TssK is a trimeric cytoplasmic protein interacting with components of both phage-like and membrane anchoring complexes of the type VI secretion system

J Biol Chem. 2013 Sep 20;288(38):27031-41. doi: 10.1074/jbc.M113.499772. Epub 2013 Aug 6.

Abstract

The Type VI secretion system (T6SS) is a macromolecular machine that mediates bacteria-host or bacteria-bacteria interactions. The T6SS core apparatus assembles from 13 proteins that form two sub-assemblies: a phage-like complex and a trans-envelope complex. The Hcp, VgrG, TssE, and TssB/C subunits are structurally and functionally related to components of the tail of contractile bacteriophages. This phage-like structure is thought to be anchored to the membrane by a trans-envelope complex composed of the TssJ, TssL, and TssM proteins. However, how the two sub-complexes are connected remains unknown. Here we identify TssK, a protein that establishes contacts with the two T6SS sub-complexes through direct interactions with TssL, Hcp, and TssC. TssK is a cytoplasmic protein assembling trimers that display a three-armed shape, as revealed by TEM and SAXS analyses. Fluorescence microscopy experiments further demonstrate the requirement of TssK for sheath assembly. Our results suggest a central role for TssK by linking both complexes during T6SS assembly.

Keywords: Bacterial Pathogenesis; Hcp; Membrane Transport; Microbiology; Protein Complexes; Protein Secretion; Sheath Assembly; TssK; TssL; Type VI Secretion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Secretion Systems / physiology*
  • Bacteriophages
  • Escherichia coli K12 / genetics
  • Escherichia coli K12 / metabolism*
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • Multiprotein Complexes / genetics
  • Multiprotein Complexes / metabolism*

Substances

  • Bacterial Secretion Systems
  • Escherichia coli Proteins
  • Multiprotein Complexes