SOPE, A SECRETED PROTEIN OF SALMONELLA-DUBLIN, IS TRANSLOCATED INTO THE TARGET EUKARYOTIC CELL VIA A SIP-DEPENDENT MECHANISM AND PROMOTES BACTERIAL ENTRY

The entry of Salmonella into cultured epithelial cells is dependent on genes located in several adjacent chromosomal loci. One of these loci encodes the recently identified secretory proteins, denoted Sips (Sal monella invasion proteins). SipB,C,D proteins are essential for the ab ility of the pathogen to invade epithelial cells, To examine if additi onal invasion-associated proteins were secreted by Salmonella dublin, the genes encoding already characterized secretory proteins were inact ivated to facilitate this analysis, The proteins produced and secreted by a double fliM/polar sipB mutant of S. dublin were analysed; this r evealed a set of novel secreted proteins, These proteins, which we den oted Sops (Salmonella outer proteins), formed large filamentous aggreg ates in the medium of bacterial culture growing at 37 degrees C. These aggregates contained five predominant proteins. Here we report the id entification and characterization of one of these proteins, SopE, whic h is a novel invasion-associated secretory protein of S. dublin. A spe cific sopE mutant of S. dublin was found to be defective for invasion into epithelial cells, Upon interaction of Salmonella with HeLa cells, SopE was found to be translocated into the cytoplasm of the target ce ll by extracellular bacteria. The translocation of SopE was shown to b e dependent on the Sip proteins because a polar sipB mutant did not tr anslocate SopE across the HeLa cell membrane.