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PubMed1999

Expression of urease does not affect the ability of Bordetella bronchiseptica to colonise and persist in the murine respiratory tract.

To investigate the role played by urease during the Bordetella bronchiseptica infection process, the ability to colonise and persist in the mouse respiratory tract of a urease-negative B. bronchiseptica BB7865 and a BB7865 derivative constitutively expressing urease was compared with that of the wild-type strain. The results obtained showed that neither constitutive expression nor abolishment of urease activity had any significant effect on the course of B. bronchiseptica infection. Therefore, under our experimental conditions, urease is not essential for B. bronchiseptica to colonise and persist within the murine host.

Animals↗
PubMed2005

Specific degradation of H. pylori urease by a catalytic antibody light chain.

Catalytic antibodies capable of digesting crucial proteins of pathogenic bacteria have long been sought for potential therapeutic use. Helicobacter pylori urease plays a crucial role for the survival of this bacterium in the highly acidic conditions of human stomach. The HpU-9 monoclonal antibody (mAb) raised against H. pylori urease recognized the alpha-subunit of the urease, but only slightly recognized the beta-subunit. However, when isolated both the light and the heavy chains of this antibody were mostly bound to the beta-subunit. The cleavage reaction catalyzed by HpU-9 light chain (HpU-9-L) followed the Michaelis-Menten equation with a K(m) of 1.6 x 10(-5) m and a k(cat) of 0.11 min(-1), suggesting that the cleavage reaction was enzymatic. In a cleavage test using H. pylori urease, HpU-9-L efficiently cleaved the beta-subunit but not the alpha-subunit, indicating that the degradation by HpU-9-L had a specificity. The cleaved peptide bonds in the beta-subunit were L121-A122, E124-G125, S229-A230, Y241-D242, and M262-A263. BSA was hardly cleaved by HpU-9-L, again indicating the digestion by HpU-9-L was specific. In summary, we succeeded in the preparation of a catalytic antibody light chain capable of specifically digesting the beta-subunit of H. pylori urease.

Amino Acid Sequence↗
PubMed1994

[Serotypes of urease producing Vibrio parahaemolyticus and their relation to possession of tdh and trh genes].

We analysed 467 isolates of Vibrio parahaemolyticus for possession of tdh/trh gene in comparison with urease production and serotypes. Strains possessing tdh+/trh-, tdh+/trh+, tdh-/trh-, and tdh-/trh- show positive urease production 2.1, 100, 65.7, 100%, respectively. Serotypes of O1:K69, O3:K6, O3:K72, O6:K18, O6:K46 and O1:KUT were frequently positive (100% except 91.7% of the latest one) in urease production. All isolates of O3:K6 prossessed trh, whereas all isolates of certain serotypes including O1:K69 and O3:K72 possessed both trh and trh and tdh genes. Among these, most of O1:K69 and O3:K72 were urease producer. From these results, we speculate that urease production is closely related to the presence of the trh gene or/and lesser production of TDH. We also found the new combination of serovar, O3:K25, O4:K37 and O13:K72 in Kanagawa phenomenon-positive strains.

Genes, Bacterial↗
PubMed1979

Urease-producing species of intestinal anaerobes and their activities.

Urease activities of anaerobic bacteria that constituted predominant gut flora were examined. It was demonstrated that some strains of Eubacterium aerofaciens, E. lentum, and Peptostreptococcus products produced urease. They were the most numerous species in human feces. All strains of Bifidobacterium infantis and some strains of Bacteroides multiacidus, B. bifidum, Clostridium symbiosum, Fusobacterium necrophorum, F. varium, Lactobacillus fermentum, Peptococcus asaccharolyticus, and P. prevotii produced urease. The optimum pH of the Lactobacillus urease was found to be 4.0, whereas the pH value of B. multiacidus urease was 8.0.

Anaerobiosis↗
PubMed1986

Cloning of urease gene sequences from Providencia stuartii.

Providencia stuartii was the most prevalent isolate recovered from urine specimens taken weekly over a 1-year period from 51 nursing home patients with urinary catheters in place. Thirty percent of the isolates were urease positive. Urease, which is implicated in renal stone formation, was shown to be transmissible on an 82-kilobase conjugative plasmid in one isolate. Plasmid DNA isolated from this strain was digested with EcoRI, ligated into the EcoRI site of pBR322, and used to transform Escherichia coli HB101. Ampicillin-resistant clones were replica plated onto urea segregation agar, and a urease-positive clone, designated pMID101, was isolated. Recombinant and native urease from cell lysates had identical electrophoretic mobilities on nondenaturing polyacrylamide urease activity gels. The native enzyme was induced fourfold when cells were grown in the presence of 0.1% urea and had a km of 9.4 mM and a Vmax of 3.2 mumol of NH3 per min per mg of protein. Its molecular weight was estimated to be 375,000 +/- 35,000 by Sephacryl S-300 chromatography. The enzyme was cytoplasmic in P. stuartii, was inhibited in vitro by hydroxyurea, acetohydroxamic acid, and EDTA, and appears to have a complex subunit structure and a unique molecular size within genera of the Proteeae tribe.

Cell Compartmentation↗
PubMed1991

Cytotoxicity of the HpmA hemolysin and urease of Proteus mirabilis and Proteus vulgaris against cultured human renal proximal tubular epithelial cells.

Proteus mirabilis, a common agent of nosocomially acquired and catheter-associated bacteriuria, can cause acute pyelonephritis. In ascending infections, bacteria colonize the bladder and ascend the ureters to the proximal tubules of the kidney. We postulate that Proteus species uses the HpmA hemolysin and urease to elicit tissue damage that allows entry of these bacteria into the kidney. To study this interaction, strains of Proteus mirabilis and P. vulgaris and their isogenic hemolysin-negative (hpmA) or isogenic urease-negative (ureC) constructs were overlaid onto cultures of human renal proximal tubular epithelial cells (HRPTEC) isolated from kidneys obtained by immediate autopsy. Cytotoxicity was measured by release of soluble lactate dehydrogenase (LDH). Two strains of P. mirabilis inoculated at 10(6) CFU caused a release of 80% of total LDH after 6 h, whereas pyelonephritogenic hemolytic Escherichia coli CFT073 released only 25% at 6 h (P less than 0.012). Ten P. mirabilis isolates and five P. vulgaris isolates were all hemolytic and cytotoxic and produced urease which was induced by urea. The HpmA hemolysin is apparently responsible for the majority of cytotoxicity in vitro since the hemolysin-negative (hpmA) mutants of P. mirabilis and P. vulgaris were significantly less cytotoxic than wild-type strains. P. mirabilis WPM111 (hemolysin negative) was used to test the effect of urease-catalyzed urea hydrolysis on HRPTEC viability. In the presence of 50 mM urea, WPM111 caused the release of 42% of LDH versus 1% at 6 h in the absence of substrate (P = 0.003). We conclude that the HpmA hemolysin of Proteus species acts as a potent cytotoxin against HRPTEC. In addition, urease apparently contributes to this process when substrate urea is available.

Bacterial Proteins↗
PubMed1991

Essential role of urease in pathogenesis of gastritis induced by Helicobacter pylori in gnotobiotic piglets.

A mutant strain of Helicobacter pylori with weak urease activity was created by using N-methyl-N'-nitro-N-nitrosoguanidine. The urease activity of the mutant (0.036 +/- 0.009 nmol of urea per micrograms of bacterial protein per min) was 0.4% of that of the parental strain (8.20 +/- 2.30 nmol of urea per micrograms of bacterial protein per min). The mutant was otherwise indistinguishable from the parental strain. Both demonstrated prominent catalase and oxidase activities, and both produced vacuolating cytotoxin. Restriction endonuclease and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns and ultrastructure were identical for the two strains. The mutant was fully motile, as evaluated by spreading in soft agar and by direct microscopic examination. Growth rate and colony size and morphology were identical for the mutant and parental strains. Seventeen gnotobiotic piglets were challenged with either the mutant or the parental strain and sacrificed 3 or 21 days after challenge. Gastric tissue was examined histologically and cultured for H. pylori. Of seven piglets challenged with the parental strain, all became infected. H. pylori was not recovered from any of 10 piglets challenged with the urease-negative strain. Lymphofollicular gastritis was present in all seven piglets challenged with the parental strain but in none of the piglets challenged with the urease-negative strain. These results suggest that prominent urease activity is essential for colonization by H. pylori.

Animals↗
PubMed1994

Recombinant antigens prepared from the urease subunits of Helicobacter spp.: evidence of protection in a mouse model of gastric infection.

Urease is an important virulence factor for gastric Helicobacter spp. To elucidate the efficacy of individual urease subunits to act as mucosal immunogens, the genes encoding the respective urease subunits (UreA and UreB) of Helicobacter pylori and Helicobacter felis were cloned in an expression vector (pMAL) and expressed in Escherichia coli cells as translational fusion proteins. The recombinant UreA and UreB proteins were purified by affinity and anion-exchange chromatography techniques and had predicted molecular masses of approximately 68 and 103 kDa, respectively. Western blotting (immunoblotting) studies indicated that the urease components of the fusion proteins were strongly immunogenic and were specifically recognized by polyclonal rabbit anti-Helicobacter sp. sera. The fusion proteins (50 micrograms) were used, in combination with a mucosal adjuvant (cholera toxin), to orogastrically immunize mice against H. felis infection. Gastric tissues from H. felis-challenged mice were assessed by the biopsy urease test and by histology. In mice immunized with recombinant H. felis UreB, 60% of animals (n = 7) were histologically negative for H. felis bacteria after challenge at 17 weeks. This compared with 25% (n = 8) for mice immunized with the heterologous H. pylori UreB antigen. Neither the homologous nor the heterologous UreA subunit elicited protective responses against H. felis infection in mice. The study demonstrated that a recombinant subunit antigen could induce an immunoprotective response against gastric Helicobacter infection.

Animals↗
PubMed1994

Molecular analysis of urease genes from a newly identified uncultured species of Helicobacter.

"Gastrospirillum hominis" is an uncultured gastric spiral bacterium that has recently been shown by 16S rDNA sequence analysis to be a newly recognized species of Helicobacter that infects humans, and it has been provisionally designated "Helicobacter heilmannii." We used PCR to directly amplify the urease structural genes of "H. heilmannii" from infected gastric tissue. DNA sequence analysis identified two open reading frames, ureA and ureB, which code for polypeptides with predicted molecular weights of 25,729 and 61,831, respectively. The urease subunit genes from "H. heilmannii" were cloned and expressed in Escherichia coli. Western blot (immunoblot) analysis showed that antiserum directed against the ureA and ureB gene products from H. pylori was cross-reactive with the corresponding polypeptides from "H. heilmannii." Analysis of the derived amino acid sequences of "H. heilmannii" UreA and UreB demonstrated that "H. heilmannii" urease is more highly related to the urease from H. felis (found in the stomachs of cats and dogs) than to the urease from H. pylori. These data are consistent with 16S rDNA sequence analysis and suggest that "H. heilmannii" is phylogenetically most closely related to H. felis.

Amino Acid Sequence↗
PubMed1994

A urease-negative mutant of Helicobacter pylori constructed by allelic exchange mutagenesis lacks the ability to colonize the nude mouse stomach.

The urease of Helicobacter pylori has been proposed to be one of its pathogenic factors. A kanamycin resistance determinant was inserted in a cloned urease gene, and transformation-mediated allelic exchange mutagenesis was carried out to introduce the disrupted gene into the corresponding wild-type chromosomal region of a clinical isolate of H. pylori, CPY3401. The resulting mutant, HPT73, had the null activity of urease. Nude mouse stomachs were challenged with these two isogenic strains to examine the role of urease in pathogenesis. Gastritis was found in the CPY3401-challenged stomachs, from which bacteria indistinguishable from CPY3401 were recovered. There was no gastritis in the HPT73-challenged stomachs, and we could not recover H. pylori from them. These results indicated that H. pylori urease is essential for colonizing the nude mouse stomach.

Alleles↗
PubMed1997

Urease is not involved in the virulence of Yersinia pseudotuberculosis in mice.

A chromosomal locus (ure) involved in the production of urease activity in the bacterial pathogen Yersinia pseudotuberculosis was characterized. The genetic organization of the Y. pseudotuberculosis ure locus closely resembles that of the related ureolytic Yersinia species Y. enterocolitica. This locus encompasses seven open reading frames encoding polypeptides with predicted molecular weights of 10,894 (UreA), 15,820 (UreB), 61,001 (UreC), 25,801 (UreE), 24,551 (UreF), 20,330 (UreG), and 31,308 (UreD). The polypeptides have 85 to 96% identity with the corresponding Ure polypeptides of Y. enterocolitica serotype 0:8. Restriction fragment length polymorphisms of the ure loci from 12 unrelated Y. pseudotuberculosis strains produced by HaeIII and MboI indicate a low level of genetic variability of this locus in this species. The role of urease in the pathogenicity of Y. pseudotuberculosis was studied by constructing an isogenic urease-negative mutant obtained by disruption of structural gene ureB by aphA-3', which encodes kanamycin resistance. Experimental infection of mice with this mutant demonstrates that urease is not essential for Y. pseudotuberculosis virulence. Urease might be required mostly during the saprophytic life of this pathogen.

Amino Acid Sequence↗
PubMed1998

Mice are protected from Helicobacter pylori infection by nasal immunization with attenuated Salmonella typhimurium phoPc expressing urease A and B subunits.

Live Salmonella typhimurium phoPc bacteria were tested as mucosal vaccine vectors to deliver Helicobacter pylori antigens. The genes encoding the A and B subunits of H. pylori urease were introduced into S. typhimurium phoPc and expressed under the control of a constitutive tac promoter (tac-ureAB) or a two-phase T7 expression system (cT7-ureAB). Both recombinant Salmonella strains expressed the two urease subunits in vitro and were used to nasally immunize BALB/c mice. The plasmid carrying cT7-ureAB was stably inherited by bacteria growing or persisting in the spleen, lungs, mesenteric or cervical lymph nodes, and Peyer's patches of immunized mice, while the plasmid carrying tac-ureAB was rapidly lost. Spleen and Peyer's patch CD4+ lymphocytes from mice immunized with S. typhimurium phopc cT7-ureAB proliferated in vitro in response to urease, whereas cells from mice given S. typhimurium phoPc alone did not. Splenic CD4+ cells from mice immunized with phoPc cT7-ureAB secreted gamma interferon and interleukin 10, while Peyer's patch CD4+ cells did not secrete either cytokine. Specific H. pylori anti-urease immunoglobulin G1 (IgG1) and IgG2A antibodies were detected following immunization, confirming that both Th1- and Th2-type immune responses were generated by the live vaccine. Sixty percent of the mice (9 of 15) immunized with S. typhimurium phoPc cT7-ureAB were found to be resistant to infection by H. pylori, while all mice immunized with phoPc tac-ureAB (15 of 15) or phoPc (15 of 15) were infected. Our data demonstrate that H. pylori urease delivered nasally by using a vaccine strain of S. typhimurium can trigger Th1- and Th2-type responses and induce protective immunity against Helicobacter infection.

Animals↗
PubMed1998

The Helicobacter pylori UreI protein is not involved in urease activity but is essential for bacterial survival in vivo.

We produced defined isogenic Helicobacter pylori ureI mutants to investigate the function of UreI, the product of one of the genes of the urease cluster. The insertion of a cat cassette had a strong polar effect on the expression of the downstream urease genes, resulting in very weak urease activity. Urease activity, measured in vitro, was normal in a strain in which ureI was almost completely deleted and replaced with a nonpolar cassette. In contrast to previous reports, we thus found that the product of ureI was not necessary for the synthesis of active urease. Experiments with the mouse-adapted H. pylori SS1 strain carrying the nonpolar ureI deletion showed that UreI is essential for H. pylori survival in vivo and/or colonization of the mouse stomach. The replacement of ureI with the nonpolar cassette strongly reduced H. pylori survival in acidic conditions (1-h incubation in phosphate-buffered saline solution at pH 2.2) in the presence of 10 mM urea. UreI is predicted to be an integral membrane protein and may therefore be involved in a transport process essential for H. pylori survival in vivo.

Acids↗
PubMed2001

Identification of an antigenic epitope in Helicobacter pylori urease that induces neutralizing antibody production.

We previously reported a mouse monoclonal antibody (MAb), termed L2, specific for Helicobacter pylori urease strongly inhibited its enzymatic activity. Here, to gain insight into how this antibody affects urease activity, the epitope that was recognized by the antibody was determined. By screening a panel of overlapping synthetic peptides covering the entire sequence of the two subunits (UreA and UreB), we identified a stretch of UreB-derived 19 amino acid (aa) residues (UB-33; aa 321 to 339, CHHLDKSIKEDVQFADSRI) that was specifically recognized by the L2 antibody. Further sequential amino acid deletion of the 19-mer peptide from either end allowed us to determine the minimal epitope as 8 amino acid residues (F8; SIKEDVQF) for L2 reactivity. This epitope appears to lie exactly on a short sequence which formed a flap over the active site of urease, suggesting that binding of the L2 antibody sterically inhibits access of urea, the substrate of urease. Finally, immunization of rabbits with either the 19-mer peptide or the 8-mer minimal epitope resulted in generation of antiurease antibodies that were capable of inhibiting the enzymatic activity. Since urease is critical for virulence of H. pylori, antigenic peptides that induce production of antibodies to inhibit its enzymatic activity may potentially be a useful tool as a vaccine for prevention and treatment of H. pylori infection.

Amino Acid Sequence↗
PubMed2001

Selection for urease activity during Helicobacter pylori infection of rhesus macaques (Macaca mulatta).

Helicobacter pylori strain J166 recovered from experimentally inoculated rhesus monkeys had up to a 250-fold-increased urease activity over that before inoculation. This was found to result from the selection of urease positive J166 clones from a heterogeneous inoculum, which was predominantly urease negative due to a 1-bp insertion in the ureA gene. These results confirm the importance of urease for H. pylori colonization. Strain J166 is particularly well adapted to the rhesus monkey, since it colonized preferentially despite the fact that less than 0.1% of the inoculum was urease positive.

Animals↗
PubMed2002

Urease of enterohemorrhagic Escherichia coli: evidence for regulation by fur and a trans-acting factor.

Recent genomic analyses of Escherichia coli O157:H7 strain EDL933 revealed two loci encoding urease gene homologues (ureDABCEFG), which are absent in nonpathogenic E. coli strain K-12. This report demonstrates that the cloned EDL933 ure gene cluster is capable of synthesizing urease in an E. coli DH5alpha background. However, when the gene fragment is transformed back into the native EDL933 background, the enzymatic activity of the cloned determinants is undetectable. We speculate that an unidentified trans-acting factor in enterohemorrhagic E. coli (EHEC) is responsible for this regulation of ure expression. In addition, Fur-like recognition sites are present in three independent O157:H7 isolates upstream of ureD and ureA. Enzymatic assays confirmed a difference in urease expression of cloned EHEC ure clusters in E. coli MC3100Deltafur. Likewise, interruption of fur in O157:H7 isolate IN1 significantly diminished urease activity. We propose that, similar to the function of Fur in regulating the acid response of Salmonella enterica serovar Typhimurium, it modulates urease expression in EHEC, perhaps contributing to the acid tolerance of the organism.

Bacterial Proteins↗
PubMed1988

Multiple proteins encoded within the urease gene complex of Proteus mirabilis.

Chromosomal DNA fragments from a uropathogenic isolate of Proteus mirabilis were inserted into the cosmid vector pHC79 to construct a genomic library in Escherichia coli HB101. A urease-positive recombinant cosmid, designated pSKW1, was recovered. Sequential recombinant manipulation of pSKW1 yielded a 10.2-kilobase plasmid, designated pSKW4, which encoded three urease isozymes with electrophoretic mobilities identical to those of the donor P. mirabilis strain. Plasmid pSKW4 gene sequences encode seven proteins designated 68K (apparent molecular weight, of 68,000), 28K, 25K, 22.5K, 18.5K, 7.5K, and 5.2K within the limits of the urease gene complex. Insertion mutations in genes encoding the 68K, 28K, 25K, 22.5K, 7.5K, and 5.2K proteins resulted in complete or partial (22.5K) loss of urease activity. There was no reduction in urease activity when the gene encoding the 18.5K protein was inactivated.

Cloning, Molecular↗
PubMed1988

Proteus mirabilis urease: genetic organization, regulation, and expression of structural genes.

Proteus mirabilis, a cause of serious urinary tract infection, produces urease, an important virulence factor for this species. The enzyme hydrolyzes urea to CO2 and NH3, which initiates struvite or apatite stone formation. Genes encoding urease were localized on a P. mirabilis chromosomal DNA gene bank clone in Escherichia coli by deletion analysis, subcloning, Bal31 nuclease digestion, transposon Tn5 mutagenesis, and in vitro transcription-translation. A region of DNA between 4.0 and 5.4 kilobases (kb) in length was necessary for urease activity and was located within an 18.5-kb EcoRI fragment. The operon was induced by urea and encoded a multimeric, cytoplasmic enzyme comprising subunit polypeptides of 8,000, 10,000, and 73,000 daltons that were encoded by a single polycistronic mRNA and transcribed in that order. Seventeen urease-negative transposon insertions were isolated that synthesized either none of the structural subunit polypeptides, the 8,000-dalton polypeptide alone, or both the 8,000- and 10,000-dalton subunit polypeptides. The molecular weight of the native enzyme was estimated to be 212,000 by Superose-6 chromatography. Homologous sequences encoding the urease of Providencia stuartii synthesized subunit polypeptides of similar sizes and showed a similar genetic arrangement. However, restriction maps of the operons from the two species were distinct, indicating significant divergence.

Autoradiography↗