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, agents (PubMed:22461501). Hydrolyzes GTP, but in contrast to other family members, does not produce GMP (PubMed:20180847). GTP + H2O = GDP + H(+) + phosphate Homodimer (PubMed:21151871). Heterodimer with other family members, including GBP1, GBP2, GBP3 and GBP4 (PubMed:21151871). Dimerization is nucleotide-dependent; isoform 1 and isoform 2 form dimers when GTP-bound. GDP-bound isoform 2 is monomeric, while isoform 1 remains dimeric (PubMed:20180847). Dimerization regulates subcellular location. May also form tetramers (dimer of dimers) in the presence of GTP (PubMed:20180847). Interacts with NLRP3, possibly in its tetrameric form, and promotes PYCARD/ASC polymerization (PubMed:22461501). Expressed in peripheral blood monocytes (at protein level). By IFNG in endothelial cells and in LPS-primed macrophages. Isoprenylation is required for proper subcellular location. Antigenic tumor-specific truncated splice form. Belongs to the TRAFAC class dynamin-like GTPase superfamily. GB1/RHD3 GTPase family. GB1 subfamily.