In situ and high‐resolution cryo‐EM structure of a bacterial type VI secretion system membrane complex. (15th March 2019)

• Record Type: Journal Article
• Authors: Rapisarda, Chiara; Cherrak, Yassine; Kooger, Romain; Schmidt, Victoria; Pellarin, Riccardo; Logger, Laureen; Cascales, Eric; Pilhofer, Martin; Durand, Eric; Fronzes, Rémi
• Is Part Of: EMBO journal. Volume 38:Number 10(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2019-03-15
• Subjects: cryo‐electron microscopy -- membrane protein complex -- type VI secretion systems; Molecular biology -- Periodicals; 572.805
• DOI: 10.15252/embj.2018100886
• Languages: English
• ISSNs: 0261-4189

Abstract

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. Synopsis: The type VI secretion system (T6SS) is a phage tail‐related contractile machine used by bacteria to deliver a wide range of effector proteins into bacterial or eukaryotic cells. This study reveals the detailed structure of the T6SS membrane complex from enteroaggregative Escherichia coli . Cryo‐electron tomography shows the 5‐fold symmetry of the T6SS membrane complex structure in its native bacterial membrane environment. High‐resolution cryo‐electron microscopy reveals the detailed structure of the periplasmic part of the T6SS membrane complex. The new structure uncovers the 3:2:2 stochiometry of the TssJ, TssL and TssM subunits of the complex. The study identifies novel structural features of the T6SS periplasmic gate that are essential for T6SS assembly. Abstract : The detailed structure of the membrane‐embedded T6SS complex from enteroaggregative E. coli reveals novel structural features essential for its assembly.