1 Theodor-Boveri-Institut für Biowissenschaften, Lehrstuhl für Mikrobiologie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
2 Molecular Immunology Unit, Chiron Vaccines, Via Fiorentina 1, 53100 Siena, Italy
Correspondence
Dagmar Beier
d.beier{at}biozentrum.uni-wuerzburg.de
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ABSTRACT |
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INTRODUCTION |
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Bacterial chemotaxis is a bias of movement towards beneficial or away from harmful chemicals. It has been reported that in vitro, H. pylori exhibits chemotaxis towards urea and various amino acids, while bile acids act as chemorepellents (Yoshiyama et al., 1999; Cerda et al., 2003
; Worku et al., 2004
). The biochemical processes governing chemotactic behaviour have been extensively studied in Escherichia coli (reviewed by Szurmant & Ordal, 2004
; Wadhams & Armitage, 2004
). Briefly, binding of a ligand to the extracytoplasmic domain of a methyl-accepting chemotaxis protein (MCP) induces a conformational change of its cytoplasmic signalling domain which interacts with the adaptor protein CheW and the histidine kinase CheA. Changes in MCP conformation alter the autokinase activity of CheA and phosphorylated CheA transfers the phosphoryl group from the conserved histidine residue of its P1 domain to the response regulator CheY. The phosphorylated CheY (CheY
P) interacts directly with the protein FliM in the flagellar motor switch complex to change the direction of flagellar rotation. The response is terminated by CheZ which accelerates the hydrolysis of CheY
P.
From the genome sequence, which contains nine orthologues to known chemotaxis genes (Alm et al., 1999; Tomb et al., 1997
), it can be predicted that chemotactic signalling in H. pylori differs from the enterobacterial paradigm. H. pylori encodes three classical MCPs (HP0082, HP0099, HP0103), which are likely to sense ligands external to the cell, a soluble MCP orthologue (HP0599) which might respond to internal physiological signals, a coupling protein CheW (HP0391), a histidine kinase CheA containing a C-terminal CheY-like receiver domain (CheAY2/HP0392) and a separate CheY response regulator (CheY1/HP1067). Orthologues of the genes cheR encoding a methyltransferase and cheB encoding a response regulator with methylesterase activity are not present. In E. coli CheR and CheB are part of a stimulus-adaptation system which acts by modulating the ability of the MCPs to induce CheA autophosphorylation through the reversible methylation of glutamic acid residues in the cytoplasmic methylation region of the MCPs. Interestingly, the H. pylori MCPs contain several of the conserved glutamate residues of the methylation domain and the closely related organisms Helicobacter hepaticus, Campylobacter jejuni and Wolinella succinogenes encode orthologues of CheR and CheB; however, these CheB-like proteins do not contain a receiver domain (Parkhill et al., 2000
; Baar et al., 2003
; Suerbaum et al., 2003
). H. pylori contains three orthologues of the CheV protein which was first described in Bacillus subtilis and was shown to be involved in the adaptation to attractants in this organism. CheV consists of an N-terminal CheW-like domain and a C-terminal receiver domain. Phosphorylation of the receiver domain of CheV is required for efficient adaptation (Karatan et al., 2001
). Inactivation of cheV1 (HP0019) significantly reduced swarming of H. pylori on semi-solid agar plates, while swarming was unchanged in insertion mutants of cheV2 (HP0616) and cheV3 (HP0393), respectively, and in a cheV2/cheV3 double mutant (Pittman et al., 2001
). Therefore, the mechanisms of adaptation adopted by H. pylori remain unclear.
An orthologue of the CheYP-specific phosphatase CheZ, which is involved in signal termination in
- and
-Proteobacteria, is missing in H. pylori. However, the presence of a CheY protein (CheY2) fused to the C terminus of the histidine kinase CheA as well as of a separate CheY response regulator (CheY1) is reminiscent of the chemotaxis system of Sinorhizobium meliloti. This organism encodes two separate CheY proteins which are both rapidly phosphorylated by CheA. However, only one CheY protein (CheY2) interacts with the flagellar motor when phosphorylated and, therefore, controls flagellar rotation directly, while the second CheY protein (CheY1) functions as a modulator of the chemotactic response by acting as a phosphate sink which drains away the phosphoryl group from CheY2
P via retro-phosphorylation of the histidine kinase CheA. Since CheY1 is present in S. meliloti in a tenfold excess over CheA, retro-phosphorylation in the signal transduction chain is an efficient mechanism for dephosphorylation of CheY2
P (Schmitt, 2002
).
Since virtually nothing is known about the molecular mechanisms controlling chemotaxis, which is an important virulence trait, in H. pylori, we purified the recombinant two-component chemotaxis proteins to investigate the phosphotransfer reactions between the different signalling modules in vitro. We show that CheY1, CheY2 and the three CheV proteins dephosphorylate CheAP efficiently, but exhibit different affinities towards CheA. Furthermore, our data indicate that CheAY2 is retrophosphorylated by CheY1
P, suggesting a role of the C-terminal CheY2 domain of CheAY2 as a phosphate sink to modulate the half-life of CheY1
P.
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METHODS |
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In vitro phosphorylation assays.
In vitro phosphorylation assays were carried out at 30 °C in a final volume of 25 µl reaction buffer (50 mM Tris/HCl, pH 7·5, 50 mM KCl, 10 mM MgCl2, 0·2 mM ATP) containing CheAY2 or CheA' and, where appropriate, the respective response regulator proteins. The concentration of proteins and the reaction times applied are specified in the figure legends. Autophosphorylation of CheAY2 and CheA', as well as transphosphorylation of CheY1, CheY1-D53N, CheY2, CheV1, CheV2 and CheV3 in the presence of CheAY2 and CheA', respectively, under multiple turnover conditions, was initiated by the addition of 50 nM [-32P]ATP (5000 Ci mmol1). Phosphotransfer reactions from CheA'
P to CheY1, CheY1-D53N, CheY2, CheV1, CheV2 and CheV3, respectively, were initiated by the addition of the respective response regulator protein to CheA' which had been incubated for 15 min in the presence of 50 nM [
-32P]ATP (5000 Ci mmol1) in reaction buffer. To determine the dephosphorylation rates of CheAY2
P and CheA'
P, either 2 µM CheAY2 or 2 µM CheA' were phosphorylated in the presence of 50 nM [
-32P]ATP at 30 °C for 10 and 15 min, respectively. Subsequently, both reactions were chased by the addition of unlabelled ATP to a final concentration of 10 mM. To analyse the dephosphorylation rate of CheY2 in the presence of other chemotaxis response regulator proteins, CheA' and CheY2 were incubated with 50 nM [
-32P]ATP for 15 min at 30 °C. Then unlabelled ATP and/or the respective response regulator protein was added. The reactions were stopped at the indicated time points by the addition of sample buffer (60 mM Tris/HCl, pH 7·5, 50 mM Na2EDTA, 10 % glycerol, 2 % SDS, 5 %
-mercaptoethanol, 0·05 % bromophenol blue) and the reaction mixtures were separated by electrophoresis on SDS-15 % polyacrylamide gels (1·5 mm). Quantification of the signals was performed using a Typhoon 9200 Variable Mode Imager (Amersham Biosciences) and ImageMaster TotalLab Software (Amersham Biosciences). All experiments were performed at least three times independently.
In vitro phosphorylation of the purified response regulator proteins with radioactively labelled acetyl phosphate was performed by incubating CheY1, CheY2, CheV1, CheV2 and CheV3, respectively, for 10 min at room temperature in a final volume of 25 µl in reaction buffer (50 mM Tris/HCl, pH 7·5, 50 mM KCl, 10 mM MgCl2) containing 5 µCi 32P-labelled acetyl phosphate (80 Ci mmol1; Hartmann Analytic). The dephosphorylation rates of CheY1P and CheY2
P in the absence of CheA' were determined by phosphorylating the response regulators in the presence of 5 µCi 32P-labelled acetyl phosphate (80 Ci mmol1) for 10 min at room temperature and subsequently chasing the reactions by the addition of unlabelled acetyl phosphate to a final concentration of 10 mM. Retrophosphorylation experiments were performed in a final volume of 50 µl reaction buffer in the presence of 5 µCi 32P-labelled acetyl phosphate (80 Ci mmol1). The analysis of samples and signal quantification was performed as described above.
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RESULTS |
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We then performed a chase experiment to measure the decay of CheY2P in the absence of multiple phosphorylation turnover. When an excess of unlabelled ATP was added to CheA' and CheY2 which were preincubated in the presence of [
32-P]ATP for 15 min, the kinetics of CheY2
P hydrolysis was very similar to the time course obtained after addition of CheY1 to the reaction mixture (compare Fig. 4b and 4c
). Under these experimental conditions the half-life of CheY2
P was determined to be 3·3 min. The simultaneous addition of CheY1 and unlabelled ATP had no pronounced effect on the half-life of CheY2
P (3·0 min; Fig. 4c
). The difference in the kinetics of dephosphorylation of CheY2
P observed in the absence or presence of an excess of unlabelled ATP indicated that, in the unchased reaction, phosphorylation of CheA' and phosphotransfer to CheY2 continuously occurred in the investigated time period, resulting in the presence of a higher relative amount of CheY2
P after 30 min incubation. It should be noted that CheA'
P was hardly detectable in the time-course experiments (data not shown). Therefore, we conclude that the effect on the half-life of CheY2
P observed after addition of CheY1 to a mixture of CheA' and CheY2 in the presence of [
32-P]ATP is due to the almost exclusive phosphorylation of CheY1 by newly formed CheA'
P as a consequence of a more efficient interaction with CheA'
P. Consequently, the prevalence of CheY1 in the competition for the phosphoryl group donor CheA'
P almost completely blocks any further phosphorylation of CheY2. These data suggest that CheY1 interacts more efficiently with CheA'
P, possibly through a higher affinity for the histidine kinase than CheY2. This is also supported by the observation that CheY1 caused the complete dephosphorylation of CheA'
P within 10 s at 0 °C when it was added to CheA' phosphorylated with [
32-P]ATP for 15 min, while about 20 % of the initial amount of CheA'
P was still detectable when CheY2 was investigated under the same experimental conditions (data not shown).
Phosphorylation of CheY1 and CheY2 by acetyl phosphate and retrophosphorylation of CheAY2 by CheY1P
Several response regulator proteins including CheY of E. coli are phosphorylated in vitro in the presence of low-molecular-mass phosphate donors like acetyl phosphate (McCleary & Stock, 1994; Lukat et al., 1992
). When the recombinant CheY1 and CheY2 proteins of H. pylori were incubated with 32P-labelled acetyl phosphate, phosphorylation of both response regulators was observed (Fig. 5
). However, the efficiency of in vitro phosphorylation differed significantly since CheY2 had to be present at a concentration of 24 µM to detect CheY2
P (Fig. 5
, lane 1), while a strong phosphorylation signal was obtained when CheY1 was included in the reaction mixture at a concentration of 7 µM (Fig. 5
, lane 2). In vitro phosphorylation of CheV2 by acetyl phosphate could also be detected (Fig. 5
, lane 4), while CheV1 and CheV3 were not phosphorylated under these conditions (Fig. 5
, lanes 3 and 5, respectively). However, the presence of rather low concentrations of CheV1 and CheV3 in the reaction mixtures, which was due to the lower solubility of the recombinant proteins, might account for the lack of detectable phosphorylation. Chase experiments with unlabelled acetyl phosphate revealed that CheY1
P was hydrolysed completely within 30 min of incubation, displaying a half-life of 20 s. In contrast, CheY2
P exhibited increased stability under these conditions since about 55 % of the initial amount of CheY2
P was still detectable after a 30 min chase (data not shown). As expected, the CheY-D53N protein could not be phosphorylated when incubated with 32P-labelled acetyl phosphate (data not shown), suggesting the phosphorylation of the response regulators on the conserved aspartic acid residue by the low-molecular-mass phosphate donor molecule.
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DISCUSSION |
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Both CheY1 and CheY2 caused the efficient dephosphorylation of CheAY2P and CheA'
P (Fig. 3
), while the phosphorylation state of the H. pylori histidine kinases HP244 and HP165 used as a control was unaffected by the addition of the chemotaxis response regulators (data not shown), demonstrating that CheAY2 constitutes the cognate histidine kinase for both CheY1 and CheY2. Unexpectedly, phosphorylated CheY1 did not accumulate in multiple turnover phosphotransfer reactions with CheAY2 or CheA', but this may possibly be explained by a relatively slow autophosphorylation of CheA in vitro when compared to the comparatively rapid hydrolysis of CheY1
P. For the intrinsic dephosphorylation of CheY1
P a half-life of 20 s was determined, which is in the same range as the half-life of CheY
P from E. coli (Lukat et al., 1991
) but approximately twice as long as the half-lives of CheY1 and CheY2 from S. meliloti (Sourjik & Schmitt, 1998
). As was observed with the CheY proteins of S. meliloti (Sourjik & Schmitt, 1998
), CheY1 and CheY2 of H. pylori did not exhibit phosphatase activity towards each other (Fig. 6b
). The results of three component phosphorylation assays suggested clearly that CheY1 prevails in the competition for CheA'
P over CheY2 (Fig. 4
) and we interpret this as a higher affinity of CheY1 for CheA'; however, it is possible that the intramolecular phosphotransfer reaction within the bifunctional CheAY2 protein may be favoured in vivo.
In H. pylori no homologues of proteins with a known CheYP-specific phosphatase activity like CheZ, CheC and CheX are present. CheC was identified in B. subtilis and works in concert with another chemotaxis protein CheD (Szurmant et al., 2004
). So far only the function of CheX from Thermotoga maritima was analysed in some detail, although orthologues of the cheX gene are currently found in more than 20 sequenced bacterial genomes (Park et al., 2004
). CheC and CheX share a sequence signature which is present also in the flagellar switch protein FliY from both organisms and, consequently, FliY was also demonstrated to act as a phosphatase on CheY
P (Szurmant et al., 2003
). Therefore, the observation that H. pylori contains a CheY1 protein and the bifunctional CheAY2 histidine kinase suggested a similar mechanism of termination of chemotactic signalling as originally observed in the chemotaxis system of S. meliloti. This organism harbours two CheY molecules one of which interacts with the flagellar motor (CheY2) while the other acts as a phosphate sink (CheY1) which modulates the half-life of CheY2
P. This occurs via retro-transfer of the phosphoryl group from CheY2
P to CheA and the subsequent CheA-dependent phosphorylation of CheY1 (Sourjik & Schmitt, 1996
; 1998
). Our data presented here are consistent with efficient retro-transfer of the phosphoryl group from CheY1
P to CheAY2 and suggests a role of CheY2 as a phosphate sink involved in signal termination (Fig. 6a
). In fact, in a three-component reaction where CheY1 is present predominantly in its phosphorylated form, while the P1 domain of CheA' is initially unphosphorylated, the phosphotransfer from CheA'
P is clearly biased towards CheY2 despite the higher affinity of CheY1 for CheA (Fig. 6b and c
). From the fact that in the retrophosphorylation experiments we could only detect CheAY2
P, but not CheA'
P, we conclude that the phosphorylation signal generated by CheAY2 derives mainly from the phosphorylated C-terminal CheY2 domain and not from the P1 domain. This observation further supports the idea of a rapid flow of the phosphoryl group from CheY1
P to CheY2 via the P1 domain of the CheA histidine kinase. Interestingly, an alignment of the CheY proteins of E. coli, S. meliloti, H. pylori and C. jejuni revealed two positions which might discriminate the CheY proteins interacting with the flagellar motor (CheY-Ec; CheY2-Sm; CheY1-Hp; CheY1-Cj) from those acting as a phosphate sink (CheY1-Sm; CheY2-Hp; CheY2-Cj): at the position corresponding to A74 in CheY of E. coli there is lysine in the phosphate sink proteins and the position corresponding to I95 of E. coli CheY (V in CheY1-Hp and CheY2-Sm) is substituted by lysine or arginine in the phosphate sink proteins (Fig. 7
). However, these amino acids are probably not involved in the interaction with the FliM protein (McEvoy et al., 1999
; Shukla et al., 1998
).
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We cannot, however, rule out the possibility that in H. pylori chemotaxis, a so far unknown CheY1P- or CheY2
P-specific phosphatase is involved in signal termination. Furthermore, the apparent slow half-life of CheY2
P which, according to our results should act as a phosphate sink, may suggest that there could be a phosphatase specific for this response regulator. H. pylori contains an orthologue of FliY; however, the sequence similarity to the regions conserved between FliY, CheC and CheX from B. subtilis and T. maritima which act in CheY
P hydrolysis is rather low.
Following the S. meliloti model, the CheY1 protein of H. pylori, which is freely diffusible in the cell, would interact with the flagellar motor. It was shown that the MCPs together with CheW and CheA form higher order clusters which are localized at the cell pole in E. coli and Rhodobacter sphaeroides (Maddock & Shapiro, 1993; Sourjik & Berg, 2000
; Martin et al., 2003
; Wadhams et al., 2000
). In swarmer cells of Caulobacter crescentus the chemoreceptor McpA has been demonstrated to be localized to the flagellated cell pole (Alley et al., 1992
). Assuming a similar localization of the chemoreceptor complex in the monotrichously flagellated bacterium H. pylori, direct interaction of CheAY2 with the flagellar motor is conceivable, but seems unlikely due to the complex stoichiometry of the MCP-CheW-CheA complexes which is a prerequisite for proper signal amplification (Levit et al., 2002
; Shimizu et al., 2000
).
Computerized tracking of the movement of the H. pylori strain N6 revealed a swimming pattern consisting of short straight runs with frequent changes of direction, whereas mutants of H. pylori N6 with inactivated histidine kinase CheAY2 moved in long straight runs (Foynes et al., 2000), suggesting that phosphorylation of CheAY2 induces tumbling. Furthermore, in these assays a mutant with an insertional inactivation of cheY1 exhibited excessive tumbling. This observation is not consistent with the putative interaction of CheY1 with the flagellar motor proposed by our data, but would rather suggest a role of CheY1 in the termination of chemotactic signalling. For the moment, this apparent contradiction remains unexplained.
In conclusion, through reconstitution of the H. pylori chemotaxis proteins implicated in the signalling pathway, we have evidence of a complex phosphorelay in vitro which has similarities to other systems with multiple CheY proteins. The data presented here indicate that the receiver domain present in the bifunctional CheAY2 protein acts as a phosphate sink, fine tuning the activity of the freely diffusible CheY1 protein which is thought to interact with the flagellar motor. The role of the CheV proteins remains unclear at the moment, but they may be engaged in a further fine regulation of the phosphate flow in this complex chemotaxis system.
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ACKNOWLEDGEMENTS |
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REFERENCES |
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Alm, R. A., Ling, L.-S. L., Moir, D. T. & 20 other authors (1999). Genomic-sequence comparison of two unrelated isolates of the human gastric pathogen Helicobacter pylori. Nature 397, 176180.[CrossRef][Medline]
Baar, C., Eppinger, M., Raddatz, G. & 12 other authors (2003). Complete genome sequence and analysis of Wolinella succinogenes. Proc Natl Acad Sci U S A 100, 1169011695.
Beier, D. & Frank, R. (2000). Molecular characterization of two-component systems of Helicobacter pylori. J Bacteriol 182, 20682076.
Beier, D., Spohn, G., Rappuoli, R. & Scarlato, V. (1997). Identification and characterization of an operon of Helicobacter pylori that is involved in motility and stress adaptation. J Bacteriol 179, 46764683.
Blaser, M. J. (1992). Helicobacter pylori: its role in disease. Clin Infect Dis 5, 386391.
Bourret, R. B., Hess, J. F. & Simon, M. I. (1990). Conserved aspartate residues and phosphorylation in signal transduction by the chemotaxis protein CheY. Proc Natl Acad Sci U S A 87, 4145.
Cerda, O., Rivas, A. & Toledo, H. (2003). Helicobacter pylori strain ATCC 700392 encodes a methyl-accepting chemotaxis receptor protein (MCP) for arginine and sodium bicarbonate. FEMS Microbiol Lett 224, 175181.[CrossRef][Medline]
Eaton, K. A., Morgan, R. R. & Krakowka, S. (1992). Motility as a factor in the colonization of gnotobiotic piglets by Helicobacter pylori. J Med Microbiol 37, 123127.[Abstract]
Eaton, K. A., Suerbaum, S., Josenhans, C. & Krakowka, S. (1996). Colonization of gnotobiotic piglets by Helicobacter pylori deficient in two flagellin genes. Infect Immun 64, 24452448.[Abstract]
Foynes, S., Dorrell, N., Ward, S. J., Stabler, R. A., McColm, A. A., Rycroft, A. N. & Wren, B. W. (2000). Helicobacter pylori possesses two CheY response regulators and a histidine kinase sensor, CheA, which are essential for chemotaxis and colonization of the gastric mucosa. Infect Immun 68, 20162023.
Fredrick, K. L. & Helmann, J. D. (1994). Dual chemotaxis signaling pathways in Bacillus subtilis: a sigma D-dependent gene encodes a novel protein with both CheW and CheY homologous domains. J Bacteriol 176, 27272735.[Abstract]
Georgellis, G., Lynch, A. S. & Lin, E. C. C. (1997). In vitro phosphorylation study of the Arc two-component signal transduction system of Escherichia coli. J Bacteriol 179, 54295435.
Karatan, E., Saulmon, M. M., Bunn, M. W. & Ordal, G. W. (2001). Phosphorylation of the response regulator CheV is required for adaptation to attractants during Bacillus subtilis chemotaxis. J Biol Chem 276, 4361843626.
Levit, M. N., Grebe, T. W. & Stock, J. B. (2002). Organization of the receptor-kinase signalling array that regulates Escherichia coli chemotaxis. J Biol Chem 277, 3674836754.
Lukat, G. S., Lee, B. H., Mottonen, J. M., Stock, A. M. & Stock, J. B. (1991). Roles of the highly conserved aspartate and lysine residues in the response regulator of bacterial chemotaxis. J Biol Chem 266, 83488354.
Lukat, G. S., McCleary, W. R., Stock, A. M. & Stock, J. B. (1992). Phosphorylation of bacterial response regulator proteins by low molecular weight phospho-donors. Proc Natl Acad Sci U S A 89, 718722.
Maddock, J. R. & Shapiro, L. (1993). Polar location of the chemoreceptor complex in the Escherichia coli cell. Science 259, 17171723.[Medline]
Martin, A. C., Nair, U., Armitage, J. P. & Maddock, J. R. (2003). Polar localization of CheA2 in Rhodobacter sphaeroides requires specific Che homologs. J Bacteriol 185, 46674671.
McCleary, W. R. & Stock, J. B. (1994). Acetyl phosphate and the activation of two-component response regulators. J Biol Chem 269, 3156731572.
McEvoy, M. M., Bren, A., Eisenbach, M. & Dahlquist, F. W. (1999). Identification of the binding interfaces on CheY for two of its targets, the phosphatase CheZ and the flagellar switch protein FliM. J Mol Biol 289, 14231433.[CrossRef][Medline]
McGee, D. J., Langford, M. L., Watson, E. L., Carter, J. E., Chen, Y.-T. & Ottemann, K. M. (2005). Colonization and inflammation deficiencies in mongolian gerbils infected by Helicobacter pylori chemotaxis mutants. Infect Immun 73, 18201827.
Ottemann, K. M. & Lowenthal, A. (2002). Helicobacter pylori uses motility for both initial colonization and to attain robust infection. Infect Immun 70, 19841990.
Park, S.-Y., Chao, X., Gonzalez-Bonet, G., Beel, B. D., Bilwes, A. M. & Crane, B. R. (2004). Structure and function of an unusual family of protein phosphatases: the bacterial chemotaxis proteins CheC and CheX. Mol Cell 16, 563574.[CrossRef][Medline]
Parkhill, J., Wren, B. W., Mungall, K. & 18 other authors (2000). The genome sequence of the food-borne pathogen Campylobacter jejuni reveals hypervariable sequences. Nature 403, 665668.[CrossRef][Medline]
Perraud, A.-L., Kimmel, B., Weiss, V. & Gross, R. (1998). Specificity of the BvgAS and EvgAS phosphorelay is mediated by the C-terminal HPt domains of the sensor proteins. Mol Microbiol 27, 875887.[CrossRef][Medline]
Peterson, W. L. (1991). Helicobacter pylori and peptic ulcer disease. N Engl J Med 324, 10431048.[Medline]
Pittman, M. S., Goodwin, M. & Kelly, D. J. (2001). Chemotaxis in the human gastric pathogen Helicobacter pylori: different roles for CheW and the three CheV paralogues, and evidence for CheV2 phosphorylation. Microbiology 147, 24932504.[Medline]
Schmitt, R. (2002). Sinorhizobial chemotaxis: a departure from the enterobacterial paradigm. Microbiology 148, 627631.[Medline]
Shimizu, T. S., Le Novere, N., Levin, M. D., Beavil, A. J., Sutton, B. J. & Bray, D. (2000). Molecular model of a lattice of signalling proteins involved in bacterial chemotaxis. Nature Cell Biol 2, 792796.[CrossRef][Medline]
Shukla, D., Zhu, X. Y. & Matsumura, P. (1998). Flagellar motor-switch binding face of Chey and the biochemical basis of suppression by CheY mutants that compensate for motor-switch defects in Escherichia coli. J Biol Chem 273, 2399323999.
Sourjik, V. & Berg, H. C. (2000). Localization of the components of the chemotaxis machinery of Escherichia coli using fluorescent protein fusions. Mol Microbiol 37, 740751.[CrossRef][Medline]
Sourjik, V. & Schmitt, R. (1996). Different roles of CheY1 and CheY2 in the chemotaxis of Rhizobium meliloti. Mol Microbiol 22, 427436.[CrossRef][Medline]
Sourjik, V. & Schmitt, R. (1998). Phosphotransfer between CheA, CheY1, and CheY2 in the chemotaxis signal transduction chain of Rhizobium meliloti. Biochemistry 37, 23272335.[CrossRef][Medline]
Suerbaum, S., Josenhans, C., Sterzenbach, T. & 19 other authors (2003). The complete genome sequence of the carcinogenic bacterium Helicobacter hepaticus. Proc Natl Acad Sci U S A 100, 79017906.
Szurmant, H. & Ordal, G. W. (2004). Diversity in chemotaxis mechanisms among the bacteria and archaea. Microbiol Mol Biol Rev 68, 301319.
Szurmant, H., Bunn, M. W., Cannistraro, V. J. & Ordal, G. W. (2003). Bacillus subtilis hydrolyzes CheY-P at the location of its action, the flagellar switch. J Biol Chem 278, 4861148616.
Szurmant, H., Muff, T. J. & Ordal, G. W. (2004). Bacillus subtilis CheC and FliY are members of a novel class of CheYP-hydrolyzing proteins in the chemotactic signal transduction cascade. J Biol Chem 279, 2178721792.
Terry, K., Williams, S. M., Connolly, L. & Ottemann, K. M. (2005). Chemotaxis plays multiple roles during Helicobacter pylori animal infection. Infect Immun 73, 803811.
Tomb, J.-F., White, O., Kerlavage, A. R. & 39 other authors (1997). The complete genome sequence of the gastric pathogen Helicobacter pylori. Nature 388, 539547.[CrossRef][Medline]
Uemura, N. S., Okamoto, S., Yamamoto, S., Matsumura, N., Yamaguchi, S., Yamakido, M., Taniyama, K., Sasaki, N. & Schlemper, R. J. (2001). Helicobacter pylori infection and the development of gastric cancer. N Engl J Med 345, 784789.
Wadhams, G. H. & Armitage, J. P. (2004). Making sense of it all: bacterial chemotaxis. Nat Rev Mol Cell Biol 5, 10241037.[CrossRef][Medline]
Wadhams, G. H., Martin, A. C. & Armitage, J. P. (2000). Identification and localization of a methyl-accepting chemotaxis protein in Rhodobacter sphaeroides. Mol Microbiol 36, 12221233.[CrossRef][Medline]
Worku, M. L., Karim, Q. N., Spencer, J. & Sidebotham, R. L. (2004). Chemotactic response of Helicobacter pylori to human plasma and bile. J Med Microbiol 53, 807811.
Xiang, Z., Censini, S., Bayeli, P. F., Telford, J. L., Figura, N., Rappuoli, R. & Covacci, A. (1995). Analysis of expression of CagA and VacA virulence factors in 43 strains of Helicobacter pylori reveals that clinical isolates can be divided into two major types and that CagA is not necessary for expression of the vacuolating cytotoxin. Infect Immun 63, 9498.[Abstract]
Yoshiyama, H., Nakamura, H., Kimoto, M., Okita, K. & Nakazawa, T. (1999). Chemotaxis and motility of Helicobacter pylori in a viscous environment. J Gastroenterol 34, 1823.[CrossRef]
Received 24 May 2005;
revised 25 July 2005;
accepted 26 July 2005.
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