Binds GTP, GDP and GMP. Hydrolyzes GTP very efficiently; GDP rather than GMP is the major reaction product. Plays a role in erythroid differentiation. GTP + H2O = GDP + H(+) + phosphate Heterodimer with other family members, including GBP1, GBP2 and GBP5. Dimerization regulates subcellular location. Heterodimers with GBP1, GBP2 and GBP5 localize in the compartment of the prenylated GBPs: with GBP1 in a vesicle-like compartment, with GBP2, around the nucleus and with GBP-5, at the Golgi apparatus. Brain, lung, heart, spleen, kidney, liver and intestine. By IFNG/IFN-gamma, IFNB1/IFN-beta and TNF-alpha (PubMed:9659399, PubMed:18025219). Up-regulated upon infection by T.gondii or L.monocytogenes (PubMed:18025219). Belongs to the TRAFAC class dynamin-like GTPase superfamily. GB1/RHD3 GTPase family. GB1 subfamily.