Hydrolyzes GTP to GMP in 2 consecutive cleavage reactions (PubMed:21551061). Confers protection to several pathogens, including the bacterial pathogens Listeria monocytogenes and Mycobacterium bovis BCG as well as the protozoan pathogen Toxoplasma gondii (PubMed:21551061, PubMed:18025219). Promotes IFN-gamma-mediated host defense against bacterial infections by regulating bacteriolytic peptide generation through its interaction with ubiquitin-binding protein SQSTM1, which delivers monoubiquitylated proteins to autolysosomes for the generation of bacteriolytic peptides (PubMed:21551061). Exhibits antiviral activity against influenza virus (By similarity). GTP + H2O = GDP + H(+) + phosphate Homodimer; homodimerization occurs upon GTP-binding and is required for the second hydrolysis step from GDP to GMP. Heterodimer with other family members, including GBP2, GBP3, GBP4 and GBP5. Dimerization regulates subcellular location to membranous structures (By similarity). Interacts with SQSTM1 (PubMed:21551061). Secreted from endothelial cells in the cerebrospinal fluid, upon bacterial challenge and independently of IFNG induction. Golgi membrane localization requires isoprenylation and the presence of another IFNG-induced factor (By similarity). By IFNG/IFN-gamma and CpG oligodeoxynucleotides (PubMed:1753106, PubMed:18025219). Up-regulated upon infection by T.gondii or L.monocytogenes (PubMed:18025219). Isoprenylation of mouse GBP1 is incomplete. It persistently exists in the cell as a mixture of C20-modified and (more predominantly) unmodified form. Prenylation is required for proper subcellular location (By similarity). Mice exhibit normal T-cell, B-cell, and phagocytic cell profiles in the spleen and Ly6G(+)neutrophils in peripheral blood but macrophages show impaired killing activities (PubMed:21551061). Infection of Gbp1-/- mice results in severe listeriosis or M. bovis BCG-induced morbidity owing to massively increased bacterial replication in the target organs, whereas wild-type mice can control the infection (PubMed:21551061). Belongs to the TRAFAC class dynamin-like GTPase superfamily. GB1/RHD3 GTPase family. GB1 subfamily.