UC Santa Cruz

The human pathogen and carcinogenic bacterium Helicobacter pylori infects half of the world’s population. H. pylori colonizes the stomach and is equipped with strategies to survive in the harsh environment. A particular challenge is the oxygen radicals generated by host immune cells. Moreover, H. pylori infection triggers chronic inflammation that leads to high host production of reactive oxygen species (ROS), including hydrogen peroxide. One way H. pylori navigates the host environment is through a chemotaxis system that permits directional motility. Chemotaxis signaling is critical for infection in numerous pathogens, including H. pylori. H. pylori has four chemoreceptors, including one named TlpD. TlpD contains three domains: an N-terminal domain with unknown function, a middle MA domain for signal transduction interactions with coupling proteins CheW and CheV1, and a C-terminal CZB domain. In this work, we sought to evaluate the role of the individual TlpD domains in TlpD function, using protein expression in H. pylori. The role of each domain was examined for its role in TlpD localization, association with chemotaxis signaling proteins, and effect on motility. Our results suggest that an intact cytosolic chemoreceptor is required to build a chemotaxis array with CheV coupling proteins, and particularly point to the importance of the region C-terminal to the CZB domain. These findings provide insight into the workings of cytoplasmic sensing proteins, particularly ones with a CZB domain, and lay the foundation for future work with these proteins. Another way that H. pylori can overcome exogenous reactive oxygen species is by using enzymes to decompose these harmful molecules. One interesting enzyme is Cytochrome c peroxidase (CCP), a protein shown to use hydrogen peroxide as a terminal electron acceptor in other microbes. CCP allows bacteria to gain a metabolic benefit from the decomposition of this oxygen radical. H. pylori encodes a putative CCP that contains 56% conserved amino acid identity with the CCP of C. jejuni but there are no studies on this putative H. pylori CCP. Therefore, we sought to evaluate the role of this putative CCP in H. pylori. Our results suggest that CCP plays a crucial role in H. pylori growth and survival in normal media, but did not appear to confer a benefit when exogenous hydrogen peroxide was added. These findings support the hypothesis that H. pylori CCP may not confer an advantage from ROS. Future studies utilizing the generated strains would provide a more complete characterization of this putative CCP. Altogether, findings from this work lay the foundation for future studies that can translate into therapies to treat or prevent H. pylori infection.