SALMONELLA-TYPHIMURIUM SECRETED INVASION DETERMINANTS ARE HOMOLOGOUS TO SHIGELLA IPA PROTEINS

Salmonella typhimurium secreted proteins (Ssp) were previously implica ted in epithelial cell invasion, Here we describe four genes (sspB, ss pC, sspD and sspA), located between spaT and prgH, which encode protei ns of 63, 42, 36, and 87 kDa, respectively, These Ssp are homologous t o Shigella flexneri secreted proteins IpaB, IpaC, IpaD and IpaA. A non -invasive mutant with a transposon insertion in sspC lacks Ssp of 87, 42 and 36 kDa. Complementation analyses show that sspC and sspD encode the 42 and the 36 kDa Ssp, while the 87 kDa Ssp is encoded by sspA, s spC and sspD but not sspA, are required for invasion, Amino-terminal s equencing shows that SspC and SspA are secreted without amino-terminal processing. We further demonstrate that Ssp secretion requires protei ns encoded by prgHIJK, homologous to the Shigella Ipa secretion system , since SspA is abundantly secreted by wild-type bacteria but is compl etely retained within the cellular fraction of a prgHIJK mutant, A pre cipitate containing abundant SspC and three other major Ssp of 63, 59 and 22 kDa was isolated from culture supernatants of wild-type bacteri a, These data indicate that major secreted invasion determinants of S. typhimurium are structurally and functionally homolgous to S. flexner i Ipa proteins.