Human guanylate binding protein 1 (hGBP1) belongs to the dynamin superfamily of GTPases and conveys host defense against intracellular bacteria and parasites. During infection, hGBP1 is recruited to pathogen-containing vacuoles, such as Chlamydia trachomatis inclusions, restricts pathogenic growth, and induces the activation of the inflammasome pathway. hGBP1 has a unique catalytic activity to hydrolyze GTP to GMP in two consecutive cleavage steps. However, the functional significance of this activity in host defense remains elusive. In this thesis, a structure-guided mutant that specifically abrogates GMP production, while maintaining fast cooperative GTP hydrolysis, was generated. Complementation experiments in human monocytes/macrophages show that hGBP1-mediated GMP production is dispensable for restricting Chlamydia trachomatis growth but is required for inflammasome activation. Mechanistically, GMP is catabolized to uric acid, which in turn activates the NLRP3 inflammasome via induction of mitochondrial ROS. Our study demonstrates that the unique enzymology of hGBP1 coordinates bacterial growth restriction and inflammasome signaling.
