Dissection of the TssB-TssC interface during type VI secretion sheath complex formation

PLoS One. 2013 Nov 25;8(11):e81074. doi: 10.1371/journal.pone.0081074. eCollection 2013.


The Type VI secretion system (T6SS) is a versatile machine that delivers toxins into either eukaryotic or bacterial cells. At a molecular level, the T6SS is composed of a membrane complex that anchors a long cytoplasmic tubular structure to the cell envelope. This structure is thought to resemble the tail of contractile bacteriophages. It is composed of the Hcp protein that assembles into hexameric rings stacked onto each other to form a tube similar to the phage tail tube. This tube is proposed to be wrapped by a structure called the sheath, composed of two proteins, TssB and TssC. It has been shown using fluorescence microscopy that the TssB and TssC proteins assemble into a tubular structure that cycles between long and short conformations suggesting that, similarly to the bacteriophage sheath, the T6SS sheath undergoes elongation and contraction events. The TssB and TssC proteins have been shown to interact and a specific α-helix of TssB is required for this interaction. Here, we confirm that the TssB and TssC proteins interact in enteroaggregative E. coli. We further show that this interaction requires the N-terminal region of TssC and the conserved α-helix of TssB. Using site-directed mutagenesis coupled to phenotypic analyses, we demonstrate that an hydrophobic motif located in the N-terminal region of this helix is required for interaction with TssC, sheath assembly and T6SS function.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacteriophages / metabolism*
  • Microscopy, Fluorescence
  • Mutagenesis, Site-Directed
  • Viral Proteins / genetics
  • Viral Proteins / metabolism


  • Viral Proteins

Grant support

Work in E.C. laboratory is supported by the Centre National de la Recherche Scientifique (CNRS), the Aix-Marseille Université and a grant from the Agence Nationale de la Recherche (ANR-10-JCJC- 1303-03) to E.C. Work in C.C. laboratory is supported by the CNRS, the Aix-Marseille Université, the Plateforme Technologique de Recherche en Sciences Biologiques (IBiSA) and a grant from the Fondation pour la Recherche Médicale (FRM DEQ2011-0421282). X.Y.Z. was supported by the ANR-10-JCJC-1303-03 grant, Y.R.B by a doctoral fellowship from the French Ministère de la Recherche, and B.D. by the FRM-DEQ2011-0421282 grant. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.