IglF mediates type VI secretion system spike assembly and promotes <i>Francisella</i> virulence
Abstract
Type VI secretion systems (T6SSs) are widely distributed among Gram-negative bacteria, where they mostly act to promote bacterial warfare. Bacteria from the Francisella genus possess T6SSs that phylogenetically diverge from all other T6SSs and constitute the T6SSii subtype. Francisella tularensis, the agent of tularemia, relies on its T6SS to secrete effectors into host cells. Despite the key role of this nanomachine in Francisella virulence, the structure of T6SSii and the mechanism underlying its assembly are still poorly understood. Here, using Francisella novicida , we focused on understanding the structure and assembly of the spike, the most apical T6SS complex coupling effector delivery and membrane-puncturing activity. We solved the structure of the protein of unknown function, IglF, in complex with the N-terminal domain of IglG, the T6SSii PAAR protein. Interaction between IglF and IglG enabled the assembly of a mature T6SS spike complex both in Francisella and in a heterologous expression system. In contrast, disrupting IglF:IglG interactions prevented assembly of the PAAR protein with the central spike complex and invalidated T6SS assembly, as visualized by monitoring T6SS dynamics or secretion. Accordingly, IglF:IglG interactions were required for F. novicida virulence in vitro and in a mouse model of tularemia. Altogether, our findings shed light on the assembly mechanism of the Francisella T6SSii spike complex and its importance in virulence.
Article Details
Journal Info
Proceedings of the National Academy of Sciences
National Academy of Sciences
Authors (16)
Manon Degabriel
Centre International de Recherche en Infectiologie, Inserm, U1111, CNRS UMR5308, UCBL1, Ecole Normale Supérieure de Lyon
Esteban Guiot
Centre International de Recherche en Infectiologie, Inserm, U1111, CNRS UMR5308, UCBL1, Ecole Normale Supérieure de Lyon
Mélissa Marcotte
Centre International de Recherche en Infectiologie, Inserm, U1111, CNRS UMR5308, UCBL1, Ecole Normale Supérieure de Lyon
Coline Berthollier
Molecular Microbiology and Structural Biochemistry, Microbiologie Moléculaire et Biochimie Structurale, Institut de Biologie et Chimie des protéines, CNRS, UMR 5086, Université Claude Bernard Lyon 1
Diane Soussan
Centre International de Recherche en Infectiologie, Inserm, U1111, CNRS UMR5308, UCBL1, Ecole Normale Supérieure de Lyon
Laure Bataille
Clémence Journeau
Centre International de Recherche en Infectiologie, Inserm, U1111, CNRS UMR5308, UCBL1, Ecole Normale Supérieure de Lyon
Adrien Ducret
Molecular Microbiology and Structural Biochemistry
Sarah Dayet
Centre International de Recherche en Infectiologie, Inserm, U1111, CNRS UMR5308, UCBL1, Ecole Normale Supérieure de Lyon
Amandine Mosnier
Centre International de Recherche en Infectiologie, Inserm, U1111, CNRS UMR5308, UCBL1, Ecole Normale Supérieure de Lyon
Amandine Martin
Centre International de Recherche en Infectiologie, Inserm, U1111, CNRS UMR5308, UCBL1, Ecole Normale Supérieure de Lyon
Virginie Gueguen-Chaignon
Structure Fédérative de Recherche Biosciences, Université Claude Bernard Lyon 1, CNRS UAR3444, Inserm US8, Ecole Normale Supérieure de Lyon
Sandrine Boisset
Centre International de Recherche en Infectiologie, Inserm, U1111, CNRS UMR5308, UCBL1, Ecole Normale Supérieure de Lyon
Rémi Fronzes
European Institute of Chemistry and Biology, CNRS UMR 5234 Microbiologie Fondamentale et Pathogénicité, Univ. Bordeaux
Laurent Terradot
Thomas Henry
Centre International de Recherche en Infectiologie, Inserm, U1111, CNRS UMR5308, UCBL1, Ecole Normale Supérieure de Lyon