Molecular functions of the murine guanylate binding protein (mGBP) 2 in the immune defense against Toxoplasma gondii

• Applicant: Professor Dr. Klaus Pfeffer
• Subject Area: Parasitology and Biology of Tropical Infectious Disease Pathogens ; Immunology
• Term: from 2013 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 233613836

Interferon gamma (IFNgamma) is a proinflammatory cytokine which plays a crucial role in the containment and clearance of infections. Patients with genetic defects, murine model systems as well as in vitro experiments have demonstrated that IFNgamma is an essential cytokine for host defense leading to effective control, especially of intracellular pathogens. IFNgamma receptor stimulation results in activation of cells, primarily through a Jak/Stat mediated massive transcriptional response. Prominently, Guanylate-binding proteins (GBPs) belong to a major family of GTPases being abundantly expressed in response to IFNgamma stimulation. GBPs have been shown to be crucial for restriction of the replication of intracellular parasites, i.e. the worldwide distributed Toxoplasma gondii. T. gondii growth restriction is mediated by recruitment of a set of GBPs to the membrane of the parasitophorous vacuole (PV), translocation into the PV space, and, ultimately, the association of GBP molecules with the membrane of the T. gondii parasite. Employing biochemical and imaging (Laser Scanning Microscopy / Multiparameter Fluorescence Image Spectroscopy) techniques it could be demonstrated that murine GBPs (mGBPs) reside in at least two discrete subcellular reservoirs and attack the parasitophorous vacuole membrane (PVM) as orchestrated, supramolecular complexes forming large, densely packed multimers comprising up to several thousand monomers. The dramatic mGBP enrichment results in the loss of PVM integrity, followed by a direct assault of mGBP2 upon the plasma membrane of the parasite. Recently, we could identify novel interaction partners of mGBP2, such as Cytoskeleton associated protein (Ckap4), Annexin A5 (AnxA5), Galectin 9 (Gal9), and Interferon Stimulated Gene 15 (ISG15) which can be detected at the PV of T. gondii. In the upcoming funding period, the intra- and intermolecular preconditions of the PVM and parasite interactions of mGBP2 will be unraveled and the roles and effector functions of Ckap4, Anxa5, Gal9, and ISG15 in toxoplasma infection will be investigated. Furthermore, novel interactions partners of mGBP2 with anti-parasitic activities will be identified. This project will provide vital dynamic and molecular perceptions into cell-autonomous immunity mediated by GBP effector molecules in host defense against important intracellular pathogens.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Daniel Degrandi