ABSTRACT
Objective To determine the effects of Che A and CheY proteins of Campylobacter jejuni regulating the bacterial chemotaxis in vitro and colonization in vivo. Methods By using pET42a plasmid and E. coli BL21DE3 as expression vector and expression strain, respectively, prokaryotic expression systems of cheA and cheY genes of C. jejuni strain NCTC11168 was constructed. Rabbits were immunized with the target recombinant expression proteins, rCheA and rCheY, to prepare the antisera. rCheA-IgG and rCheY-IgG in the antisera were separated using DEAE-52 ion exchange column. pBluescript- II -SK was applied to construct suicide plasmid which used to generate cheA gene knock-out mutant (cheA-). A chemotaxis model in vitro of C. jejuni based on DOC-HAP, the chemotactic ability of cheA' mutant as well as the effect of rCheA-IgG and closantel inhibiting the bacterial chemotaxis were demonstrated. The phosphorylation levels of CheA and CheY after DOC treatment were examined by using either rCheA-IgG or CheY-IgG capture method. The difference of colonization ability between cheA- mutant and wild-type of C. jejuni in mice were checked and then compared. Results The constructed prokaryotic expression systems could efficiently express rCheA and rCheY. The data from PCR and sequencing confirmed the cheA gene knock out from cheA- mutant chromosome. cheA- mutant lost its chemotactic ability towards DOC. Both the rCheA-IgG and closantel could inhibit the chemotaxis of wild-type of C. jejuni (P < 0.05 ). When treatment of DOC, the phosphorylation levels of CheA and CheY in wild-type of C. jejuni rapidly decreased (P < 0. 05 ). The colonization ability in murine jejunum of cheA- mutant was also lower than that of the wild-type ( P<0.05 ) . Conclusion Chemotaxis-associated two-component signaling system (Che-TCSS) of C. jejuni are composed of CheA and CheY, and the two proteins are activated by dephosphorylation. CheA in the Che-TCSS play a critical role in chemotaxis in vitro and colonization in vivo of C. jejuni, and this protein can be used as a target for developing novel anti- C. jejuni drugs.
ABSTRACT
Objective To determine the effect of cheA gene of Helicobacter pylori in the bacterial chemotaxis in vitro and colonization in vivo. Methods The entire cheA and cheY genes were amplified and cloned from genomic DNA of H. pylori NCTC11637 strain. Subsequently, the prokaryotic expression systems of cheA and cheY genes were generated and the target recombinant proteins rCheA and rCheY were extracted by Ni-NTA affinity chromatography. Rabbits were immunized with either rCheA or rCheY for obtaining antisera, and rCheA-IgG and rCheY-IgG in the antisera were prepared using ammonium sulfate precipitation plus DEAE-52 column chromatography. A suicide plasmid of cheA gene was constructed and then a cheA gene knock-out mutant ( cheA - ) was generated based on homologous recombinant exchange using the suicide plasmid. The cheA- mutant was identified using PCR and sequencing. The phosphorylation levels of CheA and CheY molecules of cheA - and wild-type strain were determined by using rCheA-IgG and rCheY-IgG anchoring the target proteins and protein phosphorylation detection kit. The differences of chemotaxis in vitro and colonization in vivo between cheA- mutant and wild-type strain were compared using chemotactic model and BALB/c infection model of H. pylori. Results The cheA gene knock-out in genome of cheA- mutant was confirmed by the results of PCR and sequencing. After treated with 0. 001-0. 1 mol/L HCI for 10 min, the phosphorylation levels of CheA and CheY molecules of wild-type strain were rapidly descended from ( 59.6 ±11.5) μmol and (55.5 ± 10.2) μmol to ( 10.8 ± 2.6) and (5. 5 ± 1.2) μmol (P ＜ 0.05 ), while the phosphorylation of CheY molecule of cheA - mutant was no markedly changed with a persistent lower level ( P ＞0.05). The diameters [(10-20) ± (2-3) mm] of chemotactic aggregative rings of cheA- mutant were significantly less than those [(16-24) ± (2-3)mm] of wild-type strain (P ＜0.05). The positive isolation rate (90%) of H. pylori in gastric biopsy specimens of mice that infected with wild-type strain was remarkably higher than that (40%) of mice that infected with cheA- mutant (P ＜0.05). The result of fluorescence quantitative was also showed that the numbers (6.3 × 103 ±2.1 × 103 copies/mg) of H. pylori in gastric biopsy specimens of wild-type strain infected mice were significantly larger than those (8.3 × 101 ±3. 1 × 101 copies/mg) in gastric biopsy specimens ofcheA- mutant infected mice (P＜0.05). Conclusion The cheA gene of H. pylori has an important role in the bacterial chemotaxis in vitro and colonization in vivo.