title: FrancisellaIglG protein and the DUF4280 proteins: PAAR-like proteins in non-canonical Type VI secretion systems?
abstract: Type VI secretion systems (T6SS) are bacterial molecular machines translocating effector proteins into target cells. T6SS are widely present in Gram-negative bacteria where they predominantly act to kill neighboring bacteria. This secretion system is reminiscent of the tail of contractile bacteriophages and consists of a contractile sheath anchored in the bacterial envelope and an inner tube made of stacks of the Hcp protein. The Hcp tube is capped with a VgrG trimer and a spike protein termed PAAR, which acts as the membrane-puncturing device.Francisella tularensis, the agent of tularemia, is an intracellular bacterium replicating within the host cytosol. Upon entry into the host cell,F. tularensisrapidly lyses the host vacuolar membrane to reach the host cytosol. This escape is dependent on theFrancisellaPathogenicity Island (FPI), which is encoding an atypical T6SS. Among the 17 proteins encoded by the FPI, most of them required for virulence, eight have some homology to canonical T6SS proteins. We recently identified the function of one protein of unknown function encoded within the FPI, IglG. By three-dimensional modelling and following validation by different techniques, we found that IglG adopts a fold resembling the one of PAAR proteins. Importantly, IglG features a domain of unknown function DUF4280, present in numerous bacterial species. We thus propose to rename this domain of unknown function, PAAR-like domain, and discuss here the characteristics of this domain and its distribution in both Gram-negative and Gram-positive bacteria.
authors.affiliation: CIRI, Centre International de Recherche en Infectiologie, Inserm, U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, École Normale Supérieure de Lyon, Univ Lyon, F-69007, LYON, France. ; LabEX Ecofect, Eco-evolutionary dynamics of infectious diseases, Lyon, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Lays
authors.affiliation: LabEX Ecofect, Eco-evolutionary dynamics of infectious diseases, Lyon, France. ; INRIA Rhône-Alpes, 655 av de l'Europe, F-38334 Montbonnot, France, LBBE, UMR5558, Université Claude Bernard Lyon 1, Univ Lyon, F-69007, Lyon, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Tannier
authors.affiliation: CIRI, Centre International de Recherche en Infectiologie, Inserm, U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, École Normale Supérieure de Lyon, Univ Lyon, F-69007, LYON, France. ; LabEX Ecofect, Eco-evolutionary dynamics of infectious diseases, Lyon, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Henry
keywords: DUF4280; Francisella; PAAR; PF14107; T6SS; phage; type VI secretion system