Horticultural Sciences Department and Plant Molecular and Cellular Biology, University of Florida, Gainesville, FL 32611.
J Cell Biol. 2014 Apr 14;205(1):51-65. doi: 10.1083/jcb.201311057. Epub 2014 Apr 7.
The twin-arginine translocase (Tat) transports folded proteins across tightly sealed membranes. cpTatC is the core component of the thylakoid translocase and coordinates transport through interactions with the substrate signal peptide and other Tat components, notably the Tha4 pore-forming component. Here, Cys-Cys matching mapped Tha4 contact sites on cpTatC and assessed the role of signal peptide binding on Tha4 assembly with the cpTatC-Hcf106 receptor complex. Tha4 made contact with a peripheral cpTatC site in nonstimulated membranes. In the translocase, Tha4 made an additional contact within the cup-shaped cavity of cpTatC that likely seeds Tha4 polymerization to form the pore. Substrate binding triggers assembly of Tha4 onto the interior site. We provide evidence that the substrate signal peptide inserts between cpTatC subunits arranged in a manner that conceivably forms an enclosed chamber. The location of the inserted signal peptide and the Tha4-cpTatC contact data suggest a model for signal peptide-gated Tha4 entry into the chamber to form the translocase.
双精氨酸转运体（Tat）将折叠蛋白转运穿过紧密密封的膜。cpTatC 是类囊体转运体的核心组成部分，并通过与底物信号肽和其他 Tat 成分（特别是 Tha4 形成孔的成分）的相互作用来协调转运。在这里，我们将 Cys-Cys 匹配映射到 cpTatC 上的 Tha4 接触位点，并评估信号肽结合对 Tha4 与 cpTatC-Hcf106 受体复合物组装的作用。在未受刺激的膜中，Tha4 与 cpTatC 的外周位点接触。在转运体中，Tha4 与 cpTatC 的杯状腔内部的另一个位点接触，这可能为 Tha4 聚合形成孔提供了种子。底物结合触发 Tha4 组装到内部位点上。我们提供的证据表明，底物信号肽插入到以一种可能形成封闭腔的方式排列的 cpTatC 亚基之间。插入的信号肽的位置和 Tha4-cpTatC 接触数据表明了一种信号肽门控 Tha4 进入腔形成转运体的模型。
