Beijing NMR Center, Peking University, Beijing 100871, China.
J Am Chem Soc. 2010 Nov 17;132(45):15942-4. doi: 10.1021/ja1053785. Epub 2010 Aug 20.
The twin-arginine transport (Tat) system translocates folded proteins across the bacterial cytoplasmic or chloroplast thylakoid membrane of plants. The Tat system in most Gram-positive bacteria consists of two essential components, the TatA and TatC proteins. TatA is considered to be a bifunctional subunit, which can form a protein-conducting channel by self-oligomerization and can also participate in substrate recognition. However, the molecular mechanism underlying protein translocation remains elusive. Herein, we report the solution structure of the TatA(d) protein from Bacillus subtilis by NMR spectroscopy, the first structure of the Tat system at atomic resolution. TatA(d) shows an L-shaped structure formed by a transmembrane helix and an amphipathic helix, while the C-terminal tail is largely unstructured. Our results strongly support the postulated topology of TatA(d) in which the transmembrane helix is inserted into the lipid bilayer while the amphipathic helix lies at the membrane-water interface. Moreover, the structure of TatA(d) revealed the structural importance of several conserved residues at the hinge region, thus shedding new light on further elucidation of the protein transport mechanism of the Tat system.
双精氨酸转运（Tat）系统将折叠的蛋白质穿过细菌细胞质或植物叶绿体类囊体膜进行转运。大多数革兰氏阳性菌中的 Tat 系统由两个必需成分组成，即 TatA 和 TatC 蛋白。TatA 被认为是一种具有双功能的亚基，它可以通过自身寡聚化形成蛋白质传导通道，并且还可以参与底物识别。然而，蛋白质转运的分子机制仍然难以捉摸。在此，我们通过 NMR 光谱法报道了来自枯草芽孢杆菌的 TatA(d)蛋白的溶液结构，这是原子分辨率下 Tat 系统的第一个结构。TatA(d)呈现出由跨膜螺旋和两亲性螺旋形成的 L 形结构，而 C 端尾部则很大程度上没有结构。我们的结果强烈支持 TatA(d)的假定拓扑结构，其中跨膜螺旋插入脂质双层，而两亲性螺旋位于膜-水界面。此外，TatA(d)的结构揭示了铰链区域中几个保守残基的结构重要性，从而为进一步阐明 Tat 系统的蛋白质转运机制提供了新的线索。
