GRA71

GRA71 is a Toxoplasma gondii dense granule protein that acts within a host-defense-countering effector module during intracellular infection (PMID:37459303, PMID:36916910). It assembles into a heterotrimeric complex with GRA57 and GRA70, demonstrated by reciprocal co-immunoprecipitation, and this complex is required for parasite survival in IFNγ-activated human fibroblasts (PMID:37459303, PMID:36916910). Mechanistically, the GRA71-containing complex suppresses premature parasite egress from IFNγ-stimulated host cells, and its loss triggers early egress (PMID:36916910). Deletion of GRA71 also reduces host-mediated ubiquitination of the parasitophorous vacuole, a change the authors interpret as a secondary consequence of complex disruption rather than the primary basis of IFNγ resistance (PMID:37459303). Beyond these findings, the molecular activity of GRA71 and the biochemical basis by which the complex restrains egress have not been characterized in the available corpus.

1. 2023 High

   Whether GRA71 functions alone or as part of an effector assembly was unknown; establishing its complex membership defined the functional unit relevant to IFNγ resistance.

   Evidence Targeted CRISPR screen, gene knockout, and reciprocal co-immunoprecipitation in Toxoplasma gondii, replicated across two independent studies

   PMID:37459303 PMID:36916910

   Open questions at the time

   • Stoichiometry and structural organization of the GRA57/GRA70/GRA71 complex are not resolved
   • The direct host or parasite molecular targets of the complex are not identified
2. 2023 Medium

   The subcellular compartment from which GRA71 acts was unclear; assigning it to dense granules placed it among secreted vacuole-modifying effectors.

   Evidence Localization inferred from co-immunoprecipitation with GRA32 and known dense granule proteins in Toxoplasma gondii

   PMID:36916910

   Open questions at the time

   • Localization inferred from co-IP context rather than direct live-imaging or fractionation
   • Whether GRA71 is trafficked to the vacuole membrane or lumen is not established
3. 2023 Medium

   The cellular phenotype underlying GRA71-dependent survival was unknown; showing that deletion causes early egress established that the complex suppresses premature exit under IFNγ pressure.

   Evidence Gene knockout and parasite egress assay in IFNγ-stimulated primary human fibroblasts, confirmed in multiple knockout lines across two studies

   PMID:36916910

   Open questions at the time

   • The molecular signal linking complex loss to premature egress is unknown
   • Whether egress suppression is direct or downstream of vacuole integrity is unresolved
4. 2023 Medium

   How GRA71 loss alters the host response was tested; reduced vacuole ubiquitination was found but interpreted as a secondary consequence rather than the causal mechanism of IFNγ resistance.

   Evidence Gene knockout with assessment of host-mediated vacuole ubiquitination in IFNγ-stimulated human cells

   PMID:37459303

   Open questions at the time

   • Causal relationship between ubiquitination change and survival is not established; authors flag it as secondary
   • The host ubiquitin machinery involved is not identified

• The molecular activity of GRA71 and the mechanism by which the GRA57/GRA70/GRA71 complex restrains egress and modulates host defense remain undefined.
• No enzymatic or biochemical activity assigned to GRA71
• No direct interacting host factors identified
• No structural model of the heterotrimeric complex