Assembly and molecular mode of action of the Helicobacter pylori Cag type IV secretion apparatus

Bacterial type IV secretion systems (T4SS) form supramolecular protein complexes that are capable of transporting DNA or protein substrates across the bacterial cell envelope and, in many cases, also across eukaryotic target cell membranes. Because of these characteristics, they are often used by pathogenic bacteria for the injection of host cell-modulating virulence factors. One example is the human pathogen Helicobacter pylori, which uses the Cag-T4SS to induce a pro-inflammatory response and multiple cytoskeletal and gene regulatory effects in gastric epithelial cells. Work in recent years has shown that the Cag-T4SS exhibits marked differences in relation to other systems, both with respect to the composition of its secretion apparatus and the molecular details of its secretion mechanisms. This review describes the molecular properties of the Cag-T4SS and compares these with prototypical systems of this family of protein transporters.