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Journal of Bacteriology, December 2003, p. 6950-6967, Vol. 185, No. 23
0021-9193/03/$08.00+0 DOI: 10.1128/JB.185.23.6950-6967.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Institute of Microbiology, D-BIOL, ETH Zürich, 8092 Zürich, Switzerland,1 Departments of Microbiology and Medicine, University of Washington, Seattle, Washington 981952
Received 8 May 2003/ Accepted 18 August 2003
Salmonella enterica subspecies 1 serovar Typhimurium encodes a type III secretion system (TTSS) within Salmonella pathogenicity island 1 (SPI-1). This TTSS injects effector proteins into host cells to trigger invasion and inflammatory responses. Effector proteins are recognized by the TTSS via signals encoded in their N termini. Specific chaperones can be involved in this process. The chaperones InvB, SicA, and SicP are encoded in SPI-1 and are required for transport of SPI-1-encoded effectors. Several key effector proteins, like SopE and SopE2, are located outside of SPI-1 but are secreted in an SPI-1-dependent manner. It has not been clear how these effector proteins are recognized by the SPI-1 TTSS. Using pull-down and coimmunoprecipitation assays, we found that SopE is copurified with InvB, the known chaperone for the SPI-1-encoded effector protein Sip/SspA. We also found that InvB is required for secretion and translocation of SopE and SopE2 and for stabilization of SopE2 in the bacterial cytosol. Our data demonstrate that effector proteins encoded within and outside of SPI-1 use the same chaperone for secretion via the SPI-1 TTSS.
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