The type III secretion system tip complex and translocon

Mol Microbiol. 2008 Jun;68(5):1085-95. doi: 10.1111/j.1365-2958.2008.06237.x. Epub 2008 Apr 8.


The type III secretion machinery of Gram-negative bacteria, also known as the injectisome or needle complex, is composed of a basal body spanning both bacterial membranes and the periplasm, and an external needle protruding from the bacterial surface. A set of three proteins, two hydrophobic and one hydrophilic, are required to allow translocation of proteins from the bacterium to the host cell cytoplasm. These proteins are involved in the formation of a translocation pore, the translocon, in the host cell membrane. Exciting progress has recently been made on the interaction between the translocators and the injectisome needle and the assembly of the translocon in the host cell membrane. As expected, the two hydrophobic translocators insert into the target cell membrane. Unexpectedly, the third, hydrophilic translocator, forms a complex on the distal end of the injectisome needle, the tip complex, and serves as an assembly platform for the two hydrophobic translocators.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Antigens, Bacterial / genetics
  • Antigens, Bacterial / physiology*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / isolation & purification
  • Bacterial Proteins / metabolism*
  • Biological Transport
  • Cytoplasm / metabolism
  • Gram-Negative Bacteria / genetics
  • Gram-Negative Bacteria / pathogenicity*
  • Membrane Proteins / metabolism*
  • Pore Forming Cytotoxic Proteins


  • Antigens, Bacterial
  • Bacterial Proteins
  • Membrane Proteins
  • Pore Forming Cytotoxic Proteins