{"gene":"TG_211680","gene_symbol":"PDI","run_date":"2026-09-08T11:06:23","timeline":{"discoveries":[{"year":2005,"finding":"NcPDI (94% identical to TgPDI) localizes to the cytoplasm near the nuclear membrane, micronemes, and parasite cell surface of Neospora caninum tachyzoites, but is absent from rhoptries and dense granules. Preincubation with sulfhydryl blockers DTNB and pCMBA, the PDI inhibitor bacitracin, or affinity-purified anti-NcPDI antibodies reduced tachyzoite adhesion to host cells, implicating surface-associated PDI in host cell interaction.","method":"Immunogold-EM localization; immunofluorescence; adhesion inhibition assays with sulfhydryl blockers (DTNB, pCMBA), bacitracin, and blocking antibodies","journal":"International journal for parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization by immunogold-EM plus functional inhibition by multiple reagents, but all in Neospora caninum (ortholog), single lab","pmids":["16129440"],"is_preprint":false,"attribution":[{"species":"Neospora caninum","strain":""}]},{"year":2002,"finding":"A 49 kDa antigen from T. gondii tachyzoites was identified as protein disulfide isomerase (PDI) by mass spectrometry; the complete ORF was determined and recombinant PDI was expressed, confirming recognition by human mucosal IgA antibodies in tears.","method":"Mass spectrometric identification; recombinant expression and immunoblot with human IgA antibodies","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MS identification plus recombinant expression and functional antibody recognition, single lab","pmids":["12095627"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2002,"finding":"sIgA epitopes on T. gondii PDI are confined to conserved regions including the functionally essential thioredoxin-like domain. Binding to this domain on immunoblot could be abrogated by competition with peptide constituting the same domain, demonstrating that natural human IgA targets the catalytic thioredoxin domain of TgPDI.","method":"Immunoblot with truncated recombinant PDI variants; peptide competition assay","journal":"International immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — truncation mapping plus peptide competition with multiple orthogonal approaches, single lab","pmids":["12407020"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2016,"finding":"Recombinant TgPDI (52 kDa thioredoxin) interfered with T. gondii invasion of human epithelial and retinal cell lines when added at small amounts, and PDI inhibitors bacitracin and nitroblue tetrazolium reduced the percentage of infected cells, establishing a functional role for TgPDI in the adhesion and invasion steps of infection. TgPDI gene expression was lower after parasite entry into host cells.","method":"Invasion inhibition assays with recombinant TgPDI protein and PDI inhibitors (bacitracin, nitroblue tetrazolium); gene expression analysis during in vitro infection","journal":"Experimental parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — functional inhibition with multiple reagents and recombinant protein, single lab, no mutagenesis or structural validation","pmids":["26896642"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2022,"finding":"TgPDI was identified as a putative basigin-ligand on T. gondii by proteomic screen. Recombinant TgPDI produced in E. coli bound directly to host basigin, pretreatment of tachyzoites with a PDI inhibitor decreased parasite attachment to host cells, and mutagenesis of the active-site cysteines of TgPDI abolished enzyme binding to basigin. This establishes TgPDI as a T. gondii surface ligand that engages host basigin via its catalytic active site during parasite attachment.","method":"Proteomic screen for basigin-interacting T. gondii proteins; recombinant TgPDI–basigin binding assay; PDI inhibitor pretreatment attachment assay; active-site cysteine mutagenesis","journal":"Infection and immunity","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — direct binding assay with recombinant protein, active-site mutagenesis abolishing binding, and functional inhibitor assay in same study; single lab but three orthogonal methods","pmids":["35913173"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2024,"finding":"TgPDI8 is an ER-localized protein disulfide isomerase whose conditional knockdown causes a complete block in plaque formation and significant reduction in intracellular proliferation and invasion, while TgPDI6 knockdown shows no fitness defect. The CXXC active-site cysteines within TgPDI8's thioredoxin domains are essential for its enzymatic activity and function. TurboID proximity labeling revealed close association of PDI8 with canonical secretory proteins, and loss of PDI8 substantially reduces expression of secretory proteins from micronemes and dense granules.","method":"Conditional knockdown (inducible); plaque assay; invasion assay; active-site cysteine mutagenesis with complementation; TurboID-based proximity labeling and proteomics","journal":"mBio","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — conditional knockdown with clean phenotype, active-site mutagenesis, and proximity proteomics in one study; multiple orthogonal methods in single rigorous study","pmids":["39162526"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2026,"finding":"TgPDIA3 is an ER-localized PDI in T. gondii that regulates both ER redox activity and ER calcium sequestration. Loss of TgPDIA3 function disrupts ER redox homeostasis and calcium homeostasis, impairing microneme protein maturation and secretion, parasite invasion, and replication, thereby linking ER redox regulation to calcium-dependent lytic cycle progression.","method":"Localization studies; conditional loss-of-function; ER redox and calcium measurements; microneme secretion and invasion assays; identification of interacting protein substrates","journal":"mBio","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct localization, loss-of-function with defined cellular phenotypes (redox, calcium, microneme secretion, invasion, replication), and substrate identification in one rigorous study","pmids":["41919918"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2025,"finding":"TgPDIA3 (preprint version of the above peer-reviewed study) coordinates ER redox homeostasis and ER calcium regulation, with its interacting protein substrates identified; disruption impairs lytic cycle progression. (Superseded by the 2026 peer-reviewed publication PMID:41919918.)","method":"Localization; loss-of-function; ER redox and calcium assays; substrate identification by interactomics","journal":"bioRxiv","confidence":"High","confidence_rationale":"Tier 2 / Moderate — same study as PMID:41919918, preprint version; multiple orthogonal methods","pmids":["40463016"],"is_preprint":true,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"T. gondii encodes multiple functionally distinct ER-localized protein disulfide isomerases (PDIs): TgPDI8 is essential for parasite growth and facilitates oxidative folding of secretory proteins in micronemes and dense granules via its CXXC active-site cysteines; TgPDIA3 coordinates ER redox homeostasis with calcium sequestration to drive lytic cycle progression including microneme secretion and invasion; and a surface-exposed TgPDI (the originally described 49–52 kDa form) mediates parasite attachment to host cells through direct, active-site-dependent binding to the host receptor basigin, with inhibition of its thioredoxin/disulfide-exchange activity reducing host cell adhesion and invasion."},"narrative":{"mechanistic_narrative":"In apicomplexan parasites, protein disulfide isomerase (PDI) activity supports both intracellular oxidative folding of secretory-pathway proteins and, in a surface-associated pool, direct engagement of host cells during invasion [PMID:35913173, PMID:39162526]. Two ER-resident PDIs drive the lytic cycle: TgPDI8, whose thioredoxin-domain CXXC active-site cysteines are required for enzymatic function, is essential for parasite growth, invasion, and intracellular proliferation, associates with canonical secretory proteins by proximity labeling, and is needed for normal expression of microneme and dense-granule proteins [PMID:39162526]; TgPDIA3 couples ER redox homeostasis to ER calcium sequestration, and its loss disrupts both, impairing microneme protein maturation and secretion, invasion, and replication and thereby linking ER redox control to calcium-dependent lytic-cycle progression [PMID:41919918]. A distinct surface-exposed TgPDI (the originally described 49–52 kDa antigen) acts as a parasite ligand for the host receptor basigin: recombinant TgPDI binds basigin directly, active-site cysteine mutagenesis abolishes this binding, and PDI inhibitors reduce parasite attachment and invasion, establishing an active-site-dependent adhesion function [PMID:26896642, PMID:35913173]. This surface PDI is also a target of human mucosal IgA, whose epitopes map to the catalytic thioredoxin domain [PMID:12095627, PMID:12407020].","teleology":[{"year":2002,"claim":"Establishing the molecular identity of a prominent T. gondii tachyzoite antigen defined PDI as a parasite protein recognized by the host mucosal immune response.","evidence":"Mass-spectrometric identification and recombinant expression of a 49 kDa tachyzoite antigen, immunoblotted against human tear IgA","pmids":["12095627","12407020"],"confidence":"Medium","gaps":["Did not test a catalytic or adhesion function for the protein","Epitope mapping localized IgA binding to the thioredoxin domain but did not test whether antibody binding neutralizes enzymatic activity"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2005,"claim":"Localizing the ortholog to the parasite surface and showing that sulfhydryl blockers and inhibitors reduce adhesion linked surface-associated PDI to host-cell interaction.","evidence":"Immunogold-EM and immunofluorescence localization plus adhesion-inhibition assays with DTNB, pCMBA, bacitracin, and blocking antibodies in Neospora caninum tachyzoites","pmids":["16129440"],"confidence":"Medium","gaps":["Shown in the Neospora caninum ortholog, not T. gondii","Inhibitors are not PDI-specific and no host receptor was identified"],"attribution":[{"species":"Neospora caninum","strain":""}]},{"year":2016,"claim":"Functional inhibition and recombinant-protein interference tests established that TgPDI participates in the adhesion and invasion steps of infection.","evidence":"Invasion-inhibition assays with recombinant TgPDI and PDI inhibitors (bacitracin, nitroblue tetrazolium) plus infection-stage gene expression analysis in human epithelial and retinal cells","pmids":["26896642"],"confidence":"Medium","gaps":["No host binding partner identified","Relied on non-specific inhibitors without genetic or active-site validation"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2022,"claim":"Identifying host basigin as the receptor and showing active-site-dependent binding defined the molecular mechanism of surface TgPDI-mediated attachment.","evidence":"Proteomic screen for basigin ligands, direct recombinant TgPDI–basigin binding assay, active-site cysteine mutagenesis abolishing binding, and inhibitor-pretreatment attachment assay","pmids":["35913173"],"confidence":"High","gaps":["Did not resolve how an ER-type PDI reaches the parasite surface","Downstream signaling or invasion consequences of the PDI–basigin interaction not defined"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2024,"claim":"Genetic dissection distinguished an essential ER PDI (TgPDI8) from a dispensable one (TgPDI6) and tied its function to oxidative folding of secretory proteins.","evidence":"Conditional knockdown with plaque and invasion assays, active-site cysteine mutagenesis with complementation, and TurboID proximity proteomics in T. gondii","pmids":["39162526"],"confidence":"High","gaps":["Specific folding substrates responsible for the growth defect not individually validated","Relationship of TgPDI8 to the surface basigin-binding PDI not addressed"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2026,"claim":"Characterizing TgPDIA3 revealed that a second ER PDI couples ER redox state to calcium sequestration, connecting redox homeostasis to calcium-dependent lytic-cycle progression.","evidence":"Localization, conditional loss-of-function, ER redox and calcium measurements, microneme secretion and invasion assays, and substrate identification in T. gondii (peer-reviewed; preprint version also in the timeline)","pmids":["41919918","40463016"],"confidence":"High","gaps":["Mechanism by which redox activity controls calcium sequestration not fully resolved","Functional overlap or division of labor with TgPDI8 not delineated"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"How the ER-resident PDI machinery relates to the surface-exposed basigin-binding PDI—including trafficking to the cell surface and whether distinct or shared gene products underlie the intracellular folding and adhesion functions—remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No study reconciles surface localization with ER residency","Division of function among the multiple T. gondii PDIs not fully mapped"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":["HOST BASIGIN (BSG) — DIRECT ACTIVE-SITE-DEPENDENT LIGAND OF SURFACE TGPDI [#4]","MICRONEME AND DENSE-GRANULE SECRETORY PROTEINS — PROXIMITY PARTNERS/SUBSTRATES OF TGPDI8 [#5]","ER PROTEIN SUBSTRATES OF TGPDIA3 [#6]"],"other_free_text":["T. gondii encodes multiple functionally distinct PDIs: essential TgPDI8, redox/calcium-coupling TgPDIA3, dispensable TgPDI6, and a surface-exposed 49–52 kDa TgPDI [#4, #5, #6].","The catalytic thioredoxin-domain CXXC cysteines are required both for TgPDI8 enzymatic function [#5] and for surface TgPDI binding to basigin [#4].","The surface TgPDI thioredoxin domain is the epitope targeted by human mucosal IgA [#2]."]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"16129440","id":"PMC_16129440","title":"Neospora caninum protein disulfide isomerase is involved in tachyzoite-host cell interaction.","date":"2005","source":"International journal for parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/16129440","citation_count":45,"is_preprint":false},{"pmid":"15991490","id":"PMC_15991490","title":"Identification and characterization of cross-reactive antigens from Neospora caninum and Toxoplasma gondii.","date":"2005","source":"Parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/15991490","citation_count":36,"is_preprint":false},{"pmid":"23967128","id":"PMC_23967128","title":"Toxoplasma gondii protein disulfide isomerase (TgPDI) is a novel vaccine candidate against toxoplasmosis.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23967128","citation_count":33,"is_preprint":false},{"pmid":"12095627","id":"PMC_12095627","title":"Protein disulfide isomerase of Toxoplasma gondii is targeted by mucosal IgA antibodies in humans.","date":"2002","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/12095627","citation_count":33,"is_preprint":false},{"pmid":"12407020","id":"PMC_12407020","title":"Conserved regions of protein disulfide isomerase are targeted by natural IgA antibodies in humans.","date":"2002","source":"International immunology","url":"https://pubmed.ncbi.nlm.nih.gov/12407020","citation_count":28,"is_preprint":false},{"pmid":"26896642","id":"PMC_26896642","title":"Role of the 52 KDa thioredoxin protein disulfide isomerase of Toxoplasma gondii during infection to human cells.","date":"2016","source":"Experimental parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/26896642","citation_count":8,"is_preprint":false},{"pmid":"39162526","id":"PMC_39162526","title":"Protein disulfide isomerase PDI8 is indispensable for parasite growth and associated with secretory protein processing in Toxoplasma gondii.","date":"2024","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/39162526","citation_count":5,"is_preprint":false},{"pmid":"35913173","id":"PMC_35913173","title":"A Role for Basigin in Toxoplasma gondii Infection.","date":"2022","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/35913173","citation_count":5,"is_preprint":false},{"pmid":"40463016","id":"PMC_40463016","title":"A Protein Disulfide Isomerase Coordinates Redox Homeostasis and ER Calcium Regulation for Optimal Lytic Cycle Progression in Toxoplasma gondii.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/40463016","citation_count":0,"is_preprint":false},{"pmid":"41919918","id":"PMC_41919918","title":"A protein disulfide isomerase coordinates redox homeostasis and ER calcium regulation for optimal lytic cycle progression in Toxoplasma gondii.","date":"2026","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/41919918","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7824,"output_tokens":2474,"usd":0.030291,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":7947,"output_tokens":3361,"usd":0.06188,"stage2_stop_reason":"end_turn"},"total_usd":0.092171,"stage1_batch_id":"msgbatch_01WokvBYTB6JLnYrpD4rXnyV","stage2_batch_id":"msgbatch_01M7hsQDvz6AqVC9DLVjQzzc","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"NcPDI (94% identical to TgPDI) localizes to the cytoplasm near the nuclear membrane, micronemes, and parasite cell surface of Neospora caninum tachyzoites, but is absent from rhoptries and dense granules. Preincubation with sulfhydryl blockers DTNB and pCMBA, the PDI inhibitor bacitracin, or affinity-purified anti-NcPDI antibodies reduced tachyzoite adhesion to host cells, implicating surface-associated PDI in host cell interaction.\",\n      \"method\": \"Immunogold-EM localization; immunofluorescence; adhesion inhibition assays with sulfhydryl blockers (DTNB, pCMBA), bacitracin, and blocking antibodies\",\n      \"journal\": \"International journal for parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization by immunogold-EM plus functional inhibition by multiple reagents, but all in Neospora caninum (ortholog), single lab\",\n      \"pmids\": [\"16129440\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Neospora caninum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"A 49 kDa antigen from T. gondii tachyzoites was identified as protein disulfide isomerase (PDI) by mass spectrometry; the complete ORF was determined and recombinant PDI was expressed, confirming recognition by human mucosal IgA antibodies in tears.\",\n      \"method\": \"Mass spectrometric identification; recombinant expression and immunoblot with human IgA antibodies\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS identification plus recombinant expression and functional antibody recognition, single lab\",\n      \"pmids\": [\"12095627\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"sIgA epitopes on T. gondii PDI are confined to conserved regions including the functionally essential thioredoxin-like domain. Binding to this domain on immunoblot could be abrogated by competition with peptide constituting the same domain, demonstrating that natural human IgA targets the catalytic thioredoxin domain of TgPDI.\",\n      \"method\": \"Immunoblot with truncated recombinant PDI variants; peptide competition assay\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — truncation mapping plus peptide competition with multiple orthogonal approaches, single lab\",\n      \"pmids\": [\"12407020\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Recombinant TgPDI (52 kDa thioredoxin) interfered with T. gondii invasion of human epithelial and retinal cell lines when added at small amounts, and PDI inhibitors bacitracin and nitroblue tetrazolium reduced the percentage of infected cells, establishing a functional role for TgPDI in the adhesion and invasion steps of infection. TgPDI gene expression was lower after parasite entry into host cells.\",\n      \"method\": \"Invasion inhibition assays with recombinant TgPDI protein and PDI inhibitors (bacitracin, nitroblue tetrazolium); gene expression analysis during in vitro infection\",\n      \"journal\": \"Experimental parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — functional inhibition with multiple reagents and recombinant protein, single lab, no mutagenesis or structural validation\",\n      \"pmids\": [\"26896642\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"TgPDI was identified as a putative basigin-ligand on T. gondii by proteomic screen. Recombinant TgPDI produced in E. coli bound directly to host basigin, pretreatment of tachyzoites with a PDI inhibitor decreased parasite attachment to host cells, and mutagenesis of the active-site cysteines of TgPDI abolished enzyme binding to basigin. This establishes TgPDI as a T. gondii surface ligand that engages host basigin via its catalytic active site during parasite attachment.\",\n      \"method\": \"Proteomic screen for basigin-interacting T. gondii proteins; recombinant TgPDI–basigin binding assay; PDI inhibitor pretreatment attachment assay; active-site cysteine mutagenesis\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct binding assay with recombinant protein, active-site mutagenesis abolishing binding, and functional inhibitor assay in same study; single lab but three orthogonal methods\",\n      \"pmids\": [\"35913173\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TgPDI8 is an ER-localized protein disulfide isomerase whose conditional knockdown causes a complete block in plaque formation and significant reduction in intracellular proliferation and invasion, while TgPDI6 knockdown shows no fitness defect. The CXXC active-site cysteines within TgPDI8's thioredoxin domains are essential for its enzymatic activity and function. TurboID proximity labeling revealed close association of PDI8 with canonical secretory proteins, and loss of PDI8 substantially reduces expression of secretory proteins from micronemes and dense granules.\",\n      \"method\": \"Conditional knockdown (inducible); plaque assay; invasion assay; active-site cysteine mutagenesis with complementation; TurboID-based proximity labeling and proteomics\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — conditional knockdown with clean phenotype, active-site mutagenesis, and proximity proteomics in one study; multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"39162526\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TgPDIA3 is an ER-localized PDI in T. gondii that regulates both ER redox activity and ER calcium sequestration. Loss of TgPDIA3 function disrupts ER redox homeostasis and calcium homeostasis, impairing microneme protein maturation and secretion, parasite invasion, and replication, thereby linking ER redox regulation to calcium-dependent lytic cycle progression.\",\n      \"method\": \"Localization studies; conditional loss-of-function; ER redox and calcium measurements; microneme secretion and invasion assays; identification of interacting protein substrates\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization, loss-of-function with defined cellular phenotypes (redox, calcium, microneme secretion, invasion, replication), and substrate identification in one rigorous study\",\n      \"pmids\": [\"41919918\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TgPDIA3 (preprint version of the above peer-reviewed study) coordinates ER redox homeostasis and ER calcium regulation, with its interacting protein substrates identified; disruption impairs lytic cycle progression. (Superseded by the 2026 peer-reviewed publication PMID:41919918.)\",\n      \"method\": \"Localization; loss-of-function; ER redox and calcium assays; substrate identification by interactomics\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — same study as PMID:41919918, preprint version; multiple orthogonal methods\",\n      \"pmids\": [\"40463016\"],\n      \"is_preprint\": true,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"T. gondii encodes multiple functionally distinct ER-localized protein disulfide isomerases (PDIs): TgPDI8 is essential for parasite growth and facilitates oxidative folding of secretory proteins in micronemes and dense granules via its CXXC active-site cysteines; TgPDIA3 coordinates ER redox homeostasis with calcium sequestration to drive lytic cycle progression including microneme secretion and invasion; and a surface-exposed TgPDI (the originally described 49–52 kDa form) mediates parasite attachment to host cells through direct, active-site-dependent binding to the host receptor basigin, with inhibition of its thioredoxin/disulfide-exchange activity reducing host cell adhesion and invasion.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"In apicomplexan parasites, protein disulfide isomerase (PDI) activity supports both intracellular oxidative folding of secretory-pathway proteins and, in a surface-associated pool, direct engagement of host cells during invasion [#4, #5]. Two ER-resident PDIs drive the lytic cycle: TgPDI8, whose thioredoxin-domain CXXC active-site cysteines are required for enzymatic function, is essential for parasite growth, invasion, and intracellular proliferation, associates with canonical secretory proteins by proximity labeling, and is needed for normal expression of microneme and dense-granule proteins [#5]; TgPDIA3 couples ER redox homeostasis to ER calcium sequestration, and its loss disrupts both, impairing microneme protein maturation and secretion, invasion, and replication and thereby linking ER redox control to calcium-dependent lytic-cycle progression [#6]. A distinct surface-exposed TgPDI (the originally described 49\\u201352 kDa antigen) acts as a parasite ligand for the host receptor basigin: recombinant TgPDI binds basigin directly, active-site cysteine mutagenesis abolishes this binding, and PDI inhibitors reduce parasite attachment and invasion, establishing an active-site-dependent adhesion function [#3, #4]. This surface PDI is also a target of human mucosal IgA, whose epitopes map to the catalytic thioredoxin domain [#1, #2].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Establishing the molecular identity of a prominent T. gondii tachyzoite antigen defined PDI as a parasite protein recognized by the host mucosal immune response.\",\n      \"evidence\": \"Mass-spectrometric identification and recombinant expression of a 49 kDa tachyzoite antigen, immunoblotted against human tear IgA\",\n      \"pmids\": [\"12095627\", \"12407020\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not test a catalytic or adhesion function for the protein\", \"Epitope mapping localized IgA binding to the thioredoxin domain but did not test whether antibody binding neutralizes enzymatic activity\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Localizing the ortholog to the parasite surface and showing that sulfhydryl blockers and inhibitors reduce adhesion linked surface-associated PDI to host-cell interaction.\",\n      \"evidence\": \"Immunogold-EM and immunofluorescence localization plus adhesion-inhibition assays with DTNB, pCMBA, bacitracin, and blocking antibodies in Neospora caninum tachyzoites\",\n      \"pmids\": [\"16129440\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Shown in the Neospora caninum ortholog, not T. gondii\", \"Inhibitors are not PDI-specific and no host receptor was identified\"],\n      \"attribution\": [{\"species\": \"Neospora caninum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Functional inhibition and recombinant-protein interference tests established that TgPDI participates in the adhesion and invasion steps of infection.\",\n      \"evidence\": \"Invasion-inhibition assays with recombinant TgPDI and PDI inhibitors (bacitracin, nitroblue tetrazolium) plus infection-stage gene expression analysis in human epithelial and retinal cells\",\n      \"pmids\": [\"26896642\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No host binding partner identified\", \"Relied on non-specific inhibitors without genetic or active-site validation\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identifying host basigin as the receptor and showing active-site-dependent binding defined the molecular mechanism of surface TgPDI-mediated attachment.\",\n      \"evidence\": \"Proteomic screen for basigin ligands, direct recombinant TgPDI\\u2013basigin binding assay, active-site cysteine mutagenesis abolishing binding, and inhibitor-pretreatment attachment assay\",\n      \"pmids\": [\"35913173\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve how an ER-type PDI reaches the parasite surface\", \"Downstream signaling or invasion consequences of the PDI\\u2013basigin interaction not defined\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Genetic dissection distinguished an essential ER PDI (TgPDI8) from a dispensable one (TgPDI6) and tied its function to oxidative folding of secretory proteins.\",\n      \"evidence\": \"Conditional knockdown with plaque and invasion assays, active-site cysteine mutagenesis with complementation, and TurboID proximity proteomics in T. gondii\",\n      \"pmids\": [\"39162526\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific folding substrates responsible for the growth defect not individually validated\", \"Relationship of TgPDI8 to the surface basigin-binding PDI not addressed\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Characterizing TgPDIA3 revealed that a second ER PDI couples ER redox state to calcium sequestration, connecting redox homeostasis to calcium-dependent lytic-cycle progression.\",\n      \"evidence\": \"Localization, conditional loss-of-function, ER redox and calcium measurements, microneme secretion and invasion assays, and substrate identification in T. gondii (peer-reviewed; preprint version also in the timeline)\",\n      \"pmids\": [\"41919918\", \"40463016\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which redox activity controls calcium sequestration not fully resolved\", \"Functional overlap or division of labor with TgPDI8 not delineated\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the ER-resident PDI machinery relates to the surface-exposed basigin-binding PDI\\u2014including trafficking to the cell surface and whether distinct or shared gene products underlie the intracellular folding and adhesion functions\\u2014remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No study reconciles surface localization with ER residency\", \"Division of function among the multiple T. gondii PDIs not fully mapped\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003756\", \"supporting_discovery_ids\": [4, 5, 6], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0015035\", \"supporting_discovery_ids\": [2, 5], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0038023\", \"supporting_discovery_ids\": [4], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005788\", \"supporting_discovery_ids\": [5, 6], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0009986\", \"supporting_discovery_ids\": [0, 4], \"attribution\": [{\"species\": \"Neospora caninum\", \"strain\": \"\"}, {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0034975\", \"supporting_discovery_ids\": [5, 6], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0044409\", \"supporting_discovery_ids\": [3, 4], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0006874\", \"supporting_discovery_ids\": [6], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"Host basigin (BSG) \\u2014 direct active-site-dependent ligand of surface TgPDI [#4]\",\n      \"Microneme and dense-granule secretory proteins \\u2014 proximity partners/substrates of TgPDI8 [#5]\",\n      \"ER protein substrates of TgPDIA3 [#6]\"\n    ],\n    \"other_free_text\": [\n      \"T. gondii encodes multiple functionally distinct PDIs: essential TgPDI8, redox/calcium-coupling TgPDIA3, dispensable TgPDI6, and a surface-exposed 49\\u201352 kDa TgPDI [#4, #5, #6].\",\n      \"The catalytic thioredoxin-domain CXXC cysteines are required both for TgPDI8 enzymatic function [#5] and for surface TgPDI binding to basigin [#4].\",\n      \"The surface TgPDI thioredoxin domain is the epitope targeted by human mucosal IgA [#2].\"\n    ]\n  },\n  \"strain_conflicts\": []\n}","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_211680","name":"PDI","product":"protein disulfide isomerase","uniprot_acc":"A0A125YQJ0","chromosome":"TGME49_chrIV","start_pos":1626416},{"strain":"GT1","gene_id":"TGGT1_211680","name":null,"product":"protein disulfide isomerase","uniprot_acc":null,"chromosome":"TGGT1_chrIV","start_pos":1556190},{"strain":"RH88","gene_id":"TGRH88_008470","name":null,"product":"protein disulfide isomerase","uniprot_acc":null,"chromosome":"CM023085","start_pos":1648297},{"strain":"VEG","gene_id":"TGVEG_211680","name":null,"product":"protein disulfide isomerase","uniprot_acc":"A0A0F7UU04","chromosome":"TGVEG_chrIV","start_pos":1650648}]}