Involved in the maturation of [NiFe] hydrogenases. Required for nickel insertion into the metal center of the hydrogenase (PubMed:7601092, PubMed:8756471). Exhibits a low intrinsic GTPase activity, which is essential for nickel insertion (PubMed:7601092, PubMed:21544686, PubMed:27951644). In the presence of GDP, nickel, but not zinc, is transferred from the HypB GTPase domain (G-domain) to HypA (PubMed:23899293, PubMed:27951644). Binding of zinc or nickel in the G-domain decreases GTPase activity (PubMed:21544686). Once GTP hydrolysis is triggered, probably via a GTPase activating protein, the GDP-loaded state may enhance HypA-HypB complex formation and reduces the affinity of HypB for nickel, which is then transferred to HypA (PubMed:27951644). In contrast to nickel, zinc reduces the formation of complexes with HypA (PubMed:27951644). kcat is 0.18 min(-1) for GTPase activity. kcat is 0.04 min(1) for GTPase activity in the presence of 1 uM Zn(II). kcat is 0.10 min(-1) for GTPase activity in the presence of 10 uM Ni(II). Monomer (PubMed:21544686). Can form homodimers, but dimerization does not have a critical role in the hydrogenase maturation pathway (PubMed:21544686). Forms complexes with HypA and SlyD (PubMed:15995183, PubMed:15569666, PubMed:23899293). The N-terminal region contains a high-affinity nickel-binding site and the C-terminal G-domain contains a low-affinity metal-binding site, which is not selective for nickel and could possibly accommodate other divalent metals (PubMed:16142921, PubMed:18942856). Both metal sites are critical for the maturation of the hydrogenases (PubMed:18942856). Belongs to the SIMIBI class G3E GTPase family. HypB/HupM subfamily.