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In situ and high-resolution Cryo-EM structure of the Type VI secretion membrane complex

Abstract : Bacteria have evolved macromolecular machineries that secrete effectors and toxins to survive and thrive in diverse environments. The type VI secretion system (T6SS) is a contractile machine that is related to Myoviridae phages. It is composed of a phage tail-like structure inserted in the bacterial cell envelope by a membrane complex (MC) comprising the TssJ, TssL and TssM proteins. We previously reported the low-resolution negative-stain electron microscopy structure of the enteroaggregative Escherichia coli MC, and proposed a rotational 5-fold symmetry with a TssJ:TssL:TssM stoichiometry of 2:2:2. Here, cryo-electron tomography analyses of the T6SS MC confirm the 5-fold symmetry in situ and identify the regions of the structure that insert into the bacterial membranes. A high-resolution model obtained by single particle cryo-electron microscopy highlights new features: five additional copies of TssJ, yielding a TssJ:TssL:TssM stoichiometry of 3:2:2, an 11-residue loop in TssM, protruding inside the lumen of the MC and constituting a functionally important periplasmic gate, and hinge regions. Based on these data, we propose an updated model on T6SS structure, assembly and function.
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Submitted on : Friday, November 1, 2019 - 4:36:56 PM
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Chiara Rapisarda, Yassine Cherrak, Romain Kooger, Victoria Schmidt, Riccardo Pellarin, et al.. In situ and high-resolution Cryo-EM structure of the Type VI secretion membrane complex. EMBO Journal, EMBO Press, 2019, 38 (10), ⟨10.15252/embj.2018100886⟩. ⟨hal-02342926⟩

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