title: Channel formation by FhaC, the outer membrane protein involved in the secretion of the Bordetella pertussis filamentous hemagglutinin.
abstract: 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 beta-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 beta-barrel channel in the outer membrane for the outward translocation of FHA.
authors.affiliation: INSERM U447, Institut de Biologie de Lille, Institut Pasteur de Lille, 1 rue Calmette, 59019 Lille Cedex, France. francoise.jacob@pasteur-lille.fr
authors.forename: F
authors.initials: F
authors.lastname: Jacob-Dubuisson
authors.forename: C
authors.initials: C
authors.lastname: El-Hamel
authors.forename: N
authors.initials: N
authors.lastname: Saint
authors.forename: S
authors.initials: S
authors.lastname: Guédin
authors.forename: E
authors.initials: E
authors.lastname: Willery
authors.forename: G
authors.initials: G
authors.lastname: Molle
authors.forename: C
authors.initials: C
authors.lastname: Locht
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000302:isolation & purification / Q000502:physiology*; D001483:Base Sequence; D001886:Bordetella pertussis / Q000378:metabolism* / Q000472:pathogenicity; D002846:Chromatography, Affinity; D002852:Chromatography, Ion Exchange; D002942:Circular Dichroism; D017931:DNA Primers; D006388:Hemagglutinins / Q000378:metabolism*; D006358:Hot Temperature; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D017931:DNA Primers; D006388:Hemagglutinins; C098052:fhaC protein, Bordetella pertussis