Channel Formation by FhaC, the Outer Membrane Protein Involved in the Secretion of the Bordetella pertussis Filamentous Hemagglutinin

• Published in: The Journal of biological chemistry 1999-12, Vol.274 (53), p.37731-37735
• Main Authors: Françoise Jacob-Dubuisson, Chahrazed El-Hamel, Nathalie Saint, Sandrine Guédin, Eve Willery, Gérard Molle, Camille Locht
• Format: Article
• Language: English
• Subjects: Bacterial Outer Membrane Proteins - isolation & purification; Bacterial Outer Membrane Proteins - physiology; Base Sequence; Bordetella pertussis; Bordetella pertussis - metabolism; Bordetella pertussis - pathogenicity; Chromatography, Affinity; Chromatography, Ion Exchange; Circular Dichroism; DNA Primers; FhaC protein; Hemagglutinins - metabolism; Hot Temperature; Subcellular Fractions - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.274.53.37731

Many virulence factors of pathogenic microorganisms are presented at the cell surface. However, protein secretion across the outer membrane of Gram-negative bacteria remains poorly understood. Here we used the extremely efficient secretion of the Bordetella pertussis filamentous hemagglutinin (FHA) to decipher this process. FHA secretion requires a single specific accessory protein, FhaC, the prototype of a family of proteins necessary for the extracellular localization of various virulence proteins in Gram-negative bacteria. We show that FhaC is heat-modifiable and localized in the outer membrane. Circular dichroism spectra indicated that FhaC is rich in β-strands, in agreement with structural predictions for this protein. We further demonstrated that FhaC forms pores in artificial membranes, as evidenced by single-channel conductance measurements through planar lipid bilayers, as well as by liposome swelling assays and patch-clamp experiments using proteoliposomes. Single-channel conductance appeared to fluctuate very fast, suggesting that the FhaC channels frequently assume a closed conformation. We thus propose that FhaC forms a specific β-barrel channel in the outer membrane for the outward translocation of FHA.