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Journal of Bacteriology, April 2006, p. 2411-2420, Vol. 188, No. 7
0021-9193/06/$08.00+0     doi:10.1128/JB.188.7.2411-2420.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

The First 45 Amino Acids of SopA Are Necessary for InvB Binding and SPI-1 Secretion

Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907

Received 21 October 2005/ Accepted 11 January 2006

Salmonella enterica serovar Typhimurium encodes two type III secretion systems (TTSSs) within pathogenicity 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, SopE_78-240, 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. SopA_1-45, but not SopA_1-44, is also able to bind to its chaperone, InvB, indicating that SPI-1 type III secretion and translocation of SopA require its chaperone.