FUNCTIONAL CONSERVATION OF THE SECRETION AND TRANSLOCATION MACHINERY FOR VIRULENCE PROTEINS OF YERSINIAE, SALMONELLAE AND SHIGELLAE

Virulent bacteria of the genera Yersinia, Shigella and Salmonella secr ete a number of virulence determinants, Yops, Ipas and Sips respective ly, by a type III secretion pathway, The IpaB protein of Shigella flex neri was expressed in Yersinia pseudotuberculosis and found to be secr eted under the same conditions required for Yop secretion, Likewise, Y opE was secreted by the wild-type strain LT2 of Salmonella typhimurium , but YopE was not secreted by the isogenic invA mutant, Secretion of both IpaB and YopE required their respective chaperones, IpgC and YerA ., In addition, yopE-containing S.typhimurium expressed a YopE-mediate d cytotoxicity on cultured HeLa cells. YopE was detected in the cytoso l of the infected HeLa cells and the amount of translocated YopE corre lated with the degree of cytotoxicity, Both translocation and cytotoxi city were prevented by the addition of gentamicin. Treatment of HeLa c ells with cytochalasin D prior to infection prevented internalization of bacteria, but translocation of YopE was still observed, These resul ts favour the hypothesis that YopE is translocated through the plasma membrane by surface-located bacteria, We propose that virulent Salmone lla and Shigella deliver virulence effector molecules into the target cell through the utilization of a functionally conserved secretion/tra nslocation machinery similar to that shown for Yersinia.