Donor-strand exchange in chaperone-assisted pilus assembly revealed in atomic detail by molecular dynamics
Donor-strand exchange in chaperone-assisted pilus assembly revealed in atomic detail by molecular dynamics
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DOI：
10.1016/j.jmb.2007.10.077
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发表时间：
2008-01-25
影响因子：
5.6
通讯作者：
Paci, Emanuele
中科院分区：
文献类型：
--
作者：
Rose, Rebecca J.;Welsh, Thomas S.;Paci, Emanuele
粘附性多亚基纤维通过分子伴侣引导途径组装在许多病原菌的表面上。在周质中，分子伴侣向菌毛亚基提供β链以补充其不完整的免疫球蛋白样折叠。在外膜处，这被通过供体链交换（DSE）机制由传入菌毛亚基的N-末端延伸（Nte）形成的β链取代。该反应先前已被证明是通过协调机制进行的，其中Nte与分子伴侣：亚基复合物在分子伴侣被置换之前相互作用，形成三元中间体。此后，假定菌毛和伴侣蛋白β-链通过“拉链进-拉链出”机制进行链交换，由此伴侣蛋白链一个残基接一个残基地拉链出，因为Nte同时拉链进，尽管拉链机制的直接实验证据仍然缺乏。在这里，分子动力学模拟已被用来探测DSE机制在形成的Saf菌毛从沙门氏菌在原子水平上，允许直接调查的拉链在拉链的假设。模拟提供了一个解释如何传入的Nte能够对接和启动DSE由于内在的动态波动的伴侣：亚基复合物。在模拟中，分子伴侣供体链被认为是从菌毛亚基，残基的残基，直接支持拉链在拉链的假设。此外，看到朝向Nte的N-末端的残基与相邻菌毛亚基上的特异性结合口袋（P*）的相互作用稳定DSE产物免于解结合，这也在模拟中通过拉链机制进行。总之，这项研究提供了一个深入的图片DSE，包括第一个原子的见解分子事件发生在拉链拉链机制。(c)2007爱思唯尔有限公司保留所有权利。
Adhesive multi-subunit fibres are assembled on the surface of many pathogenic bacteria via the chaperone-usher pathway. In the periplasm, a chaperone donates a beta-strand to a pilus subunit to complement its incomplete immunoglobulin-like fold. At the outer membrane, this is replaced with a beta-strand formed from the N-terminal extension (Nte) of an incoming pilus subunit by a donor-strand exchange (DSE) mechanism. This reaction has previously been shown to proceed via a concerted mechanism, in which the Nte interacts with the chaperone:subunit complex before the chaperone has been displaced, forming a ternary intermediate. Thereafter, the pilus and chaperone beta-strands have been postulated to undergo a strand swap by a 'zip-in-zip-out' mechanism, whereby the chaperone strand zips out, residue by residue, as the Nte simultaneously zips in, although direct experimental evidence for a zippering mechanism is still lacking. Here, molecular dynamics simulations have been used to probe the DSE mechanism during formation of the Saf pilus from Salmonella enterica at the atomic level, allowing the direct investigation of the zip-in-zip-out hypothesis. The simulations provide an explanation of how the incoming Nte is able to dock and initiate DSE due to inherent dynamic fluctuations within the chaperone:subunit complex. In the simulations, the chaperone donor strand was seen to unbind from the pilus subunit, residue by residue, in direct support of the zip-in-zip-out hypothesis. In addition, an interaction of a residue towards the N-terminus of the Nte with a specific binding pocket (P*) on the adjacent pilus subunit was seen to stabilise the DSE product against unbinding, which also proceeded in the simulations by a zippering mechanism. Together, the study provides an in-depth picture of DSE, including the first atomistic insights into the molecular events occurring during the zip-in-zip-out mechanism. (c) 2007 Elsevier Ltd. All rights reserved.