The Helicobacter pylori Cag Type IV Secretion System

The Cag T4SS has a key role in the pathogenesis of H. pylori-associated gastric cancer. Recent advances in molecular imaging have facilitated investigation of the H. pylori Cag T4SS structure. The H. pylori Cag T4SS contains multiple components unrelated to components of T4SSs in other bacterial species, and the molecular architecture of the H. pylori Cag T4SS is substantially more complex than that of prototype T4SSs. T4SSs are a heterogeneous group of secretion systems with diverse functions. Despite a low level of sequence relatedness among corresponding components of T4SSs from different bacterial species, there are shared structural features among all T4SSs analyzed thus far. Colonization of the human stomach with Helicobacter pylori strains containing the cag pathogenicity island is a risk factor for development of gastric cancer. The cag pathogenicity island contains genes encoding a secreted effector protein (CagA) and components of a type IV secretion system (Cag T4SS). The molecular architecture of the H. pylori Cag T4SS is substantially more complex than that of prototype T4SSs in other bacterial species. In this review, we discuss recent discoveries pertaining to the structure and function of the Cag T4SS and its role in gastric cancer pathogenesis. Colonization of the human stomach with Helicobacter pylori strains containing the cag pathogenicity island is a risk factor for development of gastric cancer. The cag pathogenicity island contains genes encoding a secreted effector protein (CagA) and components of a type IV secretion system (Cag T4SS). The molecular architecture of the H. pylori Cag T4SS is substantially more complex than that of prototype T4SSs in other bacterial species. In this review, we discuss recent discoveries pertaining to the structure and function of the Cag T4SS and its role in gastric cancer pathogenesis. a region of chromosomal DNA, present in some H. pylori strains but not in others, which contains genes encoding CagA and components of a T4SS. a T4SS composed of proteins encoded by genes in the H. pylori cag PAI. the only known effector protein transported by the Cag T4SS, designated as a bacterial oncoprotein. class of T4SSs (composed of Tra components) that mediate DNA exchange between bacteria. a type of T4SS present in Legionella pneumophila (the causative agent of Legionnaire’s disease). a Gram-negative bacterium that colonizes the human stomach. a T4SS subassembly containing ATPases, localized in association with the inner membrane and extending into the cytoplasm. a proinflammatory cytokine. a T4SS subassembly localized within the periplasm, in contact with the outer membrane. a T4SS subassembly localized within the periplasm. a diverse family of bacterial secretion systems with multiple possible functions (e.g., delivery of effector proteins into target cells or bacterial conjugation). a prototype form of T4SS present in Agrobacterium tumefaciens (which delivers T-DNA into plant cells, resulting in crown gall disease).