Affinage · Toxoplasma gondii

ROP18

rhoptry protein ROP18 · UniProt A0A125YQL1

Annotated
2026-09-05
100 papers in source corpus 33 papers cited in narrative 32 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

ROP18 is a polymorphic serine-threonine protein kinase secreted from Toxoplasma gondii rhoptries into the host cell during invasion, where it acts as a virulence effector that subverts host innate immunity and is essential for both acute pathogenesis and chronic infection (PMID:17170305, PMID:17170306, PMID:27165797). Following secretion it relocalizes to the cytosolic face of the parasitophorous vacuole membrane (PVM), a tethering event mediated by its arginine-rich N-terminal domain; loss of this domain abolishes PVM association, IRG phosphorylation, and virulence despite normal secretion (PMID:17305424, PMID:22906355). Its central function is the phosphorylation of mouse immunity-related GTPases (IRGs), specifically Irga6, on two conserved switch-I threonines, which biochemically inactivates the GTPase and prevents its accumulation on the PVM, thereby blocking clearance in IFN-γ-activated macrophages (PMID:21147463, PMID:21203588, PMID:26247512). This activity operates within a multiprotein PVM complex: the ROP5 pseudokinase both regulates ROP18 catalytic activity and allosterically primes IRG substrates for phosphorylation, the co-active kinase ROP17 targets adjacent switch-I threonines, and dense granule proteins GRA7 and GRA60 act in the same IRG-resistance pathway (PMID:22802726, PMID:23144612, PMID:24390541, PMID:24832449, PMID:33040458). ROP18 kinase activity is regulated by autophosphorylation of its N-terminal extension, which relieves autoinhibition, and a second ligand-binding pocket outside the active site independently contributes to virulence (PMID:19197235, PMID:24129568). Beyond IRG evasion, ROP18 phosphorylates and destabilizes host targets including ATF6β to suppress CD8 T-cell responses, and phosphorylates Smad1, RTN1-C, and vimentin, linking it to modulation of host signalling, ER stress, and apoptosis (PMID:21670204, PMID:29784816, PMID:29104504, PMID:28087594). Allelic and expression polymorphism—including loss of an upstream regulatory element in the type III lineage—accounts for much of the strain-dependent variation in virulence (PMID:19266027).

Mechanistic history

Synthesis pass · year-by-year structured walk · 23 steps
  1. 2006 High

    Established that a single secreted parasite kinase can determine acute virulence, defining ROP18 as a genetically mapped effector rather than a passive antigen.

    Evidence QTL mapping and positional cloning with transfection of the virulent allele into a nonpathogenic type III strain and kinase-dead mutant analysis in a mouse virulence assay

    PMID:17170305 PMID:17170306

    Open questions at the time
    • Host substrate(s) not yet identified
    • Mechanism connecting kinase activity to virulence unknown
    • Subcellular site of action not resolved
  2. 2007 High

    Confirmed ROP18 is an intrinsically active serine-threonine kinase and localized it to rhoptries with re-targeting to the PVM upon invasion, placing the enzyme at the host-parasite interface.

    Evidence In vitro kinase assay with recombinant catalytic domain, transgenic overexpression with kinase-dead control, and immunofluorescence/fractionation in RH

    PMID:17305424

    Open questions at the time
    • Identity of the ~70 kDa substrate not established
    • Mechanism of PVM re-localization unknown
    • No host substrate identified
  3. 2009 High

    Defined how the kinase is switched on, showing autophosphorylation of the N-terminal extension relieves autoinhibition of the ATP-binding pocket.

    Evidence X-ray structures of ROP2/ROP8 pseudokinases used for homology modelling plus autophosphorylation assays, mutagenesis, and mass spectrometry

    PMID:19197235

    Open questions at the time
    • Autoinhibition model later challenged by direct ROP18 kinase structure
    • Physiological ROP2/ROP8 phosphorylation significance unclear
  4. 2009 Medium

    Explained natural virulence variation by linking three ROP18 alleles and an upstream regulatory element to expression differences, showing loss of the element silenced ROP18 in the ancient type III lineage.

    Evidence Population sequencing of natural isolates, promoter deletion, expression measurement, and virulence assays across strains

    PMID:19266027

    Open questions at the time
    • Molecular basis of allelic activity differences not fully resolved
    • Regulatory element trans-factors unknown
  5. 2010 High

    Identified the key host substrate class, showing ROP18 phosphorylates IRGs (Irga6) on switch-I threonines to inactivate them and block PVM recruitment, defining the mechanism of macrophage evasion.

    Evidence Co-IP, in vitro phosphorylation with substrate profiling, Δrop18 knockout, IFN-γ macrophage clearance and mouse virulence assays; phospho-site mapping and GTPase activity readouts

    PMID:21147463 PMID:21203588

    Open questions at the time
    • Full IRG substrate range not yet delimited
    • Requirement for co-factors not yet appreciated
    • Human-cell relevance unaddressed
  6. 2011 High

    Extended ROP18's targets beyond IRGs to the host ER transcription factor ATF6β, linking the kinase to suppression of adaptive (CD8 T-cell) immunity.

    Evidence Reciprocal Co-IP, mammalian overexpression, Δrop18, proteasome inhibition, and ATF6β-KO mouse challenge in RH

    PMID:21670204

    Open questions at the time
    • Direct phospho-site on ATF6β not mapped
    • E3 ligase mediating degradation unknown
  7. 2011 High

    Placed ROP18 genetically upstream of GBP-mediated killing and revealed its dependence on ROP5, showing both are required to prevent Gbp1 recruitment.

    Evidence Δrop18/Δrop5 knockouts, Gbp1−/− macrophages and mice, systematic ROP16/ROP18/GRA15 knockout comparison with confocal imaging

    PMID:23633952 PMID:21931713

    Open questions at the time
    • Direct versus indirect effect on GBPs vs IRGs not separated
    • Mechanism of ROP5 dependence not yet defined
  8. 2012 High

    Resolved the co-factor requirement, showing ROP5 pseudokinases directly regulate ROP18 catalytic activity and allosterically prime IRG substrates, and that PVM tethering via the arginine-rich N-terminus is essential for function.

    Evidence Allelic swaps, structural/biochemical IRG binding and oligomerization assays, in vitro kinase activity assays, N-terminal deletion mutagenesis with virulence readouts, and human vs mouse cell comparison

    PMID:22761577 PMID:22802726 PMID:23144612 PMID:22906355

    Open questions at the time
    • Structural detail of the ROP5–ROP18–IRG ternary arrangement incomplete
    • Human-cell IRG-independent function undefined at this stage
  9. 2013 High

    Refined the activation model by determining the ROP18 kinase-domain crystal structure, which contradicted the earlier autoinhibition model and revealed a second ligand-binding pocket required for virulence.

    Evidence X-ray crystallography with sucrose-bound pocket, mutagenesis of the second pocket, and mouse virulence assays in RH

    PMID:24129568

    Open questions at the time
    • Physiological ligand of the second pocket unknown
    • Reconciliation with N-terminal autophosphorylation model incomplete
  10. 2013 Medium

    Demonstrated cross-species conservation and regulatory-element origin, showing H. hammondi ROP18 complements T. gondii and that the promoter element silenced in type III was ancestrally active.

    Evidence Genomic sequencing, cross-species complementation in T. gondii, promoter deletion, and virulence assays

    PMID:23589877

    Open questions at the time
    • Functional divergence of H. hammondi complex components unresolved
  11. 2014 High

    Defined the full PVM virulence complex, showing ROP18 associates with ROP5, ROP17, ROP2/ROP8, and GRA7, and that ROP17 and ROP18 cooperatively phosphorylate adjacent switch-I threonines.

    Evidence Tandem affinity purification-MS in T. gondii, Co-IP, in vitro kinase assays, single and double knockouts, IRG polymerization and recruitment assays in RH

    PMID:24390541 PMID:24832449

    Open questions at the time
    • Stoichiometry and assembly order of the complex not resolved
    • Division of labor among kinases only partially defined
  12. 2014 Medium

    Showed via heterologous gain-of-function that ROP18 kinase activity is the decisive functional difference distinguishing virulent T. gondii from related parasites carrying a ROP18 pseudogene.

    Evidence Transgenic TgROP18 expression in Neospora caninum with mouse virulence and IRG phosphorylation assays

    PMID:24927100

    Open questions at the time
    • Whether N. caninum provides all cognate co-factors unclear
  13. 2015 High

    Established Irga6 as the specific ROP18 target and clarified GRA7's role, showing GRA7 tethers to the PVM via ROP5 and enhances Irga6 phosphorylation.

    Evidence Co-IP (GRA7–ROP5), in vitro phosphorylation against a panel of IRG proteins, knockouts, and mouse virulence assays in RH

    PMID:26247512

    Open questions at the time
    • Why other IRGs are not phosphorylated not fully explained mechanistically
  14. 2015 High

    Broadened the evolutionary significance of ROP18 by showing complete virulence attenuation upon deletion across divergent South American strains, contrasting with partial attenuation in RH.

    Evidence CRISPR-Cas9 deletion and complementation in type 4, 8, and 10 strains with mouse virulence assays

    PMID:26291965

    Open questions at the time
    • Strain-specific co-factor differences underlying the phenotype not resolved
  15. 2016 Medium

    Uncovered a kinase-independent, PVM-localization-dependent role for ROP18 in host manipulation, distinct from its IRG-phosphorylating function.

    Evidence Δrop18 and PVM-localization mutants in an antitumor immunity mouse ovarian cancer model

    PMID:27447180

    Open questions at the time
    • Molecular effector of the kinase-independent function unknown
  16. 2016 High

    Extended ROP18's essentiality to chronic infection, showing kinase activity and PVM association are required for IRG resistance and cyst formation in type II.

    Evidence Systematic ROPK-locus deletions, kinase-dead and localization mutants, and cyst-burden/virulence assays in ME49 (type II)

    PMID:27165797

    Open questions at the time
    • Type II vs type I mechanistic differences in cyst context not fully resolved
  17. 2017 Medium

    Systematically expanded the host substrate repertoire via proteome-array screening, identifying Smad1 (Ser-187), p53, p38, and UBE2N and vimentin as ROP18 targets linked to degradation and invasion control.

    Evidence Human proteome array probed with recombinant ROP18, in vitro kinase assays, phospho-site mutagenesis, proteasome inhibition, and vimentin-KO infection assays in RH

    PMID:28087594 PMID:29104504

    Open questions at the time
    • Which substrates are phosphorylated in vivo during infection not established
    • Physiological consequences of most targets not fully mapped
  18. 2018 Medium

    Connected ROP18 to CNS pathology by identifying RTN1-C as a phospho-substrate whose modification triggers ER-stress apoptosis in neural cells.

    Evidence Proteome-array pull-down, Co-IP, in vitro phosphorylation with site mapping, ER-stress markers, and HDAC activity assays in RH

    PMID:29784816

    Open questions at the time
    • In vivo relevance to encephalitis not directly established
    • Link between phosphorylation and GRP78 acetylation mechanistically incomplete
  19. 2019 Medium

    Revealed a cell-type-specific anti-apoptotic function, showing ROP18 interacts with the ATP-gated channel P2X1 to block mitochondrial apoptosis.

    Evidence FRET, Co-IP, flow cytometry for apoptosis/Ca2+ influx, and apoptosis-marker western blotting in P2X1-expressing SF268 cells in RH

    PMID:31164145

    Open questions at the time
    • Whether interaction requires kinase activity unclear
    • In vivo relevance not tested
  20. 2020 Medium

    Added GRA60 to the IRG-resistance pathway, showing it associates with ROP18 and its loss phenocopies Δrop5 for IRG recruitment.

    Evidence Co-IP, single and double knockouts, IRG (Irgb10/Irga6) recruitment confocal assays, and virulence assays in RH

    PMID:33040458

    Open questions at the time
    • Direct biochemical role of GRA60 in the complex undefined
  21. 2021 Medium

    Defined ROP18-mediated evasion in human cells by targeting TRIM21 for lysosomal degradation, reducing PVM ubiquitination and parasite killing.

    Evidence Co-IP, degradation and lysosomal-inhibitor assays, TRIM21 knockdown/overexpression, and PVM ubiquitination confocal microscopy for TgROP18I in RH

    PMID:34124071

    Open questions at the time
    • Direct phosphorylation of TRIM21 not conclusively mapped
    • Relationship to IRG-independent human resistance incomplete
  22. 2022 Medium

    Showed ROP18 suppresses type I interferon and autophagic PVM targeting by interacting with IRF3, p62, and TRAF6 in both murine and human cells.

    Evidence Co-IP, IFN-β reporter assay, p62 phosphorylation and PVM ubiquitin/LC3 western blotting and confocal microscopy for TgROP18I

    PMID:35084749

    Open questions at the time
    • Whether these interactions require kinase activity not resolved
    • In vivo contribution not quantified
  23. 2025 Medium

    Linked ROP18 to reproductive pathology, showing it lowers CD73 on decidual macrophages via LSD1/SNAIL1 signalling to impair maternal-fetal immune tolerance.

    Evidence RH-Δrop18 infection of pregnant mice and human decidual tissue, flow cytometry, western blotting, and ChIP assays in RH

    PMID:39994736

    Open questions at the time
    • Whether the effect is direct or downstream of general infection burden not fully separated
    • Kinase-dependence not established

Open questions

Synthesis pass · forward-looking unresolved questions
  • How ROP18's many reported host substrates and interactions (Smad1, p53, p38, RTN1-C, vimentin, TRIM21, IRF3, P2X1) are prioritized and coordinated in vivo, and how kinase-dependent versus kinase-independent PVM functions are integrated, remain unresolved.
  • No unified model separating in-vivo-relevant substrates from proteome-array hits
  • Structural basis reconciling autophosphorylation activation with the crystal-structure autoinhibition rebuttal not settled
  • Kinase-independent PVM effector remains unidentified

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
ATF6Β (HOST, DEGRADED)GRA60 (DENSE GRANULE PROTEIN, IRG-RESISTANCE PATHWAY)GRA7 (DENSE GRANULE PROTEIN, IRGA6 BINDING)IRF3, P62, TRAF6 (HOST SIGNALLING)IRGA6 / IMMUNITY-RELATED GTPASES (SUBSTRATE)P2X1 (HOST ION CHANNEL)ROP17 (CO-ACTIVE KINASE, ADJACENT SWITCH-I THREONINES)ROP5 (PSEUDOKINASE CO-FACTOR AND CATALYTIC REGULATOR)RTN1-C (HOST SUBSTRATE)SMAD1 / P53 / P38 / UBE2N (HOST SUBSTRATES)TRIM21 (HOST, DEGRADED)VIMENTIN (HOST SUBSTRATE)
Complex memberships
ROP18–GRA60 IRG-resistance associationROP18–ROP2/ROP8–GRA7 PVM complexROP18–ROP5 pseudokinase–ROP17–GRA7 PVM virulence complex

Evidence

Reading pass · 32 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2006 ROP18 is a polymorphic serine-threonine kinase secreted into the host cell during parasite invasion. Transfection of the virulent ROP18 allele into a nonpathogenic type III strain increased growth and enhanced mortality by 4–5 logs, and these attributes required kinase activity, establishing ROP18 as a secreted effector kinase essential for acute virulence. Genetic mapping (QTL), positional cloning, transfection/complementation in type III strain, kinase-dead mutant analysis, mouse virulence assay Science High 17170305 17170306
2007 Recombinant ROP18 catalytic domain (aa 243–539) possesses serine-threonine protein kinase activity in vitro and phosphorylates a ~70 kDa tachyzoite substrate. Overexpression of ROP18 in transgenic parasites dramatically increases intra-vacuolar parasite multiplication rate in a kinase-activity-dependent manner. ROP18 localises to rhoptries and re-localises to the parasitophorous vacuole membrane (PVM) upon invasion. In vitro kinase assay with recombinant protein, transgenic overexpression, kinase-dead mutant, immunofluorescence/subcellular fractionation PLoS pathogens High 17305424
2009 X-ray crystal structures of pseudokinases ROP2 and ROP8 provided a template for homology modelling of ROP18. Autophosphorylation of key residues in the N-terminal extension activates ROP18; this phosphorylated N-terminus relieves autoinhibition caused by aliphatic side-chain insertion into the ATP-binding pocket. Mutagenesis and mass spectrometry confirmed this activation mechanism, and activated ROP18 in turn phosphorylates ROP2 and ROP8. X-ray crystallography, homology modelling, autophosphorylation assay, mutagenesis, mass spectrometry The EMBO journal High 19197235
2010 ROP18 binds to and phosphorylates multiple immunity-related GTPases (IRGs) on a conserved motif within switch region I of the GTPase domain. This modification prevents IRG recruitment to the PVM, blocks clearance within IFN-γ-activated macrophages and inflammatory monocytes, and is necessary and sufficient to confer parasite survival and virulence in vivo. Substrate profiling revealed the ROP18 phosphorylation consensus. Co-immunoprecipitation, in vitro phosphorylation assay, substrate profiling, genetic knockout (Δrop18), IFN-γ-activated macrophage clearance assay, mouse virulence assay Cell host & microbe High 21147463
2010 The type I virulent allele of ROP18 phosphorylates mouse Irga6 at two threonines in the nucleotide-binding domain (switch I region), biochemically inactivating the GTPase and inhibiting its accumulation at the PVM. This phosphorylation event is strain-specific (type I > type II/III) and correlates with virulence in mice. In vitro phosphorylation assay, phospho-site mapping, GTPase activity assay, confocal microscopy of IRG recruitment, mouse virulence comparison PLoS biology High 21203588
2011 ROP18 targets the host ER-bound transcription factor ATF6β. The N-terminal extension of ROP18 interacts with ATF6β and destabilizes it; ROP18 kinase activity is required for proteasome-dependent degradation of ATF6β, which downregulates CD8 T cell-mediated adaptive immune responses. ATF6β-deficient mice are highly susceptible to ROP18-deficient parasites, confirming this axis in vivo. Co-immunoprecipitation, overexpression in mammalian cells, ROP18 gene disruption (Δrop18), proteasome inhibitor experiments, ATF6β-KO mice challenge The Journal of experimental medicine High 21670204
2011 ROP18 (active kinase) and ROP5 (pseudokinase) are both required for avoidance of Gbp1 recruitment to the PVM; virulent strains lacking either ROP18 or ROP5 show increased Gbp1 accumulation and clearance in IFN-γ-activated macrophages. The virulence defect of Δrop18 mutants was reversed in Gbp1−/− cells and mice, demonstrating that ROP18 function is upstream of Gbp1-mediated killing. Genetic knockouts (Δrop18, Δrop5), IFN-γ-activated macrophage clearance assay, Gbp1−/− mice, confocal microscopy PLoS pathogens High 23633952
2012 The arginine-rich N-terminal domain of ROP18 (upstream of the kinase domain) is required for tethering ROP18 to the cytosolic face of the PVM following secretion. Mutants lacking this domain are secreted but fail to associate with the PVM, cannot phosphorylate Irga6, cannot prevent IRG loading onto the PVM, and are avirulent in mice, demonstrating that PVM targeting is essential for ROP18 function. N-terminal deletion/mutagenesis, confocal microscopy, in vitro phosphorylation assay (Irga6), mouse virulence assay Cellular microbiology High 22906355
2012 ROP18 can only efficiently inhibit IRG accumulation on the PVM in strains that co-express virulent ROP5 alleles. ROP5 can directly interact with one or more IRGs and can reduce IRG coating even in the absence of ROP18. Neither ROP18 nor ROP5 markedly affect survival in IFN-γ-activated human cells (which lack the IRG system), indicating that ROP18/ROP5 evolved specifically to block murine IRGs. Genetic knockouts and allelic swaps, IRG recruitment assay, human cell infection assay, mouse virulence assay PLoS pathogens High 22761577
2012 ROP5 proteins (pseudokinases) act as essential co-factors for ROP18 by binding adjacent to the nucleotide-binding domain of IRG targets and inducing an allosteric change: this prevents IRG oligomerization and reorients the two threonine residues in switch I that are targeted for phosphorylation by ROP18, thereby preparing the substrate for phosphorylation by ROP18. Genetic and biochemical binding assays, structural analysis (ROP5 pseudokinase domain), IRG oligomerization assays, in vitro phosphorylation PLoS biology High 22802726
2012 ROP5 directly regulates the catalytic activity of ROP18 in vitro. Both ROP5 and ROP18 are necessary to avoid IRG recruitment and clearance in IFN-γ-activated macrophages. The virulence defects of Δrop5 and Δrop18 were fully restored in Irgm3−/− mice, placing ROP18 activity genetically downstream of ROP5 and upstream of Irgm3-dependent IRG function. In vitro kinase activity assay (ROP18 ± ROP5), genetic knockouts, macrophage clearance assay, Irgm3−/− mice epistasis PLoS pathogens High 23144612
2013 Crystal structure of the ROP18 kinase domain was determined. The structure is inconsistent with a previously proposed autoinhibitory mechanism. A sucrose molecule bound outside the active-site cleft identifies a second ligand-binding pocket; mutational analysis confirmed that this pocket is important for acute virulence in mice. X-ray crystallography, mutagenesis of second ligand-binding pocket, mouse virulence assay The Journal of biological chemistry High 24129568
2014 ROP18 exists in a protein complex with pseudokinases ROP8/ROP2 and the dense granule protein GRA7 at the PVM. GRA7 directly binds the active dimer of Irga6 in a GTP-dependent manner, leading to enhanced IRG polymerization and rapid turnover/disassembly. ROP18 and GRA7 act together (synergistically and in the same pathway) to target IRGs by distinct mechanisms; a combined gra7/rop18 double knockout is avirulent while single mutants are only partially attenuated. Tandem affinity purification-MS, co-immunoprecipitation, in vitro GTPase/polymerization assay, genetic knockouts (Δgra7, Δrop18, double KO), IRG recruitment assay, mouse virulence assay Proceedings of the National Academy of Sciences High 24390541
2014 ROP5 forms physical complexes with the active kinases ROP18 and ROP17 (identified by tandem affinity purification in T. gondii). ROP18 and ROP17 together target adjacent essential threonine residues in switch I of IRGs; combined activities of ROP17 and ROP18 are required to prevent IRG recruitment to the PVM and protect the parasite in IFN-γ-activated macrophages. Tandem affinity purification-MS in T. gondii, in vitro kinase assay, genetic knockouts, IRG recruitment/macrophage clearance assay Cell host & microbe High 24832449
2014 ROP18 kinase activity and PVM association are both necessary for resistance to host IRGs in type II T. gondii. Deletion of ROP18 (and ROP5, ROP17) in type II severely reduces cyst burdens and >100-fold reduces virulence, establishing ROP18 as essential for chronic infection and not only acute pathogenesis. Targeted gene deletion of 26 ROPK loci, kinase-dead mutant, PVM-localization mutant, IRG resistance assay, mouse virulence/cyst burden assay mBio High 27165797
2015 GRA7 association with the PVM is mediated by direct binding to ROP5, and GRA7 absence results in reduced phosphorylation of Irga6, increased IRG amounts on the vacuole, and attenuated virulence. Among all IRG proteins, Irga6 is the only specific target of ROP18; similarly, GRA7 is strictly an Irga6-specific virulence effector. ROP18's specificity for Irga6 was experimentally demonstrated using phosphorylation assays against multiple IRG family members. Co-immunoprecipitation (GRA7–ROP5 binding), in vitro phosphorylation assay (panel of IRG proteins), IRG recruitment assay, genetic knockouts, mouse virulence assay Cellular microbiology High 26247512
2015 Deletion of ROP18 in South American type 4, 8, and 10 strains results in complete attenuation of virulence in mice (compared to only partial attenuation in type I RH), confirming that ROP18 is a conserved virulence factor across genetically divergent strains that evolved to resist innate immune defenses. CRISPR-Cas9 gene deletion, mouse virulence assay (multiple South American strains), genetic complementation PLoS genetics High 26291965
2009 Three principal alleles of ROP18 exist across natural isolates; expression differences (driven by presence/absence of an upstream regulatory element) and allelic differences between these three alleles account for much of the variation in acute mouse virulence. Loss of the upstream element in the most ancient (type III) lineage eliminated ROP18 expression and virulence. Population genetics/sequencing of natural isolates, promoter deletion analysis, expression measurement, mouse virulence assay across isolates PLoS genetics Medium 19266027
2011 IFN-γ-dependent accumulation of murine Gbp1 on the PVM is regulated by the parasite virulence factors ROP16, ROP18, and GRA15. ROP18 (together with ROP5) prevents Gbp1 recruitment in a strain-dependent manner; all three factors were identified by systematic knockout comparison. Systematic knockout of ROP16, ROP18, GRA15; confocal imaging of mGBP1 localization; co-immunoprecipitation of mGBP2/4/5 with mGBP1 PLoS one Medium 21931713
2013 H. hammondi orthologs of TgROP5 and TgROP18 are functionally active when expressed in T. gondii: HhROP18 complemented a T. gondii background. A 107 bp promoter element absent in type III TgROP18 is necessary for ROP18 expression, indicating this element was active in the common ancestor of T. gondii and H. hammondi and was inactivated in the type III lineage progenitor. Genomic sequencing, cross-species complementation in T. gondii, promoter deletion analysis, mouse virulence assay Proceedings of the National Academy of Sciences Medium 23589877
2014 Expression of T. gondii ROP18 (TgROP18) in Neospora caninum (whose endogenous ROP18 is a pseudogene) significantly increases intracellular proliferation and virulence in mice, and the transgenic N. caninum can phosphorylate IRGs as T. gondii does, demonstrating that TgROP18 kinase activity is the key functional difference explaining virulence differences between these two related parasites. Transgenic expression of TgROP18 in N. caninum Nc1, mouse virulence assay, IRG phosphorylation assay, invasion/motility assays PLoS one Medium 24927100
2018 ROP18 phosphorylates host RTN1-C (an ER protein preferentially expressed in the CNS) at Ser7/134 and Thr4/8/118. ROP18-mediated phosphorylation of RTN1-C triggers ER stress-mediated apoptosis in neural cells and enhances GRP78 acetylation by attenuating HDAC activity, identifying a molecular mechanism for ROP18-dependent neuropathogenesis/encephalitis. Proteomics/mass spectrometry (active ROP18 pull-down from human proteome array), co-immunoprecipitation, in vitro phosphorylation (site-directed mapping), ER stress marker western blotting, HDAC activity assay Proceedings of the National Academy of Sciences Medium 29784816
2019 ROP18 interacts with host cell P2X1 (an ATP-gated ion channel on neural cells) and inhibits ATP-induced apoptosis through the mitochondrial pathway by blocking P2X1-mediated Ca2+ influx, cytochrome C release, and caspase activation. This effect is cell-type specific (SF268 glioblastoma cells expressing P2X1, not RAW264.7 or THP-1 lacking P2X1). FRET, co-immunoprecipitation, flow cytometry (apoptosis/Ca2+ influx), western blotting (caspase/Bax/Bcl2/cytochrome C), overexpression experiments Parasites & vectors Medium 31164145
2017 ROP18 interacts with host cell vimentin and phosphorylates it. Vimentin knockout HBMEC cells show increased T. gondii infection rates, indicating that host vimentin restricts parasite invasion; ROP18-mediated phosphorylation alters vimentin solubility and dynamics. ROP18 contributes to regulation of vimentin phosphorylation and expression patterns during infection. Co-immunoprecipitation, in vitro kinase assay (vimentin phosphorylation), vimentin KO/knockdown cells, infection rate assay, western blotting International journal of biological sciences Medium 29104504
2017 Using a human proteome array probed with bioactive recombinant ROP18, 68 putative host substrates were identified. Among validated targets, ROP18 phosphorylates Smad1 at Ser-187, triggering its proteasome-dependent degradation. ROP18 also targets p53, p38, and UBE2N for degradation. Human proteome array, in vitro kinase assay, phospho-site mutagenesis (Smad1 Ser-187), proteasome inhibitor experiments, western blotting for degradation Molecular & cellular proteomics Medium 28087594
2022 ROP18 type I allele (TgROP18I) inhibits IFN-β production through direct interaction with IRF3, impeding the cGAS-STING signalling pathway. Additionally, TgROP18I interacts with p62 and TRAF6, inhibiting their interaction and p62 phosphorylation, thereby restricting ubiquitin/p62/LC3 recruitment to the PVM in both murine and human IFN-γ-stimulated cells. Co-immunoprecipitation, IFN-β reporter assay, western blotting (p62 phosphorylation, ubiquitin/LC3 on PVM), confocal microscopy FASEB journal Medium 35084749
2021 ROP18 type I allele (TgROP18I) interacts with human TRIM21 (an E3 ligase) and promotes its phosphorylation, causing TRIM21 degradation through the lysosomal pathway. Loss of TRIM21 reduces ubiquitin labeling on the PVM (preventing PV acidification and parasite killing), providing a mechanism for ROP18-dependent immune evasion in human cells. Co-immunoprecipitation, western blotting (TRIM21 degradation), lysosomal pathway inhibitor assay, TRIM21 knockdown/overexpression, confocal microscopy (PVM ubiquitination) Frontiers in cell and developmental biology Medium 34124071
2016 ROP18 association with the PVM is essential for ROP18-dependent antitumor immune activation (kinase-independent function), demonstrating a kinase-independent, PVM-localization-dependent role for ROP18 in host cell manipulation distinct from IRG evasion. Targeted deletion of ROP18, PVM-localization mutants, antitumor immunity assay in mouse ovarian cancer model PLoS genetics Medium 27447180
2015 ROP18 inhibits neural stem cell (C17.2 NSC) differentiation into neurons, at least partly by inhibiting the Wnt/β-catenin signalling pathway and downregulating Ngn1 and Ngn2. ROP18 reduces β-catenin levels and decreases Wnt/β-catenin transcriptional activity as measured by TOP/FOP flash reporter. Recombinant adenovirus (Ad-ROP18) transduction of C17.2 NSCs, immunoblot for βIII-tubulin/β-catenin, qRT-PCR for Ngn1/Ngn2, luciferase reporter (TOP/FOP flash) Parasites & vectors Low 29169404
2025 TgROP18 significantly reduces CD73 expression on decidual macrophages (dMφ) via the LSD1/SNAIL1 epigenetic pathway. Reduced CD73 subsequently decreases arginase-1 and IL-10 via the adenosine/A2AR/PKA/p-CREB/C/EBPβ pathway, impairing maternal-fetal immune tolerance. RH-Δrop18 infection caused less severe adverse pregnancy outcomes and less CD73 reduction than wild-type RH. RH-Δrop18 KO parasite infection of pregnant mice and human decidual tissues, flow cytometry (CD73/Arg-1/IL-10), western blot (LSD1/SNAIL1/signaling intermediates), ChIP assay Parasites & vectors Medium 39994736
2014 NOTE — PMID:24648522 (Du et al., JBC, 'ROP18 inhibits NF-κB pathway by promoting p65 degradation') was subsequently WITHDRAWN by the journal and should not be used as evidence. WITHDRAWN paper — excluded The Journal of biological chemistry Low 24648522
2020 GRA60 localises to the vacuolar space and PVM and is found associated with ROP18 as part of the virulence complex. Deletion of GRA60 leads to IRG (Irgb10 and Irga6) recruitment to the PVM comparable to Δrop5, and double knockout GRA60/ROP5 parasites show IRG recruitment comparable to single knockouts, placing GRA60 in the same resistance pathway as ROP18. Confocal microscopy (IRG recruitment), co-immunoprecipitation (GRA60-ROP18 association), genetic knockout (ΔGra60, ΔGra60Δrop5), mouse virulence assay Cellular microbiology Medium 33040458

Source papers

Stage 0 corpus · 100 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2006 Polymorphic secreted kinases are key virulence factors in toxoplasmosis. Science (New York, N.Y.) 455 17170306
2006 A secreted serine-threonine kinase determines virulence in the eukaryotic pathogen Toxoplasma gondii. Science (New York, N.Y.) 434 17170305
2014 Efficient gene disruption in diverse strains of Toxoplasma gondii using CRISPR/CAS9. mBio 395 24825012
2010 Phosphorylation of immunity-related GTPases by a Toxoplasma gondii-secreted kinase promotes macrophage survival and virulence. Cell host & microbe 239 21147463
2014 The Toxoplasma pseudokinase ROP5 forms complexes with ROP18 and ROP17 kinases that synergize to control acute virulence in mice. Cell host & microbe 202 24832449
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2009 A single polymorphic amino acid on Toxoplasma gondii kinase ROP16 determines the direct and strain-specific activation of Stat3. The Journal of experimental medicine 196 19901082
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2009 Selection at a single locus leads to widespread expansion of Toxoplasma gondii lineages that are virulent in mice. PLoS genetics 112 19266027
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2014 WITHDRAWN: Toxoplasma gondii virulence factor ROP18 inhibits the host NF-κB pathway by promoting p65 degradation. The Journal of biological chemistry 62 24648522
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2016 Secretion of Rhoptry and Dense Granule Effector Proteins by Nonreplicating Toxoplasma gondii Uracil Auxotrophs Controls the Development of Antitumor Immunity. PLoS genetics 47 27447180
2018 NADPH Oxidase and Guanylate Binding Protein 5 Restrict Survival of Avirulent Type III Strains of Toxoplasma gondii in Naive Macrophages. mBio 45 30154263
2013 Evaluation of protective effect of multiantigenic DNA vaccine encoding MIC3 and ROP18 antigen segments of Toxoplasma gondii in mice. Parasitology research 43 23591483
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2012 The arginine-rich N-terminal domain of ROP18 is necessary for vacuole targeting and virulence of Toxoplasma gondii. Cellular microbiology 40 22906355
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2014 Th1 and Th2 immune response to P30 and ROP18 peptides in human toxoplasmosis. Medical microbiology and immunology 38 24816543
2013 Hammondia hammondi, an avirulent relative of Toxoplasma gondii, has functional orthologs of known T. gondii virulence genes. Proceedings of the National Academy of Sciences of the United States of America 38 23589877
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2018 Encephalitis is mediated by ROP18 of Toxoplasma gondii, a severe pathogen in AIDS patients. Proceedings of the National Academy of Sciences of the United States of America 34 29784816
2018 Immunization With a DNA Vaccine Cocktail Encoding TgPF, TgROP16, TgROP18, TgMIC6, and TgCDPK3 Genes Protects Mice Against Chronic Toxoplasmosis. Frontiers in immunology 32 30008721
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2013 Enhancement of protective immune response to recombinant Toxoplasma gondii ROP18 antigen by ginsenoside Re. Experimental parasitology 31 23896123
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2011 The secreted kinase ROP18 defends Toxoplasma's border. BioEssays : news and reviews in molecular, cellular and developmental biology 28 21773979
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2017 Association of ROP18 and ROP5 was efficient as a marker of virulence in atypical isolates of Toxoplasma gondii obtained from pigs and goats in Piauí, Brazil. Veterinary parasitology 27 29080759
2016 Induction of specific humoral immune response in mice immunized with ROP18 nanospheres from Toxoplasma gondii. Parasitology research 27 27785602
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2019 Influence of Two Major Toxoplasma Gondii Virulence Factors (ROP16 and ROP18) on the Immune Response of Peripheral Blood Mononuclear Cells to Human Toxoplasmosis Infection. Frontiers in cellular and infection microbiology 24 31867288
2019 Protective Immunity Induced by Incorporating Multiple Antigenic Proteins of Toxoplasma gondii Into Influenza Virus-Like Particles. Frontiers in immunology 24 30666253
2015 T. gondii rhoptry protein ROP18 induces apoptosis of neural cells via endoplasmic reticulum stress pathway. Parasites & vectors 23 26489755
2020 Adjuvantic cytokine IL-33 improves the protective immunity of cocktailed DNA vaccine of ROP5 and ROP18 against toxoplasma gondii infection in mice. Parasite (Paris, France) 22 32315596
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2015 Protective efficacy of recombinant canine adenovirus type-2 expressing TgROP18 (CAV-2-ROP18) against acute and chronic Toxoplasma gondii infection in mice. BMC infectious diseases 21 25886737
2013 Structure of the Toxoplasma gondii ROP18 kinase domain reveals a second ligand binding pocket required for acute virulence. The Journal of biological chemistry 21 24129568
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2018 Genetic diversity of Toxoplasma gondii isolates obtained from free-living wild birds rescued in Southeastern Brazil. International journal for parasitology. Parasites and wildlife 20 30479944
2018 A Gene-Based Positive Selection Detection Approach to Identify Vaccine Candidates Using Toxoplasma gondii as a Test Case Protozoan Pathogen. Frontiers in genetics 20 30177953
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2019 Toxoplasma gondii ROP18 inhibits human glioblastoma cell apoptosis through a mitochondrial pathway by targeting host cell P2X1. Parasites & vectors 19 31164145
2017 Host Cell Vimentin Restrains Toxoplasma gondii Invasion and Phosphorylation of Vimentin is Partially Regulated by Interaction with TgROP18. International journal of biological sciences 18 29104504
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2012 Inhibition of ATF6β-dependent host adaptive immune response by a Toxoplasma virulence factor ROP18. Virulence 18 22286708
2018 Immuno-efficacy of DNA vaccines encoding PLP1 and ROP18 against experimental Toxoplasma gondii infection in mice. Experimental parasitology 16 29626423
2017 A Human Proteome Array Approach to Identifying Key Host Proteins Targeted by Toxoplasma Kinase ROP18. Molecular & cellular proteomics : MCP 16 28087594
2019 Toxoplasma gondii in invasive animals on the Island of Fernando de Noronha in Brazil: Molecular characterization and mouse virulence studies of new genotypes. Comparative immunology, microbiology and infectious diseases 15 31546127
2012 Interactions between the ROP18 kinase and host cell proteins that aid in the parasitism of Toxoplasma gondii. Acta tropica 15 22365922
2021 Toxoplasma gondii Type-I ROP18 Targeting Human E3 Ligase TRIM21 for Immune Escape. Frontiers in cell and developmental biology 14 34124071
2019 Virus-like particles containing multiple antigenic proteins of Toxoplasma gondii induce memory T cell and B cell responses. PloS one 14 31465461
2019 Toxoplasma gondii in four captive kangaroos (Macropus spp.) in China: Isolation of a strain of a new genotype from an eastern grey kangaroo (Macropus giganteus). International journal for parasitology. Parasites and wildlife 14 30923671
2020 Detection and genotypes of Toxoplasma gondii DNA in feces of domestic cats in Colombia. Parasite (Paris, France) 13 32302287
2017 A mechanistic study of Toxoplasma gondii ROP18 inhibiting differentiation of C17.2 neural stem cells. Parasites & vectors 13 29169404
2025 A novel combined quadrivalent self-amplifying mRNA-LNP vaccine provokes protective immunity against acute and chronic toxoplasmosis in mice. Infectious diseases of poverty 7 40551280
2025 IL-24 Is a Promising Molecular Adjuvant for Enhancing Protective Immunity Induced by DNA Vaccination Against Toxoplasma gondii. Microorganisms 7 40732170
2024 Vaccination with a DNA vaccine cocktail encoding TgROP2, TgROP5, TgROP9, TgROP16, TgROP17, and TgROP18 confers limited protection against Toxoplasma gondii in BALB/c mice. Parasitology research 7 39724445
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2025 In Silico Analysis and Characterization of the Immunogenicity of Toxoplasma gondii Rhoptry Protein 18. Bioinformatics and biology insights 4 39925787
2025 Isolation of Toxoplasma gondii from the placenta of northern fur seals (Callorhinus ursinus) and potential transplacental transmission of the parasite. Parasite (Paris, France) 3 40749113
2025 Structural Prediction and Antigenic Analysis of ROP18, MIC4, and SAG1 Proteins to Improve Vaccine Design against Toxoplasma gondii: An In silico Approach. Infectious disorders drug targets 2 39350555
2025 New genetic variants of Toxoplasma gondii isolates and a novel ROP5 allele in free-range chickens from Tabasco, México. Parasitology 2 40588766
2025 Toxoplasma gondii ROP18 induces maternal-fetal dysfunction by downregulating CD73 expression on decidual macrophages. Parasites & vectors 2 39994736
2025 Investigation of Virulence-Related Markers in Atypical Strains of Toxoplasma gondii from Brazil. Microorganisms 2 40005667
2025 Evaluation of a DNA vector plasmid encoding a partial rop18 gene from toxoplasma gondii in domestic cats as a vaccine candidate. Vaccine 1 40054140
2025 First molecular characterization of Toxoplasma gondii and molecular analysis of Neospora caninum in American mink (Neogale vison) introduced in Argentina. Research in veterinary science 1 41109155
2025 First isolation of viable Toxoplasma gondii from a black mangabey (Lophocebus aterrimus) reveals the emergence of the Africa 1 lineage in East Asia. PLoS neglected tropical diseases 1 40700374
2026 Toxoplasma gondii and a Cancer Biology Dichotomy: A Systematic Review of Experimental Studies of Its Antitumor and Pro-Tumor Effects. Pathogens (Basel, Switzerland) 0 42075678
2026 Gene-edited live-attenuated vaccines against Toxoplasma gondii: recent advances and future frontiers. Parasites & vectors 0 42252477
2026 The Potential Function of Toxoplasma gondii in Tumour Immunotherapy. Immunology 0 42108599
2026 Dual transcriptomic analysis of Toxoplasma gondii infection in a human PBMC ex vivo model. Biochemical and biophysical research communications 0 42322816
2026 Resveratrol modulates inflammatory gene expression in Toxoplasma gondii-infected microglia and shows structurally plausible interactions with parasite virulence proteins. Microbial pathogenesis 0 42142636
2026 First report of viable Toxoplasma gondii isolation from African lions (Panthera leo): Evidence for their status as intermediate hosts. Food and waterborne parasitology 0 41675383
2025 Toxoplasma gondii PPM3H regulates the parasite virulence and modulates host immune and inflammatory responses in mice. Veterinary research 0 40859392