Activation of Urease Apoprotein of Helicobacter pylori

H. pylori produces urease abundantly amounting to 6% of total protein of bacterial mass. Urease genes are composed of a cluster of 9 genes of ureC, ureD, ureA, ureB, ureI, ureE, ureF, ureG, ureH. Production of H. pylori urease in E. coli was studied with genetic cotransformation. Structural genes ureA and ureB produce urease apoprotein in E, coli but the apoprotein has no enzymatic activity. ureC and ureD do not affect urease production nor enzyme activity ureF, ureG, and ureH are essential to produce the catalytically active H. pylori urease of structural genes (ureA and ureB) in E.coli. The kinetics of activation of H. pylori urease apoprotein were examined to understand the production of active H. pylori urease. Activation of H. pylori urease apoprotein, pH dependency, reversibility of CO2 binding, irreversibility of CO2 and Ni2+ incorporation, and CO2 dependency of initial rate of urease activity have been observed in vitro. The intrinsic reactivity (ko) for carbamylation of urease apoprotein coexpressed with accessory genes was 17-fold greater than that of urease apoprotein expressed without accessory genes. It is concluded that accessory genes function in maximizing the carbamylating deprotonated E-amino group of Lys 219 of urease B subunit and metallocenter of urease apoprotein is supposed to be assembled by reaction of a deprotonated protein side chain with an activating CO2 molecule to generate ligands that facilitate productive nickel binding.

Control Mechanism for Production and Activation of Helicobacter pylori Urease

To define the genes for production of catalytically active H. pylori urease, we camed out study to elucidate the structure of urease gene transcript, to delineate the genetic region which affected the extent of the expression and the activation of urease structural subunits. UreC and ureD were confirmed not to affect the expression of structural genes and active enzyme production, meaning that these genes are not components of the urease gene cluster of H. pylori. p-independent transcriptional stop signal was found in 12 bp down-stream of ureH stop codon. RNA extension test showed that the transcript starts with 267 bp upstream of ureA start codon. Although accessory genes did not affect the extent of the expression of the structural subunits, they were essential for assembling the active urease in E. coli. E. coli transformants of plasmid clones containing ureAB produced catalytically active urease when they are complemented with the plasmid clones of ureIEFGH or coexisted with ureIEFGH, meaning that accessory gene products could be trans-acting as well as cis-acting. The extent of production of urease structural subunits depended on the region of 241 to 57 bp upstream of ureA start codon. E. coli transformant of pBeloBACII clone containing the urease gene cluster, which is maintained with a single copy in host, did not express the urease. Proteins (60, 38, 30, 29, 27, and 24 kDa) that could hold nickel ions were identified in the cell extract of H. pylori. The results in this study will provide the basis to understand the control mechanism for urease gene expression and formation of the active urease.