DNA通過接合從一種細(xì)菌轉(zhuǎn)移到另一種是細(xì)菌演化中的一個主要因素,，并且作為抗生素抗性和毒性基因交換的一個機制也有實用意義。人體的多數(shù)致病細(xì)菌是革蘭氏陰性的,，在其中IV-型分泌體系調(diào)控這種DNA轉(zhuǎn)移,。該體系由三個蛋白組成，它們結(jié)合在一起,，形成跨越內(nèi)膜和外膜的一個核心,。
現(xiàn)在，一個IV-型分泌體系的外膜復(fù)合物的晶體結(jié)構(gòu)已被確定,。該復(fù)合物的大小為0.6兆道爾頓,，它是結(jié)構(gòu)已知的最大外膜復(fù)合物。它的結(jié)構(gòu)顯示了DNA穿過細(xì)菌細(xì)胞膜的機制,，并為開發(fā)以IV-型分泌體系為作用目標(biāo)來抑制抗生素抗性和毒性因子擴散的藥物提供了一個步驟,。（生物谷Bioon.com）
生物谷推薦原始出處：
Nature 462, 1011-1015 (24 December 2009) | doi:10.1038/nature08588
Structure of the outer membrane complex of a type IV secretion system
Vidya Chandran1,5, Rémi Fronzes1,5, Stéphane Duquerroy2,3, Nora Cronin1, Jorge Navaza4 & Gabriel Waksman1
1 Institute of Structural and Molecular Biology, University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK
2 Institut Pasteur, Unité de Virologie Structurale, Virology Department and CNRS URA 3015, Paris, 25–28 Rue du Dr Roux, F-75724 Paris, France
3 Université Paris-Sud, F-91405 Orsay, France
4 Laboratoire de Microscopie Electronique, Institut de Biologie Structurale J.P. Ebel, 41 rue Jules Horowitz, F-38027 Grenoble Cedex 1, France
5 These authors contributed equally to this work.
Correspondence to: Gabriel Waksman1 Correspondence and requests for materials should be addressed to G.W.
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 ~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.
