The Legionella IcmS–IcmW protein complex is important for Dot/Icm-mediated protein translocation

Authors

  • Shira Ninio,

    1. Section of Microbial Pathogenesis, Yale University School of Medicine, Boyer Center for Molecular Medicine, Room 354b, 295 Congress Avenue, New Haven, CT 06511, USA.
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    • These authors contributed equally to this work.

  • Deborah M. Zuckman-Cholon,

    1. Section of Microbial Pathogenesis, Yale University School of Medicine, Boyer Center for Molecular Medicine, Room 354b, 295 Congress Avenue, New Haven, CT 06511, USA.
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    • Present address: Washington University School of Medicine, Campus Box 8208, 660 S. Euclid Ave., St. Louis, MO 63110, USA.

    • These authors contributed equally to this work.

  • Eric D. Cambronne,

    1. Section of Microbial Pathogenesis, Yale University School of Medicine, Boyer Center for Molecular Medicine, Room 354b, 295 Congress Avenue, New Haven, CT 06511, USA.
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  • Craig R. Roy

    Corresponding author
    1. Section of Microbial Pathogenesis, Yale University School of Medicine, Boyer Center for Molecular Medicine, Room 354b, 295 Congress Avenue, New Haven, CT 06511, USA.
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E-mail Craig.roy@yale.edu; Tel. (+1) 203 737 2408; Fax (+1) 203 737 2630.

Summary

The intracellular pathogen Legionella pneumophila can infect and replicate within macrophages of a human host. To establish infection, Legionella require the Dot/Icm secretion system to inject protein substrates directly into the host cell cytoplasm. The mechanism by which substrate proteins are engaged and translocated by the Dot/Icm system is not well understood. Here we show that two cytosolic components of the Dot/Icm secretion machinery, the proteins IcmS and IcmW, play an important role in substrate translocation. Biochemical analysis indicates that IcmS and IcmW form a stable protein complex. In Legionella, the IcmW protein is rapidly degraded in the absence of the IcmS protein. Substrate proteins translocated into mammalian host cells by the Dot/Icm system were identified using the IcmW protein as bait in a yeast two-hybrid screen. It was determined that the IcmS–IcmW complex interacts with these substrates and plays an important role in translocation of these proteins into mammalian cells. These data are consistent with the IcmS–IcmW complex being involved in the recognition and Dot/Icm-dependent translocation of substrate proteins during Legionella infection of host cells.

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