title: A Salmonella type three secretion effector/chaperone complex adopts a hexameric ring-like structure.
abstract: Many bacterial pathogens use type three secretion systems (T3SS) to inject virulence factors, named effectors, directly into the cytoplasm of target eukaryotic cells. Most of the T3SS components are conserved among plant and animal pathogens, suggesting a common mechanism of recognition and secretion of effectors. However, no common motif has yet been identified for effectors allowing T3SS recognition. In this work, we performed a biochemical and structural characterization of the Salmonella SopB/SigE chaperone/effector complex by small-angle X-ray scattering (SAXS). Our results showed that the SopB/SigE complex is assembled in dynamic homohexameric-ring-shaped structures with an internal tunnel. In this ring, the chaperone maintains a disordered N-terminal end of SopB molecules, in a good position to be reached and processed by the T3SS. This ring dimensionally fits the ring-organized molecules of the injectisome, including ATPase hexameric rings; this organization suggests that this structural feature is important for ATPase recognition by T3SS. Our work constitutes the first evidence of the oligomerization of an effector, analogous to the organization of the secretion machinery, obtained in solution. As effectors share neither sequence nor structural identity, the quaternary oligomeric structure could constitute a strategy evolved to promote the specificity and efficiency of T3SS recognition.
authors.affiliation: INRA Biopolymères, Interactions et Assemblages, Nantes, France Synchrotron SOLEIL, Gif sur Yvette, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Roblin
authors.affiliation: Unité de Glycobiologie Structurale et Fonctionnelle, CNRS UMR8576, Université Lille Nord de France, Villeneuve d'Ascq, France.
authors.forename: Frédérique
authors.initials: F
authors.lastname: Dewitte
authors.affiliation: Unité de Glycobiologie Structurale et Fonctionnelle, CNRS UMR8576, Université Lille Nord de France, Villeneuve d'Ascq, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Villeret
authors.affiliation: Unité de Glycobiologie Structurale et Fonctionnelle, CNRS UMR8576, Université Lille Nord de France, Villeneuve d'Ascq, France.
authors.forename: Emanuele G
authors.initials: EG
authors.lastname: Biondi
authors.affiliation: Unité de Glycobiologie Structurale et Fonctionnelle, CNRS UMR8576, Université Lille Nord de France, Villeneuve d'Ascq, France coralie.bompard@univ-lille1.fr.
authors.forename: Coralie
authors.initials: C
authors.lastname: Bompard
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D058947:Bacterial Secretion Systems; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012486:Salmonella typhimurium / Q000737:chemistry / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D053838:Scattering, Small Angle; D012808:Sigma Factor / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D018832:Molecular Chaperones; D012808:Sigma Factor; C060972:SopB protein, Bacteria; C111259:sigE protein, Bacteria