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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >An escort mechanism for cycling of export chaperones during flagellum assembly
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An escort mechanism for cycling of export chaperones during flagellum assembly

机译：鞭毛组装过程中出口伴侣分子循环的护送机制

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摘要

Assembly of the bacterial flagellar filament requires a type III export pathway for ordered delivery of structural subunits from the cytosol to the cell surface. This is facilitated by transient interaction with chaperones that protect subunits and pilot them to dock at the membrane export ATPase complex. We reveal that the essential export protein FIiJ has a novel chaperone escort function in the pathway, specifically recruiting unladen chaperones for the minor filament-class subunits of the filament cap and hook-filament junction substructures. FIiJ did not recognize unchaperoned subunits or chaperone-subunit complexes, and it associated with the membrane ATPase complex, suggesting a function postdocking. Empty chaperones that were recruited by FIiJ in vitro were efficiently captured from FliJ-chaperone complexes by cognate subunits. FIiJ and subunit bound to the same region on the target chaperone, but the cognate subunit had a approximate to 700-fold greater affinity for chaperone than did FliJ. The data show that FIiJ recruits chaperones and transfers them to subunits, and indicate that this is driven by competition for a common binding site. This escort mechanism provides a means by which free export chaperones can be cycled after subunit release, establishing a new facet of the secretion process. As FIiJ does not escort the chaperone for the major filament subunit, cycling may offer a mechanism for export selectivity and thus promote assembly of the junction and cap substructures required for initiation of flagellin polymerization.
机译：细菌鞭毛丝的组装需要III型输出途径，以将结构亚基从胞质溶胶有序地递送至细胞表面。与保护分子亚基并引导它们停靠在膜输出ATPase复合物上的分子伴侣的短暂相互作用促进了这一过程。我们揭示了基本的出口蛋白FIiJ在该途径中具有新颖的伴侣护卫功能，特别是为细丝帽和钩-细丝连接亚结构的次要细丝类亚基募集了空载的伴侣。 FIiJ无法识别未陪伴的亚基或伴侣-亚基复合物，并且与膜ATPase复合物相关，提示其功能存在对接。由FIiJ体外募集的空分子伴侣可通过同源亚基有效地从FliJ-分子伴侣复合物中捕获。 FIiJ和亚基结合到目标伴侣上的相同区域，但同源亚基对伴侣的亲和力比FliJ高约700倍。数据显示，FIiJ招募分子伴侣并将其转移至亚基，并表明这是由竞争共同结合位点驱动的。这种护送机制提供了一种手段，通过该手段可以在释放亚基后循环释放输出分子伴侣，从而建立分泌过程的新方面。由于FIiJ不陪伴主要长丝亚基的分子伴侣，因此循环可提供输出选择性的机制，从而促进鞭毛蛋白聚合反应所需的连接和帽亚结构的组装。

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