Science 320, 1651–1654 (2008)

Two types of disease-causing bacterium use a special injection system to deliver proteins into host cells, researchers have found. The proteins involved contain regions known as 'Anks' (ankyrin repeat homology domains), which often form scaffolds that enable other proteins to interact.

Craig Roy and his colleagues at Yale University School of Medicine in New Haven, Connecticut, report that Legionella pneumophila, the bacterium that causes Legionnaires' disease, injects four Ank proteins into mammalian cells via a complex called a 'type IV secretion system'. Coxiella burnetti, which causes Q fever, injects eight such proteins.

One of the L. pneumophila proteins, AnkX, prevents host vesicles — bags of membrane-bound fluid that contain the bacteria — from moving towards the lysosome, where the bacteria would be destroyed. This may contribute to the bacterium's virulence.