Bacterial type IV secretions systems move DNA and proteins out of a cell. This helps bacteria give and gain DNA quickly which greatly increases the variability and therefore survivability of the bacteria. Usually transfer of this DNA/proteins requires cell-to-cell contact, however one type of T4SS releases DNA from the extracellular milieu. [1]
GENERAL STRUCTURE FEATURES OF TYPE 4 SECRETION SYSTEMS
With different functions comes many variations on the structure of T4SS, however the most well understood set of structures were studied through the Gram-negative bacteria A. tumefaciens. It is called the VirB/VirD4 system[2].
VirB is made up of 11 different VirB proteins systhesized from the virB operon. Most T4SS have homologes of these 12 proteins (11 from VirB and 1 from VirD)
Overview of T4SS structures
[1]The diameter of the channel changes from 55 angstroms on the cytoplasmic side to 10 angstroms leading to the exterior of the cell. This indicates there are structural changes to the protein or DNA that is being transferred while in the secretion system[2]
TYPE 4 SECRETION SYSTEMS ENERGETICS
VirB7, VirB7 and VirB10 initiate the assembly of the core of the T4SS. The complex forms spontaneously with out the input of external energy like ATP.
Overview of formation of T4SS
[1]VirB4, VirB11 and VirD4 are ATPases that energizes the secretion system from the cytoplasmic side of the cell [2].
