Helicobacter pylori CagI is associated with the stability of CagA

•We constructed an isogenic mutant of cagI via allelic exchange.•We performed immunoprecipitation, MALDI-TOF and pull-down to verify the interation between CagA and CagI.•We carried out qRT-PCR and Western blotting to show that CagA was unstable in the absence of CagI.

The type Ⅳ secretion system (T4SS) of H. pylori encoded by cag pathogenicity island mediates the injection of the toxin CagA, which is considered as a paradigm for bacterial carcinogenesis. T4SS is generally composed of a set of proteins, the majority of which still remain unclear. In this study, we have identified CagI, one of the T4SS proteins, which interacted with CagA and played an important role for CagA stability.