Binds GTP, GDP and GMP. Hydrolyzes GTP very efficiently; GDP rather than GMP is the major reaction product. Plays a role in erythroid differentiation (By similarity). GTP + H2O = GDP + H(+) + phosphate Heterodimer with other family members, including GBP1, GBP2 and GBP5 (PubMed:21151871). 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. By IFNG during macrophage activation. Belongs to the TRAFAC class dynamin-like GTPase superfamily. GB1/RHD3 GTPase family. GB1 subfamily. Extended N-terminus.