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In situ and high‐resolution cryo‐EM structure of a bacterial type VI secretion system membrane complex

DOI: 10.15252/embj.2018100886 DOI Help

Authors: Chiara Rapisarda (University of Bordeaux) , Yassine Cherrak (Aix‐Marseille Université ‐ CNRS) , Romain Kooger (Eidgenössische Technische Hochschule Zürich) , Victoria Schmidt (Aix‐Marseille Université ‐ CNRS) , Riccardo Pellarin (Institut Pasteur, CNRS UMR 3528) , Laureen Logger (Aix‐Marseille Université ‐ CNRS) , Eric Cascales (Aix‐Marseille Université ‐ CNRS) , Martin Pilhofer (Technische Hochschule Zürich) , Eric Durand (Institut de Microbiologie de la Méditerranée (IMM), UMR7255, INSERM) , Remi Fronzes (University of Bordeaux)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: The Embo Journal

State: Published (Approved)
Published: March 2019

Open Access Open Access

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 MC structure and dynamics during T6SS assembly and function.

Journal Keywords: cryo‐electron microscopy; Membrane protein complex; Type VI secretion systems

Subject Areas: Biology and Bio-materials

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