UC Santa Cruz

Helicobacter pylori translates environmental cues into a swimming response using its chemotactic signaling system. Generally, chemotactic signaling in H. pylori follows the enteric paradigm. The H. pylori system, however, has three additional proteins called CheVs that are hybrid proteins combining a CheW domain with a response receiver (REC) domain. Studies on H. pylori have shown that each CheV participates in wild-type chemotaxis although the exact role of each protein in the chemotactic signaling system is unclear. The goal of this study is to better understand the function of CheVs in the pathway, by specifically testing spatial localization of the CheV proteins and whether they prefer specific chemoreceptors. We carried out subcelluar fractionation followed by western analysis to determine whether any of the H. pylori CheV proteins prefer the TlpA or TlpB chemoreceptors. Additionally, immunofluorescence was applied to observe the localization of each CheV in wild-type H. pylori, in isogenic strains having only TlpA or TlpB, and in isogenic strains lacking one CheV or CheW. We found that all three CheV proteins are detected in membrane fractions with either TlpA or TlpB, and surprisingly, even in the absence of all receptors. This outcome suggested that CheV proteins associate with the membrane independently of the chemoreceptors. In wild type, we found that the CheVs are primarily localized at the cell poles. In contrast, strains lacking chemoreceptors had CheV proteins diffused throughout the cytoplasm. Strains bearing a single chemoreceptor had CheVs both at the poles and diffused within the cell. In the absence of CheV1, both CheV2 and CheV3 where diffused; on the contrary, loss of either CheV2 or CheV3 did not affect the localization of the remaining CheV proteins. Immunofluorescence studies also suggested that both CheV1 and CheW are involved in localizing the chemoreceptors to the cell pole. These results suggest that either TlpA or TlpB can guide the localization of CheVs to the cell pole. In a cell with only a single chemoreceptor, the quantity of chemoreceptor complex formed by TlpA or TlpB is altered and appears to affect CheV localization. These studies suggest that the H. pylori CheV proteins do not prefer TlpA or TlpB, and instead interact with all chemoreceptors equally. Unlike the other CheV proteins, CheV1 showed a significant effect on the polar localization of chemoreceptors, and concomitantly, CheV2 and CheV3. CheW similarly was required for polar chemoreceptors. These studies thus show that the H. pylori CheV1 and CheW proteins have a major role in the spatial localization of chemotaxis transduction proteins.