{"gene":"TG_310160","gene_symbol":"AGO","run_date":"2026-09-08T15:15:13","timeline":{"discoveries":[{"year":2010,"finding":"Toxoplasma gondii encodes a single Argonaute protein (Tg-AGO) that binds both plant-like heterochromatic siRNAs and metazoan-like miRNAs. Mass spectrometric analysis of the Tg-AGO protein complex revealed association with virtually all known RISC components (as characterized in human and Drosophila) as well as novel RNA metabolism proteins. Tg-AGO also associates substoichiometrically with components of chromatin-repressing complexes, consistent with its loading with heterochromatic small RNAs.","method":"Mass spectrometry of immunoprecipitated Tg-AGO complex; co-sedimentation with polyribosomes; small RNA sequencing","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP/MS with multiple orthogonal methods (polyribosome co-sedimentation, small RNA profiling, mass spectrometry) in a single rigorous study","pmids":["20523899"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2010,"finding":"Tg-AGO lacks canonical catalytic residues in its PIWI domain, consistent with its inability to perform slicer (endonuclease) activity. Toxoplasma miRNAs co-sediment with polyribosomes, suggesting Tg-AGO acts as a translational regulator rather than a direct RNA slicer.","method":"Sequence analysis of PIWI domain; polyribosome co-sedimentation assay","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — domain mutagenesis inference combined with polyribosome co-sedimentation, multiple orthogonal methods in one rigorous study","pmids":["20523899"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2012,"finding":"The PIWI-like domain of TgAgo lacks the canonical DDE/H catalytic triad, explaining its weak target RNA cleavage activity. TgAgo associates with a Tudor staphylococcal nuclease (TSN) and with protein arginine methyltransferase PRMT1. PRMT1 methylates the N-terminal RGG-repeat domain of TgAgo, and this methylation correlates with recruitment of TSN to the complex. TSN provides a stronger, Ca2+-dependent RNA slicer activity requiring imperfect guide RNA complementarity, while TgAgo's own slicer activity is Mg2+-dependent and requires perfect complementarity.","method":"Co-immunoprecipitation; mutational analysis of RGG-repeat domain; in vitro RNA cleavage assays; PRMT1 knockout parasites; chemical inhibition of arginine methylation","journal":"Cellular microbiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, mutational analysis, in vitro enzymatic assays, and genetic knockouts, multiple orthogonal methods in a single study","pmids":["22309152"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2012,"finding":"AGO knockout parasites showed essentially normal growth in vitro, indicating TgAgo is not essential for parasite viability under standard conditions.","method":"Genetic knockout of TgAgo with growth assay","journal":"Cellular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single lab, single method (genetic KO with growth readout)","pmids":["22309152"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"Toxoplasma gondii encodes a single Argonaute protein (Tg-AGO) that lacks canonical PIWI catalytic residues and therefore has weak intrinsic slicer activity; instead, it forms a RISC-like complex by binding both heterochromatic siRNAs and miRNAs, acting primarily as a translational regulator, and recruits a Tudor staphylococcal nuclease (TSN) as a surrogate slicer—a recruitment event that depends on PRMT1-mediated arginine methylation of TgAgo's N-terminal RGG-repeat domain."},"narrative":{"mechanistic_narrative":"Toxoplasma gondii encodes a single Argonaute protein (Tg-AGO) that serves as the core effector of a RISC-like small-RNA silencing machinery, binding both plant-like heterochromatic siRNAs and metazoan-like miRNAs and assembling a complex containing essentially all canonical RISC components together with novel RNA-metabolism factors [PMID:20523899]. Because its PIWI-like domain lacks the canonical DDE/H catalytic triad, Tg-AGO has only weak intrinsic slicer activity, and its associated miRNAs co-sediment with polyribosomes, indicating it acts predominantly as a translational regulator rather than a direct RNA-cleaving enzyme [PMID:20523899]. To acquire robust cleavage capacity, Tg-AGO recruits a Tudor staphylococcal nuclease (TSN) as a surrogate slicer: TSN provides a Ca2+-dependent activity requiring imperfect guide-target complementarity, distinct from Tg-AGO's own Mg2+-dependent activity requiring perfect complementarity [PMID:22309152]. This recruitment is governed by PRMT1, which methylates the N-terminal RGG-repeat domain of Tg-AGO, an event that correlates with TSN incorporation into the complex [PMID:22309152]. Tg-AGO is dispensable for parasite viability under standard in vitro growth conditions [PMID:22309152].","teleology":[{"year":2010,"claim":"Establishing that a single Argonaute in Toxoplasma binds two distinct small-RNA classes and nucleates a full RISC-like assembly answered whether this early-branching parasite possesses a functional RNAi effector machinery.","evidence":"Mass spectrometry of immunoprecipitated Tg-AGO complex, polyribosome co-sedimentation, and small RNA sequencing in T. gondii","pmids":["20523899"],"confidence":"High","gaps":["Substoichiometric chromatin-repressor associations were not functionally dissected","Direct targets of the siRNA versus miRNA pathways were not defined"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2010,"claim":"Recognizing that Tg-AGO lacks canonical PIWI catalytic residues and that its miRNAs partition with polyribosomes reframed the protein as a translational regulator rather than a slicer.","evidence":"PIWI domain sequence analysis and polyribosome co-sedimentation assay in T. gondii","pmids":["20523899"],"confidence":"High","gaps":["The precise molecular mechanism of translational repression was not resolved","How silencing is achieved without robust slicer activity was left open"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2012,"claim":"Identifying TSN as a recruited surrogate slicer and PRMT1-mediated RGG-domain methylation as the recruitment switch explained how a catalytically weak Argonaute achieves cleavage competence.","evidence":"Co-immunoprecipitation, RGG-repeat mutational analysis, in vitro RNA cleavage assays, PRMT1 knockout parasites, and chemical inhibition of arginine methylation in T. gondii","pmids":["22309152"],"confidence":"High","gaps":["Whether TSN slicing operates on endogenous targets in vivo was not demonstrated","The stoichiometry and regulation of methylation-dependent TSN loading was not quantified"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2012,"claim":"Deleting TgAgo tested whether the silencing machinery is required for parasite fitness, showing it is dispensable under standard culture.","evidence":"Genetic knockout of TgAgo with in vitro growth assay in T. gondii","pmids":["22309152"],"confidence":"Medium","gaps":["Single method (growth readout) in one lab; no stress or in vivo conditions tested","Transcriptomic or heterochromatin consequences of knockout not assessed"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"The endogenous target repertoire and biological function of Tg-AGO-mediated silencing during infection remain undefined.","evidence":"","pmids":[],"confidence":"Low","gaps":["No in vivo phenotype or condition under which Tg-AGO is required has been identified","Direct mRNA and heterochromatin targets have not been mapped","The functional division between siRNA-directed and miRNA-directed pathways is uncharacterized"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["RISC-like complex (Tg-AGO with canonical RISC components and novel RNA metabolism proteins)","Tg-AGO / TSN / PRMT1 assembly"],"partners":["TSN (TUDOR STAPHYLOCOCCAL NUCLEASE)","PRMT1 (PROTEIN ARGININE METHYLTRANSFERASE 1)","CHROMATIN-REPRESSING COMPLEX COMPONENTS (SUBSTOICHIOMETRIC)"],"other_free_text":["PIWI-like domain lacks the canonical DDE/H catalytic triad, giving weak intrinsic slicer activity","N-terminal RGG-repeat domain is arginine-methylated by PRMT1, correlating with TSN recruitment","Tg-AGO slicer activity is Mg2+-dependent and requires perfect guide complementarity; TSN slicer activity is Ca2+-dependent and requires imperfect complementarity","Binds both plant-like heterochromatic siRNAs and metazoan-like miRNAs","Dispensable for parasite viability under standard in vitro growth conditions"]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"20523899","id":"PMC_20523899","title":"A complex small RNA repertoire is generated by a plant/fungal-like machinery and effected by a metazoan-like Argonaute in the single-cell human parasite Toxoplasma gondii.","date":"2010","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/20523899","citation_count":84,"is_preprint":false},{"pmid":"22309152","id":"PMC_22309152","title":"PRMT1 methylates the single Argonaute of Toxoplasma gondii and is important for the recruitment of Tudor nuclease for target RNA cleavage by antisense guide RNA.","date":"2012","source":"Cellular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/22309152","citation_count":30,"is_preprint":false},{"pmid":"23790262","id":"PMC_23790262","title":"Balamuthia mandrillaris: in vitro interactions with selected protozoa and algae.","date":"2013","source":"The Journal of eukaryotic microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/23790262","citation_count":10,"is_preprint":false},{"pmid":"36816026","id":"PMC_36816026","title":"piRNA pathway evolution beyond gonad context: Perspectives from apicomplexa and trypanosomatids.","date":"2023","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/36816026","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":4523,"output_tokens":1245,"usd":0.016122,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":6252,"output_tokens":2638,"usd":0.048605,"stage2_stop_reason":"end_turn"},"total_usd":0.064727,"stage1_batch_id":"msgbatch_01S6GjoYQm8LTPUsdhASdqag","stage2_batch_id":"msgbatch_01VX63RTMdBJqsG6gQMqoCjz","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"Toxoplasma gondii encodes a single Argonaute protein (Tg-AGO) that binds both plant-like heterochromatic siRNAs and metazoan-like miRNAs. Mass spectrometric analysis of the Tg-AGO protein complex revealed association with virtually all known RISC components (as characterized in human and Drosophila) as well as novel RNA metabolism proteins. Tg-AGO also associates substoichiometrically with components of chromatin-repressing complexes, consistent with its loading with heterochromatic small RNAs.\",\n      \"method\": \"Mass spectrometry of immunoprecipitated Tg-AGO complex; co-sedimentation with polyribosomes; small RNA sequencing\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP/MS with multiple orthogonal methods (polyribosome co-sedimentation, small RNA profiling, mass spectrometry) in a single rigorous study\",\n      \"pmids\": [\"20523899\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Tg-AGO lacks canonical catalytic residues in its PIWI domain, consistent with its inability to perform slicer (endonuclease) activity. Toxoplasma miRNAs co-sediment with polyribosomes, suggesting Tg-AGO acts as a translational regulator rather than a direct RNA slicer.\",\n      \"method\": \"Sequence analysis of PIWI domain; polyribosome co-sedimentation assay\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — domain mutagenesis inference combined with polyribosome co-sedimentation, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"20523899\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The PIWI-like domain of TgAgo lacks the canonical DDE/H catalytic triad, explaining its weak target RNA cleavage activity. TgAgo associates with a Tudor staphylococcal nuclease (TSN) and with protein arginine methyltransferase PRMT1. PRMT1 methylates the N-terminal RGG-repeat domain of TgAgo, and this methylation correlates with recruitment of TSN to the complex. TSN provides a stronger, Ca2+-dependent RNA slicer activity requiring imperfect guide RNA complementarity, while TgAgo's own slicer activity is Mg2+-dependent and requires perfect complementarity.\",\n      \"method\": \"Co-immunoprecipitation; mutational analysis of RGG-repeat domain; in vitro RNA cleavage assays; PRMT1 knockout parasites; chemical inhibition of arginine methylation\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, mutational analysis, in vitro enzymatic assays, and genetic knockouts, multiple orthogonal methods in a single study\",\n      \"pmids\": [\"22309152\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"AGO knockout parasites showed essentially normal growth in vitro, indicating TgAgo is not essential for parasite viability under standard conditions.\",\n      \"method\": \"Genetic knockout of TgAgo with growth assay\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single lab, single method (genetic KO with growth readout)\",\n      \"pmids\": [\"22309152\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"Toxoplasma gondii encodes a single Argonaute protein (Tg-AGO) that lacks canonical PIWI catalytic residues and therefore has weak intrinsic slicer activity; instead, it forms a RISC-like complex by binding both heterochromatic siRNAs and miRNAs, acting primarily as a translational regulator, and recruits a Tudor staphylococcal nuclease (TSN) as a surrogate slicer—a recruitment event that depends on PRMT1-mediated arginine methylation of TgAgo's N-terminal RGG-repeat domain.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Toxoplasma gondii encodes a single Argonaute protein (Tg-AGO) that serves as the core effector of a RISC-like small-RNA silencing machinery, binding both plant-like heterochromatic siRNAs and metazoan-like miRNAs and assembling a complex containing essentially all canonical RISC components together with novel RNA-metabolism factors [#0]. Because its PIWI-like domain lacks the canonical DDE/H catalytic triad, Tg-AGO has only weak intrinsic slicer activity, and its associated miRNAs co-sediment with polyribosomes, indicating it acts predominantly as a translational regulator rather than a direct RNA-cleaving enzyme [#1]. To acquire robust cleavage capacity, Tg-AGO recruits a Tudor staphylococcal nuclease (TSN) as a surrogate slicer: TSN provides a Ca2+-dependent activity requiring imperfect guide-target complementarity, distinct from Tg-AGO's own Mg2+-dependent activity requiring perfect complementarity [#2]. This recruitment is governed by PRMT1, which methylates the N-terminal RGG-repeat domain of Tg-AGO, an event that correlates with TSN incorporation into the complex [#2]. Tg-AGO is dispensable for parasite viability under standard in vitro growth conditions [#3].\",\n  \"teleology\": [\n    {\n      \"year\": 2010,\n      \"claim\": \"Establishing that a single Argonaute in Toxoplasma binds two distinct small-RNA classes and nucleates a full RISC-like assembly answered whether this early-branching parasite possesses a functional RNAi effector machinery.\",\n      \"evidence\": \"Mass spectrometry of immunoprecipitated Tg-AGO complex, polyribosome co-sedimentation, and small RNA sequencing in T. gondii\",\n      \"pmids\": [\"20523899\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Substoichiometric chromatin-repressor associations were not functionally dissected\",\n        \"Direct targets of the siRNA versus miRNA pathways were not defined\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Recognizing that Tg-AGO lacks canonical PIWI catalytic residues and that its miRNAs partition with polyribosomes reframed the protein as a translational regulator rather than a slicer.\",\n      \"evidence\": \"PIWI domain sequence analysis and polyribosome co-sedimentation assay in T. gondii\",\n      \"pmids\": [\"20523899\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The precise molecular mechanism of translational repression was not resolved\",\n        \"How silencing is achieved without robust slicer activity was left open\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identifying TSN as a recruited surrogate slicer and PRMT1-mediated RGG-domain methylation as the recruitment switch explained how a catalytically weak Argonaute achieves cleavage competence.\",\n      \"evidence\": \"Co-immunoprecipitation, RGG-repeat mutational analysis, in vitro RNA cleavage assays, PRMT1 knockout parasites, and chemical inhibition of arginine methylation in T. gondii\",\n      \"pmids\": [\"22309152\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether TSN slicing operates on endogenous targets in vivo was not demonstrated\",\n        \"The stoichiometry and regulation of methylation-dependent TSN loading was not quantified\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Deleting TgAgo tested whether the silencing machinery is required for parasite fitness, showing it is dispensable under standard culture.\",\n      \"evidence\": \"Genetic knockout of TgAgo with in vitro growth assay in T. gondii\",\n      \"pmids\": [\"22309152\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single method (growth readout) in one lab; no stress or in vivo conditions tested\",\n        \"Transcriptomic or heterochromatin consequences of knockout not assessed\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The endogenous target repertoire and biological function of Tg-AGO-mediated silencing during infection remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No in vivo phenotype or condition under which Tg-AGO is required has been identified\",\n        \"Direct mRNA and heterochromatin targets have not been mapped\",\n        \"The functional division between siRNA-directed and miRNA-directed pathways is uncharacterized\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 1], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0004521\", \"supporting_discovery_ids\": [2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0035198\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0016442\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0016441\", \"supporting_discovery_ids\": [0, 2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0035195\", \"supporting_discovery_ids\": [1], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [\n      \"RISC-like complex (Tg-AGO with canonical RISC components and novel RNA metabolism proteins)\",\n      \"Tg-AGO / TSN / PRMT1 assembly\"\n    ],\n    \"partners\": [\n      \"TSN (Tudor staphylococcal nuclease)\",\n      \"PRMT1 (protein arginine methyltransferase 1)\",\n      \"chromatin-repressing complex components (substoichiometric)\"\n    ],\n    \"other_free_text\": [\n      \"PIWI-like domain lacks the canonical DDE/H catalytic triad, giving weak intrinsic slicer activity\",\n      \"N-terminal RGG-repeat domain is arginine-methylated by PRMT1, correlating with TSN recruitment\",\n      \"Tg-AGO slicer activity is Mg2+-dependent and requires perfect guide complementarity; TSN slicer activity is Ca2+-dependent and requires imperfect complementarity\",\n      \"Binds both plant-like heterochromatic siRNAs and metazoan-like miRNAs\",\n      \"Dispensable for parasite viability under standard in vitro growth conditions\"\n    ]\n  },\n  \"strain_conflicts\": []\n}","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_310160","name":"AGO","product":"argonaute AGO","uniprot_acc":"S8GCU1","chromosome":"TGME49_chrXI","start_pos":1099768},{"strain":"GT1","gene_id":"TGGT1_310160","name":null,"product":"argonaute AGO","uniprot_acc":null,"chromosome":"TGGT1_chrXI","start_pos":1062667},{"strain":"RH88","gene_id":"TGRH88_049650","name":null,"product":"argonaute AGO","uniprot_acc":null,"chromosome":"CM023092","start_pos":1148232},{"strain":"VEG","gene_id":"TGVEG_310160","name":null,"product":"argonaute AGO","uniprot_acc":"A0A125YL70","chromosome":"TGVEG_chrXI","start_pos":1108814}]}