title: Structure of the outer membrane complex of a type IV secretion system.
abstract: 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.
authors: Institute of Structural and Molecular Biology, University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK.
authors: Vidya
authors: V
authors: Chandran
authors: Rémi
authors: R
authors: Fronzes
authors: Stéphane
authors: S
authors: Duquerroy
authors: Nora
authors: N
authors: Cronin
authors: Jorge
authors: J
authors: Navaza
authors: Gabriel
authors: G
authors: Waksman
mesh_terms: 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
chemical_list: D001425:Bacterial Outer Membrane Proteins