Molik S, Karnauchov I, Weidlich C, Herrmann R G, Klösgen R B
Institut für Pflanzenphysiologie, Martin-Luther-Universität Halle-Wittenberg, Weinbergweg 10, D-06120 Halle (Saale), Germany.
J Biol Chem. 2001 Nov 16;276(46):42761-6. doi: 10.1074/jbc.M106690200. Epub 2001 Aug 28.
The Rieske Fe/S protein, a nuclear-encoded subunit of the cytochrome b(6)/f complex in chloroplasts, is retarded in the stromal space after import into the chloroplast and only slowly translocated further into the thylakoid membrane system. As shown by the sensitivity to nigericin and to specific competitor proteins, thylakoid transport takes place by the DeltapH-dependent TAT pathway. The Rieske protein is an untypical TAT substrate, however. It is only the second integral membrane protein shown to utilize this pathway, and it is the first authentic substrate without a cleavable signal peptide. Transport is instead mediated by the NH(2)-terminal membrane anchor, which lacks, however, the twin-arginine motif indicative of DeltapH/TAT-dependent transport signals. Furthermore, transport is affected by sodium azide as well as by competitor proteins for the Sec pathway in chloroplasts, demonstrating for the first time some cross-talk of the two pathways. This might take place in the stroma where the Rieske protein accumulates after import in several complexes of high molecular mass, among which the cpn60 complex is the most prominent. These untypical features suggest that the Rieske protein represents an intermediate or early state in the evolution of the thylakoidal protein transport pathways.
Rieske铁硫蛋白是叶绿体中细胞色素b(6)/f复合物的一个核编码亚基，导入叶绿体后在基质空间中移动受阻，并且只是缓慢地进一步转运到类囊体膜系统中。如对尼日利亚菌素和特异性竞争蛋白的敏感性所示，类囊体转运是通过依赖于ΔpH的TAT途径进行的。然而，Rieske蛋白是一种非典型的TAT底物。它是第二个被证明利用该途径的整合膜蛋白，并且是第一个没有可裂解信号肽的真实底物。相反，转运是由NH(2)末端膜锚介导的，然而，该膜锚缺乏指示ΔpH/TAT依赖性转运信号的双精氨酸基序。此外，转运受到叠氮化钠以及叶绿体中Sec途径竞争蛋白的影响，首次证明了这两条途径之间存在一些相互作用。这种相互作用可能发生在基质中，Rieske蛋白导入后在几种高分子量复合物中积累，其中cpn60复合物最为突出。这些非典型特征表明，Rieske蛋白代表了类囊体蛋白转运途径进化中的一个中间或早期状态。
