The proposed model for urease maturation.

<p>(A) The nickel-charged UreG dimer can form a complex with UreF/UreH and urease. It is anticipated that complex formation induces conformational changes in urease. After formation of the preactivation complex, bicarbonate stimulates the GTPase activity of UreG, leading to the delivery of nickel ion into the urease active site. (B) There are two possible mechanisms for how the preactivation complex (UreG/UreF/UreH/urease) receives its nickel from UreE. In proposal A (red arrows), the UreG/UreF/UreH first forms a complex with urease. UreE may interact with and transfer nickel to the complex as proposed by Hausinger et al. <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001678#pbio.1001678-Farrugia1" target="_blank">[26]</a>. In proposal B (blue arrows), binding of GTP promotes dissociation of UreG from the UreG/UreF/UreH complex. The GTP-bound UreG then receives its nickel from UreE, giving rise to the GTP/nickel-charged UreG dimer, which can activate UreF/UreH-bound apo-urease in a GTP-hydrolysis-dependent process.