Metal ions at the top of the Irvine-Williams series such as Ni2+ are toxic because they can displace weaker ions such as Mg2+ from the active site of essential enzymes (e.g. GTPase). To avoid toxicity, cells have evolved metallochaperones, or metal carrier proteins, to deliver the toxic ions to specific protein complexes. Urease is a nickel-containing enzyme that hydrolyses urea into ammonia, which helps the pathogen Helicobacter pylori to survive in acidic human stomach. Biosynthesis of active urease requires the delivery of nickel ions to a buried carbamylated lysine residue at the active site. This maturation process is assisted by four urease accessory proteins, UreD, UreE, UreF and UreG. Our group has determined the crystal structures of UreFD, GDP-bound UreGFD, Ni/GMPPNP-bound UreE2G2 complexes and Ni/GMPPNP-bound UreG dimer. We showed how a metallochaperone UreG couples GTP binding and hydrolysis to allosterically regulate the binding or release of nickel ions and to switch protein binding partners along the nickel delivery pathway. We have recently determined the cryoEM structure of H. pylori UreFD/urease and Klebsiella pneumoniae UreD/urease at 2.3 and 2.7 Å resolutions, respectively. Combined with mutagenesis and biochemical studies, we show that the formation of UreFD/urease complex opens a 100-Å long tunnel, where the nickel ion is delivered through UreFD to the active site of urease. Through the nickel delivery pathway of urease maturation, nickel ions are delivered from one protein to another within the protein complexes so that the toxic metal ions do not diffuse to the cytoplasm.