Fekkes P, Driessen A J
Department of Microbiology and Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9751 NN Haren, The Netherlands.
Microbiol Mol Biol Rev. 1999 Mar;63(1):161-73. doi: 10.1128/MMBR.63.1.161-173.1999.
Proteins that perform their activity within the cytoplasmic membrane or outside this cell boundary must be targeted to the translocation site prior to their insertion and/or translocation. In bacteria, several targeting routes are known; the SecB- and the signal recognition particle-dependent pathways are the best characterized. Recently, evidence for the existence of a third major route, the twin-Arg pathway, was gathered. Proteins that use either one of these three different pathways possess special features that enable their specific interaction with the components of the targeting routes. Such targeting information is often contained in an N-terminal extension, the signal sequence, but can also be found within the mature domain of the targeted protein. Once the nascent chain starts to emerge from the ribosome, competition for the protein between different targeting factors begins. After recognition and binding, the targeting factor delivers the protein to the translocation sites at the cytoplasmic membrane. Only by means of a specific interaction between the targeting component and its receptor is the cargo released for further processing and translocation. This mechanism ensures the high-fidelity targeting of premembrane and membrane proteins to the translocation site.
在细胞质膜内或细胞边界之外发挥活性的蛋白质，在插入和/或转运之前必须被靶向转运位点。在细菌中，已知有几种靶向途径；SecB 依赖途径和信号识别颗粒依赖途径是研究得最为透彻的。最近，有证据表明存在第三条主要途径，即双精氨酸途径。使用这三种不同途径之一的蛋白质具有特殊特征，使其能够与靶向途径的组分进行特异性相互作用。这种靶向信息通常包含在 N 端延伸序列，即信号序列中，但也可以在靶向蛋白质的成熟结构域中找到。一旦新生链开始从核糖体中出现，不同靶向因子之间就会开始对蛋白质进行竞争。识别并结合后，靶向因子将蛋白质输送到细胞质膜上的转运位点。只有通过靶向组分与其受体之间的特异性相互作用，货物（即蛋白质）才会被释放以进行进一步加工和转运。这种机制确保了膜前蛋白和膜蛋白高精度地靶向转运位点。
