10 - Type IV Secretion Systems Flashcards
What are T4SS’s used for?
- E. coli conjugation
- Helicobacter pseudopodium formation
- A. tumefaciens Ti plasmid insertion
- Bordetella pertussis PT toxin contact-independent secretion
- Rickettsia and Legionella vacuole modification
What gene products are involved in the Vir T4SS?
Vir B1-11 and Vir D4
What are the energetic components of the T4SS?
VirB4, VirB11 and VirD4
What is the pilus composed of?
VirB2 with some associated VirB5.
VirB1 and 7 are also pilus components that degrade the OM peptidoglycan and stabilise lipoproteins respectively.
What are the putative channel components?
VirB2, B3, B4, B6, B8 and VirB7, B9, B10
What subunits is the core (OM) complex constructed of and in what numbers?
VirB7, VirB9, VirB10
14 of each, 42 total.
What is the structure of the core (OM) complex?
600kDa complex constructed from an Outer and Inner layer topped by a transmembrane cap. This forms a hollow interior partly filled by a middle platform.
Made of 14 trimers of VirB7, 9 and 10 which arrange concentrically. VirB7 as the inside ring/cap creating the pore and transmembrane regions, coated in VirB9 that extends downwards and the smaller VirB10 outside of that.
Cap structure is mostly hydrophobic with a ring of negative charge on the exocellular rim.
Which domain connects the OM complex to the IM complex?
The stalk region, which grows from the IM complex to attach to a middle platform in the OM complex.
It is thought to potentially be the point from which the pilus grows.
What is the subunit composition of the IM/stalk complex?
24x VirB6 and twelve each of: VirB3 VirB4 VirB5 VirB8
72 total subunits.
What is the structure of the IM complex?
A wide, circular inner membrane localised domain, with two periplasmic arches that possess long flexible linkes that attach to the OM complex.
Two identical large cytoplasmic regions made of three horizontal layers, including the VirB11 and a VirB4 ATPase hexamer in each. Each of these regions is a power unit for pilus biogenesis.
Why is VirD4 important?
It is thought to be responsible for recruiting the T4SS substrate (VirB2) to the machinery that will build it into a pilus.
What is the role of VirB10 thought to be?
B10 spans both complexes, and is thought to be responsible for opening and closing the pore at the OM complex through positioning of the Lever Arm Shelf.
This is thought to be controlled by transmission of conformational changes induced by the ATP binding state of VirB11 and VirB4.
What is a relaxosome?
A complex that prepares DNA for conjugation through a T4SS by nicking it to allow for rolling circle replication.
What proteins are involved in the RP4 relaxosome?
TraI (relaxase)
TraK (a binding protein)
TraJ & amp; H (stabilising accessory proteins)
How is the relaxosome formed?
To form the Relaxosome TraJ binds to an inverted repeat at the nic site at the oriT. This sequence is the closest binding site to the cleavage site. TraI then binds to the oriT/TraJ complex and the entire complex is then stabilised by the binding of TraH.
