9.B.437. The ESCRT-interacting Dense Granule Protein GRA64 (GRA64) Family
GRA64 (TGME49_202620) is a transmembrane dense granule protein of 330 aas and 2 TMSs, N- and C-terminal, on the parasitophorous vacuolar membrane (PVM) of the intracellular parasite Toxoplasma gondii. It is partially exposed to the host cell cytoplasm in both tachyzoite and bradyzoite parasitophorous vacuoles (Mayoral et al. 2022). GRA64 interacts with components of the host endosomal sorting complexes required for transport (ESCRT) (TC# 3.A.31). Δgra64 tissue cysts, enlarged vesicular structures underneath the cyst membrane, suggesting a role for GRA64 in organizing the recruitment of ESCRT proteins and subsequent intracystic vesicle formation. There seem to be very few homologs of this protein based on NCBI BLAST searchs on 7/1/2022.
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GRA64 of 330 aas and 2 TMSs, N- and C-terminal. Part of T. gondii's success lies in its ability to infect diverse organisms and host cells and to persist as a latent infection within parasite-constructed structures called tissue cysts. Mayoral et al. 2022 characterized GRA64. On the vacuolar membrane, this protein is exposed to the host cell cytosol and interacts with host ESCRT proteins. Parasites lacking the GRA64 protein exhibit ultrastructural changes in tissue cysts during chronic infection (Mayoral et al. 2022). LC3-dependent extracellular vesicle (EV) loading and secretion (LDELS) is a secretory autophagy pathway in which the macroautophagy/autophagy machinery facilitates the packaging of cytosolic cargos, such as RNA-binding proteins, into EVs for secretion outside of the cell. Gardner et al. 2023 identified TFRC (transferrin receptor), one of the first proteins found to be secreted via EVs, as a transmembrane cargo of the LDELS pathway. Similar to other LDELS targets, TFRC secretion via EVs genetically requires components of the MAP1LC3/LC3-conjugation machinery but is independent of other ATGs involved in classical autophagosome formation. The packaging and secretion of TFRC into EVs depends on multiple ESCRT pathway components and the small GTPase, RAB27A. It was suggested that the LDELS pathway promotes TFRC incorporation into EVs and its subsequent secretion outside the cell (Gardner et al. 2023).
GRA64 of Toxoplasma gondii ME49
Uncharacterized protein of 311 aas and 2 TMSs, N- and C-terminal.
UP of Neospora caninum Liverpool
Uncharacterized protein of 288 aas and 2 TMSs, N- and C-terminal.
UP of Besnoitia besnoiti