D (2006) The first 45 amino acids of SopA are necessary for InvB binding and SPI-1 secretion

Salmonella enterica serovar Typhimurium encodes two type III secretion systems (TTSSs) within pathoge-nicity island 1 (SPI-1) and island 2 (SPI-2). These type III protein secretion and translocation systems transport a panel of bacterial effector proteins across both the bacterial and the host cell membranes to promote bacterial entry and subsequent survival inside host cells. Effector proteins contain secretion and translocation signals that are often located at their N termini. We have developed a ruffling-based translocation reporter system that uses the secretion- and translocation-deficient catalytic domain of SopE, SopE78–240, as a reporter. Using this assay, we determined that the N-terminal 45 amino acid residues of Salmonella SopA are necessary and sufficient for directing its secretion and translocation through the SPI-1 TTSS. SopA1–45, but not SopA1–44, is also able to bind to its chaperone, InvB, indicating that SPI-1 type III secretion and translocation of SopA require its chaperone. Salmonella spp. are the causes of many intestinal infections, ranging from mild gastroenteritis to severe typhoid fever. Once in the intestinal tract, Salmonella initiates infection by invading intestinal epithelial cells. The invasion ability is achieved through the type III protein secretion and translocation system encoded by Salmonella pathogenicity island 1 (SPI-1). Com-ponents of this type III protein transport system share exten-sive amino acid and architectural similarities with the flagellar export apparatus (19). The SPI-1 type III protein transport system functions to deliver a panel of bacterial virulence pro-teins, termed effectors, into the mammalian host cells. The secretion and subsequent translocation of SPI-1 type III effec-tor proteins often require cognate chaperones (28). It has been reported that signals that direct the secretion of these proteins are within the N-terminal amino acid or th