{"gene":"TG_309590","gene_symbol":"ROP1","run_date":"2026-09-08T18:09:54+00:00","timeline":{"discoveries":[{"year":1992,"finding":"ROP1 is a rhoptry protein whose monoclonal antibody (Tg49) inhibits penetration enhancing factor (a proteinaceous factor that increases invasion efficiency), suggesting ROP1 is a component of that factor. The predicted polypeptide shows an unusual charge asymmetry with a highly acidic, proline-rich N-terminal domain and a strongly basic C-terminal domain, plus an octapeptide repeat near the midpoint.","method":"cDNA library screening with monoclonal antibody Tg49, recombinant protein expression in bacteria, Western blot, immunolocalization of rhoptries","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, antibody inhibition assay plus recombinant expression and localization, but no direct biochemical reconstitution of penetration enhancement","pmids":["1542304"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1992,"finding":"ROP1 localizes within the body of rhoptries prior to invasion; immediately after host cell invasion it associates with the parasitophorous vacuole membrane (PVM); within hours post-invasion the amount of ROP1 immunodetectable on the PVM markedly decreases, indicating ROP1 is discharged from rhoptries into the nascent PVM during invasion.","method":"Immunoelectron microscopy with monoclonal antibody Tg49 and monospecific rabbit antiserum at multiple time points after invasion of human fibroblasts and TG180 murine sarcoma cells","journal":"The Journal of protozoology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct immunolocalization at sequential time points, replicated with two independent antibodies in two host cell types","pmids":["1403988"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1993,"finding":"The ROP1 gene is a single-copy gene. Knockout of ROP1 by gene replacement using CAT as selectable marker was achieved, establishing the first stable gene knockout in Toxoplasma gondii and demonstrating ROP1 is dispensable for in vitro growth under standard conditions.","method":"Homologous recombination gene replacement with CAT selectable marker, Southern blot confirmation","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct genetic knockout with molecular confirmation, published in high-impact journal, foundational result","pmids":["8235614"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1993,"finding":"ROP1 is discharged from rhoptries at the apical area of the tachyzoite within minutes of invasion and associates with the parasitophorous vacuole membrane; the kinetics of rhoptry secretion differ from dense granule secretion.","method":"Immunofluorescence assay (IFA) and immunoelectron microscopy at sequential stages after infection","journal":"Parasitology research","confidence":"High","confidence_rationale":"Tier 2 / Strong — IFA and immunoelectron microscopy at defined time points, consistent with independent studies","pmids":["8415546"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1995,"finding":"ROP1 knockout parasites show no significant alteration in growth rate, host specificity, invasiveness, or virulence in the RH strain, but their rhoptries display an altered ultrastructure — thinner and homogeneously electron-dense rather than the normal mottled/honeycombed appearance. Complementation with wild-type ROP1 rescues the ultrastructural phenotype, establishing a causal link between ROP1 and rhoptry electron-opacity.","method":"Knockout by homologous recombination, electron microscopy of rhoptry ultrastructure, complementation by co-transfection with cosmid carrying ROP1 plus phleomycin selectable marker, Southern blot","journal":"Molecular and biochemical parasitology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout and rescue (complementation) with defined ultrastructural readout, rigorous controls","pmids":["8719248"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":"RH"}]},{"year":1997,"finding":"During host cell invasion, ROP1 is discharged from rhoptries in a second step (after apical MIC2 release) to form the nascent parasitophorous vacuole (PV); ROP1 is fully discharged into the vacuole by the time invasion is complete, while dense granule markers are released later (peaking ~20 min post-invasion). This sequential secretion implies separate signals govern each compartment's release.","method":"Immunofluorescence, immunoelectron microscopy, and quantitative immunoassays tracking secretion kinetics during invasion of human fibroblasts","journal":"European journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (IFA, IEM, quantitative immunoassay) with temporal resolution, corroborated by independent studies","pmids":["9208224"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1998,"finding":"ROP1 is synthesized as a pre-pro-protein; the pre-sequence and 'pro' region are removed by proteolytic cleavage in the nascent rhoptries of dividing parasites late in the secretory pathway (demonstrated using brefeldin A and reduced-temperature blocks). Processing occurs after the protein enters the secretory pathway.","method":"Engineered ROP1 constructs introduced into ROP1-knockout background, brefeldin A and temperature-block experiments, immunolocalization with epitope-tagged constructs","journal":"Molecular and biochemical parasitology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple engineered constructs, pharmacological and temperature perturbations, epitope-tag immunolocalization in defined genetic background","pmids":["9851605"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1998,"finding":"GFP fusion proteins with ROP1 are correctly targeted to rhoptries in living parasites, demonstrating that ROP1 contains sorting information sufficient to direct a reporter to this organelle.","method":"GFP fusion protein expression and fluorescence microscopy in living T. gondii","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, GFP localization, corroborated by subsequent deletion analyses","pmids":["9657336"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1999,"finding":"The pro-region of ROP1 is cleaved between glutamic acid at position 83 and alanine at position 84 (the pro-mature processing site), determined by mass spectrometry of an engineered form of ROP1. Mature ROP1 lacks substantial post-translational modifications.","method":"Mass spectrometry of engineered ROP1 expressed in T. gondii ROP1-knockout background","journal":"Molecular and biochemical parasitology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mass spectrometric identification of precise cleavage site with engineered substrate, single lab","pmids":["10376998"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2001,"finding":"The ROP1 pro region alone is sufficient to target a heterologous reporter protein (VSG117 amino acids 34–471) to rhoptries. Combined with prior work showing deletion of the pro region does not abolish rhoptry targeting, this demonstrates ROP1 contains at least two independent rhoptry-targeting signals.","method":"Chimeric construct of ROP1 pro region fused to VSG117 reporter, expressed in T. gondii and localized by immunofluorescence","journal":"International journal for parasitology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — domain-swap targeting experiment with heterologous reporter in parasite, single lab with functional readout","pmids":["11513886"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2001,"finding":"The propeptide and a central 146-amino-acid region of ROP1 are sufficient to target GFP to rhoptries; more extensive deletions divert the reporter to the parasitophorous vacuole via dense granules (the default secretory pathway). ROP1-GFP fusion proteins, though correctly targeted, are not secreted during invasion, suggesting rhoptry secretion involves more than simple organelle content release.","method":"Systematic deletion analysis of ROP1-GFP fusion constructs expressed in T. gondii, fluorescence microscopy, invasion secretion assays","journal":"Molecular and biochemical parasitology","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic deletion mapping with GFP reporter in parasite, functional secretion readout, multiple constructs tested","pmids":["11254953"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2002,"finding":"Unprocessed ROP1 (lacking the pro-region cleavage) is effectively targeted to rhoptries and is secreted into the nascent parasitophorous vacuole during invasion, demonstrating that pro-region processing is not required for either rhoptry targeting or secretion.","method":"Expression of engineered unprocessed ROP1 constructs in T. gondii, localization and secretion assays","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single lab, defined genetic constructs with localization and secretion readout","pmids":["12467986"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2003,"finding":"TgSUB2, a subtilisin-like serine proteinase localizing to rhoptries, associates with ROP1 and is a candidate maturase responsible for ROP1 processing. A sequence within TgSUB2 homologous to the ROP1 cleavage site (after Glu) was mutated by site-directed mutagenesis, abolishing TgSUB2 autoprocessing, consistent with TgSUB2 being the rhoptry protein maturase with similar specificity to the ROP1 maturase.","method":"Co-immunoprecipitation/association assay (TgSUB2 with ROP1), site-directed mutagenesis of TgSUB2 cleavage site, rhoptry localization","journal":"Molecular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-localization and association data plus mutagenesis, single lab; direct cleavage of ROP1 by TgSUB2 not reconstituted in vitro","pmids":["12890015"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2021,"finding":"F-actin and the unconventional myosin motor TgMyoF control the directed transport of ROP1-positive vesicles within the T. gondii endomembrane system, and are required for apical positioning of rhoptries.","method":"Live imaging of ROP1-marked vesicles in TgMyoF-depleted and actin-perturbed parasites, fluorescence microscopy","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — live imaging of tagged vesicles with genetic perturbation of TgMyoF, single lab","pmids":["33529198"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2021,"finding":"A P207S mutation in ROP1 confers significant resistance (10.3-fold increased EC50) to the benzoquinone acyl hydrazone compound KG8; expressing ROP1-P207S in parental parasites is sufficient for resistance, and a rop1 knockout strain is insensitive to KG8, implicating ROP1 as a target or resistance determinant for this compound.","method":"In vitro chemical mutagenesis and selection, whole-genome sequencing of resistant clones, expression of ROP1 P207S in parental parasites, EC50 measurements, rop1 knockout phenotyping","journal":"Antimicrobial agents and chemotherapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal approaches (mutagenesis, sequencing, transgenic expression, knockout), single lab; mechanism downstream of ROP1-KG8 interaction not established","pmids":["33361291"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2022,"finding":"ROP1 is essential for parasite virulence and resistance to interferon-gamma-mediated innate immune restriction in both murine and human macrophages. ROP1 affects rhoptry morphology but does not affect rhoptry secretion. ROP1 co-immunoprecipitates with the host cell protein C1QBP, an emerging regulator of innate immune signaling, suggesting ROP1 counteracts innate immunity partly through interaction with C1QBP.","method":"Pooled CRISPR knockout screen in vivo, ROP1 knockout growth assays in murine and human macrophages, rhoptry morphology analysis by electron microscopy, secretion assays, co-immunoprecipitation of ROP1 with C1QBP","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — CRISPR screen plus individual KO validation, multiple cell types, Co-IP identifying host binding partner, multiple orthogonal methods in single rigorous study","pmids":["36476844"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":"Prugniaud; RH"}]},{"year":2025,"finding":"TgROP1 acts as a tether establishing membrane contact sites (MCS) between the host endoplasmic reticulum and the Toxoplasma-containing parasitophorous vacuole. ROP1 mimics a canonical FFAT motif to bind host ER proteins VAPA and VAPB. Loss of VAPA/B abolishes host ER–Toxoplasma MCS and decreases parasite growth, demonstrating these contacts are functionally important for infection.","method":"Fluorescence MCS sensor, CRISPR-based loss-of-function screen, imaging, proteomics, co-immunoprecipitation of ROP1 with VAPA/VAPB, VAPA/B knockout host cells with parasite growth assay","journal":"Nature microbiology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (CRISPR screen, imaging sensor, proteomics, Co-IP, host KO growth assay) in a single rigorous study identifying molecular mechanism","pmids":["41291278"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"TgROP1 is a rhoptry pre-pro-protein that is processed in nascent rhoptries by a subtilisin-like protease (TgSUB2) at a specific Glu83–Ala84 cleavage site; it is transported to rhoptries via at least two independent targeting signals (the pro-region and a central mature-domain region) by a TgMyoF/actin-dependent vesicle transport mechanism, and is discharged into the nascent parasitophorous vacuole membrane during host cell invasion. Beyond its structural role in rhoptry morphology, ROP1 functions as a secreted effector that establishes membrane contact sites between the parasitophorous vacuole and the host endoplasmic reticulum by mimicking a canonical FFAT motif to bind host VAPA/VAPB, and it counteracts interferon-gamma-mediated innate immune restriction at least in part through interaction with the host protein C1QBP."},"narrative":{"mechanistic_narrative":"ROP1 is a Toxoplasma gondii rhoptry protein that is discharged into the nascent parasitophorous vacuole membrane (PVM) during host cell invasion and functions both as a structural determinant of rhoptry organelle morphology and as a secreted effector that manipulates the host cell [PMID:1403988, PMID:8719248, PMID:36476844]. It is synthesized as a pre-pro-protein and processed in the secretory pathway: the pro-region is removed by cleavage between Glu83 and Ala84 within nascent rhoptries [PMID:9851605, PMID:10376998], a maturation step attributed to the rhoptry subtilisin-like serine protease TgSUB2, which associates with ROP1 and shares the relevant cleavage specificity [PMID:12890015]. Rhoptry targeting is directed by at least two independent sorting signals — the pro-region and a central mature-domain region — either of which is sufficient to route a heterologous reporter to rhoptries [PMID:11513886, PMID:11254953], while pro-region processing itself is dispensable for targeting and secretion [PMID:12467986]. ROP1-marked vesicles are delivered through the endomembrane system by an F-actin/TgMyoF-dependent transport mechanism that also positions rhoptries apically [PMID:33529198]. Genetic ablation of ROP1 does not impair in vitro growth or invasion but alters rhoptry ultrastructure, a phenotype reversed by complementation [PMID:8235614, PMID:8719248]. As an effector, ROP1 is required for virulence and for resistance to interferon-gamma-mediated innate immune restriction in macrophages, acting in part through interaction with the host regulator C1QBP [PMID:36476844], and it tethers the host endoplasmic reticulum to the parasitophorous vacuole by mimicking a canonical FFAT motif to bind host VAPA/VAPB, establishing membrane contact sites that support infection [PMID:41291278].","teleology":[{"year":1992,"claim":"Establishing ROP1 as a rhoptry-resident protein linked to invasion answered where the protein resides and hinted at a role in host penetration.","evidence":"cDNA cloning with monoclonal antibody Tg49, recombinant expression, and rhoptry immunolocalization, with antibody inhibition of penetration enhancing factor","pmids":["1542304"],"confidence":"Medium","gaps":["Direct biochemical reconstitution of penetration enhancement not demonstrated","Functional contribution to invasion not tested genetically at this stage"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1993,"claim":"Time-resolved localization established that ROP1 is discharged from rhoptries at the apical tip within minutes of invasion and deposited onto the nascent PVM, with kinetics distinct from dense granules, defining it as a rhoptry secretion marker.","evidence":"Immunoelectron microscopy and IFA at sequential invasion time points in fibroblasts and murine sarcoma cells","pmids":["1403988","8415546"],"confidence":"High","gaps":["Fate of ROP1 after PVM association not resolved","Signals governing rhoptry-specific timing unknown"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1993,"claim":"Generating the first stable T. gondii gene knockout showed ROP1 is a single-copy gene dispensable for in vitro growth, decoupling it from essential viability functions.","evidence":"Homologous-recombination gene replacement with CAT marker, Southern blot confirmation","pmids":["8235614"],"confidence":"High","gaps":["No phenotype identified at this stage","Role in vivo not tested"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1995,"claim":"Knockout-and-complementation defined ROP1's cellular role as a determinant of rhoptry electron-opacity/ultrastructure rather than of growth or invasion.","evidence":"Gene knockout, electron microscopy of rhoptry ultrastructure, and complementation rescue in the RH strain","pmids":["8719248"],"confidence":"High","gaps":["Molecular basis of the ultrastructural change unknown","No detectable virulence phenotype in RH under these conditions"],"attribution":[{"species":"Toxoplasma gondii","strain":"RH"}]},{"year":1997,"claim":"Quantitative secretion kinetics placed ROP1 discharge in a defined second step of invasion, after MIC2 release and before dense granule secretion, implying independent release signals per compartment.","evidence":"IFA, immunoelectron microscopy, and quantitative immunoassays tracking secretion during fibroblast invasion","pmids":["9208224"],"confidence":"High","gaps":["Molecular triggers of sequential secretion unknown"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1999,"claim":"Defining ROP1 as a pre-pro-protein and mapping the Glu83–Ala84 pro-mature cleavage site established the maturation logic of a rhoptry protein.","evidence":"Brefeldin A and temperature-block processing experiments with engineered constructs, plus mass spectrometry mapping the cleavage site","pmids":["9851605","10376998"],"confidence":"High","gaps":["Protease responsible not yet identified","Functional consequence of processing unresolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2001,"claim":"Domain-swap and systematic deletion mapping resolved that ROP1 carries at least two independent rhoptry-targeting signals — the pro-region and a central 146-aa region — with default routing to the PV via dense granules when both are lost.","evidence":"Chimeric pro-region/VSG117 reporter and ROP1-GFP deletion series expressed in T. gondii with fluorescence and secretion assays","pmids":["11513886","11254953","9657336"],"confidence":"High","gaps":["Trans-acting receptors recognizing these signals not identified","ROP1-GFP fusions were not secreted, indicating secretion determinants beyond targeting"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2002,"claim":"Testing unprocessed ROP1 showed pro-region cleavage is required for neither rhoptry targeting nor secretion, separating maturation from trafficking.","evidence":"Expression of engineered unprocessed ROP1 constructs with localization and secretion assays","pmids":["12467986"],"confidence":"Medium","gaps":["Physiological purpose of processing remains undefined","Single-lab construct-based readout"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2003,"claim":"Identifying TgSUB2 as a rhoptry subtilisin that associates with ROP1 and shares its cleavage specificity nominated the maturase responsible for ROP1 processing.","evidence":"Co-immunoprecipitation/association of TgSUB2 with ROP1, site-directed mutagenesis of the TgSUB2 cleavage site, rhoptry localization","pmids":["12890015"],"confidence":"Medium","gaps":["Direct cleavage of ROP1 by TgSUB2 not reconstituted in vitro","Whether TgSUB2 is the sole ROP1 maturase unknown"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2021,"claim":"Live imaging defined the transport machinery, showing F-actin and TgMyoF drive directed movement of ROP1-positive vesicles and apical rhoptry positioning.","evidence":"Live imaging of ROP1-marked vesicles under TgMyoF depletion and actin perturbation","pmids":["33529198"],"confidence":"Medium","gaps":["Adaptors linking ROP1 vesicles to TgMyoF not identified","Single-lab imaging study"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2021,"claim":"A resistance-conferring P207S mutation implicated ROP1 as a target or resistance determinant of the compound KG8, linking the protein to small-molecule susceptibility.","evidence":"Chemical mutagenesis/selection, whole-genome sequencing, transgenic P207S expression, EC50 measurements, and knockout insensitivity","pmids":["33361291"],"confidence":"Medium","gaps":["Mechanism downstream of a ROP1–KG8 interaction not established","Whether ROP1 binds KG8 directly unknown"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2022,"claim":"In vivo CRISPR screening and validation redefined ROP1 as a virulence effector required to counteract interferon-gamma-mediated immune restriction, acting through the host regulator C1QBP independently of rhoptry secretion.","evidence":"Pooled in vivo CRISPR knockout screen, ROP1 knockout growth assays in murine and human macrophages, EM morphology, secretion assays, and Co-IP with C1QBP","pmids":["36476844"],"confidence":"High","gaps":["Mechanism by which C1QBP interaction blunts IFN-gamma restriction not resolved","Reciprocal/structural validation of the ROP1–C1QBP interaction not shown"],"attribution":[{"species":"Toxoplasma gondii","strain":"Prugniaud; RH"}]},{"year":2025,"claim":"Discovery of an FFAT-motif mimic mechanism established ROP1 as a molecular tether that recruits host ER via VAPA/VAPB to form functionally important membrane contact sites with the parasitophorous vacuole.","evidence":"MCS fluorescence sensor, CRISPR loss-of-function screen, imaging, proteomics, Co-IP of ROP1 with VAPA/VAPB, and VAPA/B host knockout growth assay","pmids":["41291278"],"confidence":"High","gaps":["Downstream metabolic or signaling consequence of ER–PV contact sites for the parasite not fully defined","Relationship between the C1QBP and VAPA/B host interactions unresolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"How ROP1's structural role in rhoptry morphology mechanistically relates to its effector functions at the host interface, and how its multiple host partners are coordinated, remains open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model integrating rhoptry-morphology and effector activities","Coordination between C1QBP-dependent immune evasion and VAPA/B-dependent ER tethering unknown","Receptor(s) recognizing ROP1 rhoptry-targeting signals not identified"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":["TGSUB2 (RHOPTRY SUBTILISIN-LIKE PROTEASE, CANDIDATE MATURASE) [#12]","TGMYOF / F-ACTIN (VESICLE TRANSPORT MACHINERY) [#13]","HOST C1QBP [#15]","HOST VAPA / VAPB [#16]"],"other_free_text":["Synthesized as a pre-pro-protein; pro-region cleaved between Glu83 and Ala84 in nascent rhoptries [#6, #8]","Contains at least two independent rhoptry-targeting signals (pro-region and a central 146-aa region); pro-region processing dispensable for targeting/secretion [#9, #10, #11]","ROP1 knockout dispensable for in vitro growth but alters rhoptry ultrastructure, rescued by complementation [#2, #4]","P207S mutation confers resistance to compound KG8, implicating ROP1 as a target/resistance determinant [#14]","Secreted as an effector into the nascent PVM during invasion in a discrete second step after MIC2 release [#5]"]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"9208224","id":"PMC_9208224","title":"Sequential protein secretion from three distinct organelles of Toxoplasma gondii accompanies invasion of human fibroblasts.","date":"1997","source":"European journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/9208224","citation_count":565,"is_preprint":false},{"pmid":"8235614","id":"PMC_8235614","title":"Gene replacement in Toxoplasma gondii with chloramphenicol acetyltransferase as selectable marker.","date":"1993","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/8235614","citation_count":240,"is_preprint":false},{"pmid":"8415546","id":"PMC_8415546","title":"Kinetics and pattern of organelle exocytosis during Toxoplasma gondii/host-cell interaction.","date":"1993","source":"Parasitology research","url":"https://pubmed.ncbi.nlm.nih.gov/8415546","citation_count":158,"is_preprint":false},{"pmid":"9657336","id":"PMC_9657336","title":"Expression, selection, and organellar targeting of the green fluorescent protein in Toxoplasma gondii.","date":"1998","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/9657336","citation_count":152,"is_preprint":false},{"pmid":"12149482","id":"PMC_12149482","title":"Identification of quantitative trait loci controlling acute virulence in Toxoplasma gondii.","date":"2002","source":"Proceedings of the National Academy of Sciences of the United States of 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intracellular parasite: the cellular biology of Toxoplasma gondii.","date":"1995","source":"International journal for parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/8635882","citation_count":55,"is_preprint":false},{"pmid":"19225074","id":"PMC_19225074","title":"GRA2 and ROP1 recombinant antigens as potential markers for detection of Toxoplasma gondii-specific immunoglobulin G in humans with acute toxoplasmosis.","date":"2009","source":"Clinical and vaccine immunology : CVI","url":"https://pubmed.ncbi.nlm.nih.gov/19225074","citation_count":44,"is_preprint":false},{"pmid":"22419676","id":"PMC_22419676","title":"Induction of protective immune responses by a multiantigenic DNA vaccine encoding GRA7 and ROP1 of Toxoplasma gondii.","date":"2012","source":"Clinical and vaccine immunology : CVI","url":"https://pubmed.ncbi.nlm.nih.gov/22419676","citation_count":42,"is_preprint":false},{"pmid":"11513886","id":"PMC_11513886","title":"The pro region of Toxoplasma ROP1 is a rhoptry-targeting 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The predicted polypeptide shows an unusual charge asymmetry with a highly acidic, proline-rich N-terminal domain and a strongly basic C-terminal domain, plus an octapeptide repeat near the midpoint.\",\n      \"method\": \"cDNA library screening with monoclonal antibody Tg49, recombinant protein expression in bacteria, Western blot, immunolocalization of rhoptries\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, antibody inhibition assay plus recombinant expression and localization, but no direct biochemical reconstitution of penetration enhancement\",\n      \"pmids\": [\"1542304\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"ROP1 localizes within the body of rhoptries prior to invasion; immediately after host cell invasion it associates with the parasitophorous vacuole membrane (PVM); within hours post-invasion the amount of ROP1 immunodetectable on the PVM markedly decreases, indicating ROP1 is discharged from rhoptries into the nascent PVM during invasion.\",\n      \"method\": \"Immunoelectron microscopy with monoclonal antibody Tg49 and monospecific rabbit antiserum at multiple time points after invasion of human fibroblasts and TG180 murine sarcoma cells\",\n      \"journal\": \"The Journal of protozoology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct immunolocalization at sequential time points, replicated with two independent antibodies in two host cell types\",\n      \"pmids\": [\"1403988\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"The ROP1 gene is a single-copy gene. Knockout of ROP1 by gene replacement using CAT as selectable marker was achieved, establishing the first stable gene knockout in Toxoplasma gondii and demonstrating ROP1 is dispensable for in vitro growth under standard conditions.\",\n      \"method\": \"Homologous recombination gene replacement with CAT selectable marker, Southern blot confirmation\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct genetic knockout with molecular confirmation, published in high-impact journal, foundational result\",\n      \"pmids\": [\"8235614\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"ROP1 is discharged from rhoptries at the apical area of the tachyzoite within minutes of invasion and associates with the parasitophorous vacuole membrane; the kinetics of rhoptry secretion differ from dense granule secretion.\",\n      \"method\": \"Immunofluorescence assay (IFA) and immunoelectron microscopy at sequential stages after infection\",\n      \"journal\": \"Parasitology research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — IFA and immunoelectron microscopy at defined time points, consistent with independent studies\",\n      \"pmids\": [\"8415546\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"ROP1 knockout parasites show no significant alteration in growth rate, host specificity, invasiveness, or virulence in the RH strain, but their rhoptries display an altered ultrastructure — thinner and homogeneously electron-dense rather than the normal mottled/honeycombed appearance. Complementation with wild-type ROP1 rescues the ultrastructural phenotype, establishing a causal link between ROP1 and rhoptry electron-opacity.\",\n      \"method\": \"Knockout by homologous recombination, electron microscopy of rhoptry ultrastructure, complementation by co-transfection with cosmid carrying ROP1 plus phleomycin selectable marker, Southern blot\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout and rescue (complementation) with defined ultrastructural readout, rigorous controls\",\n      \"pmids\": [\"8719248\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"RH\"}]\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"During host cell invasion, ROP1 is discharged from rhoptries in a second step (after apical MIC2 release) to form the nascent parasitophorous vacuole (PV); ROP1 is fully discharged into the vacuole by the time invasion is complete, while dense granule markers are released later (peaking ~20 min post-invasion). This sequential secretion implies separate signals govern each compartment's release.\",\n      \"method\": \"Immunofluorescence, immunoelectron microscopy, and quantitative immunoassays tracking secretion kinetics during invasion of human fibroblasts\",\n      \"journal\": \"European journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (IFA, IEM, quantitative immunoassay) with temporal resolution, corroborated by independent studies\",\n      \"pmids\": [\"9208224\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"ROP1 is synthesized as a pre-pro-protein; the pre-sequence and 'pro' region are removed by proteolytic cleavage in the nascent rhoptries of dividing parasites late in the secretory pathway (demonstrated using brefeldin A and reduced-temperature blocks). Processing occurs after the protein enters the secretory pathway.\",\n      \"method\": \"Engineered ROP1 constructs introduced into ROP1-knockout background, brefeldin A and temperature-block experiments, immunolocalization with epitope-tagged constructs\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple engineered constructs, pharmacological and temperature perturbations, epitope-tag immunolocalization in defined genetic background\",\n      \"pmids\": [\"9851605\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"GFP fusion proteins with ROP1 are correctly targeted to rhoptries in living parasites, demonstrating that ROP1 contains sorting information sufficient to direct a reporter to this organelle.\",\n      \"method\": \"GFP fusion protein expression and fluorescence microscopy in living T. gondii\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, GFP localization, corroborated by subsequent deletion analyses\",\n      \"pmids\": [\"9657336\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The pro-region of ROP1 is cleaved between glutamic acid at position 83 and alanine at position 84 (the pro-mature processing site), determined by mass spectrometry of an engineered form of ROP1. Mature ROP1 lacks substantial post-translational modifications.\",\n      \"method\": \"Mass spectrometry of engineered ROP1 expressed in T. gondii ROP1-knockout background\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mass spectrometric identification of precise cleavage site with engineered substrate, single lab\",\n      \"pmids\": [\"10376998\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The ROP1 pro region alone is sufficient to target a heterologous reporter protein (VSG117 amino acids 34–471) to rhoptries. Combined with prior work showing deletion of the pro region does not abolish rhoptry targeting, this demonstrates ROP1 contains at least two independent rhoptry-targeting signals.\",\n      \"method\": \"Chimeric construct of ROP1 pro region fused to VSG117 reporter, expressed in T. gondii and localized by immunofluorescence\",\n      \"journal\": \"International journal for parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain-swap targeting experiment with heterologous reporter in parasite, single lab with functional readout\",\n      \"pmids\": [\"11513886\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The propeptide and a central 146-amino-acid region of ROP1 are sufficient to target GFP to rhoptries; more extensive deletions divert the reporter to the parasitophorous vacuole via dense granules (the default secretory pathway). ROP1-GFP fusion proteins, though correctly targeted, are not secreted during invasion, suggesting rhoptry secretion involves more than simple organelle content release.\",\n      \"method\": \"Systematic deletion analysis of ROP1-GFP fusion constructs expressed in T. gondii, fluorescence microscopy, invasion secretion assays\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic deletion mapping with GFP reporter in parasite, functional secretion readout, multiple constructs tested\",\n      \"pmids\": [\"11254953\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Unprocessed ROP1 (lacking the pro-region cleavage) is effectively targeted to rhoptries and is secreted into the nascent parasitophorous vacuole during invasion, demonstrating that pro-region processing is not required for either rhoptry targeting or secretion.\",\n      \"method\": \"Expression of engineered unprocessed ROP1 constructs in T. gondii, localization and secretion assays\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single lab, defined genetic constructs with localization and secretion readout\",\n      \"pmids\": [\"12467986\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"TgSUB2, a subtilisin-like serine proteinase localizing to rhoptries, associates with ROP1 and is a candidate maturase responsible for ROP1 processing. A sequence within TgSUB2 homologous to the ROP1 cleavage site (after Glu) was mutated by site-directed mutagenesis, abolishing TgSUB2 autoprocessing, consistent with TgSUB2 being the rhoptry protein maturase with similar specificity to the ROP1 maturase.\",\n      \"method\": \"Co-immunoprecipitation/association assay (TgSUB2 with ROP1), site-directed mutagenesis of TgSUB2 cleavage site, rhoptry localization\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-localization and association data plus mutagenesis, single lab; direct cleavage of ROP1 by TgSUB2 not reconstituted in vitro\",\n      \"pmids\": [\"12890015\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"F-actin and the unconventional myosin motor TgMyoF control the directed transport of ROP1-positive vesicles within the T. gondii endomembrane system, and are required for apical positioning of rhoptries.\",\n      \"method\": \"Live imaging of ROP1-marked vesicles in TgMyoF-depleted and actin-perturbed parasites, fluorescence microscopy\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live imaging of tagged vesicles with genetic perturbation of TgMyoF, single lab\",\n      \"pmids\": [\"33529198\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A P207S mutation in ROP1 confers significant resistance (10.3-fold increased EC50) to the benzoquinone acyl hydrazone compound KG8; expressing ROP1-P207S in parental parasites is sufficient for resistance, and a rop1 knockout strain is insensitive to KG8, implicating ROP1 as a target or resistance determinant for this compound.\",\n      \"method\": \"In vitro chemical mutagenesis and selection, whole-genome sequencing of resistant clones, expression of ROP1 P207S in parental parasites, EC50 measurements, rop1 knockout phenotyping\",\n      \"journal\": \"Antimicrobial agents and chemotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal approaches (mutagenesis, sequencing, transgenic expression, knockout), single lab; mechanism downstream of ROP1-KG8 interaction not established\",\n      \"pmids\": [\"33361291\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ROP1 is essential for parasite virulence and resistance to interferon-gamma-mediated innate immune restriction in both murine and human macrophages. ROP1 affects rhoptry morphology but does not affect rhoptry secretion. ROP1 co-immunoprecipitates with the host cell protein C1QBP, an emerging regulator of innate immune signaling, suggesting ROP1 counteracts innate immunity partly through interaction with C1QBP.\",\n      \"method\": \"Pooled CRISPR knockout screen in vivo, ROP1 knockout growth assays in murine and human macrophages, rhoptry morphology analysis by electron microscopy, secretion assays, co-immunoprecipitation of ROP1 with C1QBP\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — CRISPR screen plus individual KO validation, multiple cell types, Co-IP identifying host binding partner, multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"36476844\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"Prugniaud; RH\"}]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TgROP1 acts as a tether establishing membrane contact sites (MCS) between the host endoplasmic reticulum and the Toxoplasma-containing parasitophorous vacuole. ROP1 mimics a canonical FFAT motif to bind host ER proteins VAPA and VAPB. Loss of VAPA/B abolishes host ER–Toxoplasma MCS and decreases parasite growth, demonstrating these contacts are functionally important for infection.\",\n      \"method\": \"Fluorescence MCS sensor, CRISPR-based loss-of-function screen, imaging, proteomics, co-immunoprecipitation of ROP1 with VAPA/VAPB, VAPA/B knockout host cells with parasite growth assay\",\n      \"journal\": \"Nature microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (CRISPR screen, imaging sensor, proteomics, Co-IP, host KO growth assay) in a single rigorous study identifying molecular mechanism\",\n      \"pmids\": [\"41291278\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"TgROP1 is a rhoptry pre-pro-protein that is processed in nascent rhoptries by a subtilisin-like protease (TgSUB2) at a specific Glu83–Ala84 cleavage site; it is transported to rhoptries via at least two independent targeting signals (the pro-region and a central mature-domain region) by a TgMyoF/actin-dependent vesicle transport mechanism, and is discharged into the nascent parasitophorous vacuole membrane during host cell invasion. Beyond its structural role in rhoptry morphology, ROP1 functions as a secreted effector that establishes membrane contact sites between the parasitophorous vacuole and the host endoplasmic reticulum by mimicking a canonical FFAT motif to bind host VAPA/VAPB, and it counteracts interferon-gamma-mediated innate immune restriction at least in part through interaction with the host protein C1QBP.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ROP1 is a Toxoplasma gondii rhoptry protein that is discharged into the nascent parasitophorous vacuole membrane (PVM) during host cell invasion and functions both as a structural determinant of rhoptry organelle morphology and as a secreted effector that manipulates the host cell [#1, #4, #15]. It is synthesized as a pre-pro-protein and processed in the secretory pathway: the pro-region is removed by cleavage between Glu83 and Ala84 within nascent rhoptries [#6, #8], a maturation step attributed to the rhoptry subtilisin-like serine protease TgSUB2, which associates with ROP1 and shares the relevant cleavage specificity [#12]. Rhoptry targeting is directed by at least two independent sorting signals \\u2014 the pro-region and a central mature-domain region \\u2014 either of which is sufficient to route a heterologous reporter to rhoptries [#9, #10], while pro-region processing itself is dispensable for targeting and secretion [#11]. ROP1-marked vesicles are delivered through the endomembrane system by an F-actin/TgMyoF-dependent transport mechanism that also positions rhoptries apically [#13]. Genetic ablation of ROP1 does not impair in vitro growth or invasion but alters rhoptry ultrastructure, a phenotype reversed by complementation [#2, #4]. As an effector, ROP1 is required for virulence and for resistance to interferon-gamma-mediated innate immune restriction in macrophages, acting in part through interaction with the host regulator C1QBP [#15], and it tethers the host endoplasmic reticulum to the parasitophorous vacuole by mimicking a canonical FFAT motif to bind host VAPA/VAPB, establishing membrane contact sites that support infection [#16].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Establishing ROP1 as a rhoptry-resident protein linked to invasion answered where the protein resides and hinted at a role in host penetration.\",\n      \"evidence\": \"cDNA cloning with monoclonal antibody Tg49, recombinant expression, and rhoptry immunolocalization, with antibody inhibition of penetration enhancing factor\",\n      \"pmids\": [\"1542304\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct biochemical reconstitution of penetration enhancement not demonstrated\", \"Functional contribution to invasion not tested genetically at this stage\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Time-resolved localization established that ROP1 is discharged from rhoptries at the apical tip within minutes of invasion and deposited onto the nascent PVM, with kinetics distinct from dense granules, defining it as a rhoptry secretion marker.\",\n      \"evidence\": \"Immunoelectron microscopy and IFA at sequential invasion time points in fibroblasts and murine sarcoma cells\",\n      \"pmids\": [\"1403988\", \"8415546\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Fate of ROP1 after PVM association not resolved\", \"Signals governing rhoptry-specific timing unknown\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Generating the first stable T. gondii gene knockout showed ROP1 is a single-copy gene dispensable for in vitro growth, decoupling it from essential viability functions.\",\n      \"evidence\": \"Homologous-recombination gene replacement with CAT marker, Southern blot confirmation\",\n      \"pmids\": [\"8235614\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No phenotype identified at this stage\", \"Role in vivo not tested\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Knockout-and-complementation defined ROP1's cellular role as a determinant of rhoptry electron-opacity/ultrastructure rather than of growth or invasion.\",\n      \"evidence\": \"Gene knockout, electron microscopy of rhoptry ultrastructure, and complementation rescue in the RH strain\",\n      \"pmids\": [\"8719248\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Molecular basis of the ultrastructural change unknown\", \"No detectable virulence phenotype in RH under these conditions\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"RH\"}]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Quantitative secretion kinetics placed ROP1 discharge in a defined second step of invasion, after MIC2 release and before dense granule secretion, implying independent release signals per compartment.\",\n      \"evidence\": \"IFA, immunoelectron microscopy, and quantitative immunoassays tracking secretion during fibroblast invasion\",\n      \"pmids\": [\"9208224\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Molecular triggers of sequential secretion unknown\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defining ROP1 as a pre-pro-protein and mapping the Glu83\\u2013Ala84 pro-mature cleavage site established the maturation logic of a rhoptry protein.\",\n      \"evidence\": \"Brefeldin A and temperature-block processing experiments with engineered constructs, plus mass spectrometry mapping the cleavage site\",\n      \"pmids\": [\"9851605\", \"10376998\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Protease responsible not yet identified\", \"Functional consequence of processing unresolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Domain-swap and systematic deletion mapping resolved that ROP1 carries at least two independent rhoptry-targeting signals \\u2014 the pro-region and a central 146-aa region \\u2014 with default routing to the PV via dense granules when both are lost.\",\n      \"evidence\": \"Chimeric pro-region/VSG117 reporter and ROP1-GFP deletion series expressed in T. gondii with fluorescence and secretion assays\",\n      \"pmids\": [\"11513886\", \"11254953\", \"9657336\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Trans-acting receptors recognizing these signals not identified\", \"ROP1-GFP fusions were not secreted, indicating secretion determinants beyond targeting\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Testing unprocessed ROP1 showed pro-region cleavage is required for neither rhoptry targeting nor secretion, separating maturation from trafficking.\",\n      \"evidence\": \"Expression of engineered unprocessed ROP1 constructs with localization and secretion assays\",\n      \"pmids\": [\"12467986\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Physiological purpose of processing remains undefined\", \"Single-lab construct-based readout\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identifying TgSUB2 as a rhoptry subtilisin that associates with ROP1 and shares its cleavage specificity nominated the maturase responsible for ROP1 processing.\",\n      \"evidence\": \"Co-immunoprecipitation/association of TgSUB2 with ROP1, site-directed mutagenesis of the TgSUB2 cleavage site, rhoptry localization\",\n      \"pmids\": [\"12890015\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct cleavage of ROP1 by TgSUB2 not reconstituted in vitro\", \"Whether TgSUB2 is the sole ROP1 maturase unknown\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Live imaging defined the transport machinery, showing F-actin and TgMyoF drive directed movement of ROP1-positive vesicles and apical rhoptry positioning.\",\n      \"evidence\": \"Live imaging of ROP1-marked vesicles under TgMyoF depletion and actin perturbation\",\n      \"pmids\": [\"33529198\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Adaptors linking ROP1 vesicles to TgMyoF not identified\", \"Single-lab imaging study\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A resistance-conferring P207S mutation implicated ROP1 as a target or resistance determinant of the compound KG8, linking the protein to small-molecule susceptibility.\",\n      \"evidence\": \"Chemical mutagenesis/selection, whole-genome sequencing, transgenic P207S expression, EC50 measurements, and knockout insensitivity\",\n      \"pmids\": [\"33361291\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Mechanism downstream of a ROP1\\u2013KG8 interaction not established\", \"Whether ROP1 binds KG8 directly unknown\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"In vivo CRISPR screening and validation redefined ROP1 as a virulence effector required to counteract interferon-gamma-mediated immune restriction, acting through the host regulator C1QBP independently of rhoptry secretion.\",\n      \"evidence\": \"Pooled in vivo CRISPR knockout screen, ROP1 knockout growth assays in murine and human macrophages, EM morphology, secretion assays, and Co-IP with C1QBP\",\n      \"pmids\": [\"36476844\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Mechanism by which C1QBP interaction blunts IFN-gamma restriction not resolved\", \"Reciprocal/structural validation of the ROP1\\u2013C1QBP interaction not shown\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"Prugniaud; RH\"}]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Discovery of an FFAT-motif mimic mechanism established ROP1 as a molecular tether that recruits host ER via VAPA/VAPB to form functionally important membrane contact sites with the parasitophorous vacuole.\",\n      \"evidence\": \"MCS fluorescence sensor, CRISPR loss-of-function screen, imaging, proteomics, Co-IP of ROP1 with VAPA/VAPB, and VAPA/B host knockout growth assay\",\n      \"pmids\": [\"41291278\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Downstream metabolic or signaling consequence of ER\\u2013PV contact sites for the parasite not fully defined\", \"Relationship between the C1QBP and VAPA/B host interactions unresolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ROP1's structural role in rhoptry morphology mechanistically relates to its effector functions at the host interface, and how its multiple host partners are coordinated, remains open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No structural model integrating rhoptry-morphology and effector activities\", \"Coordination between C1QBP-dependent immune evasion and VAPA/B-dependent ER tethering unknown\", \"Receptor(s) recognizing ROP1 rhoptry-targeting signals not identified\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140768\", \"supporting_discovery_ids\": [16], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0005515\", \"supporting_discovery_ids\": [15, 16], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020008\", \"supporting_discovery_ids\": [0, 1, 4, 7], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0020002\", \"supporting_discovery_ids\": [1, 3, 5], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0052572\", \"supporting_discovery_ids\": [15], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"Prugniaud; RH\"}]},\n      {\"term_id\": \"GO:0034389\", \"supporting_discovery_ids\": [16], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"TgSUB2 (rhoptry subtilisin-like protease, candidate maturase) [#12]\",\n      \"TgMyoF / F-actin (vesicle transport machinery) [#13]\",\n      \"Host C1QBP [#15]\",\n      \"Host VAPA / VAPB [#16]\"\n    ],\n    \"other_free_text\": [\n      \"Synthesized as a pre-pro-protein; pro-region cleaved between Glu83 and Ala84 in nascent rhoptries [#6, #8]\",\n      \"Contains at least two independent rhoptry-targeting signals (pro-region and a central 146-aa region); pro-region processing dispensable for targeting/secretion [#9, #10, #11]\",\n      \"ROP1 knockout dispensable for in vitro growth but alters rhoptry ultrastructure, rescued by complementation [#2, #4]\",\n      \"P207S mutation confers resistance to compound KG8, implicating ROP1 as a target/resistance determinant [#14]\",\n      \"Secreted as an effector into the nascent PVM during invasion in a discrete second step after MIC2 release [#5]\"\n    ]\n  },\n  \"strain_conflicts\": []\n}\n```","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_309590","name":"ROP1","product":"rhoptry protein ROP1","uniprot_acc":"A0A125YP48","chromosome":"TGME49_chrXI","start_pos":746185},{"strain":"GT1","gene_id":"TGGT1_309590","name":null,"product":"rhoptry protein ROP1","uniprot_acc":null,"chromosome":"TGGT1_chrXI","start_pos":707942},{"strain":"RH88","gene_id":"TGRH88_049170","name":null,"product":"rhoptry protein ROP1","uniprot_acc":null,"chromosome":"CM023092","start_pos":793899},{"strain":"VEG","gene_id":"TGVEG_309590","name":null,"product":"rhoptry protein ROP1","uniprot_acc":"B6KA38","chromosome":"TGVEG_chrXI","start_pos":754757}]}