title: CagI is an essential component of the Helicobacter pylori Cag type IV secretion system and forms a complex with CagL.
abstract: Helicobacter pylori, the causative agent of type B gastritis, peptic ulcers, gastric adenocarcinoma and MALT lymphoma, uses the Cag type IV secretion system to induce a strong proinflammatory response in the gastric mucosa and to inject its effector protein CagA into gastric cells. CagA translocation results in altered host cell gene expression profiles and cytoskeletal rearrangements, and it is considered as a major bacterial virulence trait. Recently, it has been shown that binding of the type IV secretion apparatus to integrin receptors on target cells is a crucial step in the translocation process. Several bacterial proteins, including the Cag-specific components CagL and CagI, have been involved in this interaction. Here, we have examined the localization and interactions of CagI in the bacterial cell. Since the cagI gene overlaps and is co-transcribed with the cagL gene, the role of CagI for type IV secretion system function has been difficult to assess, and conflicting results have been reported regarding its involvement in the proinflammatory response. Using a marker-free gene deletion approach and genetic complementation, we show now that CagI is an essential component of the Cag type IV secretion apparatus for both CagA translocation and interleukin-8 induction. CagI is distributed over soluble and membrane-associated pools and seems to be partly surface-exposed. Deletion of several genes encoding essential Cag components has an impact on protein levels of CagI and CagL, suggesting that both proteins require partial assembly of the secretion apparatus. Finally, we show by co-immunoprecipitation that CagI and CagL interact with each other. Taken together, our results indicate that CagI and CagL form a functional complex which is formed at a late stage of secretion apparatus assembly.
authors.affiliation: Max von Pettenkofer-Institut für Hygiene und Medizinische Mikrobiologie, Ludwig-Maximilians-Universität, München, Germany.
authors.forename: Kieu Thuy
authors.initials: KT
authors.lastname: Pham
authors.forename: Evelyn
authors.initials: E
authors.lastname: Weiss
authors.forename: Luisa F
authors.initials: LF
authors.lastname: Jiménez Soto
authors.forename: Ute
authors.initials: U
authors.lastname: Breithaupt
authors.forename: Rainer
authors.initials: R
authors.lastname: Haas
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Fischer
mesh_terms: D000942:Antigens, Bacterial / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D005753:Gastric Mucosa / Q000276:immunology / Q000382:microbiology; D017353:Gene Deletion; D005816:Genetic Complementation Test; D016481:Helicobacter Infections / Q000276:immunology / Q000382:microbiology; D016480:Helicobacter pylori / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D054884:Host-Pathogen Interactions; D006801:Humans; D047468:Immunoprecipitation; D016023:Integrins / Q000235:genetics / Q000378:metabolism; D016209:Interleukin-8 / Q000096:biosynthesis / Q000276:immunology; D008969:Molecular Sequence Data; D009876:Operon; D011485:Protein Binding; D021381:Protein Transport
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D016023:Integrins; D016209:Interleukin-8; C080866:cagA protein, Helicobacter pylori; C568315:cagL protein, Helicobacter pylori