Affinage · Toxoplasma gondii

GRA23

dense granule protein GRA23 · UniProt A0A125YME4

Annotated
2026-09-08
9 papers in source corpus 6 papers cited in narrative 6 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

GRA23 is a Toxoplasma gondii dense granule protein that is secreted into the parasitophorous vacuole, where it localizes to the parasitophorous vacuole membrane (PVM) and intravacuolar network and behaves as a tightly membrane-associated, detergent-resistant complex (PMID:23583316). Functionally, GRA23 acts as a pore-forming protein related to Plasmodium EXP2: expression in Xenopus oocytes produces conductance consistent with a large non-selective pore, and GRA23 works synergistically with GRA17 to mediate passive transport of small molecules across the PVM, partially rescuing the permeability and PV-morphology defects of GRA17-deficient parasites (PMID:25974303). It operates within a broader PVM-permeability network alongside GRA47 and GRA72, with genetic epistasis and cross-complementation indicating partial but incomplete functional redundancy among these proteins (PMID:38936501). Loss of GRA23 causes aberrant PV morphology, reduced growth, and impaired chronic-stage cyst formation in type II parasites (PMID:32686022). GRA23 also engages host machinery, binding peroxisomal biogenesis factor PEX3 and the chaperone TRAP1 (PMID:40417354), though the functional consequences of these host interactions have not been characterized in the available corpus.

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 2013 Medium

    Establishing where GRA23 acts was the first question; showing it is a secreted dense granule protein targeting the PVM and intravacuolar network placed it at the parasite-host interface.

    Evidence Immunoblotting, immuno-EM, IF co-localization with GRA4/GRA7, and detergent solubility assays in T. gondii

    PMID:23583316

    Open questions at the time
    • No molecular function assigned
    • Membrane topology and complex composition not resolved
  2. 2015 High

    The central mechanistic question of what GRA23 does was answered by demonstrating it is a pore-forming protein that, synergistically with GRA17, mediates non-selective small-molecule transport across the PVM.

    Evidence Xenopus oocyte electrophysiology of GRA23, GRA17 deletion/complementation, permeability assays, and GRA17/GRA23 epistasis in T. gondii RH

    PMID:25974303

    Open questions at the time
    • Channel stoichiometry and structure not determined
    • Selectivity filter / gating mechanism unknown
    • Direct interaction between GRA23 and GRA17 not shown
  3. 2020 Medium

    Whether GRA23 matters for parasite fitness was addressed by deletion in a type II strain, revealing it is required for normal PV morphology and efficient chronic-stage cyst formation.

    Evidence CRISPR-Cas9 knockout, PV morphology, in vivo mouse virulence and cyst burden, growth rate in T. gondii Pru

    PMID:32686022

    Open questions at the time
    • Molecular basis of cyst-formation defect not defined
    • Single strain and single lab
  4. 2023 Low

    Placing GRA23 within a larger permeability network, an in vivo screen implicated GRA72 in normal GRA17/GRA23 localization and confirmed GRA17/GRA23 as IFN-γ-dependent virulence genes.

    Evidence In vivo CRISPR screen in C57BL/6 and Ifngr1-/- mice

    PMID:37269286

    Open questions at the time
    • Localization role of GRA72 is a screen-based inference not mechanistically validated
    • Direction of the GRA72-GRA17/GRA23 relationship unresolved
  5. 2024 Medium

    The degree of redundancy among PVM-permeability GRAs was tested by cross-complementation and double knockouts, showing partial but incomplete functional overlap of GRA23 with GRA17, GRA47, and GRA72.

    Evidence CRISPR-Cas9 deletions, Δgra23Δgra72 double knockout, overexpression complementation (including PfEXP2), PV morphology and permeability assays in T. gondii

    PMID:38936501

    Open questions at the time
    • Distinct mechanistic roles of each GRA not defined
    • Physical organization of the multi-GRA complex unknown
  6. 2025 Medium

    Whether GRA23 engages host machinery was addressed by interactome mapping, identifying and validating host PEX3 and TRAP1 as binding partners.

    Evidence Pull-down/mass spectrometry with BiFC and Co-IP validation in T. gondii

    PMID:40417354

    Open questions at the time
    • No functional consequence of PEX3 or TRAP1 binding established
    • Whether interactions occur across the PVM or after host-protein import is unclear

Open questions

Synthesis pass · forward-looking unresolved questions
  • How pore-forming permeability activity, cyst-formation requirement, and host PEX3/TRAP1 engagement integrate into a single mechanism remains unresolved.
  • No structure of the GRA23 pore or its multi-GRA assembly
  • Functional link between host-protein binding and PVM transport untested
  • Mechanism of chronic-stage/cyst defect unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
GRA17 (FUNCTIONAL SYNERGY IN PVM TRANSPORT)GRA47 (PARTIAL FUNCTIONAL REDUNDANCY)GRA72 (GENETIC INTERACTION; ΔGRA23ΔGRA72 ENHANCED PV DEFECT)HOST PEX3 (PEROXISOMAL BIOGENESIS FACTOR; BIFC + CO-IP)HOST TRAP1 (TNF RECEPTOR-ASSOCIATED PROTEIN 1 CHAPERONE; BIFC + CO-IP)
Complex memberships
GRA23-GRA17 PVM permeability functional moduleGenetic network with GRA47 and GRA72 at the PVM

Evidence

Reading pass · 6 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2013 TgGRA23 is a dense granule protein that localizes to the parasitophorous vacuole membrane (PVM) and the intravacuolar network after secretion from dense granules. It co-localizes with other dense granule proteins (TgGRA4 and TgGRA7) in extracellular-stage parasites. Biochemical experiments showed TgGRA23 is insoluble and forms an electrostatic complex resistant to non-ionic detergents, indicating it is a membrane-associated or tightly complexed protein. The native protein migrates at ~21 kDa. Immunoblotting with antisera raised against recombinant GST-TgGRA23; immuno-electron microscopy; immunofluorescence co-localization with GRA4 and GRA7; detergent solubility biochemical assay Parasitology international Medium 23583316
2015 GRA23 localizes to the PVM and functions synergistically with GRA17 to mediate passive transport of small molecules across the PVM. Exogenous expression of GRA23 in Xenopus oocytes alters membrane conductance in a manner consistent with a large non-selective pore, establishing GRA23 as a pore-forming protein. GRA17-deficient parasites (which have reduced PVM permeability and aberrant PV morphology) are partially rescued by GRA23, confirming functional overlap. GRA23 is related to Plasmodium EXP2. Genetic deletion of GRA17 with complementation; small-molecule permeability assays; Xenopus oocyte electrophysiology expressing GRA23; localization by imaging; genetic epistasis between GRA17 and GRA23 Cell host & microbe High 25974303
2020 CRISPR-Cas9 deletion of gra23 in the type II Pru strain causes PVs with abnormal morphology, reduced growth rate, and significant reduction in cyst formation, while slightly attenuating acute virulence. This establishes GRA23 as required for normal PV morphology and efficient chronic-stage cyst formation in type II parasites. CRISPR-Cas9 gene deletion; PV morphology assessment; in vivo mouse infection (virulence and cyst burden); parasite growth rate measurement Parasitology research Medium 32686022
2023 An in vivo CRISPR screen result suggested a role for GRA72 in normal GRA17/GRA23 localization, placing GRA72 upstream or in the same pathway as GRA17/GRA23 at the PVM. The screen also confirmed GRA17 and GRA23 as IFN-γ-dependent virulence genes. In vivo CRISPR screen in C57BL/6 and Ifngr1-/- mice Cell reports Low 37269286
2024 Overexpression of GRA23 partially rescues the aberrant PV morphology in Δgra47 and Δgra72 parasites, indicating partial functional redundancy among GRA23, GRA17, GRA47, and GRA72 in regulating PVM permeability. However, full rescue of Δgra17 and Δgra23 PV morphology required Plasmodium falciparum PfEXP2, while overexpression of one GRA only partially rescued the others, suggesting these proteins are not fully functionally redundant but work in different ways. The double-knockout Δgra23Δgra72 showed significantly more aberrant PVs than Δgra23 alone, confirming a genetic interaction between GRA23 and GRA72. Gene deletion (CRISPR-Cas9), double knockout construction, overexpression complementation, PV morphology quantification, small-molecule permeability assays International journal for parasitology Medium 38936501
2025 Pull-down assay coupled with mass spectrometry identified 35 host proteins interacting with GRA23, of which peroxisomal biogenesis factor 3 (PEX3) and TNF receptor-associated protein 1 (TRAP1) were validated as GRA23-binding partners by bimolecular fluorescence complementation (BiFC) and co-immunoprecipitation. This represents the first evidence that GRA23 directly interacts with host peroxisomal and chaperone machinery. Pull-down assay with mass spectrometry; bimolecular fluorescence complementation (BiFC); co-immunoprecipitation (Co-IP) Frontiers in veterinary science Medium 40417354

Source papers

Stage 0 corpus · 9 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2015 The Toxoplasma Dense Granule Proteins GRA17 and GRA23 Mediate the Movement of Small Molecules between the Host and the Parasitophorous Vacuole. Cell host & microbe 203 25974303
2023 Host genetics highlights IFN-γ-dependent Toxoplasma genes encoding secreted and non-secreted virulence factors in in vivo CRISPR screens. Cell reports 30 37269286
2024 Two Toxoplasma gondii putative pore-forming proteins, GRA47 and GRA72, influence small molecule permeability of the parasitophorous vacuole. mBio 24 38380952
2017 Evaluation of protective immunity induced by DNA vaccination with genes encoding Toxoplasma gondii GRA17 and GRA23 against acute toxoplasmosis in mice. Experimental parasitology 20 28625894
2013 TgGRA23, a novel Toxoplasma gondii dense granule protein associated with the parasitophorous vacuole membrane and intravacuolar network. Parasitology international 13 23583316
2020 Effect of deletion of gra17 and gra23 genes on the growth, virulence, and immunogenicity of type II Toxoplasma gondii. Parasitology research 12 32686022
2024 GRA47 is important for the morphology and permeability of the parasitophorous vacuole in Toxoplasma gondii. International journal for parasitology 11 38936501
2025 Molecular interactions of Toxoplasma gondii dense granule 23 (GRA23) with host proteins PEX3 and TRAP1. Frontiers in veterinary science 1 40417354
2023 GRA47 and GRA72 are Toxoplasma gondii pore-forming proteins that influence small molecule permeability of the parasitophorous vacuole. bioRxiv : the preprint server for biology 1 38014337