Structure of the outer membrane complex of a type IV secretion system

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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 $\sim$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
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Vidya Chandran, Rémi Fronzes, Stéphane Duquerroy, Nora Cronin, Jorge Navaza, et al.. Structure of the outer membrane complex of a type IV secretion system. Nature, Nature Publishing Group, 2009, 462 (7276), pp.1011-1015. ⟨10.1038/nature08588⟩. ⟨cea-00909632⟩

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