Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Stefan-Meier-Strasse 17 D-79104 Freiburg, Germany.
Nat Commun. 2012;3:1311. doi: 10.1038/ncomms2308.
The twin-arginine translocation (Tat) pathway of bacteria and plant chloroplasts mediates the transmembrane transport of folded proteins, which harbour signal sequences with a conserved twin-arginine motif. Many Tat translocases comprise the three membrane proteins TatA, TatB and TatC. TatC was previously shown to be involved in recognizing twin-arginine signal peptides. Here we show that beyond recognition, TatC mediates the transmembrane insertion of a twin-arginine signal sequence, thereby translocating the signal sequence cleavage site across the bilayer. In the absence of TatB, this can lead to the removal of the signal sequence even from a translocation-incompetent substrate. Hence interaction of twin-arginine signal peptides with TatB counteracts their premature cleavage uncoupled from translocation. This capacity of TatB is not shared by the homologous TatA protein. Collectively our results suggest that TatC is an insertase for twin-arginine signal peptides and that translocation-proficient signal sequence recognition requires the concerted action of TatC and TatB.
细菌和植物叶绿体的双精氨酸转运（Tat）途径介导折叠蛋白的跨膜转运，这些蛋白具有保守的双精氨酸基序的信号序列。许多 Tat 转运酶包含三个跨膜蛋白 TatA、TatB 和 TatC。先前的研究表明 TatC 参与识别双精氨酸信号肽。在这里，我们表明 TatC 不仅识别双精氨酸信号序列，还介导其跨膜插入，从而将信号序列切割位点转运穿过双层。在没有 TatB 的情况下，即使对于转运无能力的底物，也可以导致信号序列的去除。因此，双精氨酸信号肽与 TatB 的相互作用可以阻止它们在没有转运的情况下过早切割。TatA 蛋白不具有 TatB 的这种能力。总的来说，我们的结果表明 TatC 是双精氨酸信号肽的插入酶，并且转运有效的信号序列识别需要 TatC 和 TatB 的协同作用。
