THE SALMONELLA-TYPHIMURIUM TYROSINE PHOSPHATASE SPTP IS TRANSLOCATED INTO HOST-CELLS AND DISRUPTS THE ACTIN CYTOSKELETON

The Salmonella typhimurium protein tyrosine phosphatase SptP is a targ et of the centisome 63 type III protein secretion system. This system is essential for the interaction of these bacteria with host cells. We have shown here by a combination of biochemical and microscopy techni ques that S. typhimurium directs the translocation of SptP into cultur ed epithelial cells. Translocation requires the function of the secret ed proteins, SipB, SipC and SipD, as strains carrying mutations in any of the genes encoding these proteins fail to translocate SptP. Microi njection of purified GST-SptP into cultured cells results in the disru ption of the actin cytoskeleton and the disappearance of stress fibres . These changes are reversible, as microinjected cells regain the norm al appearance of their actin cytoskeleton upon prolonged incubation. M icroinjection of the catalytically inactive GST-SptP(C481S) protein re sults in changes similar to those induced by the wild-type toxin. Furt hermore, microinjection of a fusion protein between GST and the first 285 amino acids of SptP also leads to identical disruption of the host cell actin cytoskeleton, indicating that the aminoterminal half of Sp tP is sufficient to mediate this effect. However, microinjection of a fusion protein between GST and the last 259 amino acids of SptP also d isrupted the normal appearance of the cytoskeleton. These results supp ort the hypothesis that SptP is an effector protein arranged in modula r domains that may co-operate with each other to exert related functio ns.