{"gene":"RH88_020200","gene_symbol":"","run_date":"2026-09-11T11:01:00","timeline":{"discoveries":[{"year":2004,"finding":"ROP4 is a type I transmembrane protein localized to rhoptries that is secreted during host cell invasion and associates with the parasitophorous vacuole membrane (PVM), where it becomes phosphorylated at multiple sites in infected cells; a subset of phosphorylation events result from host cell protein kinase(s) or parasite kinase(s) activated by host cell factors.","method":"Monoclonal antibody screen, subcellular fractionation, immunofluorescence, immunoelectron microscopy, phosphorylation assays with kinase inhibitors","journal":"Eukaryotic cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct localization by IEM, functional consequence (PVM association, phosphorylation) established with multiple orthogonal methods in a single dedicated study","pmids":["15470260"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2008,"finding":"GRA7 (dense granule protein) associates with rhoptry proteins ROP2 and ROP4 in infected host cells, independently of GRA7 phosphorylation state; this was the first reported interaction between proteins secreted from rhoptries and dense granules.","method":"Co-immunoprecipitation from infected host cells, immunofluorescence localization","journal":"Infection and immunity","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, Co-IP from infected cells, two orthogonal detection methods but no reciprocal pull-down or in vitro reconstitution","pmids":["18809661"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2006,"finding":"ROP5, a ROP2 family member, exposes its C-terminus toward the host cell cytoplasm on the PVM (inverted topology relative to ROP2 and ROP4), indicating that ROP2 and ROP4 have the opposite orientation (N-terminus facing the host cytoplasm) and calling for reappraisal of how ROP2-family proteins associate with the PVM.","method":"Differential permeabilization of infected cells followed by immunofluorescence with topology-specific antibodies","journal":"Cellular microbiology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — topology of ROP4 inferred comparatively from ROP5 experiment; ROP4 orientation itself not directly tested but mechanistically informative","pmids":["16879455"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"finding":"A GFP motif-trap strategy identified an additional rhoptry-targeting mechanism for ROP4: GFP fused in-frame into the endogenous ROP4 locus was correctly routed to rhoptries, revealing a targeting signal within the ROP4 coding sequence.","method":"GFP motif-trap (promoter-less, methionine-less GFP integration + FACS + fluorescence microscopy)","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single lab, single method (GFP fusion from endogenous locus), demonstrates targeting signal but does not delineate the signal domain","pmids":["15279957"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2006,"finding":"ROP4 (63 kDa) and ROP2 (58 kDa) isolated from Toxoplasma membrane fractions specifically bind human lactoferrin, as demonstrated by lactoferrin affinity chromatography and competitive inhibition with biotin-labeled lactoferrin, followed by ESI/MS/MS identification.","method":"Membrane protein extraction, lactoferrin affinity chromatography, competitive inhibition assay, ESI/MS/MS protein identification","journal":"Experimental parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single lab, affinity chromatography with competitive inhibition, identity confirmed by mass spectrometry, but no reciprocal or in vitro reconstitution","pmids":["17069806"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2012,"finding":"ROP4 protein binds sulfated heparin/heparan sulfate structures; binding specificity and affinity were measured using heparin oligosaccharide microarrays and surface plasmon resonance, suggesting a role for ROP4 in parasite-host interactions inside the parasitophorous vacuole.","method":"Heparin-functionalized zeolite pulldown, heparin oligosaccharide microarrays, surface plasmon resonance","journal":"Glycobiology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — two orthogonal biophysical binding assays (microarray + SPR), single lab, no mutagenesis to confirm binding site","pmids":["22997241"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2002,"finding":"ROP4 transcript levels are developmentally regulated, decreasing during tachyzoite-to-bradyzoite differentiation, placing ROP4 among secretory organelle genes whose expression changes during stage conversion.","method":"cDNA microarray analysis measuring relative transcript abundance across tachyzoite-to-bradyzoite differentiation time points","journal":"Eukaryotic cell","confidence":"Low","confidence_rationale":"Tier 4 / Weak — transcriptomic only; no protein-level or functional mechanistic data for ROP4 specifically","pmids":["12455982"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"ROP4 is a type I transmembrane rhoptry protein that is secreted during host cell invasion, inserts into the parasitophorous vacuole membrane with a defined topology, becomes phosphorylated at multiple sites by host and/or parasite kinases activated by host cell factors, associates with the dense granule protein GRA7 and with ROP2 within infected cells, binds sulfated glycosaminoglycans and human lactoferrin via its membrane-exposed domains, and is targeted to rhoptries through a signal encoded within its coding sequence."},"narrative":{"mechanistic_narrative":"None of the findings on this card come from studying RH88: they are ROP4 results from papers that do not identify this RH88 gene (TGRH88_020200), which is probably the RH88 copy of ROP4 (card TG_295125). ROP4 is a type I transmembrane rhoptry protein of Toxoplasma gondii that is secreted during host cell invasion and associates with the parasitophorous vacuole membrane (PVM), where it becomes phosphorylated at multiple sites by kinases including host cell protein kinase(s) or parasite kinase(s) activated by host cell factors [PMID:15470260]. Its rhoptry targeting is directed by a signal encoded within the ROP4 coding sequence [PMID:15279957]. On the PVM, ROP4 adopts a topology with its N-terminus facing the host cytoplasm, opposite to that of the ROP2-family member ROP5 [PMID:16879455]. Within infected cells ROP4 is found in association with ROP2 and with the dense granule protein GRA7, the latter representing the first reported interaction between rhoptry- and dense-granule-secreted proteins [PMID:18809661]. Through its host-exposed domains ROP4 binds host ligands, including human lactoferrin [PMID:17069806] and sulfated heparin/heparan sulfate glycosaminoglycans [PMID:22997241], implicating it in parasite-host interactions at the vacuole interface. Beyond these binding and localization properties, the precise enzymatic or effector function of ROP4 has not been characterized in the available corpus.","teleology":[{"year":2002,"claim":"Whether ROP4 expression is constant or stage-regulated was unknown; profiling across differentiation showed its transcript declines during tachyzoite-to-bradyzoite conversion, placing ROP4 among developmentally regulated secretory organelle genes.","evidence":"cDNA microarray across differentiation time points","pmids":["12455982"],"confidence":"Low","gaps":["Transcript-level only; no protein-level confirmation of stage regulation","Functional consequence of downregulation not tested"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"claim":"The localization and fate of ROP4 during invasion were undefined; ROP4 was established as a type I transmembrane rhoptry protein that is secreted, associates with the PVM, and becomes multiply phosphorylated in part by host- or host-activated kinases, linking it to the host cell interface.","evidence":"Monoclonal antibody screen, subcellular fractionation, IEM, phosphorylation assays with kinase inhibitors","pmids":["15470260"],"confidence":"High","gaps":["Specific phosphosites and responsible kinases not identified","Functional consequence of PVM phosphorylation unknown"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"claim":"How ROP4 is routed to rhoptries was unknown; an in-frame GFP motif-trap at the endogenous locus was correctly targeted, revealing a rhoptry-targeting signal within the ROP4 coding sequence.","evidence":"GFP motif-trap integration with FACS and fluorescence microscopy","pmids":["15279957"],"confidence":"Medium","gaps":["The targeting signal domain was not delineated","Single method, single lab"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2006,"claim":"The membrane orientation of ROP2-family proteins was uncertain; differential permeabilization of ROP5 indicated ROP2 and ROP4 adopt the opposite topology, with their N-terminus facing the host cytoplasm.","evidence":"Differential permeabilization and topology-specific immunofluorescence","pmids":["16879455"],"confidence":"Medium","gaps":["ROP4 orientation inferred comparatively rather than tested directly","Mechanism of membrane insertion not resolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2006,"claim":"Whether ROP4 engages host ligands was unknown; membrane-derived ROP4 (63 kDa) and ROP2 were shown to specifically bind human lactoferrin, indicating direct host protein recognition.","evidence":"Lactoferrin affinity chromatography with competitive inhibition and ESI/MS/MS identification","pmids":["17069806"],"confidence":"Medium","gaps":["Binding domain not mapped","Biological role of lactoferrin binding not established","No reciprocal or reconstituted assay"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2008,"claim":"Whether rhoptry and dense granule secretory pathways converge molecularly was unknown; GRA7 was found associated with ROP2 and ROP4 in infected cells, the first reported rhoptry-dense granule protein interaction.","evidence":"Co-immunoprecipitation from infected host cells and immunofluorescence","pmids":["18809661"],"confidence":"Medium","gaps":["No reciprocal pull-down or in vitro reconstitution","Direct vs indirect nature of the interaction unresolved","Functional consequence of the complex unknown"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2012,"claim":"The nature of ROP4's carbohydrate interactions was undefined; ROP4 was shown to bind sulfated heparin/heparan sulfate with measurable specificity and affinity, extending its host-interaction repertoire to glycosaminoglycans.","evidence":"Heparin oligosaccharide microarrays and surface plasmon resonance","pmids":["22997241"],"confidence":"Medium","gaps":["Binding site not confirmed by mutagenesis","Physiological relevance within the vacuole not demonstrated"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"The core effector or enzymatic function of ROP4 — how its PVM association, phosphorylation, and host-ligand binding integrate into parasite biology or virulence — remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No knockout phenotype reported","Responsible kinases and phosphosite function unmapped","Biological role of lactoferrin/GAG binding untested"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["ROP4-ROP2-GRA7 association in infected host cells [#1]"],"partners":["ROP2 [#1, #4]","GRA7 [#1]","HUMAN LACTOFERRIN (HOST LIGAND) [#4]","HEPARIN/HEPARAN SULFATE (HOST GAG LIGAND) [#5]"],"other_free_text":["Type I transmembrane rhoptry protein secreted during invasion and inserted into the PVM with N-terminus facing host cytoplasm [#0, #2]","Multiply phosphorylated on the PVM by host and/or host-activated parasite kinases [#0]","Rhoptry targeting encoded by a signal within the ROP4 coding sequence [#3]","Transcript developmentally downregulated during tachyzoite-to-bradyzoite differentiation [#6]"]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"12455982","id":"PMC_12455982","title":"Toxoplasma gondii asexual development: identification of developmentally regulated genes and distinct patterns of gene expression.","date":"2002","source":"Eukaryotic cell","url":"https://pubmed.ncbi.nlm.nih.gov/12455982","citation_count":131,"is_preprint":false},{"pmid":"18809661","id":"PMC_18809661","title":"The Toxoplasma gondii dense granule protein GRA7 is phosphorylated upon invasion and forms an unexpected association with the rhoptry proteins ROP2 and ROP4.","date":"2008","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/18809661","citation_count":78,"is_preprint":false},{"pmid":"15470260","id":"PMC_15470260","title":"The Toxoplasma gondii rhoptry protein ROP4 is secreted into the parasitophorous vacuole and becomes phosphorylated in infected cells.","date":"2004","source":"Eukaryotic cell","url":"https://pubmed.ncbi.nlm.nih.gov/15470260","citation_count":73,"is_preprint":false},{"pmid":"16879455","id":"PMC_16879455","title":"Inverted topology of the Toxoplasma gondii ROP5 rhoptry protein provides new insights into the association of the ROP2 protein family with the parasitophorous vacuole membrane.","date":"2006","source":"Cellular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/16879455","citation_count":59,"is_preprint":false},{"pmid":"19508869","id":"PMC_19508869","title":"Toxoplasma gondii: the immunogenic and protective efficacy of recombinant ROP2 and ROP4 rhoptry proteins in murine experimental toxoplasmosis.","date":"2009","source":"Experimental parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/19508869","citation_count":51,"is_preprint":false},{"pmid":"9746591","id":"PMC_9746591","title":"Murine dendritic cells pulsed in vitro with Toxoplasma gondii antigens induce protective immunity in vivo.","date":"1998","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/9746591","citation_count":39,"is_preprint":false},{"pmid":"22445587","id":"PMC_22445587","title":"Toxoplasma gondii: the vaccine potential of three trivalent antigen-cocktails composed of recombinant ROP2, ROP4, GRA4 and SAG1 proteins against chronic toxoplasmosis in BALB/c mice.","date":"2012","source":"Experimental parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/22445587","citation_count":36,"is_preprint":false},{"pmid":"15279957","id":"PMC_15279957","title":"A GFP-based motif-trap reveals a novel mechanism of targeting for the Toxoplasma ROP4 protein.","date":"2004","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/15279957","citation_count":31,"is_preprint":false},{"pmid":"31315212","id":"PMC_31315212","title":"Influenza Virus-Like Particles Presenting both Toxoplasma gondii ROP4 and ROP13 Enhance Protection against T. gondii Infection.","date":"2019","source":"Pharmaceutics","url":"https://pubmed.ncbi.nlm.nih.gov/31315212","citation_count":27,"is_preprint":false},{"pmid":"22997241","id":"PMC_22997241","title":"Toxoplasma gondii secretory proteins bind to sulfated heparin structures.","date":"2012","source":"Glycobiology","url":"https://pubmed.ncbi.nlm.nih.gov/22997241","citation_count":27,"is_preprint":false},{"pmid":"32249951","id":"PMC_32249951","title":"Toxoplasma gondii virus-like particle vaccination alleviates inflammatory response in the brain upon T gondii infection.","date":"2020","source":"Parasite immunology","url":"https://pubmed.ncbi.nlm.nih.gov/32249951","citation_count":19,"is_preprint":false},{"pmid":"7681478","id":"PMC_7681478","title":"Subcellular localization of the 54-kDa antigen of Toxoplasma gondii.","date":"1993","source":"The Journal of parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/7681478","citation_count":17,"is_preprint":false},{"pmid":"17069806","id":"PMC_17069806","title":"Identification of Toxoplasma gondii proteins binding human lactoferrin: a new aspect of rhoptry proteins function.","date":"2006","source":"Experimental parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/17069806","citation_count":16,"is_preprint":false},{"pmid":"22892593","id":"PMC_22892593","title":"Recombinant ROP2, ROP4, GRA4 and SAG1 antigen-cocktails as possible tools for immunoprophylaxis of toxoplasmosis: what's next?","date":"2012","source":"Bioengineered","url":"https://pubmed.ncbi.nlm.nih.gov/22892593","citation_count":15,"is_preprint":false},{"pmid":"34660343","id":"PMC_34660343","title":"Mucosal Administration of Recombinant Baculovirus Displaying Toxoplasma gondii ROP4 Confers Protection Against T. gondii Challenge Infection in Mice.","date":"2021","source":"Frontiers in cellular and infection microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/34660343","citation_count":11,"is_preprint":false},{"pmid":"20734761","id":"PMC_20734761","title":"Determination of diagnostic value of Toxoplasma gondii recombinant ROP2 and ROP4 antigens in mouse experimental model.","date":"2010","source":"Polish journal of microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/20734761","citation_count":10,"is_preprint":false},{"pmid":"30419728","id":"PMC_30419728","title":"Virus-Like Particles Expressing Toxoplasma gondii Rhoptry Protein 18 Induces Better Protection Than Rhoptry Protein 4 against T. gondii Infection.","date":"2018","source":"The Korean journal of parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/30419728","citation_count":10,"is_preprint":false},{"pmid":"29657017","id":"PMC_29657017","title":"Assessment of the antigenic and neuroprotective activity of the subunit anti-Toxoplasma vaccine in T. gondii experimentally infected mice.","date":"2018","source":"Veterinary parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/29657017","citation_count":10,"is_preprint":false},{"pmid":"35214611","id":"PMC_35214611","title":"Orally Administrated Recombinant Vaccinia Virus Displaying ROP4 Induces Protection against Toxoplasma gondii Challenge Infection.","date":"2022","source":"Vaccines","url":"https://pubmed.ncbi.nlm.nih.gov/35214611","citation_count":9,"is_preprint":false},{"pmid":"28506036","id":"PMC_28506036","title":"Influenza M1 Virus-Like Particles Consisting of Toxoplasma gondii Rhoptry Protein 4.","date":"2017","source":"The Korean journal of parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/28506036","citation_count":7,"is_preprint":false},{"pmid":"29963084","id":"PMC_29963084","title":"Identification of Antigenic and Immunogenic Proteins of Toxoplasma gondii in Human and Sheep by Immunoproteomics.","date":"2018","source":"Iranian journal of parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/29963084","citation_count":6,"is_preprint":false},{"pmid":"34468217","id":"PMC_34468217","title":"Unraveling Toxoplasma gondii GT1 Strain Virulence and New Protein-Coding Genes with Proteogenomic Analyses.","date":"2021","source":"Omics : a journal of integrative biology","url":"https://pubmed.ncbi.nlm.nih.gov/34468217","citation_count":6,"is_preprint":false},{"pmid":"29203146","id":"PMC_29203146","title":"Toward detection of toxoplasmosis from urine in mice using hydro-gel nanoparticles concentration and parallel reaction monitoring mass spectrometry.","date":"2017","source":"Nanomedicine : nanotechnology, biology, and medicine","url":"https://pubmed.ncbi.nlm.nih.gov/29203146","citation_count":6,"is_preprint":false},{"pmid":"28591403","id":"PMC_28591403","title":"Preliminary multiplex microarray IgG immunoassay for the diagnosis of toxoplasmosis and rubella.","date":"2017","source":"Memorias do Instituto Oswaldo Cruz","url":"https://pubmed.ncbi.nlm.nih.gov/28591403","citation_count":5,"is_preprint":false},{"pmid":"34974663","id":"PMC_34974663","title":"Detection of Toxoplasma gondii Infections using Virus-Like Particles Displaying T. gondii ROP4 Antigen.","date":"2021","source":"The Korean journal of parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/34974663","citation_count":4,"is_preprint":false},{"pmid":"39800042","id":"PMC_39800042","title":"Protection induced by recombinant vaccinia virus targeting the ROP4 of Toxoplasma gondii in mice.","date":"2025","source":"Experimental parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/39800042","citation_count":4,"is_preprint":false},{"pmid":"39525668","id":"PMC_39525668","title":"Completing the pieces of a puzzle: in-depth probing of Toxoplasma gondii rhoptry protein 4 as a promising target for vaccination using an in-silico approach.","date":"2024","source":"Clinical and experimental vaccine research","url":"https://pubmed.ncbi.nlm.nih.gov/39525668","citation_count":4,"is_preprint":false},{"pmid":"34039408","id":"PMC_34039408","title":"Proteomics analysis reveals that the proto-oncogene eIF-5A indirectly influences the growth, invasion and replication of Toxoplasma gondii tachyzoite.","date":"2021","source":"Parasites & vectors","url":"https://pubmed.ncbi.nlm.nih.gov/34039408","citation_count":3,"is_preprint":false},{"pmid":"26541043","id":"PMC_26541043","title":"[Research Advance on Toxoplasma gondii Rhoptry Protein 2 Family as Candidate Vaccine Molecules].","date":"2015","source":"Zhongguo ji sheng chong xue yu ji sheng chong bing za zhi = Chinese journal of parasitology & parasitic diseases","url":"https://pubmed.ncbi.nlm.nih.gov/26541043","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15362,"output_tokens":1844,"usd":0.036873,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":7160,"output_tokens":3081,"usd":0.056412,"stage2_stop_reason":"end_turn"},"total_usd":0.093285,"stage1_batch_id":"msgbatch_018xTxyBPcQFK9jdgubtxgsj","stage2_batch_id":"msgbatch_01UiG5BTaJP7BvKKL6RLeyv2","note":"batch pricing = 50% of standard","hand_review_patch":"2026-09-11 AK hand-review verdicts (handoff/tools_2026-09-11/patch)","hand_review_verdict":"edit"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"ROP4 is a type I transmembrane protein localized to rhoptries that is secreted during host cell invasion and associates with the parasitophorous vacuole membrane (PVM), where it becomes phosphorylated at multiple sites in infected cells; a subset of phosphorylation events result from host cell protein kinase(s) or parasite kinase(s) activated by host cell factors.\",\n      \"method\": \"Monoclonal antibody screen, subcellular fractionation, immunofluorescence, immunoelectron microscopy, phosphorylation assays with kinase inhibitors\",\n      \"journal\": \"Eukaryotic cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization by IEM, functional consequence (PVM association, phosphorylation) established with multiple orthogonal methods in a single dedicated study\",\n      \"pmids\": [\"15470260\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GRA7 (dense granule protein) associates with rhoptry proteins ROP2 and ROP4 in infected host cells, independently of GRA7 phosphorylation state; this was the first reported interaction between proteins secreted from rhoptries and dense granules.\",\n      \"method\": \"Co-immunoprecipitation from infected host cells, immunofluorescence localization\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, Co-IP from infected cells, two orthogonal detection methods but no reciprocal pull-down or in vitro reconstitution\",\n      \"pmids\": [\"18809661\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ROP5, a ROP2 family member, exposes its C-terminus toward the host cell cytoplasm on the PVM (inverted topology relative to ROP2 and ROP4), indicating that ROP2 and ROP4 have the opposite orientation (N-terminus facing the host cytoplasm) and calling for reappraisal of how ROP2-family proteins associate with the PVM.\",\n      \"method\": \"Differential permeabilization of infected cells followed by immunofluorescence with topology-specific antibodies\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — topology of ROP4 inferred comparatively from ROP5 experiment; ROP4 orientation itself not directly tested but mechanistically informative\",\n      \"pmids\": [\"16879455\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"A GFP motif-trap strategy identified an additional rhoptry-targeting mechanism for ROP4: GFP fused in-frame into the endogenous ROP4 locus was correctly routed to rhoptries, revealing a targeting signal within the ROP4 coding sequence.\",\n      \"method\": \"GFP motif-trap (promoter-less, methionine-less GFP integration + FACS + fluorescence microscopy)\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method (GFP fusion from endogenous locus), demonstrates targeting signal but does not delineate the signal domain\",\n      \"pmids\": [\"15279957\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ROP4 (63 kDa) and ROP2 (58 kDa) isolated from Toxoplasma membrane fractions specifically bind human lactoferrin, as demonstrated by lactoferrin affinity chromatography and competitive inhibition with biotin-labeled lactoferrin, followed by ESI/MS/MS identification.\",\n      \"method\": \"Membrane protein extraction, lactoferrin affinity chromatography, competitive inhibition assay, ESI/MS/MS protein identification\",\n      \"journal\": \"Experimental parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, affinity chromatography with competitive inhibition, identity confirmed by mass spectrometry, but no reciprocal or in vitro reconstitution\",\n      \"pmids\": [\"17069806\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ROP4 protein binds sulfated heparin/heparan sulfate structures; binding specificity and affinity were measured using heparin oligosaccharide microarrays and surface plasmon resonance, suggesting a role for ROP4 in parasite-host interactions inside the parasitophorous vacuole.\",\n      \"method\": \"Heparin-functionalized zeolite pulldown, heparin oligosaccharide microarrays, surface plasmon resonance\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — two orthogonal biophysical binding assays (microarray + SPR), single lab, no mutagenesis to confirm binding site\",\n      \"pmids\": [\"22997241\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"ROP4 transcript levels are developmentally regulated, decreasing during tachyzoite-to-bradyzoite differentiation, placing ROP4 among secretory organelle genes whose expression changes during stage conversion.\",\n      \"method\": \"cDNA microarray analysis measuring relative transcript abundance across tachyzoite-to-bradyzoite differentiation time points\",\n      \"journal\": \"Eukaryotic cell\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — transcriptomic only; no protein-level or functional mechanistic data for ROP4 specifically\",\n      \"pmids\": [\"12455982\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"ROP4 is a type I transmembrane rhoptry protein that is secreted during host cell invasion, inserts into the parasitophorous vacuole membrane with a defined topology, becomes phosphorylated at multiple sites by host and/or parasite kinases activated by host cell factors, associates with the dense granule protein GRA7 and with ROP2 within infected cells, binds sulfated glycosaminoglycans and human lactoferrin via its membrane-exposed domains, and is targeted to rhoptries through a signal encoded within its coding sequence.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ROP4 is a type I transmembrane rhoptry protein of Toxoplasma gondii that is secreted during host cell invasion and associates with the parasitophorous vacuole membrane (PVM), where it becomes phosphorylated at multiple sites by kinases including host cell protein kinase(s) or parasite kinase(s) activated by host cell factors [#0]. Its rhoptry targeting is directed by a signal encoded within the ROP4 coding sequence [#3]. On the PVM, ROP4 adopts a topology with its N-terminus facing the host cytoplasm, opposite to that of the ROP2-family member ROP5 [#2]. Within infected cells ROP4 is found in association with ROP2 and with the dense granule protein GRA7, the latter representing the first reported interaction between rhoptry- and dense-granule-secreted proteins [#1]. Through its host-exposed domains ROP4 binds host ligands, including human lactoferrin [#4] and sulfated heparin/heparan sulfate glycosaminoglycans [#5], implicating it in parasite-host interactions at the vacuole interface. Beyond these binding and localization properties, the precise enzymatic or effector function of ROP4 has not been characterized in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Whether ROP4 expression is constant or stage-regulated was unknown; profiling across differentiation showed its transcript declines during tachyzoite-to-bradyzoite conversion, placing ROP4 among developmentally regulated secretory organelle genes.\",\n      \"evidence\": \"cDNA microarray across differentiation time points\",\n      \"pmids\": [\"12455982\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Transcript-level only; no protein-level confirmation of stage regulation\", \"Functional consequence of downregulation not tested\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The localization and fate of ROP4 during invasion were undefined; ROP4 was established as a type I transmembrane rhoptry protein that is secreted, associates with the PVM, and becomes multiply phosphorylated in part by host- or host-activated kinases, linking it to the host cell interface.\",\n      \"evidence\": \"Monoclonal antibody screen, subcellular fractionation, IEM, phosphorylation assays with kinase inhibitors\",\n      \"pmids\": [\"15470260\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific phosphosites and responsible kinases not identified\", \"Functional consequence of PVM phosphorylation unknown\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"How ROP4 is routed to rhoptries was unknown; an in-frame GFP motif-trap at the endogenous locus was correctly targeted, revealing a rhoptry-targeting signal within the ROP4 coding sequence.\",\n      \"evidence\": \"GFP motif-trap integration with FACS and fluorescence microscopy\",\n      \"pmids\": [\"15279957\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The targeting signal domain was not delineated\", \"Single method, single lab\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"The membrane orientation of ROP2-family proteins was uncertain; differential permeabilization of ROP5 indicated ROP2 and ROP4 adopt the opposite topology, with their N-terminus facing the host cytoplasm.\",\n      \"evidence\": \"Differential permeabilization and topology-specific immunofluorescence\",\n      \"pmids\": [\"16879455\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"ROP4 orientation inferred comparatively rather than tested directly\", \"Mechanism of membrane insertion not resolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Whether ROP4 engages host ligands was unknown; membrane-derived ROP4 (63 kDa) and ROP2 were shown to specifically bind human lactoferrin, indicating direct host protein recognition.\",\n      \"evidence\": \"Lactoferrin affinity chromatography with competitive inhibition and ESI/MS/MS identification\",\n      \"pmids\": [\"17069806\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding domain not mapped\", \"Biological role of lactoferrin binding not established\", \"No reciprocal or reconstituted assay\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Whether rhoptry and dense granule secretory pathways converge molecularly was unknown; GRA7 was found associated with ROP2 and ROP4 in infected cells, the first reported rhoptry-dense granule protein interaction.\",\n      \"evidence\": \"Co-immunoprecipitation from infected host cells and immunofluorescence\",\n      \"pmids\": [\"18809661\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No reciprocal pull-down or in vitro reconstitution\", \"Direct vs indirect nature of the interaction unresolved\", \"Functional consequence of the complex unknown\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The nature of ROP4's carbohydrate interactions was undefined; ROP4 was shown to bind sulfated heparin/heparan sulfate with measurable specificity and affinity, extending its host-interaction repertoire to glycosaminoglycans.\",\n      \"evidence\": \"Heparin oligosaccharide microarrays and surface plasmon resonance\",\n      \"pmids\": [\"22997241\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding site not confirmed by mutagenesis\", \"Physiological relevance within the vacuole not demonstrated\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The core effector or enzymatic function of ROP4 — how its PVM association, phosphorylation, and host-ligand binding integrate into parasite biology or virulence — remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No knockout phenotype reported\", \"Responsible kinases and phosphosite function unmapped\", \"Biological role of lactoferrin/GAG binding untested\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008201\", \"supporting_discovery_ids\": [5], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0005515\", \"supporting_discovery_ids\": [1, 4], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0033566\", \"supporting_discovery_ids\": [0, 3], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0020005\", \"supporting_discovery_ids\": [0, 2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0044409\", \"supporting_discovery_ids\": [0, 4, 5], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [\"ROP4-ROP2-GRA7 association in infected host cells [#1]\"],\n    \"partners\": [\"ROP2 [#1, #4]\", \"GRA7 [#1]\", \"human lactoferrin (host ligand) [#4]\", \"heparin/heparan sulfate (host GAG ligand) [#5]\"],\n    \"other_free_text\": [\n      \"Type I transmembrane rhoptry protein secreted during invasion and inserted into the PVM with N-terminus facing host cytoplasm [#0, #2]\",\n      \"Multiply phosphorylated on the PVM by host and/or host-activated parasite kinases [#0]\",\n      \"Rhoptry targeting encoded by a signal within the ROP4 coding sequence [#3]\",\n      \"Transcript developmentally downregulated during tachyzoite-to-bradyzoite differentiation [#6]\"\n    ]\n  },\n  \"strain_conflicts\": []\n}","audit_flag":null,"strains":[{"strain":"RH88","gene_id":"TGRH88_020200","name":null,"product":"rhoptry protein ROP4","uniprot_acc":null,"chromosome":"CM023081","start_pos":1422225}]}