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Infection and Immunity, September 2004, p. 5115-5125, Vol. 72, No. 9
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.9.5115-5125.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

SseK1 and SseK2 Are Novel Translocated Proteins of Salmonella enterica Serovar Typhimurium

Sonya L. Kujat Choy,1 Erin C. Boyle,1,2 Ohad Gal-Mor,1 David L. Goode,1 Yanet Valdez,1,2 Bruce A. Vallance,1,{dagger} and B. Brett Finlay1,2,3*

Biotechnology Laboratory,1 Departments of Biochemistry and Molecular Biology,3 Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada2

Received 19 February 2004/ Returned for modification 14 April 2004/ Accepted 9 June 2004

Salmonella enterica is a gram-negative, facultative intracellular pathogen that causes disease symptoms ranging from gastroenteritis to typhoid fever. A key virulence strategy is the translocation of bacterial effector proteins into the host cell, mediated by the type III secretion systems (TTSSs) encoded in Salmonella pathogenicity island 1 (SPI-1) and SPI-2. In S. enterica serovar Typhimurium LT2, we identified the protein products of STM4157 and STM2137 as novel candidate secreted proteins by comparison to known secreted proteins from enterohemorrhagic Escherichia coli and Citrobacter rodentium. The STM4157 and STM2137 proteins, which we have designated SseK1 and SseK2, respectively, are 61% identical at the amino acid level and differ mainly in their N termini. Western analysis showed that in vitro accumulation and secretion of these proteins in serovar Typhimurium were affected by mutations in the two-component systems SsrA/B and PhoP/Q, which are key mediators of intracellular growth and survival. SPI-2 TTSS-dependent translocation of recombinant SseK1::Cya was evident at 9 h postinfection of epithelial cells, while translocation of SseK2::Cya was not detected until 21 h. Remarkably, the translocation signal for SseK1 was contained within the N-terminal 32 amino acids. Fractionation of infected epithelial cells revealed that following translocation SseK1 localizes to the host cytosol, which is unusual among the currently known Salmonella effectors. Phenotypic analysis of {Delta}sseK1, {Delta}sseK2, and {Delta}sseK1/{Delta}sseK2 mutants provided evidence for a role that was not critical during systemic infection. In summary, this work demonstrates that SseK1 and SseK2 are novel translocated proteins of serovar Typhimurium.

* Corresponding author. Mailing address: Biotechnology Laboratory, University of British Columbia, Room 237, Wesbrook Building, 6174 University Blvd., Vancouver, BC, Canada V6T 1Z3. Phone: (604) 822-2210. Fax: (604) 822-9830. E-mail: bfinlay{at}interchange.ubc.ca.

Editor: V. J. DiRita

{dagger} Present address: Department of Pediatrics, Division of Gastroenterology, British Columbia's Children's Hospital, Vancouver, BC, Canada V6H-3V4.

Infection and Immunity, September 2004, p. 5115-5125, Vol. 72, No. 9
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.9.5115-5125.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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