{"gene":"TG_295125","gene_symbol":"ROP4","run_date":"2026-09-08T15:15:12","timeline":{"discoveries":[{"year":2004,"finding":"ROP4 is a type I transmembrane protein localized to rhoptries, secreted during host cell invasion, and subsequently associates with the parasitophorous vacuole membrane (PVM) where it becomes phosphorylated in the infected cell. Phosphorylation occurs on multiple sites, a subset of which result from the action of host cell protein kinase(s) or parasite kinase(s) activated by host cell factors.","method":"Monoclonal antibody screen, subcellular fractionation, immunofluorescence, immunoprecipitation, phosphorylation assays","journal":"Eukaryotic cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (localization, fractionation, phosphorylation assays) in a focused mechanistic study; partially replicated by comparison with ROP2","pmids":["15470260"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"finding":"A GFP motif-trap approach revealed that ROP4 contains a rhoptry-targeting signal, identifying an additional mechanism for targeting of this protein to rhoptries expressed from its endogenous promoter and start methionine.","method":"GFP motif-trap (integrative transfection of promoter-less GFP construct), FACS, fluorescence microscopy","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization with functional targeting signal identified; single lab, two orthogonal methods (FACS + microscopy)","pmids":["15279957"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2008,"finding":"GRA7 associates with ROP4 (and ROP2) in infected host cells, representing the first demonstrated interaction between a dense granule protein and rhoptry proteins. GRA7 localizes to strand-like structures in the host cytosol that contain rhoptry proteins within 10 min of invasion.","method":"Co-immunoprecipitation, immunofluorescence microscopy, differential extraction in infected cells","journal":"Infection and immunity","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal association shown by Co-IP and co-localization; single lab with two orthogonal methods","pmids":["18809661"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2006,"finding":"Unlike ROP2 and ROP4, which expose their N-terminus to the host cytoplasm, ROP5 exposes its C-terminus toward the host cell cytoplasm on the PVM, indicating inverted (reverse) topology compared to ROP2 and ROP4. This finding informed the reappraisal of how ROP2-family proteins associate with the PVM.","method":"Differential permeabilization of infected cells, immunofluorescence with topology-specific antibodies","journal":"Cellular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — differential permeabilization directly established membrane topology; single lab, two orthogonal methods; ROP4 topology established by contrast with ROP5","pmids":["16879455"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2006,"finding":"ROP4 (63 kDa) and ROP2 (58 kDa) from Toxoplasma gondii membrane fractions specifically bind human lactoferrin, as demonstrated by lactoferrin affinity chromatography and competitive inhibition with biotinylated lactoferrin, followed by ESI/MS/MS identification.","method":"Membrane protein extraction, lactoferrin affinity chromatography, competitive inhibition with biotin-labeled lactoferrin, ESI/MS/MS protein identification","journal":"Experimental parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — affinity pulldown with competitive inhibition control and MS identification; single lab, single experiment","pmids":["17069806"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2012,"finding":"ROP4 protein (from rhoptries) binds sulfated heparin/heparan sulfate structures. Binding specificity and affinity for natural heparin and heparin oligosaccharides were characterized by heparin oligosaccharide microarrays and surface plasmon resonance.","method":"Heparin-functionalized zeolite pulldown, heparin oligosaccharide microarrays, surface plasmon resonance","journal":"Glycobiology","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — in vitro binding assays with SPR quantification and oligosaccharide microarrays; single lab, multiple orthogonal methods","pmids":["22997241"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2002,"finding":"ROP4 transcript levels are developmentally regulated during tachyzoite-to-bradyzoite differentiation, with ROP4 identified as a bradyzoite-induced gene showing altered expression levels during asexual development.","method":"cDNA microarray analysis (~4,400 cDNAs); relative transcript abundance measurement","journal":"Eukaryotic cell","confidence":"Low","confidence_rationale":"Tier 4 / Weak — transcriptomics only; no direct protein-level or mechanistic experiment on ROP4","pmids":["12455982"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"Toxoplasma gondii ROP4 is a type I transmembrane rhoptry protein that is secreted during host cell invasion and inserts into the parasitophorous vacuole membrane (PVM) with its N-terminus exposed to the host cytoplasm, where it becomes phosphorylated by host and/or parasite kinases; it binds sulfated glycosaminoglycans (heparin/heparan sulfate) and human lactoferrin, associates with the dense granule protein GRA7 within the infected cell, and contains an intrinsic rhoptry-targeting signal, collectively positioning ROP4 as a multifunctional PVM-resident protein involved in host–parasite interface regulation."},"narrative":{"mechanistic_narrative":"Toxoplasma gondii ROP4 is a type I transmembrane rhoptry protein that functions at the host-parasite interface during and after invasion [PMID:15470260]. Secreted from rhoptries during host cell entry, ROP4 associates with the parasitophorous vacuole membrane (PVM) and adopts a topology that exposes its N-terminus to the host cytoplasm, where it is phosphorylated on multiple sites by host and/or host-factor-activated parasite kinases [PMID:15470260, PMID:16879455]. Its rhoptry delivery depends on an intrinsic rhoptry-targeting signal within the protein [PMID:15279957]. At the vacuolar interface ROP4 engages several host and parasite ligands: it associates with the dense granule protein GRA7 in host-cytosolic strand-like structures within minutes of invasion [PMID:18809661], and binds human lactoferrin [PMID:17069806] and sulfated heparin/heparan sulfate glycosaminoglycans [PMID:22997241], positioning it as a multifunctional PVM-resident protein. Beyond these binding activities and its phosphorylation, the downstream signaling consequences and precise physiological role of ROP4 have not been characterized in the available corpus.","teleology":[{"year":2002,"claim":"Before protein-level characterization, it was unknown whether ROP4 expression is stage-regulated; transcriptomics established that ROP4 is developmentally modulated during asexual differentiation, hinting at a stage-associated role.","evidence":"cDNA microarray of ~4,400 transcripts across tachyzoite-to-bradyzoite differentiation","pmids":["12455982"],"confidence":"Low","gaps":["Transcript-level only; no protein or mechanistic confirmation of stage-specific function","Does not address ROP4 localization or biochemical activity"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"claim":"The core identity of ROP4 was defined by showing it is a type I transmembrane rhoptry protein secreted during invasion that relocates to the PVM and becomes phosphorylated, establishing it as a PVM-resident protein subject to host-directed modification.","evidence":"Monoclonal antibody screen with subcellular fractionation, immunofluorescence, immunoprecipitation and phosphorylation assays in infected cells","pmids":["15470260"],"confidence":"High","gaps":["Kinases responsible for phosphorylation not identified","Functional consequence of phosphorylation unknown","No loss-of-function phenotype established"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"claim":"It was unclear how ROP4 is routed to rhoptries; a GFP motif-trap identified an intrinsic rhoptry-targeting signal, defining the trafficking determinant for endogenous ROP4.","evidence":"GFP motif-trap by integrative transfection of a promoter-less GFP construct, FACS and fluorescence microscopy","pmids":["15279957"],"confidence":"Medium","gaps":["Precise sequence/residues of the targeting signal not delimited","Trafficking machinery recognizing the signal not identified"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2006,"claim":"The membrane orientation of ROP2-family proteins was ambiguous; differential permeabilization showed ROP4 exposes its N-terminus to the host cytoplasm (opposite topology to ROP5), clarifying how ROP4 presents its modified domain to the host.","evidence":"Differential permeabilization of infected cells with topology-specific antibodies, contrasted with ROP5","pmids":["16879455"],"confidence":"Medium","gaps":["ROP4 topology inferred by contrast with ROP5 rather than directly mapped residue-by-residue","Membrane insertion mechanism not defined"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2006,"claim":"To probe host ligands, lactoferrin affinity chromatography demonstrated that ROP4 (and ROP2) specifically bind human lactoferrin, identifying a candidate host-interface interaction.","evidence":"Membrane protein extraction, lactoferrin affinity chromatography with biotinylated-lactoferrin competitive inhibition, ESI/MS/MS identification","pmids":["17069806"],"confidence":"Medium","gaps":["Single experiment; binding not confirmed in situ or during infection","Functional significance of lactoferrin binding unknown"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2008,"claim":"It was unknown whether rhoptry and dense granule proteins interact; Co-IP and co-localization revealed ROP4 associates with GRA7 in host-cytosolic strand-like structures shortly after invasion, the first demonstrated rhoptry–dense granule protein interaction.","evidence":"Co-immunoprecipitation, immunofluorescence microscopy and differential extraction in infected host cells","pmids":["18809661"],"confidence":"Medium","gaps":["Direct vs indirect nature of the ROP4–GRA7 association not resolved","Functional consequence of the interaction not established"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2012,"claim":"Extending the host-ligand repertoire, in vitro glycan-binding assays showed ROP4 binds sulfated heparin/heparan sulfate with defined specificity, implicating it in glycosaminoglycan-mediated host interactions.","evidence":"Heparin-functionalized zeolite pulldown, heparin oligosaccharide microarrays and surface plasmon resonance","pmids":["22997241"],"confidence":"Medium","gaps":["In vitro binding; physiological relevance during infection not tested","GAG-binding domain of ROP4 not mapped"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"The downstream signaling and physiological role of ROP4 remain open: the kinases that phosphorylate it, the functional consequences of its lactoferrin/GAG/GRA7 interactions, and any loss-of-function phenotype are undefined.","evidence":"No direct experimental evidence in the available corpus","pmids":[],"confidence":"Low","gaps":["No genetic knockout or phenotype for ROP4","Kinases and functional impact of phosphorylation unidentified","Biological purpose of ligand-binding activities untested in vivo"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":["GRA7","ROP2","HUMAN LACTOFERRIN (HOST)","HEPARIN/HEPARAN SULFATE (HOST GAG)"],"other_free_text":["Type I transmembrane rhoptry protein secreted during invasion and inserted into the PVM with N-terminus exposed to the host cytoplasm [#0, #3].","Phosphorylated on multiple sites in infected cells by host and/or host-factor-activated parasite kinases [#0].","Contains an intrinsic rhoptry-targeting signal directing its delivery to rhoptries [#1].","Transcript developmentally regulated during tachyzoite-to-bradyzoite differentiation (Low-confidence transcriptomic evidence) [#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":15354,"output_tokens":1852,"usd":0.036921,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":7161,"output_tokens":3447,"usd":0.06099,"stage2_stop_reason":"end_turn"},"total_usd":0.097911,"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\": 2004,\n      \"finding\": \"ROP4 is a type I transmembrane protein localized to rhoptries, secreted during host cell invasion, and subsequently associates with the parasitophorous vacuole membrane (PVM) where it becomes phosphorylated in the infected cell. Phosphorylation occurs on multiple sites, a subset of which result from the action of host cell protein kinase(s) or parasite kinase(s) activated by host cell factors.\",\n      \"method\": \"Monoclonal antibody screen, subcellular fractionation, immunofluorescence, immunoprecipitation, phosphorylation assays\",\n      \"journal\": \"Eukaryotic cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (localization, fractionation, phosphorylation assays) in a focused mechanistic study; partially replicated by comparison with ROP2\",\n      \"pmids\": [\"15470260\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"A GFP motif-trap approach revealed that ROP4 contains a rhoptry-targeting signal, identifying an additional mechanism for targeting of this protein to rhoptries expressed from its endogenous promoter and start methionine.\",\n      \"method\": \"GFP motif-trap (integrative transfection of promoter-less GFP construct), FACS, fluorescence microscopy\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization with functional targeting signal identified; single lab, two orthogonal methods (FACS + microscopy)\",\n      \"pmids\": [\"15279957\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GRA7 associates with ROP4 (and ROP2) in infected host cells, representing the first demonstrated interaction between a dense granule protein and rhoptry proteins. GRA7 localizes to strand-like structures in the host cytosol that contain rhoptry proteins within 10 min of invasion.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence microscopy, differential extraction in infected cells\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal association shown by Co-IP and co-localization; single lab with two orthogonal methods\",\n      \"pmids\": [\"18809661\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Unlike ROP2 and ROP4, which expose their N-terminus to the host cytoplasm, ROP5 exposes its C-terminus toward the host cell cytoplasm on the PVM, indicating inverted (reverse) topology compared to ROP2 and ROP4. This finding informed the reappraisal of how ROP2-family proteins associate with the PVM.\",\n      \"method\": \"Differential permeabilization of infected cells, immunofluorescence with topology-specific antibodies\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — differential permeabilization directly established membrane topology; single lab, two orthogonal methods; ROP4 topology established by contrast with ROP5\",\n      \"pmids\": [\"16879455\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ROP4 (63 kDa) and ROP2 (58 kDa) from Toxoplasma gondii membrane fractions specifically bind human lactoferrin, as demonstrated by lactoferrin affinity chromatography and competitive inhibition with biotinylated lactoferrin, followed by ESI/MS/MS identification.\",\n      \"method\": \"Membrane protein extraction, lactoferrin affinity chromatography, competitive inhibition with biotin-labeled lactoferrin, ESI/MS/MS protein identification\",\n      \"journal\": \"Experimental parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — affinity pulldown with competitive inhibition control and MS identification; single lab, single experiment\",\n      \"pmids\": [\"17069806\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ROP4 protein (from rhoptries) binds sulfated heparin/heparan sulfate structures. Binding specificity and affinity for natural heparin and heparin oligosaccharides were characterized by heparin oligosaccharide microarrays and surface plasmon resonance.\",\n      \"method\": \"Heparin-functionalized zeolite pulldown, heparin oligosaccharide microarrays, surface plasmon resonance\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro binding assays with SPR quantification and oligosaccharide microarrays; single lab, multiple orthogonal methods\",\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 during tachyzoite-to-bradyzoite differentiation, with ROP4 identified as a bradyzoite-induced gene showing altered expression levels during asexual development.\",\n      \"method\": \"cDNA microarray analysis (~4,400 cDNAs); relative transcript abundance measurement\",\n      \"journal\": \"Eukaryotic cell\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — transcriptomics only; no direct protein-level or mechanistic experiment on ROP4\",\n      \"pmids\": [\"12455982\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"Toxoplasma gondii ROP4 is a type I transmembrane rhoptry protein that is secreted during host cell invasion and inserts into the parasitophorous vacuole membrane (PVM) with its N-terminus exposed to the host cytoplasm, where it becomes phosphorylated by host and/or parasite kinases; it binds sulfated glycosaminoglycans (heparin/heparan sulfate) and human lactoferrin, associates with the dense granule protein GRA7 within the infected cell, and contains an intrinsic rhoptry-targeting signal, collectively positioning ROP4 as a multifunctional PVM-resident protein involved in host–parasite interface regulation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Toxoplasma gondii ROP4 is a type I transmembrane rhoptry protein that functions at the host-parasite interface during and after invasion [#0]. Secreted from rhoptries during host cell entry, ROP4 associates with the parasitophorous vacuole membrane (PVM) and adopts a topology that exposes its N-terminus to the host cytoplasm, where it is phosphorylated on multiple sites by host and/or host-factor-activated parasite kinases [#0, #3]. Its rhoptry delivery depends on an intrinsic rhoptry-targeting signal within the protein [#1]. At the vacuolar interface ROP4 engages several host and parasite ligands: it associates with the dense granule protein GRA7 in host-cytosolic strand-like structures within minutes of invasion [#2], and binds human lactoferrin [#4] and sulfated heparin/heparan sulfate glycosaminoglycans [#5], positioning it as a multifunctional PVM-resident protein. Beyond these binding activities and its phosphorylation, the downstream signaling consequences and precise physiological role of ROP4 have not been characterized in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Before protein-level characterization, it was unknown whether ROP4 expression is stage-regulated; transcriptomics established that ROP4 is developmentally modulated during asexual differentiation, hinting at a stage-associated role.\",\n      \"evidence\": \"cDNA microarray of ~4,400 transcripts across tachyzoite-to-bradyzoite differentiation\",\n      \"pmids\": [\"12455982\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Transcript-level only; no protein or mechanistic confirmation of stage-specific function\",\n        \"Does not address ROP4 localization or biochemical activity\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The core identity of ROP4 was defined by showing it is a type I transmembrane rhoptry protein secreted during invasion that relocates to the PVM and becomes phosphorylated, establishing it as a PVM-resident protein subject to host-directed modification.\",\n      \"evidence\": \"Monoclonal antibody screen with subcellular fractionation, immunofluorescence, immunoprecipitation and phosphorylation assays in infected cells\",\n      \"pmids\": [\"15470260\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Kinases responsible for phosphorylation not identified\",\n        \"Functional consequence of phosphorylation unknown\",\n        \"No loss-of-function phenotype established\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"It was unclear how ROP4 is routed to rhoptries; a GFP motif-trap identified an intrinsic rhoptry-targeting signal, defining the trafficking determinant for endogenous ROP4.\",\n      \"evidence\": \"GFP motif-trap by integrative transfection of a promoter-less GFP construct, FACS and fluorescence microscopy\",\n      \"pmids\": [\"15279957\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Precise sequence/residues of the targeting signal not delimited\",\n        \"Trafficking machinery recognizing the signal not identified\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"The membrane orientation of ROP2-family proteins was ambiguous; differential permeabilization showed ROP4 exposes its N-terminus to the host cytoplasm (opposite topology to ROP5), clarifying how ROP4 presents its modified domain to the host.\",\n      \"evidence\": \"Differential permeabilization of infected cells with topology-specific antibodies, contrasted with ROP5\",\n      \"pmids\": [\"16879455\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"ROP4 topology inferred by contrast with ROP5 rather than directly mapped residue-by-residue\",\n        \"Membrane insertion mechanism not defined\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"To probe host ligands, lactoferrin affinity chromatography demonstrated that ROP4 (and ROP2) specifically bind human lactoferrin, identifying a candidate host-interface interaction.\",\n      \"evidence\": \"Membrane protein extraction, lactoferrin affinity chromatography with biotinylated-lactoferrin competitive inhibition, ESI/MS/MS identification\",\n      \"pmids\": [\"17069806\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single experiment; binding not confirmed in situ or during infection\",\n        \"Functional significance of lactoferrin binding unknown\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"It was unknown whether rhoptry and dense granule proteins interact; Co-IP and co-localization revealed ROP4 associates with GRA7 in host-cytosolic strand-like structures shortly after invasion, the first demonstrated rhoptry\\u2013dense granule protein interaction.\",\n      \"evidence\": \"Co-immunoprecipitation, immunofluorescence microscopy and differential extraction in infected host cells\",\n      \"pmids\": [\"18809661\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct vs indirect nature of the ROP4\\u2013GRA7 association not resolved\",\n        \"Functional consequence of the interaction not established\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Extending the host-ligand repertoire, in vitro glycan-binding assays showed ROP4 binds sulfated heparin/heparan sulfate with defined specificity, implicating it in glycosaminoglycan-mediated host interactions.\",\n      \"evidence\": \"Heparin-functionalized zeolite pulldown, heparin oligosaccharide microarrays and surface plasmon resonance\",\n      \"pmids\": [\"22997241\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"In vitro binding; physiological relevance during infection not tested\",\n        \"GAG-binding domain of ROP4 not mapped\"\n      ],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The downstream signaling and physiological role of ROP4 remain open: the kinases that phosphorylate it, the functional consequences of its lactoferrin/GAG/GRA7 interactions, and any loss-of-function phenotype are undefined.\",\n      \"evidence\": \"No direct experimental evidence in the available corpus\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No genetic knockout or phenotype for ROP4\",\n        \"Kinases and functional impact of phosphorylation unidentified\",\n        \"Biological purpose of ligand-binding activities untested in vivo\"\n      ],\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:0005102\", \"supporting_discovery_ids\": [4], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0042803\", \"supporting_discovery_ids\": [2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020008\", \"supporting_discovery_ids\": [0, 1], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0020005\", \"supporting_discovery_ids\": [0, 3], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0016021\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006468\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0044409\", \"supporting_discovery_ids\": [0, 2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"GRA7\", \"ROP2\", \"human lactoferrin (host)\", \"heparin/heparan sulfate (host GAG)\"],\n    \"other_free_text\": [\n      \"Type I transmembrane rhoptry protein secreted during invasion and inserted into the PVM with N-terminus exposed to the host cytoplasm [#0, #3].\",\n      \"Phosphorylated on multiple sites in infected cells by host and/or host-factor-activated parasite kinases [#0].\",\n      \"Contains an intrinsic rhoptry-targeting signal directing its delivery to rhoptries [#1].\",\n      \"Transcript developmentally regulated during tachyzoite-to-bradyzoite differentiation (Low-confidence transcriptomic evidence) [#6].\"\n    ]\n  },\n  \"strain_conflicts\": []\n}","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_295125","name":"ROP4","product":"rhoptry protein ROP4","uniprot_acc":"S8FFC5","chromosome":"TGME49_chrIa","start_pos":1413184},{"strain":"GT1","gene_id":"TGGT1_295125","name":null,"product":"rhoptry protein ROP4","uniprot_acc":null,"chromosome":"TGGT1_chrIa","start_pos":1394541},{"strain":"VEG","gene_id":"TGVEG_295125","name":null,"product":"rhoptry protein ROP4","uniprot_acc":"V4Z117","chromosome":"TGVEG_chrIa","start_pos":1422093}]}