title: Structural and mechanistic insights into the bacterial amyloid secretion channel CsgG.
abstract: Curli are functional amyloid fibres that constitute the major protein component of the extracellular matrix in pellicle biofilms formed by Bacteroidetes and Proteobacteria (predominantly of the α and γ classes). They provide a fitness advantage in pathogenic strains and induce a strong pro-inflammatory response during bacteraemia. Curli formation requires a dedicated protein secretion machinery comprising the outer membrane lipoprotein CsgG and two soluble accessory proteins, CsgE and CsgF. Here we report the X-ray structure of Escherichia coli CsgG in a non-lipidated, soluble form as well as in its native membrane-extracted conformation. CsgG forms an oligomeric transport complex composed of nine anticodon-binding-domain-like units that give rise to a 36-stranded β-barrel that traverses the bilayer and is connected to a cage-like vestibule in the periplasm. The transmembrane and periplasmic domains are separated by a 0.9-nm channel constriction composed of three stacked concentric phenylalanine, asparagine and tyrosine rings that may guide the extended polypeptide substrate through the secretion pore. The specificity factor CsgE forms a nonameric adaptor that binds and closes off the periplasmic face of the secretion channel, creating a 24,000 Å(3) pre-constriction chamber. Our structural, functional and electrophysiological analyses imply that CsgG is an ungated, non-selective protein secretion channel that is expected to employ a diffusion-based, entropy-driven transport mechanism.
authors.affiliation: 1] Structural and Molecular Microbiology, Structural Biology Research Center, VIB, Pleinlaan 2, 1050 Brussels, Belgium [2] Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium.
authors.forename: Parveen
authors.initials: P
authors.lastname: Goyal
authors.affiliation: 1] Unité G5 Biologie structurale de la sécrétion bactérienne, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France [2] UMR 3528, CNRS, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France.
authors.forename: Petya V
authors.initials: PV
authors.lastname: Krasteva
authors.affiliation: 1] Structural and Molecular Microbiology, Structural Biology Research Center, VIB, Pleinlaan 2, 1050 Brussels, Belgium [2] Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium.
authors.forename: Nani
authors.initials: N
authors.lastname: Van Gerven
authors.affiliation: 1] Unité G5 Biologie structurale de la sécrétion bactérienne, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France [2] UMR 3528, CNRS, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France.
authors.forename: Francesca
authors.initials: F
authors.lastname: Gubellini
authors.affiliation: 1] Structural and Molecular Microbiology, Structural Biology Research Center, VIB, Pleinlaan 2, 1050 Brussels, Belgium [2] Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium.
authors.forename: Imke
authors.initials: I
authors.lastname: Van den Broeck
authors.affiliation: Structure et Fonction des Membranes Biologiques (SFMB), Université Libre de Bruxelles, 1050 Brussels, Belgium.
authors.forename: Anastassia
authors.initials: A
authors.lastname: Troupiotis-Tsaïlaki
authors.affiliation: 1] Structural and Molecular Microbiology, Structural Biology Research Center, VIB, Pleinlaan 2, 1050 Brussels, Belgium [2] Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium.
authors.forename: Wim
authors.initials: W
authors.lastname: Jonckheere
authors.affiliation: UMR 3528, CNRS, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France.
authors.forename: Gérard
authors.initials: G
authors.lastname: Péhau-Arnaudet
authors.affiliation: Department of Molecular Microbiology and Microbial Pathogenesis, Washington University in Saint Louis School of Medicine, St Louis, Missouri 63110-1010, USA.
authors.forename: Jerome S
authors.initials: JS
authors.lastname: Pinkner
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109-1048, USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Chapman
authors.affiliation: Department of Molecular Microbiology and Microbial Pathogenesis, Washington University in Saint Louis School of Medicine, St Louis, Missouri 63110-1010, USA.
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Hultgren
authors.affiliation: Department of Chemistry, Institute for Structural and Molecular Biology, University College London, London WC1H 0AJ, UK.
authors.forename: Stefan
authors.initials: S
authors.lastname: Howorka
authors.affiliation: 1] Unité G5 Biologie structurale de la sécrétion bactérienne, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France [2] UMR 3528, CNRS, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France.
authors.forename: Rémi
authors.initials: R
authors.lastname: Fronzes
authors.affiliation: 1] Structural and Molecular Microbiology, Structural Biology Research Center, VIB, Pleinlaan 2, 1050 Brussels, Belgium [2] Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium.
authors.forename: Han
authors.initials: H
authors.lastname: Remaut
mesh_terms: D000682:Amyloid / Q000378:metabolism*; D018441:Biofilms; D002462:Cell Membrane; D018360:Crystallography, X-Ray; D004058:Diffusion; D019277:Entropy; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D008074:Lipoproteins / Q000737:chemistry* / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism; D008954:Models, Biological; D008958:Models, Molecular; D019897:Periplasm / Q000378:metabolism; D011487:Protein Conformation; D021381:Protein Transport
chemical_list: D000682:Amyloid; C561979:CsgE protein, E coli; C534546:CsgG protein, E coli; D029968:Escherichia coli Proteins; D008074:Lipoproteins; D026901:Membrane Transport Proteins