The Helicobacter pylori cag Pathogenicity Island Protein CagN Is a Bacterial Membrane-Associated Protein That Is Processed at Its C Terminus

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Abstract
Helicobacter pylori infects nearly half the world's population and is associated with a spectrum of gastric maladies. Infections with cytotoxin-associated gene pathogenicity island ( cag PAI)-containing strains are associated with an increased risk for gastric cancer. The cag PAI contains genes encoding a type IV secretion system (T4SS) and a delivered effector, CagA, that becomes tyrosine phosphorylated upon delivery into host cells and initiates changes in cell signaling. Although some cag PAI genes have been shown to be required for CagA delivery, a subset of which are homologues of T4SS genes from Agrobacterium tumefaciens , the majority have no known function or homologues. We have performed a detailed investigation of one such cag PAI protein, CagN, which is encoded by the gene HP0538. Our results show that CagN is not delivered into host cells and instead is associated with the bacterial membrane. We demonstrate that CagN is cleaved at its C terminus by a mechanism that is independent of other cag PAI proteins. Finally, we show that a Δ cagN mutant is not impaired in its ability to deliver CagA to gastric epithelial cells and initiate cell elongation.