletion combined with unbiased proteomics and epistasis analysis (phenotypes develop after PKG/PKA down-regulation) in a single rigorous study with multiple orthogonal methods\",\n      \"pmids\": [\"39136687\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Loss of SPARK causes Toxoplasma gondii to differentiate into the chronic (bradyzoite) form of infection, a phenotype that may arise from reduced activity of a coccidian-specific PKA ortholog downstream of SPARK.\",\n      \"method\": \"Conditional genetics (SPARK depletion), differentiation assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — conditional depletion with specific differentiation phenotype established in single lab; mechanistic link to coccidian-specific PKA is inferred from proteomics/epistasis but not fully reconstituted\",\n      \"pmids\": [\"39136687\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"SPARK is a PDK1-like AGC kinase in Toxoplasma gondii that lacks a lipid-binding domain and acts upstream of PKG and PKA by complexing with an elongin-like protein to stabilize these kinases, thereby controlling Ca2+-dependent invasion, egress, and the transition between replicative (tachyzoite) and chronic (bradyzoite) life stages.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SPARK is a PDK1-like AGC kinase in Toxoplasma gondii that sits at the top of an AGC-kinase signaling hierarchy controlling the parasite's lytic cycle and life-stage transitions [#0, #1]. Despite homology to mammalian PDK1, SPARK lacks the lipid-binding domain of its mammalian counterpart, indicating a rewired pathway in the parasite [#0]. Conditional depletion impairs host-cell invasion and egress and perturbs intracellular Ca2+ stores [#0]. Mechanistically, SPARK complexes with an elongin-like protein to maintain the stability of the downstream kinases PKA and PKG, and the invasion/egress defects of SPARK-depleted parasites develop only after PKG and PKA are down-regulated, placing SPARK upstream of both [#1]. Loss of SPARK also drives differentiation from the replicative tachyzoite into the chronic bradyzoite form, a phenotype linked to reduced activity of a coccidian-specific PKA ortholog acting downstream of SPARK [#2].\",\n  \"teleology\": [\n    {\n      \"year\": 2022,\n      \"claim\": \"Establishing that SPARK is a functional kinase required for the lytic cycle answered whether this uncharacterized PDK1-homolog contributes to parasite biology, revealing a role in invasion, egress, and Ca2+ store homeostasis.\",\n      \"evidence\": \"High-throughput auxin-inducible degron (HiT) tagging with pooled/arrayed fitness screening and phenotypic invasion/egress and Ca2+ assays in Toxoplasma gondii\",\n      \"pmids\": [\"35484233\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Direct kinase substrates of SPARK not identified\",\n        \"How SPARK regulates Ca2+ stores mechanistically is unresolved\",\n        \"Absence of a lipid-binding domain implies an unknown mode of activation\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Placing SPARK within the AGC signaling hierarchy answered how its phenotypes arise, showing it complexes with an elongin-like protein to stabilize PKA and PKG and thereby acts upstream of both kinases.\",\n      \"evidence\": \"Conditional depletion, unbiased quantitative proteomics, and Co-IP/complex identification with epistasis analysis in Toxoplasma gondii\",\n      \"pmids\": [\"39136687\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether SPARK directly phosphorylates PKA/PKG or acts only through stabilization is not distinguished\",\n        \"The identity and role of the elongin-like partner in the complex is not fully defined\",\n        \"Structural basis of the SPARK-elongin complex unknown\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Testing SPARK's role in life-stage transition answered whether the kinase governs chronic-form conversion, showing its loss triggers bradyzoite differentiation likely via reduced coccidian-specific PKA activity.\",\n      \"evidence\": \"Conditional SPARK depletion and differentiation assays in Toxoplasma gondii\",\n      \"pmids\": [\"39136687\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanistic link to the coccidian-specific PKA ortholog is inferred from proteomics/epistasis and not reconstituted\",\n        \"Whether differentiation is a direct consequence of PKA loss or a secondary stress response is unclear\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The direct catalytic substrates of SPARK and the biochemical mechanism by which it activates or stabilizes PKA/PKG in the absence of a lipid-binding domain remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No direct phosphorylation substrate mapped\",\n        \"No structural or biochemical reconstitution of SPARK activity\",\n        \"Mode of SPARK activation without a lipid-binding domain unknown\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0004672\", \"supporting_discovery_ids\": [0, 1], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0019887\", \"supporting_discovery_ids\": [1], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"GO:0035556\", \"supporting_discovery_ids\": [1], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0030587\", \"supporting_discovery_ids\": [2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [\"SPARK-elongin-like protein complex\"],\n    \"partners\": [\"elongin-like protein\", \"PKA (protein kinase A)\", \"PKG (protein kinase G)\", \"coccidian-specific PKA ortholog\"],\n    \"other_free_text\": [\n      \"PDK1-like AGC kinase in Toxoplasma gondii lacking a lipid-binding domain, indicating pathway rewiring relative to mammalian PDK1 [#0]\",\n      \"Regulates host-cell invasion, egress, and intracellular Ca2+ stores [#0]\",\n      \"Acts upstream of PKA and PKG by stabilizing them [#1]\",\n      \"Controls tachyzoite-to-bradyzoite (chronic form) differentiation [#2]\"\n    ]\n  },\n  \"strain_conflicts\": []\n}\n```","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_268210","name":"SPARK","product":"store potentiating/activating regulatory kinase SPARK","uniprot_acc":"S8EXM1","chromosome":"TGME49_chrVIII","start_pos":6638313},{"strain":"GT1","gene_id":"TGGT1_268210","name":null,"product":"AGC kinase","uniprot_acc":null,"chromosome":"TGGT1_chrVIII","start_pos":6636910},{"strain":"RH88","gene_id":"TGRH88_082920","name":null,"product":"AGC kinase","uniprot_acc":null,"chromosome":"CM023089","start_pos":11756951},{"strain":"VEG","gene_id":"TGVEG_268210","name":null,"product":"AGC kinase","uniprot_acc":"V4ZMZ2","chromosome":"TGVEG_chrVIII","start_pos":6653720}]}