Structure and composition of the Shigella flexneri 'needle complex', a part of its type III secreton
Structure and composition of the Shigella flexneri 'needle complex', a part of its type III secreton
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DOI：
10.1046/j.1365-2958.2001.02200.x
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发表时间：
2001-02-01
影响因子：
3.6
通讯作者：
Allaoui, A
中科院分区：
文献类型：
--
作者：
Blocker, A;Jouihri, N;Allaoui, A
III型分泌系统(ITSS或分泌子)是许多革兰氏阴性细菌的基本毒力决定因素，用于将蛋白质直接从细菌转移到宿主细胞质中。电子显微镜(EM)显示福氏志贺氏菌的TTSS由：(1)外针；(2)跨膜区；(3)细胞质鳞茎组成。对纯化的和阴性染色的TTSS部分1、2和3的一部分进行EM分析，一起被称为“针复合体”(NC)，产生了17埃分辨率的平均图像，其中可以辨别出通过环插入到底部的底座、外环和针。NCS的分析和低温电子显微镜图像表明，针和基底部含有一个2-3 nm的中心通道，N-末端测序鉴定出5个主要的NC组分：MxiD、MxiG、MxiJ、MxiH和Mxil，推测MxiG和MxiJ是内膜蛋白，可能形成了碱基。MxiD被认为是一种外膜蛋白，形成外环。MxiH和Mxil都是小分子亲水性蛋白，缺乏这两种蛋白的突变体形成无针分泌，不能分泌IPA蛋白，因为MxiH在NCS中存在大量摩尔过剩，我们认为它是主要的针状成分。Mxil可在外部针尖处封口。
Type III secretion systems (ITSSs or secretons), essential virulence determinants of many Gramnegative bacteria, serve to translocate proteins directly from the bacteria into the host cytoplasm. Electron microscopy (EM) indicates that the TTSSs of Shigella flexneri are composed of: (1) an external needle; (2) a transmembrane domain; and (3) a cytoplasmic bulb. EM analysis of purified and negatively stained parts 1, 2 and a portion of 3 of the TTSS, together termed the 'needle complex' (NC), produced an average image at 17 Angstrom resolution in which a base, an outer ring and a needle, inserted through the ring into the base, could be discerned. This analysis and cryoEM images of NCs indicated that the needle and base contain a central 2-3 nm canal, Five major NC components, MxiD, MxiG, MxiJ, MxiH and Mxil, were identified by N-terminal sequencing, MxiG and MxiJ are predicted to be inner membrane proteins and presumably form the base. MxiD is predicted to be an outer membrane protein and to form the outer ring. MxiH and Mxil are small hydrophilic proteins, Mutants lacking either of these proteins formed needleless secretons and were unable to secrete Ipa proteins, As MxiH was present in NCs in large molar excess, we propose that it is the major needle component. Mxil may cap at the external needle tip.