The Bacterial SRP Receptor, SecA and the Ribosome Use Overlapping Binding Sites on the SecY Translocon
The Bacterial SRP Receptor, SecA and the Ribosome Use Overlapping Binding Sites on the SecY Translocon
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DOI：
10.1111/j.1600-0854.2011.01167.x
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发表时间：
2011-05-01
期刊：
影响因子：
4.5
通讯作者：
Koch, Hans-Georg
中科院分区：
文献类型：
--
作者：
Kuhn, Patrick;Weiche, Benjamin;Koch, Hans-Georg
信号识别颗粒（SRP）依赖的蛋白质靶向是一个普遍保守的过程，将蛋白质递送到细菌细胞质膜或真核生物的内质网膜。在靶向过程中至关重要的是将核糖体-新生链复合物（RNC）从SRP转移到Sec易位子。在真核生物中，这一步骤由SRP受体（SR）的SR β亚基协调，SR β亚基可能通过与转位子直接相互作用来感知空转位子。细菌缺乏SR β亚基，它们如何协调RNC转移尚不清楚。通过定点交联和荧光共振能量转移（FRET）分析，我们表明，FtsY，细菌SR α同源物，结合到暴露的C4/C5环的SecY，细菌的Sec易位的中心组成部分。同样的环也作为SecA和核糖体的结合位点。FtsY-SecY相互作用至少涉及FtsY的A结构域，其将重要功能归因于这个迄今定义不清的结构域。FtsY与SecY残基的结合（SecA和核糖体也使用SecY残基）可能允许FtsY感测可用的易位子，并将传入的SRP-RNC与蛋白质传导通道对齐。因此，大肠杆菌FtsY在一个单一蛋白质中包含真核SR α和SR β亚基的功能。
Signal recognition particle (SRP)-dependent protein targeting is a universally conserved process that delivers proteins to the bacterial cytoplasmic membrane or to the endoplasmic reticulum membrane in eukaryotes. Crucial during targeting is the transfer of the ribosome-nascent chain complex (RNC) from SRP to the Sec translocon. In eukaryotes, this step is co-ordinated by the SR beta subunit of the SRP receptor (SR), which probably senses a vacant translocon by direct interaction with the translocon. Bacteria lack the SR beta subunit and how they co-ordinate RNC transfer is unknown. By site-directed cross-linking and fluorescence resonance energy transfer (FRET) analyses, we show that FtsY, the bacterial SR alpha homologue, binds to the exposed C4/C5 loops of SecY, the central component of the bacterial Sec translocon. The same loops serve also as binding sites for SecA and the ribosome. The FtsY-SecY interaction involves at least the A domain of FtsY, which attributes an important function to this so far ill-defined domain. Binding of FtsY to SecY residues, which are also used by SecA and the ribosome, probably allows FtsY to sense an available translocon and to align the incoming SRP-RNC with the protein conducting channel. Thus, the Escherichia coli FtsY encompasses the functions of both the eukaryotic SR alpha and SR beta subunits in one single protein.