GRA19

GRA19 is a Toxoplasma gondii dense granule protein that associates with the parasitophorous vacuole membrane (PVM) through an N-terminal HT/PEXEL-like motif (RxLxD/E), whose conserved arginine and leucine residues are required for proteolytic cleavage; this cleavage promotes stable PVM association, yet unlike Plasmodium PEXEL proteins GRA19 is not exported across the PVM into the host cell (PMID:23356236). Processing at this motif is carried out by the Golgi-resident aspartyl protease ASP5, since GRA19 cleavage is abolished in Δasp5 parasites (PMID:26473595). Beyond its ASP5-dependent maturation and PVM targeting, no further mechanistic detail — including molecular function at the PVM or interacting partners — has been characterized in the available corpus.

1. 2013 Medium

   Whether GRA19's PEXEL-like motif drives host-cell export as in Plasmodium or serves a distinct role was unknown; mapping the motif established that its cleavage governs PVM association without host export, defining a Toxoplasma-specific use of the PEXEL element.

   Evidence Epitope tagging, PVM marker co-localization, site-directed mutagenesis of the RxLxD/E motif, and subcellular fractionation in T. gondii

   PMID:23356236

   Open questions at the time

   • The protease responsible for motif cleavage was not identified in this study
   • The functional consequence of PVM association for the parasite or vacuole is unknown
   • No interacting partners or downstream activity at the PVM defined
2. 2015 High

   The identity of the enzyme processing GRA19's PEXEL-like motif was open; genetic deletion of ASP5 abolished cleavage, establishing ASP5 as the specific maturase for GRA19.

   Evidence ASP5 gene knockout with cleavage assessed by western blot/immunofluorescence comparing wild-type and Δasp5 T. gondii

   PMID:26473595

   Open questions at the time

   • Whether ASP5-dependent cleavage is required for any GRA19 biological function is not resolved
   • The molecular activity of mature GRA19 at the PVM remains undefined

• The molecular function of GRA19 at the PVM and its interaction partners remain uncharacterized.
• No molecular activity assigned to GRA19
• No binding partners or complex membership identified
• No parasite phenotype associated with GRA19 loss reported