title: The Toxoplasma gondii rhoptry protein ROP18 is an Irga6-specific kinase and regulated by the dense granule protein GRA7.
abstract: In mice, avirulent strains (e.g. types II and III) of the protozoan parasite Toxoplasma gondii are restricted by the immunity-related GTPase (IRG) resistance system. Loading of IRG proteins onto the parasitophorous vacuolar membrane (PVM) is required for vacuolar rupture resulting in parasite clearance. In virulent strain (e.g. type I) infections, polymorphic effector proteins ROP5 and ROP18 cooperate to phosphorylate and thereby inactivate mouse IRG proteins to preserve PVM integrity. In this study, we confirmed the dense granule protein GRA7 as an additional component of the ROP5/ROP18 kinase complex and identified GRA7 association with the PVM by direct binding to ROP5. The absence of GRA7 results in reduced phosphorylation of Irga6 correlated with increased vacuolar IRG protein amounts and attenuated virulence. Earlier work identified additional IRG proteins as targets of T. gondii ROP18 kinase. We show that the only specific target of ROP18 among IRG proteins is in fact Irga6. Similarly, we demonstrate that GRA7 is strictly an Irga6-specific virulence effector. This identifies T. gondii GRA7 as a regulator for ROP18-specific inactivation of Irga6. The structural diversity of the IRG proteins implies that certain family members constitute additional specific targets for other yet unknown T. gondii virulence effectors.
authors.affiliation: Institute for Genetics, University of Cologne, Cologne, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hermanns
authors.affiliation: Institute for Genetics, University of Cologne, Cologne, Germany.
authors.forename: Urs B
authors.initials: UB
authors.lastname: Müller
authors.affiliation: Institute for Genetics, University of Cologne, Cologne, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Könen-Waisman
authors.affiliation: Fundação Calouste Gulbenkian, Instituto Gulbenkian de Ciência, Oeiras, Portugal.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Howard
authors.affiliation: Institute for Genetics, University of Cologne, Cologne, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Steinfeldt
mesh_terms: D000818:Animals; D000953:Antigens, Protozoan / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D005786:Gene Expression Regulation; D054884:Host-Pathogen Interactions; D051379:Mice; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D015800:Protozoan Proteins / Q000378:metabolism*; D014122:Toxoplasma / Q000235:genetics* / Q000502:physiology*
chemical_list: D000953:Antigens, Protozoan; C112573:GRA7 protein, Toxoplasma gondii; D015800:Protozoan Proteins; D017346:Protein Serine-Threonine Kinases; C556793:ROP18 protein, Toxoplasma gondii; D020558:GTP Phosphohydrolases; C491070:Iigp1 protein, mouse