Atomic structure of T6SS reveals interlaced array essential to function

Cell. 2015 Feb 26;160(5):940-951. doi: 10.1016/j.cell.2015.02.005.


Type VI secretion systems (T6SSs) are newly identified contractile nanomachines that translocate effector proteins across bacterial membranes. The Francisella pathogenicity island, required for bacterial phagosome escape, intracellular replication, and virulence, was presumed to encode a T6SS-like apparatus. Here, we experimentally confirm the identity of this T6SS and, by cryo electron microscopy (cryoEM), show the structure of its post-contraction sheath at 3.7 Å resolution. We demonstrate the assembly of this T6SS by IglA/IglB and secretion of its putative effector proteins in response to environmental stimuli. The sheath has a quaternary structure with handedness opposite that of contracted sheath of T4 phage tail and is organized in an interlaced two-dimensional array by means of β sheet augmentation. By structure-based mutagenesis, we show that this interlacing is essential to secretion, phagosomal escape, and intracellular replication. Our atomic model of the T6SS will facilitate design of drugs targeting this highly prevalent secretion apparatus.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / ultrastructure
  • Bacterial Secretion Systems*
  • Bacteriophage T4 / chemistry
  • Bacteriophages / chemistry
  • Cryoelectron Microscopy
  • Francisella / ultrastructure*
  • Models, Molecular
  • Protein Structure, Secondary


  • Bacterial Proteins
  • Bacterial Secretion Systems

Associated data

  • PDB/3J9O