Molecular Mimicry of SecA and Signal Recognition Particle Binding to the Bacterial Ribosome
Molecular Mimicry of SecA and Signal Recognition Particle Binding to the Bacterial Ribosome
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DOI：
10.1128/mbio.01317-19
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发表时间：
2019-07-01
期刊：
影响因子：
6.4
通讯作者：
Koch, Hans-Georg
中科院分区：
文献类型：
--
作者：
Knuepffer, Lara;Fehrenbach, Clara;Koch, Hans-Georg
细菌执行各种蛋白质运输系统，以维持其不同细胞区室的适当组成。SecYEG易位子作为主要的运输通道，参与运输两种不同的底物类型。内膜蛋白在被信号识别颗粒（SRP）靶向后被共翻译插入膜中。相反，分泌性蛋白质通过ATP酶SecA进行后转位。最近的数据表明，SecA也可以结合到靠近隧道出口的核糖体。我们已经绘制了SecA与翻译和非翻译核糖体的相互作用，并证明N末端和螺旋接头结构域SecA结合到核糖体蛋白uL23表面上的酸性补丁。有趣的是，这两种蛋白都深深插入核糖体隧道中，与uL23的隧道内环接触，uL23作为新生链传感器。这种结合模式与SRP的结合模式非常相似，表明两种靶向因子与核糖体的相互作用模式相同。在新生链的存在下，SecA从隧道中缩回，但保持与uL23表面的接触。我们的数据进一步表明，SecA的核糖体和膜结合是相互排斥的，因为这两个事件都依赖于SecA的N末端。我们的研究强调了细菌蛋白质转运系统的巨大可塑性，并揭示了SRP和SecA底物之间的区分已经在核糖体上开始。重要信息通过保守的SecYEG易位子的细菌蛋白质转运通常被归类为共翻译，即，当转运与翻译结合时，或翻译后，当翻译和转运分开时。我们在这里表明，ATP酶SecA，这被认为是结合其基板posteritonally，已经扫描潜在的底物的核糖体隧道。在新生链存在的情况下，SecA从隧道中缩回，但与核糖体表面保持接触。这与介导共翻译转运的信号识别颗粒的核糖体结合模式非常相似。我们的数据揭示了蛋白质转运途径的惊人可塑性，这可能使细菌能够在其短的世代时间内有效地识别和转运大量高度不同的底物。
Bacteria execute a variety of protein transport systems for maintaining the proper composition of their different cellular compartments. The SecYEG translocon serves as primary transport channel and is engaged in transporting two different substrate types. Inner membrane proteins are cotranslationally inserted into the membrane after their targeting by the signal recognition particle (SRP). In contrast, secretory proteins are posttranslationally translocated by the ATPase SecA. Recent data indicate that SecA can also bind to ribosomes close to the tunnel exit. We have mapped the interaction of SecA with translating and nontranslating ribosomes and demonstrate that the N terminus and the helical linker domain of SecA bind to an acidic patch on the surface of the ribosomal protein uL23. Intriguingly, both also insert deeply into the ribosomal tunnel to contact the intratunnel loop of uL23, which serves as a nascent chain sensor. This binding pattern is remarkably similar to that of SRP and indicates an identical interaction mode of the two targeting factors with ribosomes. In the presence of a nascent chain, SecA retracts from the tunnel but maintains contact with the surface of uL23. Our data further demonstrate that ribosome and membrane binding of SecA are mutually exclusive, as both events depend on the N terminus of SecA. Our study highlights the enormous plasticity of bacterial protein transport systems and reveals that the discrimination between SRP and SecA substrates is already initiated at the ribosome.IMPORTANCE Bacterial protein transport via the conserved SecYEG translocon is generally classified as either cotranslational, i.e., when transport is coupled to translation, or posttranslational, when translation and transport are separated. We show here that the ATPase SecA, which is considered to bind its substrates posttranslationally, already scans the ribosomal tunnel for potential substrates. In the presence of a nascent chain, SecA retracts from the tunnel but maintains contact with the ribosomal surface. This is remarkably similar to the ribosome-binding mode of the signal recognition particle, which mediates cotranslational transport. Our data reveal a striking plasticity of protein transport pathways, which likely enable bacteria to efficiently recognize and transport a large number of highly different substrates within their short generation time.