Structure of the outer membrane complex of a type IV secretion system.
Type IV secretion systems are secretion nanomachines spanning the two membranes of Gram-negative bacteria. Three proteins, VirB7, VirB9 and VirB10, assemble into a 1.05 megadalton (MDa) core spanning the inner and outer membranes. This core consists of 14 copies of each of the proteins and forms two layers, the I and O layers, inserting in the inner and outer membrane, respectively. Here we present the crystal structure of a approximately 0.6 MDa outer-membrane complex containing the entire O layer. This structure is the largest determined for an outer-membrane channel and is unprecedented in being composed of three proteins. Unexpectedly, this structure identifies VirB10 as the outer-membrane channel with a unique hydrophobic double-helical transmembrane region. This structure establishes VirB10 as the only known protein crossing both membranes of Gram-negative bacteria. Comparison of the cryo-electron microscopy (cryo-EM) and crystallographic structures points to conformational changes regulating channel opening and closing.
Chandran
Vidya
V
Institute of Structural and Molecular Biology, University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK.
Fronzes
Rémi
R
Duquerroy
Stéphane
S
Cronin
Nora
N
Navaza
Jorge
J
Waksman
Gabriel
G
D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000302:isolation & purification; D006090:Gram-Negative Bacteria / Q000737:chemistry* / Q000502:physiology*; D008958:Models, Molecular; D011485:Protein Binding; D020836:Protein Structure, Quaternary
D001425:Bacterial Outer Membrane Proteins