SseA is a chaperone for the SseB and SseD translocon components of the Salmonella pathogenicity-island-2-encoded type III secretion system

• Published in: Microbiology (Society for General Microbiology) 2003-05, Vol.149 (5), p.1103-1111
• Main Authors: Ruiz-Albert, Javier, Mundy, Rosanna, Yu, Xiu-Jun, Beuzon, Carmen R, Holden, David W
• Format: Article
• Language: English
• Subjects: Animals; Bacterial Proteins - metabolism; Bacteriology; Biological and medical sciences; Female; Fundamental and applied biological sciences. Psychology; HeLa Cells; Humans; Mice; Mice, Inbred BALB C; Microbiology; Miscellaneous; Molecular Chaperones - genetics; Molecular Chaperones - metabolism; Mutation; Operon; Salmonella; Salmonella typhimurium - genetics; Salmonella typhimurium - metabolism; Salmonella typhimurium - pathogenicity; sseA gene; SseB protein; SseC protein; SseD protein; SseF protein; SseG protein; Two-Hybrid System Techniques; Virulence
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/mic.0.26190-0

Department of Infectious Diseases, Centre for Molecular Microbiology and Infection, Imperial College School of Medicine, Armstrong Road, London SW7 2AZ, UK Correspondence David W. Holden d.holden{at}ic.ac.uk The type III secretion system (TTSS) encoded by the Salmonella pathogenicity island 2 (SPI-2) is required for bacterial replication inside macrophages and for systemic infection in mice. Many TTSS secreted proteins, including effectors and components of the translocon, require chaperones which promote their stability, prevent their premature interactions or facilitate their secretion. In this study, the function of the first gene ( sseA ) of one of the SPI-2 operons ( sseA – G ) was investigated. This operon includes genes that encode translocon components (SseB, SseC and SseD), translocated proteins (SseF and SseG) and putative chaperones (SscA and SscB). sseA encodes a 12·5 kDa protein with a C-terminal region with the potential to form a coiled-coil structure, but no sequence similarity to other proteins. Mutation of sseA results in severe virulence attenuation and an intracellular replication defect. It is shown here that SseA is not a secreted protein, but is required for SPI-2-dependent translocation of two effector proteins (SifA and PipB). Furthermore, the translocon components SseB and SseD were not detected in an sseA mutant strain. By using a yeast two-hybrid assay and column binding experiments, it is demonstrated that SseA interacts directly with SseB and SseD. These results indicate that SseA is a chaperone for SseB and SseD. The inability of an sseA mutant to assemble the SPI-2 TTSS translocon accounts for its high level of virulence attenuation in vivo . To the authors' knowledge, this is the first chaperone described for the SPI-2 TTSS. Abbreviations: CI, competitive index; HA, haemagglutinin; Sif, Salmonella -induced filament; SPI-2, Salmonella pathogenicity island 2; S . typhimurium , Salmonella enterica serovar Typhimurium; TTSS, type III secretion system Present address: Departamento de Biología Celular, Genética y Fisología, Facultad de Ciencias, Universidad de Málaga, Campus Teatinos, 29071, Málaga, Spain.