Center for Molecular Biology of the University of Heidelberg (ZMBH), ZMBH-DKFZ Alliance, Im Neuenheimer Feld 282, D-69120 Heidelberg, Germany.
Mol Cell. 2011 Feb 4;41(3):343-53. doi: 10.1016/j.molcel.2010.12.028.
In Escherichia coli, translocation of exported proteins across the cytoplasmic membrane is dependent on the motor protein SecA and typically begins only after synthesis of the substrate has already been completed (i.e., posttranslationally). Thus, it has generally been assumed that the translocation machinery also recognizes its protein substrates posttranslationally. Here we report a specific interaction between SecA and the ribosome at a site near the polypeptide exit channel. This interaction is mediated by conserved motifs in SecA and ribosomal protein L23, and partial disruption of this interaction in vivo by introducing mutations into the genes encoding SecA or L23 affects the efficiency of translocation by the posttranslational pathway. Based on these findings, we propose that SecA could interact with its nascent substrates during translation in order to efficiently channel them into the "posttranslational" translocation pathway.
在大肠杆菌中，输出蛋白跨细胞质膜的易位依赖于马达蛋白 SecA，并且通常仅在底物的合成已经完成（即翻译后）后才开始。因此，一般认为易位机制也在翻译后识别其蛋白底物。在这里，我们报告了 SecA 与核糖体在靠近多肽出口通道的位点之间的特定相互作用。这种相互作用由 SecA 和核糖体蛋白 L23 中的保守基序介导，并且通过在编码 SecA 或 L23 的基因中引入突变部分破坏这种相互作用，会影响通过翻译后途径的易位效率。基于这些发现，我们提出 SecA 可以在翻译过程中与其新生底物相互作用，以便有效地将它们引导到“翻译后”易位途径中。
