GRA70

GRA70 is a Toxoplasma gondii dense granule effector that supports parasite survival within IFNγ-activated human cells (PMID:36916910, PMID:37459303). It assembles into a multi-protein complex, forming a heterotrimeric complex with GRA57 and GRA71 and co-immunoprecipitating with GRA32 and additional GRA32 homologs (PMID:36916910, PMID:37459303). Loss of GRA70 causes premature parasite egress from IFNγ-stimulated human fibroblasts and reduces parasite persistence in IFNγ-activated cells, establishing the complex as a determinant of intracellular survival under host restriction (PMID:36916910, PMID:37459303). GRA70-knockout vacuoles show reduced host-mediated ubiquitination, but this change does not account for the IFNγ resistance phenotype and represents a secondary consequence of complex disruption (PMID:37459303). Beyond these findings, the molecular activity by which GRA70 prevents egress and confers IFNγ resistance has not been characterized in the available corpus.

1. 2023 Medium

   Establishing that GRA70 is a dense granule protein embedded in a multi-protein complex answered where it acts and with which partners, framing it as a candidate effector rather than an isolated protein.

   Evidence Reciprocal co-immunoprecipitation and gene knockout with growth assays in IFNγ-stimulated primary human fibroblasts

   PMID:36916910

   Open questions at the time

   • The stoichiometry and molecular architecture of the GRA70/GRA32-homolog association are not resolved
   • The mechanism by which complex loss triggers early egress is unknown
   • No enzymatic or biochemical activity assigned to GRA70
2. 2023 Medium

   Defining GRA70 as part of a heterotrimeric GRA57/GRA70/GRA71 complex required for survival identified the functional unit and its role in resisting IFNγ-mediated host restriction.

   Evidence Targeted CRISPR screen across two Toxoplasma strains with knockout survival assays in IFNγ-activated human foreskin fibroblasts

   PMID:37459303

   Open questions at the time

   • The host target(s) or pathway the complex neutralizes is unidentified
   • Whether GRA70 contributes catalytic versus structural function within the complex is unknown
   • The relationship between the GRA57/GRA70/GRA71 heterotrimer and the GRA32-homolog association is not defined
3. 2023 Low

   Testing whether altered vacuolar ubiquitination explains the phenotype ruled out this mechanism, showing the IFNγ resistance conferred by the complex is independent of host-mediated ubiquitination of the vacuole.

   Evidence Gene knockout and ubiquitination assay of parasite vacuoles in IFNγ-activated human cells

   PMID:37459303

   Open questions at the time

   • Single-lab, single-method dissociative result interpreted as secondary; the causal mechanism of IFNγ resistance remains unidentified
   • The direct molecular effector activity preventing premature egress is not established

• The molecular mechanism by which the GRA57/GRA70/GRA71 complex prevents premature egress and confers IFNγ resistance remains unresolved.
• No host target or biochemical activity has been assigned to GRA70
• How the complex mechanistically stabilizes the parasite against IFNγ-driven egress is unknown