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PubMed2005

Staying alive overdosed: how does Helicobacter pylori control urease activity?

Urease, a nickel metalloenzyme is an essential virulence factor of the gastric pathogen, Helicobacter pylori. This enzyme is the major actor in the resistance to acidity and, therefore, plays a central role in colonization and persistence in the host. Urease has till recently been considered to be a constitutive and permanently active enzyme. Recent advances have revealed that the activity of this abundant protein is subtly modulated at different levels. These regulatory mechanisms mainly concern nickel insertion at the urease active site with control of both the availability and incorporation of this metal ion into the structural subunits, whose production itself is induced in some conditions. Another level of regulation is the availability of the urease substrate, urea, which is controlled by UreI, an acid-gated urea channel encoded by the urease gene cluster. We calculated that under in vitro conditions without added nickel only a small proportion of the urease active sites is filled with nickel but that this is sufficient for full acid resistance. This raised the question of why this organism produces this enzyme far in excess of its needs. We propose a model in which the role of excess urease is to maintain a pool of actively bound intracellular Ni2+ ions which can be inherited by the daughter cells to provide sufficient activated urease even in case of long-term nickel deficiency.

Bacterial Proteins↗
PubMed1998

Chemical rescue of Klebsiella aerogenes urease variants lacking the carbamylated-lysine nickel ligand.

Klebsiella aerogenes urease possesses a dinuclear metallocenter in which two nickel atoms are bridged by carbamylated Lys217. To assess whether carbamate-specific chemistry is required for urease activity, site-directed mutagenesis and chemical rescue strategies were combined in efforts to place a carboxylate group at the location of this metal ligand. Urease variants with Lys217 replaced by Glu, Cys, and Ala (K217E, K217C/C319A, and K217A proteins) were purified, shown to be activated by incubation with small organic acids plus Ni(II), and structurally characterized. K217C/C319A urease possessed a second change in which Cys319 was replaced by Ala in order to facilitate efforts to chemically modify Cys217; however, this covalent modification approach did not produce active urease. Chemical rescue of the K217E, K217C/C319A, and K217A variants required 2, 2, and 10 h, respectively, to reach maximal activity levels. The highest activity generated [224 micromol of urea degraded.min-1.(mg of protein)-1, for K217C/C319A urease incubated with 500 mM formic acid and 10 mM Ni at pH 6.5] corresponded to 56% of that measured for in vitro activation of the wild-type apoprotein. While the K217E apoprotein showed minimal structural perturbations, the K217C/C319A apoprotein showed a disordering of some active site residues, and the K217A apoprotein revealed a repositioning of His219 to allow the formation of a hydrogen bond with Thr169, thus replacing the hydrogen bond between the amino group of Lys217 and Thr169 in the native enzyme. Importantly, these structures allow rationalization of the relative rates and yields of chemical rescue experiments. The crystal structures of chemically rescued K217A and K217C/C319A ureases revealed a return of the active site residues to their wild-type positions. In both cases, noncovalently bound formate was structurally equivalent to the Lys-carbamate as the bridging metallocenter ligand. We conclude that carbamate-specific chemistry is not required for urease catalysis.

Alanine↗
PubMed1999

Identification of metal-binding residues in the Klebsiella aerogenes urease nickel metallochaperone, UreE.

The urease accessory protein encoded by ureE from Klebsiella aerogenes is proposed to bind intracellular Ni(II) for transfer to urease apoprotein. While native UreE possesses a histidine-rich region at its carboxyl terminus that binds several equivalents of Ni, the Ni-binding sites associated with urease activation are internal to the protein as shown by studies involving truncated H144UreE [Brayman and Hausinger (1996) J. Bacteriol. 178, 5410-5416]. Nine potential Ni-binding residues (five His, two Cys, one Asp, and one Tyr) within H144UreE were independently substituted by mutagenesis to determine their roles in metal binding and urease activation. In vivo effects of these substitutions on urease activity were measured in Escherichia coli strains containing the K. aerogenes urease gene cluster with the mutated ureE genes. Several mutational changes led to reductions in specific activity, with substitution of His96 producing urease activity below the level obtained from a ureE deletion mutant. The metal-binding properties of purified variant UreE proteins were characterized by a combination of equilibrium dialysis and UV/visible, EPR, and hyperfine-shifted 1H NMR spectroscopic methods. Ni binding was unaffected for most H144UreE variants, but mutant proteins substituted at His110 or His112 exhibited greatly reduced affinity for Ni and bound one, rather than two, metal ions per dimer. Cys79 was identified as the Cu ligand responsible for the previously observed charge-transfer transition at 370 nm, and His112 also was shown to be associated with this chromophoric site. NMR spectroscopy provided clear evidence that His96 and His110 serve as ligands to Ni or Co. The results from these and other studies, in combination with prior spectroscopic findings for metal-substituted UreE [Colpas et al. (1998) J. Biol. Inorg. Chem. 3, 150-160], allow us to propose that the homodimeric protein possesses two nonidentical metal-binding sites, each symmetrically located at the dimer interface. The first equivalent of added Ni or Co binds via His96 and His112 residues from each subunit of the dimer, and two other N or O donors. Asp111 either functions as a ligand or may affect this site by secondary interactions. The second equivalent of Ni or Co binds via the symmetric pair of His110 residues as well as four other N or O donors. In contrast, the first equivalent of Cu binds via the His110 pair and two other N/O donors, while the second equivalent of Cu binds via the His112 pair and at least one Cys79 residue. UreE sequence comparisons among urease-containing microorganisms reveal that residues His96 and Asp111, associated with the first site of Ni binding, are highly conserved, while the other targeted residues are missing in many cases. Our data are most compatible with one Ni-binding site per dimer being critical for UreE's function as a metallochaperone.

Amino Acid Sequence↗
PubMed2000

The soybean Eu3 gene encodes an Ni-binding protein necessary for urease activity.

Mutation in Eu3 eliminates activity of both soybean ureases, the embryo-specific (encoded by Eu1) and the tissue-ubiquitous (encoded by Eu4). eu3-e1 is a completely recessive null allele. Eu3-e3 is a semi-dominant specifying 0.1% wild-type urease activity in the homozygous state and 5-10% as a heterozygote (Meyer-Bothling et al. 1987). Antibodies to plant UreG, a homologue of the bacterial urease accessory protein, revealed a 32 kDa protein (p32) in embryos of the Eu3/Eu3 precursor genotype. p32 is identical to UreG by the criteria of size, antigenicity, and its ability to bind Ni2+, a trait expected from the deduced histidine-rich N-terminus of UreG. UreG was absent in eu3-e1/eu3-e1, and lack of UreG co-segregated with eu3-e1. Eu3-e3 specified a UreG transcript which coded valine in place of alanine at residue 142 (A142V) confirming thatEu3 encodes UreG, which is renamed Eu3. Eu3 (A142V) retained Ni-binding ability. Eu3 is directly involved in urease activation, since anti-Eu3 (UreG) antibodies inhibited the in vitro activation of urease. Eu1 (embryo urease) and Eu3 accumulated in parallel in the developing embryo. The presence of Eu1 was not necessary for the high embryonic level of Eu3. However, the presence of Eu3 appeared to be important for accumulation of Eu1, perhaps by stabilizing it by Ni insertion. At the level of sensitivity employed Eu3 was detected in crude extracts of embryos but not non-embryonic tissues which have 1/500th the embryo urease activity. Functional Eu3, however, is necessary for activation of the ubiquitous urease in non-embryonic tissues.

Amino Acid Sequence↗
PubMed1976

Urease activity in the rumen of sheep and the isolation of ureolytic bacteria.

Urease activity in the sheep rumen varied with the diet of the sheep, but appeared to be largely or entirely present in the small bacterial fraction. Screening of over 1000 strains of rumen bacteria isolated on different media showed that urease activity was apparently confined to species of Staphylococcus, Lactobacillus casei var. casei and Klebsiella aerogenes. Consideration of the numbers in which these occurred and their activities suggested that the bacteria could not be responsible for the total rumen urease activity. By enrichment culture a ureolytic strain of Streptococcus faecium was isolated. This had a higher urease activity than the other bacteria and occurred in higher numbers in the rumen. It could live with other bacteria in the rumen of a gnotobiotic lamb in numbers, and with a urease activity, comparable with those in the normal sheep rumen. The other properties of the bacterium also suggested that it would grow and produce urease in the rumen, but was unlikely to retain its urease activity after isolation. It was concluded that this bacterium was the main source of rumen urease in roughage-fed, and probably other, sheep.

Acetates↗
PubMed2006

Identification of a novel gene, URE2, that functionally complements a urease-negative clinical strain of Cryptococcus neoformans.

A urease-negative serotype A strain of Cryptococcus neoformans (B-4587) was isolated from the cerebrospinal fluid of an immunocompetent patient with a central nervous system infection. The URE1 gene encoding urease failed to complement the mutant phenotype. Urease-positive clones of B-4587 obtained by complementing with a genomic library of strain H99 harboured an episomal plasmid containing DNA inserts with homology to the sudA gene of Aspergillus nidulans. The gene harboured by these plasmids was named URE2 since it enabled the transformants to grow on media containing urea as the sole nitrogen source while the transformants with an empty vector failed to grow. Transformation of strain B-4587 with a plasmid construct containing a truncated version of the URE2 gene failed to complement the urease-negative phenotype. Disruption of the native URE2 gene in a wild-type serotype A strain H99 and a serotype D strain LP1 of C. neoformans resulted in the inability of the strains to grow on media containing urea as the sole nitrogen source, suggesting that the URE2 gene product is involved in the utilization of urea by the organism. Virulence in mice of the urease-negative isolate B-4587, the urease-positive transformants containing the wild-type copy of the URE2 gene, and the urease-negative vector-only transformants was comparable to that of the H99 strain of C. neoformans regardless of the infection route. Virulence of the URE2 disruption stain of H99 was slightly reduced compared to the wild-type strain in the intravenous model but was significantly attenuated in the inhalation model. These results indicate that the importance of urease activity in pathogenicity varies depending on the strains of C. neoformans used and/or the route of infection. Furthermore, this study shows that complementation cloning can serve as a useful tool to functionally identify genes such as URE2 that have otherwise been annotated as hypothetical proteins in genomic databases.

Animals↗
PubMed1995

Essential role of urease in germination of nitrogen-limited Arabidopsis thaliana seeds.

In Arabidopsis thaliana, urease transcript levels increased sharply between 2 and 4 d after germination (DAG) and were maintained at maximal levels until at least 8 DAG. Seed urease specific activity declined upon germination but began to increase in seedlings 2 DAG, reaching approximately 75% of seed activity by 8 DAG. Urea levels showed a small transient increase 1 DAG and then approximately paralleled urease activity, reaching maximal levels at approximately 9 DAG. Urease inhibition with phenylphosphorodiamidate resulted in a 2- to 4-fold increase in urea levels throughout seedling development. Arginine pools (0-8 DAG) changed approximately in parallel with the urea pool. Consistent with arginine being a major source of urea, arginase activity increased 10-fold in the interval 0 to 6 DAG. Allopurinol, a xanthine dehydrogenase inhibitor, had no effect on urea levels up to 3 DAG but reduced the urea pool by 30 to 40% during the interval 5 to 8 DAG, suggesting that purine degradation contributed to the urea pool well after germination, if at all. in aged Arabidopsis seeds, there was correlation between phenylphosphorodiamidate inactivation of urease and germination inhibition, the latter overcome by NH4NO3 or amino acids. Since urease activity, urea precursor, and urea increase in young seedlings, and since urease inactivation results in a nitrogen-reversible inhibition of germination, we propose that urease recycles urea-nitrogen in the seedling.

Allopurinol↗
PubMed1989

Electrophoretic analysis of ureases in Streptococcus salivarius and in saliva.

Experimental conditions were established for the extraction, electrophoresis and detection of urease isoenzymes from Streptococcus salivarius. Thiol concentrations were critical and ureases from different strains varied in ease of dissociation. A characteristic pattern was obtained for 30 ureolytic S. salivarius strains isolated from; saliva (6), dental plaque (12), artificial dental plaque (6) and non-oral sources (6), and also for a ureolytic Streptococcus bovis from artificial plaque. One non-oral S. salivarius strain had ureases with slightly slower mobility. The electrophoretic pattern and mobility of ureases extracted from human mixed salivary bacteria were identical to those from S. salivarius except for an additional set of urease bands from unknown species of bacteria. There were no ureases from saliva matching those from Staphylococcus epidermidis--a contributor to ureolysis in artificial plaque. We conclude that there is considerable biochemical homogeneity among S. salivarius ureases and possibly other ureolytic streptococci. In saliva, urea is metabolized mainly by streptococcal ureases.

Dental Plaque↗
PubMed1998

The effect of test duration on the sensitivity and specificity of ultra-rapid urease test for the detection of Helicobacter pylori infection.

BACKGROUND: 'Home made' ultra-rapid urease tests are used extensively in the Asia Pacific region. Data on the reliability of these 'home made' tests are limited. AIMS: To evaluate the effect of test duration on the sensitivity and specificity of a self-prepared biopsy urease test for the detection of Helicobacter pylori. METHODS: Using histology as the 'gold standard', the effect of test duration on the sensitivity and specificity of a self prepared urease test for the detection of H. pylori was evaluated in 411 consecutive patients undergoing upper gastrointestinal endoscopy. RESULTS: Histology was positive for H. pylori in 217 of the 411 patients (52.8%). Within 24 hours of retrieving the specimen, 189 (87.1%) of the histology positives and 174 (89.7%) of the histology negatives were correctly identified by the urease test. Of the H. pylori positives, 72.0%, 81.0%, 89.9% and 100% were detected by the urease test within one minute, five minutes, three hours and 24 hours respectively. Thus, sensitivities of the urease test at one minute, five minutes, three hours and 24 hours were 62.7%, 70.5%, 78.3% and 87.1% respectively. Corresponding figures for the specificity were 93.8%, 93.3%, 92.3% and 89.7% respectively. Using a receiver-operating characteristic curve, an optimal combination of sensitivity and specificity was obtained when the urease test was read at 24 hours. CONCLUSIONS: While the biopsy urease test was positive in most cases within a minute, better results could be obtained if the test continued to be read over a 24 hour period.

Adolescent↗
PubMed2005

Characteristics of a clinical isolate of urease-negative Helicobacter pylori and its ability to induce gastric ulcers in Mongolian gerbils.

BACKGROUND: We clinically obtained urease-negative mutant strains of Helicobacter pylori. The goal of this study was to investigate the ability of the urease-negative strain to colonize and subsequently damage the gastric mucosa in Mongolian gerbils. In addition, the genes encoding the urease production in the test strain were analyzed, and other genes encoding the virulence factors, cytotoxin-associated protein and vacuolating-cytotoxin were evaluated. MATERIALS AND METHODS: The character of urease-negative isolates of H. pylori was defined. The identification of H. pylori was confirmed by polymerase chain reaction (PCR). The H. pylori isolate was transfected into Mongolian gerbils as previously described, which were followed up to 42 weeks, and the changes in their gastric mucosa were examined histologically. RESULTS AND CONCLUSION: Fifteen Mongolian gerbils orally infected with 10(7) colony forming units of urease-negative H. pylori were killed at 4, 12, 24, 36 and 42 weeks (n = 3) after infection. Culture medium without urease-negative H. pylori was given to the Mongolian gerbils as control. H. pylori continued to exist in the subject's stomach and gastric ulceration was observed and compared with the control. Clinically obtained urease-negative H. pylori continued to exist for at least 42 weeks in the subject's stomach and it induced gastric ulcers. These data demonstrated that the urease in H. pylori was not a necessary factor in the formation of gastric ulcers in the Mongolian gerbil model.

Animals↗
PubMed1993

Potent inhibitory action of the gastric proton pump inhibitor lansoprazole against urease activity of Helicobacter pylori: unique action selective for H. pylori cells.

The gastric proton pump inhibitor lansoprazole, its active analog AG-2000, and omeprazole dose dependently inhibited urease activity extracted with distilled water from Helicobacter pylori cells; the 50% inhibitory concentrations were between 3.6 and 9.5 microM, which were more potent than those of urease inhibitors, such as acetohydroxamic acid, hydroxyurea, and thiourea. These compounds also inhibited urease activity in intact cells of H. pylori and Helicobacter mustelae but did not inhibit ureases from other bacteria, such as Proteus vulgaris, Proteus mirabilis, and Providencia rettgeri. The mechanism of urease inhibition was considered to be blockage of the SH groups of H. pylori urease, since SH residues in the enzyme decreased after preincubation with lansoprazole and glutathione or dithiothreitol completely abolished the inhibitory action. The SH-blocking reagents N-ethylmaleimide and idoacetamide were also examined for their inhibition of the urease activity; their 50% inhibitory concentrations were 100- to 1,000-fold higher than those of lansoprazole. These results suggest that lansoprazole and omeprazole can potently and selectively inhibit H. pylori urease and that inhibition may be related to earlier findings indicating that these compounds have selective activity against HP growth.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed1995

Inhibitory action of lansoprazole and its analogs against Helicobacter pylori: inhibition of growth is not related to inhibition of urease.

The proton pump inhibitors omeprazole and lansoprazole and its acid-activated derivative AG-2000, which are potent and specific inhibitors of urease of Helicobacter pylori (K. Nagata, H. Satoh, T. Iwahi, T. Shimoyama, and T. Tamura, Antimicrob. Agents Chemother. 37:769-774, 1993), inhibited the growth of H. pylori. The growth was inhibited not only in urease-positive clinical isolates but also in their urease-negative derivatives which had no urease polypeptides. AG-1789, a derivative of lansoprazole with no inhibitory activity against H. pylori urease, also inhibited the growth of both strains even more strongly than the urease inhibitors lansoprazole and AG-2000. Furthermore, the antibacterial activity of omeprazole and lansoprazole was not affected by glutathione or dithiothreitol, which completely abolished the inhibitory activity of lansoprazole against H. pylori urease. These results indicated that the inhibitory action of these compounds against the growth of H. pylori was independent from the inhibitory action against urease.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed2002

Specific serum immunoglobulin G response to urease and CagA antigens of Helicobacter pylori in infected children and adults in a country with high prevalence of infection.

Few studies have analyzed the immune response to Helicobacter pylori CagA and urease antigens across age groups in the same population. The aim of this study was to analyze the serologic immunoglobulin G (IgG) response to CagA and urease proteins in children and adults with gastrointestinal symptoms and belonging to the same population and similar socioeconomic levels. The serologic response was studied in 352 children and 293 adults with gastrointestinal symptoms. IgG antibodies against CagA and urease were tested by enzyme-linked immunosorbent assay methods using highly purified recombinant antigens. H. pylori infection was defined as a positive result in a serologic assay using whole-cell H. pylori extracts as the antigen. We found, in H. pylori-positive children, a seroprevalence of 46.9% to CagA and 16.2% to urease, whereas in H. pylori-positive adults, a seroprevalence of 78.9% to CagA and 59% to urease was found. In children, the magnitude of the response to CagA was significantly higher and the response to urease was significantly lower than those in adults. The kinetics of serologic response to CagA and to urease across age groups was contrastably different. Whereas CagA is a strong immunogen, urease is a poor immunogen during natural infection. These differences in the humoral response may be important for the short-term or long-term outcome of the infection. These results add to our knowledge of the epidemiology of H. pylori infection.

Adolescent↗
PubMed2006

Iron-responsive repression of urease expression in Helicobacter hepaticus is mediated by the transcriptional regulator Fur.

Persistent colonization of mucosal surfaces by bacteria in the mammalian host requires concerted expression of colonization factors, depending on the environmental conditions. Helicobacter hepaticus is a urease-positive pathogen that colonizes the intestinal and hepatobiliary tracts of rodents. Here it is reported that urease expression of H. hepaticus is iron repressed by the transcriptional regulator Fur. Iron restriction of growth medium resulted in a doubling of urease activity in wild-type H. hepaticus strain ATCC 51449 and was accompanied by increased levels of urease subunit proteins and ureA mRNA. Insertional inactivation of the fur gene abolished iron-responsive repression of urease activity, whereas inactivation of the perR gene did not affect iron-responsive regulation of urease activity. The iron-responsive promoter element was identified directly upstream of the H. hepaticus ureA gene. Recombinant H. hepaticus Fur protein bound to this ureA promoter region in a metal-dependent matter, and binding resulted in the protection of a 41-bp, Fur box-containing operator sequence located at positions -35 to -75 upstream of the transcription start site. In conclusion, H. hepaticus Fur controls urease expression at the transcriptional level in response to iron availability. This represents a novel type of urease regulation in ureolytic bacteria and extends the already diverse regulatory repertoire of the Fur protein.

Bacterial Proteins↗
PubMed1989

Staphylococcus saprophyticus urease: characterization and contribution to uropathogenicity in unobstructed urinary tract infection of rats.

We studied the biochemical properties of the urease of Staphylococcus saprophyticus and the possible role of the urease in experimental urinary tract infections. For this purpose, the nonhemagglutinating and nonadherent strain 9325, which was isolated from a case of symptomatic urinary tract infection, was used. The urease was shown to have a Km of 6.64 mM urea and a Vmax of 4.59 mumol NH3.min-1.mg-1. The enzyme was inhibited by acetohydroxamic acid in a noncompetitive manner. By means of Sephacryl S-300 column chromatography, we determined a mean molecular weight (+/- standard error of the mean) of 420,000 +/- 16,000. To assess the contribution of S. saprophyticus urease to uropathogenicity, a urease-negative mutant was constructed by nitrosoguanidine mutagenesis. In the rat model of ascending unobstructed urinary tract infection, higher numbers of CFU.gram of tissue-1 and more-severe lesions were detected with the parent strain. Moreover, bladder stones were found in animals infected with the urease-positive strain only. Interestingly, the difference in mean bacterial counts of the bladders was found to be significant by the Wilcoxon two-sample test (P less than 0.05), whereas that between the kidney bacterial counts was not. Immunoblot studies revealed a faint antibody response in rats infected with the mutant strain, although bacteria could still be detected in the kidneys after 7 days. Sera of animals challenged with the parent strain reacted strongly with many antigens of S. saprophyticus. Our data indicate that urease is a major factor for invasiveness of S. saprophyticus, especially in the tissue of the bladder, whereas persistence in the urinary tract and nephropathogenicity of this organism are governed by factors other than urease.

Animals↗
PubMed1991

Effect of urease on HeLa cell vacuolation induced by Helicobacter pylori cytotoxin.

Concentrated broth culture supernatants from 50 to 60% of Helicobacter pylori strains induce eukaryotic cell vacuolation in vitro. A quantitative assay for cell vacuolation was developed on the basis of the rapid uptake of visibly vacuolated HeLa cells was significantly greater than that of nonvacuolated cells. By using the rapid NRU assay, we sought to determine the roles of H. pylori cytotoxin, urease, and ammonia in the vacuolation of HeLa cells. The NRU of HeLa cells incubated in medium containing ammonium chloride or ammonium sulfate was significantly greater than that of cells incubated in medium alone. In addition, ammonium salts augmented the NRU induced by H. pylori supernatants. The NRU induced by jack bean urease was augmented by the addition of urea to cell culture medium; this suggests that urease-mediated NRU occurs via the generation of ammonia. Acetohydroxamic acid blocked the NRU induced by jack bean urease and urea but failed to block the uptake induced by H. pylori supernatants. Supernatant from a non-urease-producing H. pylori mutant strain induced NRU identical to that of the urease-positive parental strain. These observations indicate that the vacuolating activity in H. pylori supernatants is not mediated solely by urease activity but that it may be potentiated by urease-mediated ammonia production.

Ammonium Chloride↗
PubMed1994

Effect of gastric pH on urease-dependent colonization of gnotobiotic piglets by Helicobacter pylori.

Thirty-seven gnotobiotic piglets from seven litters were infected with either Helicobacter pylori N6 or urease-negative H. pylori N6ureG::Km which contains an insertion in the ureG gene and produces inactive urease. To produce achlorhydria, piglets were treated throughout the experiment with omeprazole (5 mg intravenously every 12 h) and ranitidine (75 mg orally every 6 h). Treatment resulted in elevation of gastric pH to 7.0 +/- 1.1 throughout the experiment. Control piglets were not treated and remained normochlorhydric. Strain N6 colonized well in both normal and achlorhydric piglets. All 10 piglets were colonized, and colonization ranged from 4.4 +/- 1.5 log10 CFU/g of gastric mucosa in normochlorhydric piglets sacrificed after 2 days to 6.9 +/- 0.5 log10 CFU/g in normochlorhydric piglets sacrificed after 5 days. Strain N6ureG::Km did not colonize any of seven normochlorhydric piglets and was recovered only in low numbers (< 100 CFU/g) from four of nine achlorhydric piglets. In the second experiment, piglets were coinoculated with both strains N6 and N6ureG::Km. Coinoculation did not affect colonization by urease-positive N6. Urease-deficient N6ureG::Km was unable to colonize even in the presence of urease-positive bacteria. These results confirm that urease enzymatic activity (and not urease protein) is essential for colonization, that this effect is independent of diffusible products of urea metabolism, and that gastric pH protection is not a major role of urease in promoting colonization by H. pylori.

Animals↗
PubMed1998

Urease plays an important role in the chemotactic motility of Helicobacter pylori in a viscous environment.

Helicobacter pylori exhibits chemotactic responses to urea, flurofamide, acetohydroxamic acid, and sodium bicarbonate. In buffer, the chemotactic activities of a urease-positive strain were higher than those of the isogenic urease-negative strain. Moreover, the chemotactic activities of the urease-positive strain were increased in a viscous solution containing 3% polyvinylpyrrolidone, whereas those of the urease-negative mutant were not. These results are in accordance with the fact that the mutant strain did not show swarming in motility agar regardless of having flagella. Incubation of the wild-type strain with flurofamide resulted in partial inhibition of the chemotactic activities in the viscous solution. In addition, incubation with acetohydroxamic acid, a low-molecular-weight, diffusible urease inhibitor, resulted in complete loss of chemotactic activity in the viscous solution. The inhibition of the chemotactic activity by urease inhibitors paralleled the inhibition of urease. The chemotactic activity of H. pylori was also inhibited by the proton carrier carbonyl cyanide m-chlorophenylhydrazone, showing that H. pylori utilizes proton motive force for motility. These results indicate that cytoplasmic urease plays an important role in the chemotactic motility of H. pylori under a condition that mimics the ecological niche of the bacterium, the gastric mucous layer.

Benzamides↗