1.A.148.  The Toxoplasm Pore-forming Peptide (TPP) Family 

The TPP family consists of a number of proteins characterized from Toxoplasma gondii that produce peptides that form pores in the membrane of the parasitophorous vacuole (Bitew et al. 2024). Four such proteins are designated Gra17, Gra23, Gra47 and Gra72.  These proteins are all homologous (Bitew et al. 2024).  T. gondii, an intracellular parasite, uses GRA proteins secreted from dense granule organelles to mediate nutrient flux across the parasitophorous vacuole membrane (PVM). GRA17 and GRA23 are known pore-forming proteins on the PVM involved in this process. Bitew et al. 2024 identified GRA72 as synthetically lethal with GRA17. Deleting GRA72 produced similar phenotypes to Δgra17 parasites, and computational predictions suggested it forms a pore. To understand how GRA72 functions, Bitew et al. 2024 performed immunoprecipitation experiments and identified GRA47 as an interactor of GRA72. Deletion of GRA47 resulted in an aberrant "bubble vacuole" morphology with reduced small molecule permeability, mirroring the phenotype observed in GRA17 and GRA72 knockouts. Structural predictions indicated that GRA47 and GRA72 form heptameric and hexameric pores, respectively, with conserved histidine residues lining the pore. Mutational analysis highlighted the critical role of these histidines for protein functionality. Validation through electrophysiology confirmed alterations in membrane conductance, corroborating their pore-forming capabilities. Furthermore, Δgra47 parasites and parasites expressing GRA47 with a histidine mutation had reduced in vitro proliferation and attenuated virulence in mice. These findings revealed important roles of GRA47 and GRA72 in regulating PVM permeability, thereby expanding the repertoire of potential therapeutic targets against Toxoplasma infections.  The protein PIL98022.1 is of 476 aas with a hydrophobic N-terminal 200 residues followed by a 276aa hydrophilic domain. 

References: