The prodomain of the Bordetella two-partner secretion pathway protein FhaB remains intracellular yet affects the conformation of the mature C-terminal domain

Authors

  • Christopher R. Noël,

    1. Department of Microbiology and Immunology, School of Medicine, University of North Carolina, Chapel Hill, NC, USA
    2. Biomolecular Sciences and Engineering Program, University of California, Santa Barbara, CA, USA
    Search for more papers by this author
  • Joseph Mazar,

    1. Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA, USA
    Current affiliation:
    1. Sanford-Burnham Medical Research Institute at Lake Nora, Orlando, FL, USA
    Search for more papers by this author
  • Jeffrey A. Melvin,

    1. Department of Microbiology and Immunology, School of Medicine, University of North Carolina, Chapel Hill, NC, USA
    Search for more papers by this author
  • Jessica A. Sexton,

    1. Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA, USA
    Current affiliation:
    1. Infectious Diseases, Novartis Institutes for BioMedical Research, Inc., Cambridge, MA, USA
    Search for more papers by this author
  • Peggy A. Cotter

    Corresponding author
    1. Biomolecular Sciences and Engineering Program, University of California, Santa Barbara, CA, USA
    2. Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA, USA
    • Department of Microbiology and Immunology, School of Medicine, University of North Carolina, Chapel Hill, NC, USA
    Search for more papers by this author

For correspondence. E-mail peggy_cotter@med.unc.edu; Tel. (+1) 919 966 5612; Fax (+1) 919 962 8103.

Summary

Two-partner secretion (TPS) systems use β-barrel proteins of the Omp85-TpsB superfamily to transport large exoproteins across the outer membranes of Gram-negative bacteria. The Bordetella FHA/FhaC proteins are prototypical of TPS systems in which the exoprotein contains a large C-terminal prodomain that is removed during translocation. Although it is known that the FhaB prodomain is required for FHA function in vivo, its role in FHA maturation has remained mysterious. We show here that the FhaB prodomain is required for the extracellularly located mature C-terminal domain (MCD) of FHA to achieve its proper conformation. We show that the C-terminus of the prodomain is retained intracellularly and that sequences within the N-terminus of the prodomain are required for this intracellular localization. We also identify sequences at the C-terminus of the MCD that are required for release of mature FHA from the cell surface. Our data support a model in which the intracellularly located prodomain affects the final conformation of the extracellularly located MCD. We hypothesize that maturation triggers cleavage and degradation of the prodomain.

Ancillary