Bacher G, Lütcke H, Jungnickel B, Rapoport T A, Dobberstein B
Zentrum für Molekalare Biologie der Universität Heidelberg, Germany.
Nature. 1996 May 16;381(6579):248-51. doi: 10.1038/381248a0.
The signal-recognition particle (SRP) is important for the targeting of many secretory and membrane proteins to the endoplasmic reticulum (ER). Targeting is regulated by three GTPases, the 54K subunit of SRP (SRP54), and the alpha- and beta-subunits of the SRP receptor. When a signal sequence emerges from the ribosome, SRP interacts with it and targets the resulting complex to the ER membrane by binding to the SRP receptor. Subsequently, SRP releases the signal sequence into the translocation channel. Here we use a complex of a ribosome with a nascent peptide chain, the SRP and its receptor, to investigate GTP binding to SRP54, and GTP hydrolysis. Our findings indicate that a ribosomal component promotes GTP binding to the SRP54 subunit of SRP. GTP-bound SRP54 is essential for high-affinity interaction between SRP and its receptor in the ER membrane. This interaction induces the release of the signal sequence from SRP, the insertion of the nascent polypeptide chain into the translocation channel, and GTP hydrolysis. The contribution of the ribosome had previously escaped detection because only synthetic signal peptides were used in the analysis.
信号识别颗粒（SRP）对于许多分泌蛋白和膜蛋白靶向内质网（ER）至关重要。靶向作用由三种GTP酶、SRP的54K亚基（SRP54）以及SRP受体的α和β亚基调控。当信号序列从核糖体中出现时，SRP与之相互作用，并通过与SRP受体结合将形成的复合物靶向内质网膜。随后，SRP将信号序列释放到转运通道中。在此，我们使用核糖体与新生肽链、SRP及其受体的复合物来研究GTP与SRP54的结合以及GTP水解。我们的研究结果表明，核糖体成分促进GTP与SRP的SRP54亚基结合。结合GTP的SRP54对于SRP与其在内质网膜中的受体之间的高亲和力相互作用至关重要。这种相互作用诱导信号序列从SRP释放，新生多肽链插入转运通道，并引发GTP水解。核糖体的作用此前未被发现，因为分析中仅使用了合成信号肽。
