Bogsch E G, Sargent F, Stanley N R, Berks B C, Robinson C, Palmer T
Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, United Kingdom.
J Biol Chem. 1998 Jul 17;273(29):18003-6. doi: 10.1074/jbc.273.29.18003.
Proteins are transported across the bacterial plasma membrane and the chloroplast thylakoid membrane by means of protein translocases that recognize N-terminal targeting signals in their cognate substrates. Transport of many of these proteins involves the well defined Sec apparatus that operates in both membranes. We describe here the identification of a novel component of a bacterial Sec-independent translocase. The system probably functions in a similar manner to a Sec-independent translocase in the thylakoid membrane, and substrates for both systems bear a characteristic twin-arginine motif in the targeting peptide. The translocase component is encoded in Escherichia coli by an unassigned reading frame, yigU, disruption of which blocks the export of at least five twin-Arg-containing precursor proteins that are predicted to bind redox cofactors, and hence fold, prior to translocation. The Sec pathway remains unaffected in the deletion strain. The gene has been designated tatC (for twin-arginine translocation), and we show that homologous genes are present in a range of bacteria, plastids, and mitochondria. These findings suggest a central role for TatC-type proteins in the translocation of tightly folded proteins across a spectrum of biological membranes.
蛋白质通过蛋白质转运酶穿过细菌质膜和叶绿体类囊体膜，这些转运酶能识别其同源底物中的N端靶向信号。许多此类蛋白质的转运涉及在这两种膜中都起作用的明确的Sec装置。我们在此描述了一种细菌Sec非依赖性转运酶新组分的鉴定。该系统可能以与类囊体膜中Sec非依赖性转运酶类似的方式发挥作用，并且这两个系统的底物在靶向肽中都带有特征性的双精氨酸基序。该转运酶组分在大肠杆菌中由一个未指定的阅读框yigU编码，破坏该阅读框会阻断至少五种含双精氨酸的前体蛋白的输出，这些前体蛋白预计在转运之前会结合氧化还原辅因子并因此折叠。Sec途径在缺失菌株中不受影响。该基因已被命名为tatC（双精氨酸转运），并且我们表明同源基因存在于一系列细菌、质体和线粒体中。这些发现表明TatC型蛋白在紧密折叠的蛋白质跨一系列生物膜的转运中起核心作用。
