YOPT, A NEW YERSINIA YOP EFFECTOR PROTEIN, AFFECTS THE CYTOSKELETON OF HOST-CELLS

Extracellular Yersinia disarm the immune system of their host by injec ting effector Yop proteins into the cytosol of target cells. Five effe cters have been described: YopE, YopH, YpkA/YopO, YopP and YopM. Deliv ery of these effecters by Yersinia adhering at the cell surface requir es other Yops (translocators) including YopB. Effector and translocato r Yops are secreted by the type III Ysc secretion apparatus, and some Yops also need a specific cytosolic chaperone, called Syc. In this pap er, we describe a new Yop, which we have called YopT (35.5 kDa). Its s ecretion required an intact Ysc apparatus and SycT (15.0 kDa, pi 4.4), a new chaperone resembling SycE. Infection of macrophages with a Yers inia, producing a hybrid YopT-adenylate cyclase, led to the accumulati on of intracellular cAMP, indicating that YopT is delivered into the c ytosol of eukaryotic cells. Infection of HeLa cells with a mutant stra in devoid of the five known Yop effecters (Delta HOPEM strain) but pro ducing YopT resulted in the alteration of the cell cytoskeleton and th e disruption of the actin filament structure. This cytotoxic effect wa s caused by YopT and dependent on YopB. YopT is thus a new effector Yo p and a new bacterial toxin affecting the cytoskeleton of eukaryocells .