As an activator of NLRP3 inflammasome assembly, plays a role in innate immunity and inflammation. Promotes selective NLRP3 inflammasome assembly in response to microbial and soluble, but not crystalline, inflammasome activating agents (PubMed:22461501). Hydrolyzes GTP, but in contrast to other family members, such as GBP1 and GBP2, does not produce GMP (By similarity). GTP + H2O = GDP + H(+) + phosphate Homodimer. Heterodimer with other family members, including GBP1, GBP2, GBP3 and GBP4 (By similarity). Dimerization is nucleotide-dependent (By similarity). Dimerization regulates subcellular location. May also form tetramers (dimer of dimers) in the presence of GTP (By similarity). Interacts with NLRP3, possibly in its tetrameric form, and promotes PYCARD/ASC polymerization (PubMed:22461501). Low expression, if any, in many tissues in the absence of stimulation. Strongly up-regulated by IFNG and, at lower levels, by LPS. The LPS-induced increase is attenuated in the presence of dexamethasone. Up-regulated by TNF in certain strains. Up-regulation by a combination of IFNG and TNF is synergistic, even in strains that do not respond to TNF alone. Isoprenylation is required for proper subcellular location. Mutant mice exhibit impaired host defense and NLRP3-dependent inflammatory responses. During LPS-induced sepsis, knockout animals show 60 to 75% reduction in IL1B and IL-18 serum levels compared to wild-type mice. Orogastric challenge with Listeria monocytogenes leads to higher bacterial burdens, discernible weight loss, and 50 to 80% fewer leukocytes expressing active CASP1 in mesenteric lymph nodes compared to wild-type counterparts. Belongs to the TRAFAC class dynamin-like GTPase superfamily. GB1/RHD3 GTPase family. GB1 subfamily.