The tranquilizing injection of Yersinia proteins:: A pathogen's strategy to resist host defense

Pathogenic bacteria of the genus Yersinia possess a type III secretion apparatus by which they can inject up to six effector proteins into host cells. These so-called effector Yops (Yersinia outer proteins) disrupt cellular immune defense functions such as TNF-alpha release, O-2-production or phagocytosis and thereby allow Yersinia to grow extracellularly. Recent findings indicate that the effector Yops are highly active proteins that engage in crucial eukaryotic signaling mechanisms. For instance, the translocated tyrosine phosphatase YopH dephosphorylates the focal adhesion proteins paxillin and p130(Cas) within target cells. Furthermore, the Yersinia effector YopP is able to induce apoptosis in macrophages presumably by blocking MAP kinase and NF kappa B mediated signaling events. Here we discuss recent advances concerning the intracellular targets and biochemical signaling mechanisms regulated by the translocated Yersinia effecters.