The role of internal urease in acid resistance of Helicobacter pylori

Scott, David; Weeks, David L.; Hong, Charlie; Postius, Stefan; Melchers, Klaus; Sachs, George

doi:10.1016/s0016-5085(98)70633-x

Cited by 265 publications

(275 citation statements)

References 49 publications

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“…100 l of overnight culture was added to 900 l of Hp Buffer (100 mM NaH 2 PO 4 , 138 mM NaCl, 0.5 mM MgCl 2 , 1 mM CaCl 2 , 10 mM glucose, 1 mM glutamine, and 5 mM [ 14 C]urea with a specific activity of 10 mCi/mmol) at various pHs and incubated for 30 min at 37°C with constant agitation. Urease activity was measured radiometrically (16) where plastic wells containing 0.5 M KOH-soaked filter paper hung from rubber stoppers were used to collect the total 14 CO 2 that resulted from the hydrolysis of urea by urease. The reaction mixture was terminated by the addition of 5 N H 2 SO 4 to expel all 14 CO 2 from solution.…”

Section: Methodsmentioning

confidence: 99%

Mechanism of Proton Gating of a Urea Channel

Weeks

Gushansky

Scott

et al. 2004

Journal of Biological Chemistry

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The size and complexity of many pH-gated channels have frustrated the development of specific structural models. The small acid-activated six-membrane segment urea channel of Helicobacter hepaticus (HhUreI), homologous to the essential UreI of the gastric pathogen Helicobacter pylori, enables identification of all the periplasmic sites of proton gating by site-directed mutagenesis. Exposure to external acidity enhances [14 C]urea uptake by Xenopus oocytes expressing HhUreI, with half-maximal activity (pH 0.5 ) at pH 6.8. A downward shift of pH 0.5 in single site mutants identified four of six protonatable periplasmic residues (His-50 at the boundary of the second transmembrane segment TM2, Glu-56 in the first periplasmic loop, Asp-59 at the boundary of TM3, and His-170 at the boundary of TM6) that affect proton gating. Asp-59 was the only site at which a protonatable residue appeared to be essential for pH gating. Mutation of Glu-110 or Glu-114 in PL2 did not affect the pH 0.5 of gating. A chimera, where the entire periplasmic domain of HhUreI was fused to the membrane domain of Streptococcus salivarius UreI (SsUreI), retained the pH-independent properties of SsUreI. Hence, proton gating of HhUreI likely depends upon the formation of hydrogen bonds by periplasmic residues that in turn produce conformational changes of the transmembrane domain. Further studies on HhUreI may facilitate understanding of other physiologically important pH-responsive channels.

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Section: Methodsmentioning

confidence: 99%

Mechanism of Proton Gating of a Urea Channel

Weeks

Gushansky

Scott

et al. 2004

Journal of Biological Chemistry

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“…The low oxygen conditions prevailing in the gastric environment are important in the activation of H. pylori virulence genes (10). Among them, urease is required for initial gastric colonization (11), allowing the bacterium to maintain its periplasmic pH near neutrality (12,13). The expression of H. pylori CagA protein, strongly associated with duodenal ulceration, is influenced through the culture medium pH in vitro (14).…”

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confidence: 99%

Microaerophilic Conditions Permit to Mimic in VitroEvents Occurring during in Vivo Helicobacter pylori Infection and to Identify Rho/Ras-associated Proteins in Cellular Signaling

Cottet

Corthésy–Theulaz

Spertini

et al. 2002

Journal of Biological Chemistry

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Molecular dissection of the mechanisms underlyingHelicobacter pylori infection suffers from the lack of in vitro systems mimicking in vivo observations. A system was developed whereby human epithelial cells (Caco-2) grown as polarized monolayers and bacteria can communicate with each other under culture conditions optimal for each partner. Caco-2 cells grown on filter supports were inserted in a vertical position into diffusion chambers equilibrated with air and 5% CO 2 at their basolateral surface (aerophilic conditions) and 5% CO 2 , 5% O 2 , 90% N 2 (microaerophilic conditions) in the apical compartment. Remarkably, the epithelial polarized layer was stable under these asymmetric culture conditions for at least 24 h, and the presence of Caco-2 cells was necessary to maintain H. pylori growth. In contrast to previous studies conducted with non-polarized Caco-2 cells and other cell lines kept under aerophilic conditions, we found H. pylori-dependent stimulation of cytokine secretion (MCP-1 (monocyte chemoattractant protein-1), GRO-␣ (growth-regulated oncogene-␣), RANTES (regulated on activation normal T cell expressed and secreted)). This correlated with nuclear translocation of NF-B p50 and p65 subunits. Tyrosine phosphorylation of nine cellular proteins was induced or enhanced; we identified p120RasGAP , p190 RhoGAP , p62dok (downstream of tyrosine kinases), and cortactin as H. pylori-inducible targets. Moreover, reduction of H. pylori urease expression was observed in adherent bacteria as compared with bacteria in suspension. In addition to mimicking several observations seen in the inflamed gastric mucosa, the novel in vitro system was allowed to underscore complex cellular events not seen in classical in vitro analyses of microaerophilic bacteria-epithelial cell cross-talk.

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“…One hypothesis attributes this observation to a number of "characteristic PPI effects", where PPIs promote focally dilated oxyntic glands with flattened or hypertrophic parietal cells protruding into their lumen, in addition to the masking of organisms at the gastric surface and promoting their presence in somewhat obscured locations making the detection of H. pylori difficult and thus causing false-negative results [2] . Another hypothesis is related to the elevation of the intragastric pH caused by PPIs, making it an unfavorable environment to H. pylori on one hand and promoting the closure of urea channels on the other hand [20][21][22] . In addition, a direct antimicrobial effect of PPIs causing a further decrease in the H. pylori load and thus making it more difficult to detect their presence has been proposed [23,24] .…”

Section: Discussionmentioning

confidence: 99%

Influence of proton pump inhibitors on gastritis diagnosis and pathologic gastric changes

Nasser

Slim

Nassif

et al. 2015

WJG

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AIM:To investigate the influence of proton pump inhibitors (PPIs) exposure on the diagnosis of Helicobacter pylori (H. pylori) gastritis and intestinal metaplasia. METHODS:Chronic PPI use is associated with masking of H. pylori infection. Patients with H. pylori infection are predisposed to gastric and duodenal ulcers, and long-term infection with this organism has been associated with gastric mucosal atrophy and serious long-term complications, such as gastric lymphoma and adenocarcinoma. Three hundred patients diagnosed with gastritis between January 2008 and April 2010 were included in our study. The computerized medical database of these patients was reviewed retrospectively in order to assess whether the type of gastritis diagnosed (H. pylori vs non-H. pylori gastritis) is influenced by PPI exposure. H. pylori density was graded as low, if corresponding to mild density following the Updated Sydney System, or high, if corresponding to moderate or severe densities in the Updated Sydney System. RESULTS:Patients were equally distributed between males and females with a median age at the time of diagnosis of 50 years old (range: 20-87). The histological types of gastritis were classified as H. pylori gastritis (n = 156, 52%) and non-H. pylori gastritis (n = 144, 48%). All patients with non-H. pylori gastritis had inactive chronic gastritis. Patients with no previous PPI exposure were more likely to be diagnosed with H. pylori gastritis than those with previous PPI exposure (71% vs 34.2%, P < 0.001). Intestinal metaplasia ORIGINAL ARTICLE Influence of proton pump inhibitors on gastritis diagnosis and pathologic gastric changes Retrospective StudySoumana C Nasser, Mahmoud Slim, Jeanette G Nassif, Selim M Nasser

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The role of internal urease in acid resistance of Helicobacter pylori

Cited by 265 publications

References 49 publications

Mechanism of Proton Gating of a Urea Channel

Mechanism of Proton Gating of a Urea Channel

Microaerophilic Conditions Permit to Mimic in VitroEvents Occurring during in Vivo Helicobacter pylori Infection and to Identify Rho/Ras-associated Proteins in Cellular Signaling

Influence of proton pump inhibitors on gastritis diagnosis and pathologic gastric changes

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