Assembly of Preactivation Complex for Urease Maturation in Helicobacter pylori

Abstract

Colonization of Helicobacter pylori in the acidic environment of the human stomach depends on the neutralizing activity of urease. Activation of apo-urease involves carboxylation of lysine 219 and insertion of two nickel ions. In H. pylori, this maturation process involves four urease accessory proteins as follows: UreE, UreF, UreG, and UreH. It is postulated that the apo-urease interacts with UreF, UreG, and UreH to form a pre-activation complex that undergoes GTP-dependent activation of urease. The crystal structure of the UreF-UreH complex reveals conformational changes in two distinct regions of UreF upon complex formation. First, 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. Second, 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 UreG-UreF-UreH and abolishes urease maturation. Our results suggest that the C-terminal residues and helix α2 of UreF are essential for the recruitment of UreG for the formation of the pre-activation complex. The molecular mass of the UreF-UreH complex determined by static light scattering was 116 ± 2.3 kDa, which is consistent with the quaternary structure of a dimer of heterodimers observed in the crystal structure. Taking advantage of the unique 2-fold symmetry observed in both the crystal structures of H. pylori urease and the UreF-UreH complex, we proposed a topology model of the pre-activation complex for urease maturation.