Biochemical characterization of the Helicobacter pylori Cag-type IV secretion system unique component CagU

Many strains of Helicobacter pylori encode a protein secreting type IV secretion system called the Cag-T4SS. Here, we characterize one of the Cag-T4SS-specific components, CagU (HP0531). We report that CagU is a bacterial inner membrane-associated protein, partially processed at the C terminus, and that it interacts with the VirB6 and VirB8 homologs CagW and CagV, respectively. The level of expression of CagU is partially affected in the absence of cagX, cagW, and cagV. Deletion of cagU aborts surface localization of CagA and affects the expression levels of CagI and CagH, which are involved in the Cag-T4SS pilus formation. Complementation of the cagU null mutation by wild-type cagU restores all these functions, suggesting its importance for Cag-T4SS function.