Figure 1.

The Yop virulon. When Yersinia are placed at 37°C in a rich environment, the Ysc secretion channel is installed. Proteins YscD, -R, -S, -T, -U, and -V are localized in the inner membrane (IM), whereas YscC and YscP are exposed at the bacterial surface. Lipoprotein YscW stabilizes YscC. YscN belongs to the family of ATPases. A stock of Yop proteins is synthesized, and some of them are capped with their specific Syc chaperone. As long as there is no contact with a eukaryotic cell, a stop-valve, possibly made of YopN, TyeA, and LcrG, blocks the Ysc secretion channel. On contact with a eukaryotic target cell, the bacterium attaches tightly by interaction between its YadA and Inv adhesins and β-integrins, and the secretion channel opens. The Yops are then transported through the Ysc channel, and the Yop effectors are translocated across the plasma membrane, guided by the translocators YopB, YopD, and LcrV.