![]() 1b for the naming convention see Methods and Extended Data Fig. However, VirD4, VirB11, and VirB2 were absent from the structure (see Extended Data Fig. Near-atomic resolution was achieved for all except for the arches sub-complex (Extended Data Fig. Here we present a single-particle cryo-EM structure of a T4SS complex from the R388 plasmid that comprises all four sub-complexes: OMCC, stalk, arches and IMC (Fig. After contact between cells is made, the T4SS switches to a DNA-transfer mode involving VirB2–VirB11 and VirD4 16. ![]() In this pilus biogenesis mode, only the VirB2–VirB11 proteins are required 14, 15. Conjugative T4SSs must first produce a conjugative pilus, which makes contact with a recipient cell 12 and may serve as a conduit for DNA 13. NSEM provides a view of a double-barrelled IMC made of two side-by-side trimers of dimers (the barrels) of the AAA+ VirB4 ATPase, whereas cryo-ET shows a central hexamer of dimers of the same protein. However, the two approaches reveal very different IMC architectures. These sub-complexes consist of an inner membrane complex (IMC) embedded in the inner membrane, a structure bridging the OMCC and the IMC (the stalk (also called the cylinder), and a ring complex surrounding the stalk (the arches) (Extended Data Fig. The other proteins (except VirB2 (also known as TrwL), which forms the conjugative pilus and VirB5 (also known as TrwJ), which locates at the tip of the pilus) assemble to form three additional sub-complexes, which were revealed by two different low-resolution structural approaches, negative stain electron microscopy 8, 9 (NSEM) and in cellulo cryo-electron tomography 10, 11 (cryo-ET) (Extended Data Fig. Three proteins, VirB7 (also known as TrwH), VirB9 (also known as TrwF) and VirB10 (also known as TrwE), form the outer membrane core complex (OMCC), which contains an O-layer embedded in the outer membrane and an I-layer underneath 7 (Extended Data Fig. Three ATPases, VirB4 (also known as TrwK), VirB11 (also known as TrwD) and VirD4, power the system 5. This structure describes the exceptionally large protein–protein interaction network required to assemble the many components that constitute a T4SS and provides insights on the unique mechanism by which they elaborate pili.Ĭonjugative T4SSs generally contain 12 proteins, VirB1–VirB11 and VirD4 (also known as TrwB in the R388 T4SS under investigation here), one of which (VirB1 (also known as TrwN)) is non-essential 6. We added the two remaining components to the structural model using co-evolution analysis of protein interfaces, to enable the reconstitution of the entire system including the pilus. Here we present a high-resolution cryo-electron microscopy (cryo-EM) structure of a 2.8 megadalton T4SS complex composed of 92 polypeptides representing 8 of the 10 essential T4SS components involved in pilus biogenesis. ![]() The T4SS also elaborates a long extracellular filament-the conjugative pilus-that is essential for DNA transfer 4, 5. In Gram-negative bacteria, conjugation is mediated by a large transport apparatus-the conjugative type IV secretion system (T4SS)-produced by the donor cell and embedded in both its outer and inner membranes. It is the primary means by which antibiotic resistance genes spread among bacterial populations 2, 3. Bacterial conjugation is the fundamental process of unidirectional transfer of DNAs, often plasmid DNAs, from a donor cell to a recipient cell 1.
0 Comments
Leave a Reply. |