Involved in the maturation of [NiFe] hydrogenases. Required for nickel insertion into the metal center of the hydrogenase. Is also required for maturation of urease (PubMed:11123699, PubMed:12533448). Exhibits a low intrinsic GTPase activity, which is essential for nickel insertion (PubMed:12533448, PubMed:21239585, PubMed:22179820, PubMed:24338018). Metal coordination and the nucleotide-bound state of HypB directly influence each other (PubMed:24338018). Binding of nickel in the G-domain decreases GTPase activity and modulates the oligomeric state of the protein (PubMed:21239585, PubMed:24338018). Binding of zinc inhibits the GTPase activity (PubMed:21239585, PubMed:24338018). GTP and GDP modulate coordination, stoichiometry, and affinity of nickel, but not zinc (PubMed:24338018). Potassium increases the GTPase activity but has no effect on the other biochemical properties of the protein (PubMed:24338018). kcat is 0.0006 sec(-1) for the apo form. kcat is 0.0016 sec(-1) in the presence of 20 uM Ni(II). Monomer and homodimer (PubMed:12533448, PubMed:24338018, PubMed:21239585, PubMed:22179820). Dimerization is induced by nickel, but not by zinc (PubMed:21239585). Dimerization is also induced by GTP (PubMed:22179820). Forms complexes with HypA (PubMed:12533448, PubMed:22179820). Contains a metal-binding site, which can bind nickel or zinc, with a higher affinity for zinc (PubMed:21239585). His-107 is an essential nickel ligand only in the nucleotide-free state of the protein (PubMed:24338018). Mutant has negligible hydrogenase activity and is severely impaired in urease activity. Belongs to the SIMIBI class G3E GTPase family. HypB/HupM subfamily.