Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104, Freiburg, Germany.
Faculty of Biology, University of Freiburg, 79104, Freiburg, Germany.
Sci Rep. 2018 Jan 22;8(1):1326. doi: 10.1038/s41598-018-19640-3.
Twin-arginine translocation (Tat) systems transport folded proteins that harbor a conserved arginine pair in their signal peptides. They assemble from hexahelical TatC-type and single-spanning TatA-type proteins. Many Tat systems comprise two functionally diverse, TatA-type proteins, denominated TatA and TatB. Some bacteria in addition express TatE, which thus far has been characterized as a functional surrogate of TatA. For the Tat system of Escherichia coli we demonstrate here that different from TatA but rather like TatB, TatE contacts a Tat signal peptide independently of the proton-motive force and restricts the premature processing of a Tat signal peptide. Furthermore, TatE embarks at the transmembrane helix five of TatC where it becomes so closely spaced to TatB that both proteins can be covalently linked by a zero-space cross-linker. Our results suggest that in addition to TatB and TatC, TatE is a further component of the Tat substrate receptor complex. Consistent with TatE being an autonomous TatAB-type protein, a bioinformatics analysis revealed a relatively broad distribution of the tatE gene in bacterial phyla and highlighted unique protein sequence features of TatE orthologs.
双精氨酸转运（Tat）系统转运含有信号肽中保守精氨酸对的折叠蛋白。它们由六螺旋 TatC 型和单跨 TatA 型蛋白组装而成。许多 Tat 系统由两种功能不同的 TatA 型蛋白组成，分别命名为 TatA 和 TatB。一些细菌还表达 TatE，迄今为止，它被表征为 TatA 的功能替代物。对于大肠杆菌的 Tat 系统，我们在这里证明 TatE 与 TatA 不同，而是与 TatB 相似，它独立于质子动力势与 Tat 信号肽接触，并限制 Tat 信号肽的过早加工。此外，TatE 结合在 TatC 的跨膜螺旋五上，与 TatB 非常接近，以至于两个蛋白可以通过零空间交联剂共价连接。我们的结果表明，除了 TatB 和 TatC，TatE 还是 Tat 底物受体复合物的另一个组成部分。与 TatE 是自主的 TatAB 型蛋白一致，生物信息学分析显示 tatE 基因在细菌门中的分布相对广泛，并突出了 TatE 同源物的独特蛋白序列特征。
