Inhibition of the mitogen-activated protein kinase kinase superfamily by aYersinia effector

The bacterial pathogen Yersinia uses a type III secretion system to inject several virulence factors into target cells. One of the Yersinia virulence factors, YopJ, was shown to bind directly to the superfamily of MAPK (mitog en-activated protein kinase) kinases (MKKs) blocking both phosphorylation a nd subsequent activation of the MKKs. These results explain the diverse act ivities of YopJ in inhibiting the extracellular signal-regulated kinase, c- Jun amino-terminal kinase, p38, and nuclear factor kappa B signaling pathwa ys, preventing cytokine synthesis and promoting apoptosis. YopJ-related pro teins that are found in a number of bacterial pathogens of animals and plan ts may function to block MKKs so that host signaling responses can be modul ated upon infection.