{"gene":"TG_310780","gene_symbol":"GRA4","run_date":"2026-09-08T15:15:13","timeline":{"discoveries":[{"year":1992,"finding":"GRA4 was molecularly cloned and shown to encode a 40 kDa dense granule protein of Toxoplasma gondii. The deduced amino acid sequence revealed a proline-rich (12%) product with an internal hydrophobic region of 19 amino acids, a putative N-terminal signal sequence of 20 amino acids, and a potential N-glycosylation site. The GRA4 gene is single copy with no introns, and is translated in tachyzoites to yield a single ~1900 base mRNA species.","method":"Expression library screening, genomic cloning, nucleotide sequencing, Southern blot, Northern blot","journal":"Molecular and biochemical parasitology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct sequencing and structural characterization with multiple orthogonal methods (cloning, sequencing, Southern/Northern blot)","pmids":["1362450"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1998,"finding":"GRA4's transmembrane domain (TMD) and cytoplasmic tail are required for its targeting to dense granules and subsequent secretion into the tuboreticular intravacuolar network. When alkaline phosphatase was fused to the GRA4 TMD and cytoplasmic tail, the chimera localized to dense granules and was secreted into the intravacuolar network in a manner dependent on the cytoplasmic tail but not on a tyrosine-based motif within the tail.","method":"Stable transfection with reporter fusion constructs (alkaline phosphatase fused to GRA4 TMD/cytoplasmic tail), immunofluorescence, subcellular fractionation","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution with chimeric reporters plus domain deletion/mutagenesis in live parasites, multiple constructs tested","pmids":["9628889"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1999,"finding":"After secretion into the parasitophorous vacuole, GRA4 is initially distributed as a soluble protein throughout the vacuolar lumen and only later associates with the mature intravacuolar network via strong protein-protein interactions (not primarily hydrophobic interactions). Cross-linking studies established that GRA4 specifically interacts with GRA2 to form a multimeric complex stably associated with the intravacuolar network membranes.","method":"Cell fractionation, denaturing agent treatment, chemical cross-linking, immunofluorescence, immunoelectron microscopy","journal":"Molecular and biochemical parasitology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal biochemical methods (fractionation, cross-linking, denaturing agents) in a single focused study","pmids":["10498186"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1997,"finding":"During sporozoite invasion of host cells, GRA4 (present in oocyst sporozoite dense granules) is NOT exocytosed into the first parasitophorous vacuole (PV1) formed, in contrast to tachyzoite behavior. GRA4 is retained within cytoplasmic granules rather than being secreted into PV1.","method":"Immunofluorescence with anti-GRA4 antibodies on sporozoite-infected cells, comparison with tachyzoite secretion","journal":"Infection and immunity","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct immunofluorescence localization showing stage-specific secretion difference, single lab but clear positive/negative comparison","pmids":["9353039"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2002,"finding":"Toxoplasma Rab6 regulates retrograde transport from post-Golgi dense granule organelles to the Golgi. Expression of GDP-bound (Rab6(T25N)) or nucleotide-free (Rab6(N124I)) mutants caused accumulation of dense granule proteins in the Golgi and reduced secretion of GRA4, placing GRA4 secretion downstream of Rab6-mediated retrograde trafficking.","method":"Overexpression of wild-type and mutant Rab6 constructs, immunofluorescence, secretion assays measuring GRA4 release","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic perturbation with multiple Rab6 mutants showing GRA4 secretion defect, single lab","pmids":["12468555"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"finding":"The length of the GRA4 transmembrane domain (TMD) is a key determinant of its dense granule targeting. Replacing the GRA4 TMD with the longer TMDs of VSV-G or LDL receptor completely rerouted GRA4 to the Golgi and cell surface. Shortening the LDL receptor TMD to a length similar to GRA4 restored dense granule localization; lengthening the GRA4 TMD rerouted it to the Golgi. This effect was not due to specific TMD sequence motifs or membrane association strength.","method":"Stable transfection with TMD-swap chimeric constructs, mutational analysis of TMD length, immunofluorescence, subcellular fractionation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic mutagenesis and chimeric construct analysis with multiple TMD length variants, clear mechanistic conclusion","pmids":["15056659"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"finding":"GRA9, a newly characterized dense granule protein, colocalizes with GRA4 (and GRA2 and GRA6) at the intravacuolar network of tubular membranes within the parasitophorous vacuole, confirming GRA4's association with this structural network.","method":"Immunofluorescence, cryo-electron microscopy, colocalization with established GRA markers","journal":"International journal for parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct imaging by immunofluorescence and cryo-EM confirming localization, corroborates prior work","pmids":["15491588"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2011,"finding":"Genetic deletion of GRA4 in type II Toxoplasma gondii drastically reduced brain tissue cyst burdens in mice, and complementation with a functional GRA4 allele significantly restored cyst burdens. This established a functional role for GRA4 in cyst development and latent infection.","method":"Targeted gene deletion via homologous recombination in type II Δku80 strain, complementation, in vivo mouse infection model measuring brain cyst burdens","journal":"Eukaryotic cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout with genetic complementation rescue, clear phenotypic readout, rigorous genetic epistasis","pmids":["21531875"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":"ME49"}]},{"year":2019,"finding":"During cyst development in vitro, GRA4 localizes to the cyst periphery by day 1 post-differentiation (colocalizing with Dolichos biflorus agglutinin stain), then establishes a continuous matrix pattern inside the cyst by day 2. GRA4 ultimately localizes predominantly in the inner layers of the cyst wall. Deletion of GRA4 (along with other intravacuolar network GRA proteins except GRA1) reduced the rate of accumulation of cyst wall proteins at the cyst periphery relative to the cyst interior, indicating a role in cyst wall maturation.","method":"Live-cell and fixed immunofluorescence imaging during in vitro cyst differentiation, genetic deletion mutants, lectin staining (DBA)","journal":"mSphere","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct localization imaging combined with genetic loss-of-function showing specific cyst wall maturation phenotype, multiple GRA protein deletions compared","pmids":["31619500"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":"ME49"}]},{"year":2019,"finding":"Deletion of GRA4 (along with GRA2, GRA3, GRA5, GRA7, GRA12) increased MHC-I antigen presentation of parasitophorous vacuole-localized parasite antigens to CD8+ T cells in macrophages and/or dendritic cells, indicating that GRA4 participates in suppressing MHC-I antigen presentation. This suppression was cell-type and IFN-γ dependent.","method":"Genetic deletion of GRA proteins in T. gondii, infection of macrophages and dendritic cells, MHC-I antigen presentation assay with CD8+ T cell readout","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean knockout with defined immunological phenotype, but GRA4 effect was assessed together with multiple other GRAs, making GRA4-specific contribution less precisely defined","pmids":["31555296"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2024,"finding":"GRA4 functions as a negative regulator of host type I interferon (IFN-I) signaling. Mechanistically, GRA4 binds to phosphorylated TBK1 and promotes TRIM27-catalyzed K48-ubiquitination of TBK1 at Lys251 and Lys372 residues, which enhances recognition by the autophagy receptor p62, ultimately leading to autophagic degradation of TBK1 and suppressed IFN-I responses. Infection with Δgra4 mutant parasites induces stronger IFN-I responses in the host.","method":"GRA4 knockout parasites (Δgra4), co-immunoprecipitation (GRA4 binding to phospho-TBK1), ubiquitination assay (TRIM27-mediated K48-ubiquitination), autophagy flux assay (p62-dependent TBK1 degradation), site-directed mutagenesis (Lys251/Lys372), IFN-I signaling readouts","journal":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods including Co-IP, ubiquitination assay, site-specific mutagenesis, and genetic knockout with IFN-I phenotype in a single study","pmids":["39031880"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":"ME49"}]},{"year":1998,"finding":"The major B cell epitope of GRA4 was mapped to the last 11 C-terminal residues (within the region 297-345), recognized by serum IgG from infected mice, milk IgA, intestinal IgA, human sera, and sheep sera. A second weaker epitope was mapped to region 318-334. The N-terminal domain (amino acids 25-276) was poorly recognized.","method":"Recombinant truncated GRA4 fragments expressed as GST fusions, ELISA with sera from infected mice, humans, and sheep","journal":"Parasite immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic epitope mapping with multiple truncation constructs and multiple host species sera, single lab","pmids":["9618729"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2008,"finding":"GRA4-specific CD8+ T cells (H-2L(d)-restricted epitope from GRA4) predominate in multiple organ sources 2 weeks after T. gondii infection in BALB/c mice, indicating that GRA4 is processed and presented via MHC-I during acute infection. BALB/c animals infected with T. gondii mutants defective in establishing chronic infection showed altered levels of GRA4-specific CD8+ T cells.","method":"Caged MHC-I tetramer technology (~250 H-2L(d) tetramers), flow cytometry of T. gondii-specific CD8+ T cells from multiple tissues, infection with chronic-infection-defective mutant parasites","journal":"The Journal of infectious diseases","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct identification of GRA4-derived epitope using MHC tetramers, stage-specific T cell kinetics measured; single lab","pmids":["18922097"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""},{"species":"Mus musculus","strain":"BALB/c"}]},{"year":2013,"finding":"The GRA4-derived subdominant CD8+ T cell epitope does not provide significant host protection against parasite burden, in contrast to the immunodominant GRA6-specific response. Immunodominance and optimal antigen processing are determined by epitope position at the C-terminus of the precursor antigen, not by peptide-MHC affinity or naive T cell precursor frequency. GRA4's epitope is not at the C-terminus, which correlates with its subdominant status.","method":"Genetically modified parasites expressing epitope-repositioned antigens, MHC-I tetramer staining, parasite burden measurement after challenge in mice","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic manipulation of epitope position with functional immune readout, establishes GRA4 epitope's subdominant mechanism by comparison","pmids":["23818852"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2020,"finding":"The accumulation of s-WGA-binding (N-acetylglucosamine-decorated) molecules at the cyst wall is not dependent on GRA4 expression (or GRA2), whereas CST1, GRA4, and GRA6 cyst wall accumulation is GRA2-dependent. This indicates GRA2-dependent and GRA2-independent mechanisms for trafficking glycosylated cyst wall molecules, with GRA4 trafficking falling in the GRA2-dependent pathway.","method":"Lectin staining (s-WGA, DBA) of in vitro cysts in GRA2-deletion mutant background, immunofluorescence colocalization with GRA4, GRA6, CST1","journal":"mSphere","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization in genetic deletion background, clear epistatic relationship established for GRA4 cyst wall trafficking","pmids":["32132158"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":"ME49"}]}],"current_model":"GRA4 is a Toxoplasma gondii dense granule protein that is secreted as a soluble protein into the parasitophorous vacuole (PV) after host cell invasion, where it associates with the intravacuolar tubular network via strong protein-protein interactions with GRA2 in a multimeric complex; its targeting to dense granules and subsequent delivery to the intravacuolar network is governed by the short length of its single transmembrane domain (independent of specific sequence motifs) and requires its cytoplasmic tail; during cyst development, GRA4 traffics to the cyst wall (inner layers) in a GRA2-dependent manner and contributes to cyst wall maturation, with its genetic deletion drastically reducing brain cyst burdens in mice; in addition, secreted GRA4 functions as an immune evasion effector by binding phosphorylated TBK1 and promoting TRIM27-catalyzed K48-ubiquitination of TBK1 at Lys251/Lys372, leading to p62-mediated autophagic degradation of TBK1 and suppression of host type I interferon responses."},"narrative":{"mechanistic_narrative":"GRA4 is a proline-rich, 40 kDa dense granule protein of Toxoplasma gondii that is secreted into the parasitophorous vacuole (PV) after host cell invasion, where it becomes a structural component of the intravacuolar tubular network and, during bradyzoite differentiation, of the cyst wall [PMID:1362450, PMID:10498186, PMID:31619500]. Its trafficking to dense granules and subsequent delivery to the intravacuolar network are governed by the short length of its single transmembrane domain—not by specific sequence motifs—and require its cytoplasmic tail; lengthening the TMD reroutes it to the Golgi and cell surface [PMID:9628889, PMID:15056659]. Following secretion GRA4 is first soluble in the vacuolar lumen and only later associates with the mature network through strong protein-protein interactions, forming a multimeric complex with GRA2 [PMID:10498186]. GRA4 contributes to latent infection: its trafficking to the inner cyst wall layers is GRA2-dependent, it supports cyst wall maturation, and its deletion drastically reduces brain cyst burdens in mice [PMID:21531875, PMID:31619500, PMID:32132158]. Beyond its structural role, secreted GRA4 acts as an immune evasion effector that suppresses host type I interferon signaling by binding phosphorylated TBK1 and promoting TRIM27-catalyzed K48-ubiquitination of TBK1 at Lys251/Lys372, targeting it for p62-mediated autophagic degradation [PMID:39031880]. GRA4 is also a recognized antigen presented via MHC-I as a subdominant CD8+ T cell epitope, and its deletion (with other GRAs) enhances MHC-I antigen presentation [PMID:31555296, PMID:18922097, PMID:23818852].","teleology":[{"year":1992,"claim":"Establishing the molecular identity of GRA4 was the first step: cloning revealed a single-copy, intronless gene encoding a 40 kDa proline-rich dense granule protein with a signal sequence and an internal hydrophobic region, defining the protein to be studied mechanistically.","evidence":"Expression library screening, genomic cloning, sequencing, Southern and Northern blot in T. gondii","pmids":["1362450"],"confidence":"High","gaps":["Function of the internal hydrophobic region not resolved at cloning","No subcellular trafficking determinants defined yet"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1997,"claim":"Comparing sporozoite and tachyzoite behavior showed that GRA4 secretion is stage-regulated, as sporozoite dense granule GRA4 is retained rather than exocytosed into the first PV, indicating that secretion is not automatic across life stages.","evidence":"Immunofluorescence with anti-GRA4 antibodies on sporozoite-infected cells versus tachyzoites","pmids":["9353039"],"confidence":"Medium","gaps":["Mechanism of stage-specific retention unknown","Single-lab localization comparison"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1998,"claim":"To learn how GRA4 reaches dense granules and the intravacuolar network, reporter fusion experiments established that its transmembrane domain and cytoplasmic tail (but not a tyrosine-based tail motif) are the sufficient targeting/secretion determinants.","evidence":"Alkaline phosphatase–GRA4 TMD/tail chimeras, domain deletions, immunofluorescence and fractionation in transfected parasites","pmids":["9628889"],"confidence":"High","gaps":["Which TMD feature drives targeting not yet resolved","Trafficking machinery reading these determinants unidentified"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1998,"claim":"Mapping the antibody response defined GRA4's immunodominant B cell epitope to its last 11 C-terminal residues, recognized broadly across host species, establishing GRA4 as a humoral antigen.","evidence":"GST-fused truncated GRA4 fragments in ELISA against mouse, human, and sheep sera","pmids":["9618729"],"confidence":"Medium","gaps":["Protective value of the antibody response not assessed","Single-lab mapping"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":1999,"claim":"Biochemistry resolved how GRA4 joins the network: it is first soluble in the vacuolar lumen and later incorporates via strong protein-protein interactions, specifically forming a multimeric complex with GRA2, defining GRA4 as a network-building partner rather than a purely membrane-embedded protein.","evidence":"Cell fractionation, denaturant treatment, chemical cross-linking, immuno-EM in T. gondii","pmids":["10498186"],"confidence":"High","gaps":["Stoichiometry and full composition of the complex not defined","Interaction interface residues unmapped"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2002,"claim":"Perturbing trafficking machinery placed GRA4 secretion downstream of Rab6, as GDP-locked/nucleotide-free Rab6 mutants trapped dense granule proteins in the Golgi and reduced GRA4 secretion, linking retrograde transport to GRA4 delivery.","evidence":"Overexpression of wild-type and mutant Rab6, immunofluorescence, GRA4 secretion assays","pmids":["12468555"],"confidence":"Medium","gaps":["Direct versus indirect effect of Rab6 on GRA4 not distinguished","Single-lab overexpression study"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"claim":"Refining the targeting mechanism, systematic TMD swaps showed that it is the short LENGTH of the GRA4 TMD, not its sequence, that specifies dense granule targeting—lengthening it reroutes GRA4 to the Golgi and surface.","evidence":"TMD-swap chimeric constructs and TMD-length mutants, immunofluorescence, fractionation in transfected parasites","pmids":["15056659"],"confidence":"High","gaps":["Molecular sensor of TMD length unidentified","Interplay with the cytoplasmic tail determinant not integrated"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"claim":"Colocalization with the newly characterized GRA9 at the tubular network corroborated GRA4's residence in this intravacuolar structure alongside GRA2 and GRA6.","evidence":"Immunofluorescence and cryo-EM colocalization with established GRA markers","pmids":["15491588"],"confidence":"Medium","gaps":["Does not establish direct GRA4–GRA9 interaction","Structural organization of the network not resolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2008,"claim":"Identifying an H-2L(d)-restricted GRA4 epitope with MHC-I tetramers showed that GRA4 is processed and presented to CD8+ T cells during acute infection, and its response kinetics track infection stage.","evidence":"Caged MHC-I tetramer technology and flow cytometry of T. gondii-specific CD8+ T cells across tissues in BALB/c mice","pmids":["18922097"],"confidence":"Medium","gaps":["Protective contribution of GRA4-specific CD8+ T cells not established","Single-lab tetramer analysis"],"attribution":[{"species":"Toxoplasma gondii","strain":""},{"species":"Mus musculus","strain":"BALB/c"}]},{"year":2011,"claim":"Clean knockout and complementation established a physiological role for GRA4 in latent infection: deletion drastically reduced brain cyst burdens and complementation restored them, moving GRA4 from a structural protein to a chronic-infection determinant.","evidence":"Targeted deletion in type II Δku80, complementation, in vivo mouse brain cyst quantification","pmids":["21531875"],"confidence":"High","gaps":["Mechanism linking GRA4 loss to reduced cyst burden not defined at this stage","Restricted to type II strain"],"attribution":[{"species":"Toxoplasma gondii","strain":"ME49"}]},{"year":2013,"claim":"Epitope-repositioning experiments explained WHY the GRA4 CD8+ response is subdominant—immunodominance is set by C-terminal epitope position during antigen processing, and GRA4's non-terminal epitope yields a non-protective subdominant response.","evidence":"Parasites expressing epitope-repositioned antigens, MHC-I tetramer staining, parasite burden after challenge","pmids":["23818852"],"confidence":"Medium","gaps":["Does not address GRA4's own function in immune evasion","Processing rules generalize from a comparison, not exhaustive"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2019,"claim":"Live imaging plus deletion during cyst differentiation defined the mechanism behind the cyst phenotype: GRA4 traffics from the cyst periphery to the inner cyst wall layers and its loss slows cyst wall protein accumulation, implicating GRA4 in cyst wall maturation.","evidence":"Live and fixed immunofluorescence during in vitro differentiation, DBA lectin staining, GRA deletion mutants","pmids":["31619500"],"confidence":"High","gaps":["GRA4-specific contribution partly confounded by multi-GRA comparison","Molecular target of GRA4 within the wall unknown"],"attribution":[{"species":"Toxoplasma gondii","strain":"ME49"}]},{"year":2019,"claim":"Deletion assays revealed that GRA4, among a set of PV/network GRAs, participates in suppressing MHC-I presentation of vacuolar antigens in an IFN-γ- and cell-type-dependent manner, extending GRA4 into active immune modulation.","evidence":"GRA deletions, macrophage/dendritic cell infection, MHC-I antigen presentation assays with CD8+ T cell readout","pmids":["31555296"],"confidence":"Medium","gaps":["GRA4 tested alongside other GRAs, so its individual weight is imprecise","Molecular mechanism of MHC-I suppression not defined"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2020,"claim":"Lectin staining in a GRA2-deletion background placed GRA4 cyst wall trafficking in the GRA2-dependent pathway, showing that distinct GRA2-dependent and GRA2-independent routes deliver cyst wall molecules.","evidence":"s-WGA and DBA lectin staining and colocalization in GRA2-deletion in vitro cysts","pmids":["32132158"],"confidence":"Medium","gaps":["Whether the GRA2 dependence reflects the tachyzoite GRA2–GRA4 complex not directly tested","Trafficking route to the inner wall not molecularly resolved"],"attribution":[{"species":"Toxoplasma gondii","strain":"ME49"}]},{"year":2024,"claim":"A defined molecular mechanism for GRA4 immune evasion was established: secreted GRA4 binds phospho-TBK1 and drives TRIM27-mediated K48-ubiquitination at Lys251/Lys372, triggering p62-dependent autophagic degradation of TBK1 and suppressing host type I interferon responses.","evidence":"Δgra4 parasites, Co-IP with phospho-TBK1, TRIM27 ubiquitination assay, site-directed mutagenesis of Lys251/Lys372, autophagy flux and IFN-I readouts","pmids":["39031880"],"confidence":"High","gaps":["How secreted GRA4 accesses host cytosolic TBK1 not defined","Relationship of this effector role to GRA4's structural/network role unresolved"],"attribution":[{"species":"Toxoplasma gondii","strain":"ME49"}]},{"year":null,"claim":"How GRA4's dual identity—structural network/cyst wall component versus soluble cytosolic immune effector acting on host TBK1—is reconciled mechanistically, and how it crosses the vacuolar membrane to reach host signaling machinery, remains open.","evidence":"","pmids":[],"confidence":"Low","gaps":["Route of GRA4 export from the PV to the host cytosol unknown","TMD-length sensor for dense granule targeting unidentified","Full composition and stoichiometry of the GRA2–GRA4 network complex undefined"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["GRA2-GRA4 multimeric intravacuolar network complex","Intravacuolar tubular network association with GRA2, GRA6, GRA9"],"partners":["GRA2 (NETWORK ASSOCIATION AND CYST WALL TRAFFICKING DEPENDENCE)","PHOSPHORYLATED TBK1 (HOST)","TRIM27 (HOST, UBIQUITIN LIGASE)","P62 (HOST, AUTOPHAGY RECEPTOR)"],"other_free_text":["40 kDa proline-rich single-copy, intronless dense granule protein with N-terminal signal sequence and internal hydrophobic region (idx 0).","Dense granule targeting is determined by short transmembrane domain length rather than sequence, and requires the cytoplasmic tail but not a tyrosine-based motif (idx 1, idx 5).","Immunodominant C-terminal B cell epitope in residues 297-345; subdominant H-2L(d)-restricted CD8+ T cell epitope whose non-C-terminal position underlies its non-protective status (idx 11, idx 12, idx 13).","Genetic deletion drastically reduces brain cyst burdens in mice, rescued by complementation (idx 7)."]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"21531875","id":"PMC_21531875","title":"Type II Toxoplasma gondii KU80 knockout strains enable functional analysis of genes required for cyst development and latent infection.","date":"2011","source":"Eukaryotic cell","url":"https://pubmed.ncbi.nlm.nih.gov/21531875","citation_count":153,"is_preprint":false},{"pmid":"10699010","id":"PMC_10699010","title":"Recombinant antigens to detect Toxoplasma gondii-specific immunoglobulin G and immunoglobulin M in human sera by enzyme immunoassay.","date":"2000","source":"Journal of clinical microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/10699010","citation_count":132,"is_preprint":false},{"pmid":"9628889","id":"PMC_9628889","title":"The protozoan parasite Toxoplasma gondii targets proteins to dense granules and the vacuolar space using both conserved and unusual mechanisms.","date":"1998","source":"The Journal of cell 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mice.","date":"2005","source":"Vaccine","url":"https://pubmed.ncbi.nlm.nih.gov/15935521","citation_count":83,"is_preprint":false},{"pmid":"14573640","id":"PMC_14573640","title":"The MIC3 gene of Toxoplasma gondii is a novel potent vaccine candidate against toxoplasmosis.","date":"2003","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/14573640","citation_count":80,"is_preprint":false},{"pmid":"10775785","id":"PMC_10775785","title":"Induction of protective immunity against toxoplasmosis in mice by DNA immunization with a plasmid encoding Toxoplasma gondii GRA4 gene.","date":"2000","source":"Vaccine","url":"https://pubmed.ncbi.nlm.nih.gov/10775785","citation_count":75,"is_preprint":false},{"pmid":"15242945","id":"PMC_15242945","title":"Recombinant GRA4 or ROP2 protein combined with alum or the gra4 gene provides partial protection in chronic murine models of toxoplasmosis.","date":"2004","source":"Clinical and diagnostic laboratory 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\"GRA4 was molecularly cloned and shown to encode a 40 kDa dense granule protein of Toxoplasma gondii. The deduced amino acid sequence revealed a proline-rich (12%) product with an internal hydrophobic region of 19 amino acids, a putative N-terminal signal sequence of 20 amino acids, and a potential N-glycosylation site. The GRA4 gene is single copy with no introns, and is translated in tachyzoites to yield a single ~1900 base mRNA species.\",\n      \"method\": \"Expression library screening, genomic cloning, nucleotide sequencing, Southern blot, Northern blot\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct sequencing and structural characterization with multiple orthogonal methods (cloning, sequencing, Southern/Northern blot)\",\n      \"pmids\": [\"1362450\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"GRA4's transmembrane domain (TMD) and cytoplasmic tail are required for its targeting to dense granules and subsequent secretion into the tuboreticular intravacuolar network. When alkaline phosphatase was fused to the GRA4 TMD and cytoplasmic tail, the chimera localized to dense granules and was secreted into the intravacuolar network in a manner dependent on the cytoplasmic tail but not on a tyrosine-based motif within the tail.\",\n      \"method\": \"Stable transfection with reporter fusion constructs (alkaline phosphatase fused to GRA4 TMD/cytoplasmic tail), immunofluorescence, subcellular fractionation\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution with chimeric reporters plus domain deletion/mutagenesis in live parasites, multiple constructs tested\",\n      \"pmids\": [\"9628889\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"After secretion into the parasitophorous vacuole, GRA4 is initially distributed as a soluble protein throughout the vacuolar lumen and only later associates with the mature intravacuolar network via strong protein-protein interactions (not primarily hydrophobic interactions). Cross-linking studies established that GRA4 specifically interacts with GRA2 to form a multimeric complex stably associated with the intravacuolar network membranes.\",\n      \"method\": \"Cell fractionation, denaturing agent treatment, chemical cross-linking, immunofluorescence, immunoelectron microscopy\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal biochemical methods (fractionation, cross-linking, denaturing agents) in a single focused study\",\n      \"pmids\": [\"10498186\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"During sporozoite invasion of host cells, GRA4 (present in oocyst sporozoite dense granules) is NOT exocytosed into the first parasitophorous vacuole (PV1) formed, in contrast to tachyzoite behavior. GRA4 is retained within cytoplasmic granules rather than being secreted into PV1.\",\n      \"method\": \"Immunofluorescence with anti-GRA4 antibodies on sporozoite-infected cells, comparison with tachyzoite secretion\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct immunofluorescence localization showing stage-specific secretion difference, single lab but clear positive/negative comparison\",\n      \"pmids\": [\"9353039\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Toxoplasma Rab6 regulates retrograde transport from post-Golgi dense granule organelles to the Golgi. Expression of GDP-bound (Rab6(T25N)) or nucleotide-free (Rab6(N124I)) mutants caused accumulation of dense granule proteins in the Golgi and reduced secretion of GRA4, placing GRA4 secretion downstream of Rab6-mediated retrograde trafficking.\",\n      \"method\": \"Overexpression of wild-type and mutant Rab6 constructs, immunofluorescence, secretion assays measuring GRA4 release\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic perturbation with multiple Rab6 mutants showing GRA4 secretion defect, single lab\",\n      \"pmids\": [\"12468555\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The length of the GRA4 transmembrane domain (TMD) is a key determinant of its dense granule targeting. Replacing the GRA4 TMD with the longer TMDs of VSV-G or LDL receptor completely rerouted GRA4 to the Golgi and cell surface. Shortening the LDL receptor TMD to a length similar to GRA4 restored dense granule localization; lengthening the GRA4 TMD rerouted it to the Golgi. This effect was not due to specific TMD sequence motifs or membrane association strength.\",\n      \"method\": \"Stable transfection with TMD-swap chimeric constructs, mutational analysis of TMD length, immunofluorescence, subcellular fractionation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic mutagenesis and chimeric construct analysis with multiple TMD length variants, clear mechanistic conclusion\",\n      \"pmids\": [\"15056659\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"GRA9, a newly characterized dense granule protein, colocalizes with GRA4 (and GRA2 and GRA6) at the intravacuolar network of tubular membranes within the parasitophorous vacuole, confirming GRA4's association with this structural network.\",\n      \"method\": \"Immunofluorescence, cryo-electron microscopy, colocalization with established GRA markers\",\n      \"journal\": \"International journal for parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct imaging by immunofluorescence and cryo-EM confirming localization, corroborates prior work\",\n      \"pmids\": [\"15491588\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Genetic deletion of GRA4 in type II Toxoplasma gondii drastically reduced brain tissue cyst burdens in mice, and complementation with a functional GRA4 allele significantly restored cyst burdens. This established a functional role for GRA4 in cyst development and latent infection.\",\n      \"method\": \"Targeted gene deletion via homologous recombination in type II Δku80 strain, complementation, in vivo mouse infection model measuring brain cyst burdens\",\n      \"journal\": \"Eukaryotic cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout with genetic complementation rescue, clear phenotypic readout, rigorous genetic epistasis\",\n      \"pmids\": [\"21531875\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"During cyst development in vitro, GRA4 localizes to the cyst periphery by day 1 post-differentiation (colocalizing with Dolichos biflorus agglutinin stain), then establishes a continuous matrix pattern inside the cyst by day 2. GRA4 ultimately localizes predominantly in the inner layers of the cyst wall. Deletion of GRA4 (along with other intravacuolar network GRA proteins except GRA1) reduced the rate of accumulation of cyst wall proteins at the cyst periphery relative to the cyst interior, indicating a role in cyst wall maturation.\",\n      \"method\": \"Live-cell and fixed immunofluorescence imaging during in vitro cyst differentiation, genetic deletion mutants, lectin staining (DBA)\",\n      \"journal\": \"mSphere\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct localization imaging combined with genetic loss-of-function showing specific cyst wall maturation phenotype, multiple GRA protein deletions compared\",\n      \"pmids\": [\"31619500\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Deletion of GRA4 (along with GRA2, GRA3, GRA5, GRA7, GRA12) increased MHC-I antigen presentation of parasitophorous vacuole-localized parasite antigens to CD8+ T cells in macrophages and/or dendritic cells, indicating that GRA4 participates in suppressing MHC-I antigen presentation. This suppression was cell-type and IFN-γ dependent.\",\n      \"method\": \"Genetic deletion of GRA proteins in T. gondii, infection of macrophages and dendritic cells, MHC-I antigen presentation assay with CD8+ T cell readout\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean knockout with defined immunological phenotype, but GRA4 effect was assessed together with multiple other GRAs, making GRA4-specific contribution less precisely defined\",\n      \"pmids\": [\"31555296\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GRA4 functions as a negative regulator of host type I interferon (IFN-I) signaling. Mechanistically, GRA4 binds to phosphorylated TBK1 and promotes TRIM27-catalyzed K48-ubiquitination of TBK1 at Lys251 and Lys372 residues, which enhances recognition by the autophagy receptor p62, ultimately leading to autophagic degradation of TBK1 and suppressed IFN-I responses. Infection with Δgra4 mutant parasites induces stronger IFN-I responses in the host.\",\n      \"method\": \"GRA4 knockout parasites (Δgra4), co-immunoprecipitation (GRA4 binding to phospho-TBK1), ubiquitination assay (TRIM27-mediated K48-ubiquitination), autophagy flux assay (p62-dependent TBK1 degradation), site-directed mutagenesis (Lys251/Lys372), IFN-I signaling readouts\",\n      \"journal\": \"Advanced science (Weinheim, Baden-Wurttemberg, Germany)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods including Co-IP, ubiquitination assay, site-specific mutagenesis, and genetic knockout with IFN-I phenotype in a single study\",\n      \"pmids\": [\"39031880\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}]\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The major B cell epitope of GRA4 was mapped to the last 11 C-terminal residues (within the region 297-345), recognized by serum IgG from infected mice, milk IgA, intestinal IgA, human sera, and sheep sera. A second weaker epitope was mapped to region 318-334. The N-terminal domain (amino acids 25-276) was poorly recognized.\",\n      \"method\": \"Recombinant truncated GRA4 fragments expressed as GST fusions, ELISA with sera from infected mice, humans, and sheep\",\n      \"journal\": \"Parasite immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic epitope mapping with multiple truncation constructs and multiple host species sera, single lab\",\n      \"pmids\": [\"9618729\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GRA4-specific CD8+ T cells (H-2L(d)-restricted epitope from GRA4) predominate in multiple organ sources 2 weeks after T. gondii infection in BALB/c mice, indicating that GRA4 is processed and presented via MHC-I during acute infection. BALB/c animals infected with T. gondii mutants defective in establishing chronic infection showed altered levels of GRA4-specific CD8+ T cells.\",\n      \"method\": \"Caged MHC-I tetramer technology (~250 H-2L(d) tetramers), flow cytometry of T. gondii-specific CD8+ T cells from multiple tissues, infection with chronic-infection-defective mutant parasites\",\n      \"journal\": \"The Journal of infectious diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct identification of GRA4-derived epitope using MHC tetramers, stage-specific T cell kinetics measured; single lab\",\n      \"pmids\": [\"18922097\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}, {\"species\": \"Mus musculus\", \"strain\": \"BALB/c\"}]\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The GRA4-derived subdominant CD8+ T cell epitope does not provide significant host protection against parasite burden, in contrast to the immunodominant GRA6-specific response. Immunodominance and optimal antigen processing are determined by epitope position at the C-terminus of the precursor antigen, not by peptide-MHC affinity or naive T cell precursor frequency. GRA4's epitope is not at the C-terminus, which correlates with its subdominant status.\",\n      \"method\": \"Genetically modified parasites expressing epitope-repositioned antigens, MHC-I tetramer staining, parasite burden measurement after challenge in mice\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic manipulation of epitope position with functional immune readout, establishes GRA4 epitope's subdominant mechanism by comparison\",\n      \"pmids\": [\"23818852\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The accumulation of s-WGA-binding (N-acetylglucosamine-decorated) molecules at the cyst wall is not dependent on GRA4 expression (or GRA2), whereas CST1, GRA4, and GRA6 cyst wall accumulation is GRA2-dependent. This indicates GRA2-dependent and GRA2-independent mechanisms for trafficking glycosylated cyst wall molecules, with GRA4 trafficking falling in the GRA2-dependent pathway.\",\n      \"method\": \"Lectin staining (s-WGA, DBA) of in vitro cysts in GRA2-deletion mutant background, immunofluorescence colocalization with GRA4, GRA6, CST1\",\n      \"journal\": \"mSphere\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization in genetic deletion background, clear epistatic relationship established for GRA4 cyst wall trafficking\",\n      \"pmids\": [\"32132158\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}]\n    }\n  ],\n  \"current_model\": \"GRA4 is a Toxoplasma gondii dense granule protein that is secreted as a soluble protein into the parasitophorous vacuole (PV) after host cell invasion, where it associates with the intravacuolar tubular network via strong protein-protein interactions with GRA2 in a multimeric complex; its targeting to dense granules and subsequent delivery to the intravacuolar network is governed by the short length of its single transmembrane domain (independent of specific sequence motifs) and requires its cytoplasmic tail; during cyst development, GRA4 traffics to the cyst wall (inner layers) in a GRA2-dependent manner and contributes to cyst wall maturation, with its genetic deletion drastically reducing brain cyst burdens in mice; in addition, secreted GRA4 functions as an immune evasion effector by binding phosphorylated TBK1 and promoting TRIM27-catalyzed K48-ubiquitination of TBK1 at Lys251/Lys372, leading to p62-mediated autophagic degradation of TBK1 and suppression of host type I interferon responses.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GRA4 is a proline-rich, 40 kDa dense granule protein of Toxoplasma gondii that is secreted into the parasitophorous vacuole (PV) after host cell invasion, where it becomes a structural component of the intravacuolar tubular network and, during bradyzoite differentiation, of the cyst wall [#0, #2, #8]. Its trafficking to dense granules and subsequent delivery to the intravacuolar network are governed by the short length of its single transmembrane domain\\u2014not by specific sequence motifs\\u2014and require its cytoplasmic tail; lengthening the TMD reroutes it to the Golgi and cell surface [#1, #5]. Following secretion GRA4 is first soluble in the vacuolar lumen and only later associates with the mature network through strong protein-protein interactions, forming a multimeric complex with GRA2 [#2]. GRA4 contributes to latent infection: its trafficking to the inner cyst wall layers is GRA2-dependent, it supports cyst wall maturation, and its deletion drastically reduces brain cyst burdens in mice [#7, #8, #14]. Beyond its structural role, secreted GRA4 acts as an immune evasion effector that suppresses host type I interferon signaling by binding phosphorylated TBK1 and promoting TRIM27-catalyzed K48-ubiquitination of TBK1 at Lys251/Lys372, targeting it for p62-mediated autophagic degradation [#10]. GRA4 is also a recognized antigen presented via MHC-I as a subdominant CD8+ T cell epitope, and its deletion (with other GRAs) enhances MHC-I antigen presentation [#9, #12, #13].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Establishing the molecular identity of GRA4 was the first step: cloning revealed a single-copy, intronless gene encoding a 40 kDa proline-rich dense granule protein with a signal sequence and an internal hydrophobic region, defining the protein to be studied mechanistically.\",\n      \"evidence\": \"Expression library screening, genomic cloning, sequencing, Southern and Northern blot in T. gondii\",\n      \"pmids\": [\"1362450\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Function of the internal hydrophobic region not resolved at cloning\", \"No subcellular trafficking determinants defined yet\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Comparing sporozoite and tachyzoite behavior showed that GRA4 secretion is stage-regulated, as sporozoite dense granule GRA4 is retained rather than exocytosed into the first PV, indicating that secretion is not automatic across life stages.\",\n      \"evidence\": \"Immunofluorescence with anti-GRA4 antibodies on sporozoite-infected cells versus tachyzoites\",\n      \"pmids\": [\"9353039\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of stage-specific retention unknown\", \"Single-lab localization comparison\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"To learn how GRA4 reaches dense granules and the intravacuolar network, reporter fusion experiments established that its transmembrane domain and cytoplasmic tail (but not a tyrosine-based tail motif) are the sufficient targeting/secretion determinants.\",\n      \"evidence\": \"Alkaline phosphatase\\u2013GRA4 TMD/tail chimeras, domain deletions, immunofluorescence and fractionation in transfected parasites\",\n      \"pmids\": [\"9628889\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which TMD feature drives targeting not yet resolved\", \"Trafficking machinery reading these determinants unidentified\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Mapping the antibody response defined GRA4's immunodominant B cell epitope to its last 11 C-terminal residues, recognized broadly across host species, establishing GRA4 as a humoral antigen.\",\n      \"evidence\": \"GST-fused truncated GRA4 fragments in ELISA against mouse, human, and sheep sera\",\n      \"pmids\": [\"9618729\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Protective value of the antibody response not assessed\", \"Single-lab mapping\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Biochemistry resolved how GRA4 joins the network: it is first soluble in the vacuolar lumen and later incorporates via strong protein-protein interactions, specifically forming a multimeric complex with GRA2, defining GRA4 as a network-building partner rather than a purely membrane-embedded protein.\",\n      \"evidence\": \"Cell fractionation, denaturant treatment, chemical cross-linking, immuno-EM in T. gondii\",\n      \"pmids\": [\"10498186\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and full composition of the complex not defined\", \"Interaction interface residues unmapped\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Perturbing trafficking machinery placed GRA4 secretion downstream of Rab6, as GDP-locked/nucleotide-free Rab6 mutants trapped dense granule proteins in the Golgi and reduced GRA4 secretion, linking retrograde transport to GRA4 delivery.\",\n      \"evidence\": \"Overexpression of wild-type and mutant Rab6, immunofluorescence, GRA4 secretion assays\",\n      \"pmids\": [\"12468555\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect effect of Rab6 on GRA4 not distinguished\", \"Single-lab overexpression study\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Refining the targeting mechanism, systematic TMD swaps showed that it is the short LENGTH of the GRA4 TMD, not its sequence, that specifies dense granule targeting\\u2014lengthening it reroutes GRA4 to the Golgi and surface.\",\n      \"evidence\": \"TMD-swap chimeric constructs and TMD-length mutants, immunofluorescence, fractionation in transfected parasites\",\n      \"pmids\": [\"15056659\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular sensor of TMD length unidentified\", \"Interplay with the cytoplasmic tail determinant not integrated\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Colocalization with the newly characterized GRA9 at the tubular network corroborated GRA4's residence in this intravacuolar structure alongside GRA2 and GRA6.\",\n      \"evidence\": \"Immunofluorescence and cryo-EM colocalization with established GRA markers\",\n      \"pmids\": [\"15491588\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not establish direct GRA4\\u2013GRA9 interaction\", \"Structural organization of the network not resolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identifying an H-2L(d)-restricted GRA4 epitope with MHC-I tetramers showed that GRA4 is processed and presented to CD8+ T cells during acute infection, and its response kinetics track infection stage.\",\n      \"evidence\": \"Caged MHC-I tetramer technology and flow cytometry of T. gondii-specific CD8+ T cells across tissues in BALB/c mice\",\n      \"pmids\": [\"18922097\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Protective contribution of GRA4-specific CD8+ T cells not established\", \"Single-lab tetramer analysis\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}, {\"species\": \"Mus musculus\", \"strain\": \"BALB/c\"}]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Clean knockout and complementation established a physiological role for GRA4 in latent infection: deletion drastically reduced brain cyst burdens and complementation restored them, moving GRA4 from a structural protein to a chronic-infection determinant.\",\n      \"evidence\": \"Targeted deletion in type II \\u0394ku80, complementation, in vivo mouse brain cyst quantification\",\n      \"pmids\": [\"21531875\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking GRA4 loss to reduced cyst burden not defined at this stage\", \"Restricted to type II strain\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Epitope-repositioning experiments explained WHY the GRA4 CD8+ response is subdominant\\u2014immunodominance is set by C-terminal epitope position during antigen processing, and GRA4's non-terminal epitope yields a non-protective subdominant response.\",\n      \"evidence\": \"Parasites expressing epitope-repositioned antigens, MHC-I tetramer staining, parasite burden after challenge\",\n      \"pmids\": [\"23818852\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not address GRA4's own function in immune evasion\", \"Processing rules generalize from a comparison, not exhaustive\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Live imaging plus deletion during cyst differentiation defined the mechanism behind the cyst phenotype: GRA4 traffics from the cyst periphery to the inner cyst wall layers and its loss slows cyst wall protein accumulation, implicating GRA4 in cyst wall maturation.\",\n      \"evidence\": \"Live and fixed immunofluorescence during in vitro differentiation, DBA lectin staining, GRA deletion mutants\",\n      \"pmids\": [\"31619500\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"GRA4-specific contribution partly confounded by multi-GRA comparison\", \"Molecular target of GRA4 within the wall unknown\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Deletion assays revealed that GRA4, among a set of PV/network GRAs, participates in suppressing MHC-I presentation of vacuolar antigens in an IFN-\\u03b3- and cell-type-dependent manner, extending GRA4 into active immune modulation.\",\n      \"evidence\": \"GRA deletions, macrophage/dendritic cell infection, MHC-I antigen presentation assays with CD8+ T cell readout\",\n      \"pmids\": [\"31555296\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GRA4 tested alongside other GRAs, so its individual weight is imprecise\", \"Molecular mechanism of MHC-I suppression not defined\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Lectin staining in a GRA2-deletion background placed GRA4 cyst wall trafficking in the GRA2-dependent pathway, showing that distinct GRA2-dependent and GRA2-independent routes deliver cyst wall molecules.\",\n      \"evidence\": \"s-WGA and DBA lectin staining and colocalization in GRA2-deletion in vitro cysts\",\n      \"pmids\": [\"32132158\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the GRA2 dependence reflects the tachyzoite GRA2\\u2013GRA4 complex not directly tested\", \"Trafficking route to the inner wall not molecularly resolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A defined molecular mechanism for GRA4 immune evasion was established: secreted GRA4 binds phospho-TBK1 and drives TRIM27-mediated K48-ubiquitination at Lys251/Lys372, triggering p62-dependent autophagic degradation of TBK1 and suppressing host type I interferon responses.\",\n      \"evidence\": \"\\u0394gra4 parasites, Co-IP with phospho-TBK1, TRIM27 ubiquitination assay, site-directed mutagenesis of Lys251/Lys372, autophagy flux and IFN-I readouts\",\n      \"pmids\": [\"39031880\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How secreted GRA4 accesses host cytosolic TBK1 not defined\", \"Relationship of this effector role to GRA4's structural/network role unresolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How GRA4's dual identity\\u2014structural network/cyst wall component versus soluble cytosolic immune effector acting on host TBK1\\u2014is reconciled mechanistically, and how it crosses the vacuolar membrane to reach host signaling machinery, remains open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Route of GRA4 export from the PV to the host cytosol unknown\", \"TMD-length sensor for dense granule targeting unidentified\", \"Full composition and stoichiometry of the GRA2\\u2013GRA4 network complex undefined\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [2, 6, 8], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0019904\", \"supporting_discovery_ids\": [2, 10], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0031625\", \"supporting_discovery_ids\": [10], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020026\", \"supporting_discovery_ids\": [0, 1, 3, 5], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0020003\", \"supporting_discovery_ids\": [1, 2, 6], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0070288\", \"supporting_discovery_ids\": [8, 14], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006890\", \"supporting_discovery_ids\": [4], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0032480\", \"supporting_discovery_ids\": [10], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"ME49\"}]},\n      {\"term_id\": \"GO:0002479\", \"supporting_discovery_ids\": [9, 12, 13], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [\n      \"GRA2-GRA4 multimeric intravacuolar network complex\",\n      \"Intravacuolar tubular network association with GRA2, GRA6, GRA9\"\n    ],\n    \"partners\": [\n      \"GRA2 (network association and cyst wall trafficking dependence)\",\n      \"phosphorylated TBK1 (host)\",\n      \"TRIM27 (host, ubiquitin ligase)\",\n      \"p62 (host, autophagy receptor)\"\n    ],\n    \"other_free_text\": [\n      \"40 kDa proline-rich single-copy, intronless dense granule protein with N-terminal signal sequence and internal hydrophobic region (idx 0).\",\n      \"Dense granule targeting is determined by short transmembrane domain length rather than sequence, and requires the cytoplasmic tail but not a tyrosine-based motif (idx 1, idx 5).\",\n      \"Immunodominant C-terminal B cell epitope in residues 297-345; subdominant H-2L(d)-restricted CD8+ T cell epitope whose non-C-terminal position underlies its non-protective status (idx 11, idx 12, idx 13).\",\n      \"Genetic deletion drastically reduces brain cyst burdens in mice, rescued by complementation (idx 7).\"\n    ]\n  },\n  \"strain_conflicts\": []\n}","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_310780","name":"GRA4","product":"dense granule protein GRA4","uniprot_acc":"S8EUV6","chromosome":"TGME49_chrXI","start_pos":1588347},{"strain":"GT1","gene_id":"TGGT1_310780","name":null,"product":"dense granule protein GRA4","uniprot_acc":null,"chromosome":"TGGT1_chrXI","start_pos":1552761},{"strain":"RH88","gene_id":"TGRH88_050290","name":null,"product":"dense granule protein GRA4","uniprot_acc":null,"chromosome":"CM023092","start_pos":1638396},{"strain":"VEG","gene_id":"TGVEG_310780","name":null,"product":"dense granule protein GRA4","uniprot_acc":"A0A125YIA4","chromosome":"TGVEG_chrXI","start_pos":1601110}]}