This domain is found in HypB, a hydrogenase expression / formation protein, and UreG a urease accessory protein. Both these proteins contain a P-loop nucleotide binding motif. HypB has GTPase activity and is a guanine nucleotide binding protein. It is not known whether UreG binds GTP or some other nucleotide. Both enzymes are involved in nickel binding. HypB can store nickel and is required for nickel dependent hydrogenase expression. UreG is required for functional incorporation of the urease nickel metallocenter. GTP hydrolysis may required by these proteins for nickel incorporation into other nickel proteins. This family of domains also contains P47K, a Pseudomonas chlororaphis protein needed for nitrile hydratase expression, and the cobW gene product, which may be involved in cobalamin biosynthesis in Pseudomonas denitrificans.