A refined model of the prototypical Salmonella SPI-1 T3SS basal body reveals the molecular basis for its assembly

PLoS Pathog. 2013;9(4):e1003307. doi: 10.1371/journal.ppat.1003307. Epub 2013 Apr 25.


The T3SS injectisome is a syringe-shaped macromolecular assembly found in pathogenic Gram-negative bacteria that allows for the direct delivery of virulence effectors into host cells. It is composed of a "basal body", a lock-nut structure spanning both bacterial membranes, and a "needle" that protrudes away from the bacterial surface. A hollow channel spans throughout the apparatus, permitting the translocation of effector proteins from the bacterial cytosol to the host plasma membrane. The basal body is composed largely of three membrane-embedded proteins that form oligomerized concentric rings. Here, we report the crystal structures of three domains of the prototypical Salmonella SPI-1 basal body, and use a new approach incorporating symmetric flexible backbone docking and EM data to produce a model for their oligomeric assembly. The obtained models, validated by biochemical and in vivo assays, reveal the molecular details of the interactions driving basal body assembly, and notably demonstrate a conserved oligomerization mechanism.

Publication types

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

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism
  • Bacterial Secretion Systems*
  • Cell Membrane / metabolism*
  • Crystallography, X-Ray
  • Membrane Proteins / chemistry*
  • Membrane Proteins / metabolism
  • Models, Molecular
  • Protein Structure, Tertiary
  • Salmonella typhimurium / metabolism*


  • Bacterial Proteins
  • Bacterial Secretion Systems
  • Membrane Proteins

Associated data

  • PDB/4G08
  • PDB/4G1I
  • PDB/4G2S