Assembly of the Preactivation Complex for Urease Maturation in Helicobacter pylori

Colonization of Helicobacter pylori in the acidic environment of the human stomach depends on the neutralizing activity of urease. Activation of apo-urease involves carbamylation of lysine-219 and insertion of two nickel ions. In H. pylori, this maturation process involves four urease accessory proteins: UreE, UreF, UreG and UreH. It is postulated that the apo-urease interacts with UreF, UreG and UreH to form a preactivation complex that undergoes GTP-dependent activation of urease.;Comparison between the crystal structures of UreF and UreF-UreH complex revealed conformational changes in two distinct regions of UreF upon complex formation. Firstly, the flexible C-terminal residues of UreF become ordered, forming an extra helix α10 and a loop structure stabilized by hydrogen bonds involving Arg-250. Secondly, the first turn of helix α2 uncoils to expose a conserved residue, Tyr-48. Substitution of R250A or Y48A in UreF abolishes the formation of the heterotrimeric complex of UreF-UreH-UreG, and abolishes urease maturation. Our results suggest that the C-terminal residues and helix α2 of UreF are essential to the recruitment of UreG for the formation of the preactivation complex.;The crystal structure of the UreF-UreH-UreG complex revealed that the UreG dimer interacts strictly with UreF only, with each UreG protomer forming interactions with the C-terminal loop structure from both UreF protomers. A Site directed mutagenesis study suggests that UreF-UreH-UreG functions as an integral homodimeric unit. Taking advantage of the unique 2-fold symmetry observed in both the crystal structures of H. pylori urease and the UreF-UreH-UreG complex, we proposed a topology model of the preactivation complex for urease maturation.