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Characterizing the role of the coupling proteins CheV1 and CheW in Helicobacter pylori chemotaxis

  • Author(s): Abedrabbo, Samar
  • Advisor(s): Ottemann, Karen M
  • et al.
Abstract

Many microbes use chemotaxis as a system for thriving and colonizing their various environmental niches. Chemotaxis is the ability of organisms to swim toward favorable environments and away from toxic environments. Helicobacter pylori is a chemotactic pathogen that infects over half the world’s population and successfully colonizes the gastric mucosa of humans. Chemotaxis is an important virulence factor that helps H. pylori effectively colonize the human stomach. The chemotaxis complex system consists of various proteins: chemoreceptors, coupling proteins, and the CheA kinase. Chemoreceptors sense the environment and transmit the response to the CheA kinase through coupling proteins. Coupling proteins of the CheW or CheV type physically link chemoreceptors to the CheA kinase. H. pylori has a unique chemotaxis system that contains multiple coupling proteins, 1 CheW and 3 CheV proteins—CheV1, CheV2, and CheV3 respectively that all play a role in chemotaxis. It is unknown why some chemotaxis systems contain multiple types of coupling proteins. In this thesis, the role and function of the coupling proteins CheV1 and CheW was investigated, as well as the stoichiometry of the chemotaxis proteins that make up the chemoreceptor-CheA kinase complex in H. pylori. CheV1 and CheW had similar protein interaction networks in vivo and in vitro with the chemoreceptors, the CheA kinase, and themselves. Both proteins promoted CheA autophosphorylation activity with CheW having slightly better CheA activation than CheV1. CheV1 and CheW were also both needed to retain the CheA kinase at the cell membrane where the chemotaxis complex is found. Cellular localization of the chemoreceptors and CheA kinase required the presence of both CheV1 and CheW. Ultimately, these results indicate that CheV1 and CheW work together to promote super chemotaxis cluster formation at cell poles which is important for eliciting a chemotaxis response. Also reported here are the concentration and ratio of the chemotaxis proteins in H. pylori. H. pylori possessed significantly higher concentrations of chemoreceptors, coupling proteins, and the CheA kinase in comparison to E. coli and B. subtilis. Despite these differences, a chemoreceptor trimer of dimers to one CheA dimer was maintained in H. pylori. There was also a conserved ratio of 1.8 CheW to 1 CheA dimer like B. subtilis and E. coli. The stoichiometry of the chemotaxis proteins was also analyzed in cheV1 and cheW mutants. cheW mutants had approximately half the amount of CheA kinase as wildtype similar to a receptorless mutant. Addition of a protease inhibitor restored CheA amounts in mutants indicating that protein interactions within the chemotaxis complex protect proteins from degradation thus ultimately maintaining optimal chemotaxis. Finally, we found that cheV1 mutants rapidly accumulate suppressor mutants in a soft agar assay.

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