Klein Marco J, Grage Stephan L, Muhle-Goll Claudia, Bürck Jochen, Afonin Sergii, Ulrich Anne S
Karlsruhe Institute of Technology, Institute of Organic Chemistry and CFN, Germany.
Biochim Biophys Acta. 2012 Dec;1818(12):3025-31. doi: 10.1016/j.bbamem.2012.08.002. Epub 2012 Aug 10.
Tat signal peptides provide the key signature for proteins that get exported by the bacterial twin arginine translocase. We have characterized the structure of the PhoD signal peptide from Bacillus subtilis in suitable membrane-mimicking environments. High-resolution ¹³C/¹⁵N NMR analysis in detergent micelles revealed a helical stretch in the signal peptide between positions 5 and 15, in good agreement with secondary structure prediction and circular dichroism results. This helix was found to be aligned parallel to the membrane surface according to oriented circular dichroism experiments carried out with planar lipid bilayers. The N-terminal α-helix exhibits a pronounced amphiphilic character, in contrast to the general view in the literature. So far, signal sequences had been supposed to consist of a positively charged N-terminal domain, followed by an α-helical hydrophobic segment, plus a C-terminal domain carrying the peptidase cleavage site. Based on our new structural insights, we propose a model for the folding and membrane interactions of the Tat signal sequence from PhoD.
Tat信号肽为通过细菌双精氨酸转运酶输出的蛋白质提供了关键特征。我们已在合适的模拟膜环境中对枯草芽孢杆菌的PhoD信号肽结构进行了表征。在去污剂胶束中进行的高分辨率¹³C/¹⁵N NMR分析显示，信号肽在第5至15位之间存在一段螺旋结构，这与二级结构预测和圆二色性结果高度一致。根据在平面脂质双层上进行的定向圆二色性实验，发现该螺旋与膜表面平行排列。与文献中的普遍观点相反，N端α螺旋表现出明显的两亲性。到目前为止，信号序列被认为由带正电荷的N端结构域、随后的α螺旋疏水片段以及携带肽酶切割位点 的C端结构域组成。基于我们新的结构见解，我们提出了PhoD的Tat信号序列折叠和膜相互作用的模型。
