A translocator-specific export signal establishes the translocator–effector secretion hierarchy that is important for type III secretion system function

Authors

  • Amanda G. Tomalka,

    1. Department of Molecular Biology and Microbiology, Case Western Reserve University, Cleveland, OH, USA
    Search for more papers by this author
  • Charles M. Stopford,

    1. Department of Molecular Biology and Microbiology, Case Western Reserve University, Cleveland, OH, USA
    Current affiliation:
    1. Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, NC, USA.
    Search for more papers by this author
  • Pei-Chung Lee,

    1. Department of Molecular Biology and Microbiology, Case Western Reserve University, Cleveland, OH, USA
    Search for more papers by this author
  • Arne Rietsch

    Corresponding author
    • Department of Molecular Biology and Microbiology, Case Western Reserve University, Cleveland, OH, USA
    Search for more papers by this author

For correspondence. E-mail arne.rietsch@case.edu; Tel. (+1) 216 368 2249; Fax (+1) 216 368 3055.

Summary

Type III secretion systems are used by many Gram-negative pathogens to directly deliver effector proteins into the cytoplasm of host cells. To accomplish this, bacteria secrete translocator proteins that form a pore in the host-cell membrane through which the effector proteins are then introduced into the host cell. Evidence from multiple systems indicates that the pore-forming translocator proteins are exported before effectors, but how this secretion hierarchy is established is unclear. Here we used the Pseudomonas aeruginosa translocator protein PopD as a model to identify its export signals. The N-terminal secretion signal and chaperone, PcrH, are required for export under all conditions. Two novel signals in PopD, one proximal to the chaperone binding site and one at the very C-terminus of the protein, are required for export of PopD before effector proteins. These novel export signals establish the translocator–effector secretion hierarchy, which in turn, is critical for the delivery of effectors into host cells.

Ancillary