title: Conformational dynamics of protein transporter FhaC: large-scale motions of plug helix.
abstract: FhaC is an integral outer membrane protein of the whooping cough agent Bordetella pertussis that mediates the transport to the cell surface of a major virulence factor, the filamentous haemagglutinin adhesin FHA. The FHA/FhaC pair is a prototypic TpsA/TpsB system of the widespread 'Two-Partner Secretion' pathway, dedicated to the transport of long extracellular proteins in various pathogenic and environmental Gram-negative bacteria. FhaC belongs to the ubiquitous Omp85 superfamily of protein transporters. The X-ray structure of FhaC shows that the transmembrane β-barrel channel hypothesized to serve as the FHA-conducting pore is obstructed by two structural elements conserved among TpsB transporters, an N-terminal α helix and an extracellular loop. Here, we provide evidence for conformational dynamics of FhaC related to the secretion mechanism. Using paramagnetic electron resonance, electrophysiology and in vivo approaches, we showed that FhaC exchanges between open and closed conformations. The interaction with its secretory partner FHA alters this distribution of conformations. The open conformation of FhaC implies a large displacement from the channel of the N-terminal 'plug' helix, which remains in the periplasm during FHA secretion. The membrane environment favours the dynamics of the TpsB transporter.
authors.affiliation: Institut Pasteur de Lille, Center for Infection and Immunity, Lille, France; CNRS UMR8204, Lille, France; INSERM U1019, Lille, France; Univ Lille Nord de France, Lille, France.
authors.forename: Jérémy
authors.initials: J
authors.lastname: Guérin
authors.forename: Catherine
authors.initials: C
authors.lastname: Baud
authors.forename: Nadia
authors.initials: N
authors.lastname: Touati
authors.forename: Nathalie
authors.initials: N
authors.lastname: Saint
authors.forename: Eve
authors.initials: E
authors.lastname: Willery
authors.forename: Camille
authors.initials: C
authors.lastname: Locht
authors.forename: Hervé
authors.initials: H
authors.lastname: Vezin
authors.forename: Françoise
authors.initials: F
authors.lastname: Jacob-Dubuisson
mesh_terms: D018829:Adhesins, Bacterial / Q000378:metabolism*; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D058947:Bacterial Secretion Systems; D001886:Bordetella pertussis / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D008958:Models, Molecular; D011487:Protein Conformation; D010566:Virulence Factors, Bordetella / Q000378:metabolism*
chemical_list: D018829:Adhesins, Bacterial; D001425:Bacterial Outer Membrane Proteins; D058947:Bacterial Secretion Systems; D010566:Virulence Factors, Bordetella; C098052:fhaC protein, Bordetella pertussis; C065273:filamentous hemagglutinin adhesin, Bordetella pertussis