In vivostructures of theHelicobacter pylori cagtype IV secretion system

Summary The bacterial type IV secretion system (T4SS) is a versatile nanomachine that translocates diverse effector molecules between microbes and into eukaryotic cells. Using electron cryotomography, here we reveal the molecular architecture of the cancer-associated Helicobacter pylori cag T4SS. Although most components are unique to H. pylori , the cag T4SS exhibits remarkable architectural similarity to previously studied T4SSs. When H. pylori encounters host cells, however, the bacterium elaborates rigid, membranous tubes perforated by lateral ports. Dense, pilus-like rod structures extending from the inner membrane were also observed. We propose that the membrane tubes assemble out of the T4SS and are the delivery system for cag T4SS cargo. These studies reveal the architecture of a dynamic molecular machine that evolved to function in the human gastric niche.