title: Substrate recognition by the POTRA domains of TpsB transporter FhaC.
abstract: Widespread in Gram-negative bacteria, the two-partner secretion (TPS) pathway mediates the secretion of large, β-helical 'TpsA' proteins with various functions. TpsA proteins harbour a conserved, N-proximal TPS domain essential for secretion. TpsB transporters specifically recognize their TpsA partners in the periplasm and mediate their translocation across the outer membrane through a hydrophilic channel. The FHA/FhaC pair of Bordetella pertussis represents a model TPS system. FhaC is composed of a β barrel preceded by two periplasmic POTRA domains in tandem. Here we show that both POTRAs are involved in FHA recognition. Surface plasmon resonance analyses indicated an interaction of micromolar affinity between the POTRAs and the TPS domain with fast association and dissociation steps, consistent with the transient character of this interaction in vivo. Major interaction sites in POTRAs correspond to hydrophobic grooves formed by a β sheet edge and the flanking α helix, well-suited to accommodate extended, amphipathic strands of the substrate and consistent with β augmentation. The initial recruitment of the TPS domain to POTRAs appears to be facilitated by electrostatic attractions. A domain corresponding to the first part of the repeat-rich central region of FHA is also recognized by the POTRAs, suggesting successive interactions in the course of secretion.
authors.affiliation: Inserm U1019, Center for Infection and Immunity of Lille, F-59019 Lille, France.
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Delattre
authors.forename: Nathalie
authors.initials: N
authors.lastname: Saint
authors.forename: Bernard
authors.initials: B
authors.lastname: Clantin
authors.forename: Eve
authors.initials: E
authors.lastname: Willery
authors.forename: Guy
authors.initials: G
authors.lastname: Lippens
authors.forename: Camille
authors.initials: C
authors.lastname: Locht
authors.forename: Vincent
authors.initials: V
authors.lastname: Villeret
authors.forename: Françoise
authors.initials: F
authors.lastname: Jacob-Dubuisson
mesh_terms: D018829:Adhesins, Bacterial / Q000378:metabolism*; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D001886:Bordetella pertussis / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D020349:Surface Plasmon Resonance; D010566:Virulence Factors, Bordetella / Q000378:metabolism*
chemical_list: D018829:Adhesins, Bacterial; D001425:Bacterial Outer Membrane Proteins; D010566:Virulence Factors, Bordetella; C098052:fhaC protein, Bordetella pertussis; C065273:filamentous hemagglutinin adhesin, Bordetella pertussis