GRA83

GRA83 is a Toxoplasma gondii dense granule effector that localizes to the parasitophorous vacuole in both tachyzoites and bradyzoites and acts to stimulate host innate immunity during infection (PMID:37768053). Genetic disruption of GRA83 reduces host IL-12 production by infected macrophages in vitro and lowers both IL-12 and IFN-γ in vivo, establishing GRA83 as required for driving host innate cytokine responses (PMID:37768053). Mechanistically, GRA83 promotes nuclear translocation of the NF-κB p65 subunit in host cells, and epistasis analysis with ∆gra83/∆gra15 double knockouts shows no additive loss of p65 translocation, placing GRA83 and GRA15 in converging pathways that regulate host NF-κB activity (PMID:37768053). The direct effectors mediating p65 translocation are uncharacterized: proximity labeling has identified only candidate parasite-derived interacting partners not yet validated by orthogonal methods (PMID:37768053).

1. 2023 Medium

   Establishing where GRA83 resides was the first step in defining it as a secreted effector; localization to the parasitophorous vacuole across both life stages positioned it at the host-parasite interface in acute and chronic infection.

   Evidence Immunofluorescence localization in tachyzoites and bradyzoites

   PMID:37768053

   Open questions at the time

   • No functional consequence directly tied to PV localization
   • Whether GRA83 is exported beyond the PV membrane into the host cell is not resolved
2. 2023 High

   Whether GRA83 shapes host immunity was answered by knockout, which showed GRA83 is required for infected macrophages to mount IL-12 responses and for downstream IL-12/IFN-γ production in vivo, defining a role in innate cytokine stimulation.

   Evidence ∆gra83 knockout with in vitro macrophage IL-12 ELISA and in vivo cytokine measurement

   PMID:37768053

   Open questions at the time

   • Molecular mechanism linking GRA83 to cytokine gene induction not defined
   • Effect on parasite burden and host survival not fully quantified in this entry
3. 2023 Medium

   The signaling node engaged by GRA83 was identified as NF-κB: loss of GRA83 reduces p65 nuclear translocation, connecting the cytokine phenotype to a defined host transcriptional pathway.

   Evidence p65 nuclear translocation assay in ∆gra83-infected host cells

   PMID:37768053

   Open questions at the time

   • Single method for a single readout
   • Direct molecular target of GRA83 in the NF-κB cascade unknown
4. 2023 Medium

   Whether GRA83 acts independently of the known NF-κB effector GRA15 was tested by double-knockout epistasis, which showed no additive loss and placed the two effectors in converging rather than parallel pathways.

   Evidence ∆gra83/∆gra15 double-knockout epistasis with p65 nuclear translocation readout

   PMID:37768053

   Open questions at the time

   • Point of convergence in the NF-κB pathway not mapped
   • Single lab, single readout
5. 2023 Low

   To identify the biochemical basis of GRA83 action, proximity labeling generated a candidate interactome, providing the first list of potential partners to test.

   Evidence Proximity labeling (BioID or similar) identifying T. gondii-derived candidate partners

   PMID:37768053

   Open questions at the time

   • Candidate partners not validated by reciprocal Co-IP or independent methods
   • No host-cell interacting partners defined
   • Functional relevance of candidates to NF-κB activation untested

• The direct molecular mechanism by which GRA83 promotes p65 nuclear translocation and converges with GRA15 remains unknown, including the identity of validated host or parasite partners that transduce the signal.
• No validated direct interactor
• Convergence point with GRA15 not molecularly defined
• No structural or biochemical activity assigned to GRA83