Hannavy K, Barr G C, Dorman C J, Adamson J, Mazengera L R, Gallagher M P, Evans J S, Levine B A, Trayer I P, Higgins C F
Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, England.
J Mol Biol. 1990 Dec 20;216(4):897-910. doi: 10.1016/S0022-2836(99)80009-6.
The tonB gene product is required for several outer membrane transport processes in bacteria. The tonB gene from Salmonella typhimurium was sequenced and found to be similar to that of Escherichia coli. The TonB protein is highly proline-rich and includes an unusual segment consisting of multiple X-Pro dipeptide repeats. A synthetic peptide corresponding to this segment has been used to raise anti-TonB antibodies. TonB was shown to be associated with the cytoplasmic membrane, apparently anchored via a single hydrophobic N-terminal segment. Protease accessibility studies, and the use of a series of TonB-beta-lactamase fusions, showed that the rest of the TonB protein is periplasmic. Unusually, export of TonB is not accompanied by cleavage of the N-terminal signal peptide. In the accompanying paper, we show that TonB interacts directly with the outer membrane FhuA (TonA) receptor. Thus, TonB must span the periplasm, providing a link between the cytoplasmic membrane and receptors in the outer membrane. On the basis of these data, and those published by other laboratories, we propose a model whereby TonB serves as a "mechanical" linkage that, by transmitting protein conformational changes from the cytoplasmic membrane across the periplasm, acts as a means of coupling energy to outer membrane transport processes. Such a mechanism has general implications for signal transduction within and between proteins.
TonB基因产物是细菌中几种外膜转运过程所必需的。对鼠伤寒沙门氏菌的tonB基因进行了测序，发现它与大肠杆菌的tonB基因相似。TonB蛋白富含脯氨酸，并且包含一个由多个X-Pro二肽重复序列组成的特殊片段。与该片段对应的合成肽已被用于制备抗TonB抗体。结果表明，TonB与细胞质膜相关联，显然是通过单个疏水的N端片段锚定在质膜上。蛋白酶可及性研究以及一系列TonB-β-内酰胺酶融合蛋白的使用表明，TonB蛋白的其余部分位于周质空间。不同寻常的是，TonB的输出并不伴随着N端信号肽的切割。在随附的论文中，我们表明TonB直接与外膜FhuA（TonA）受体相互作用。因此，TonB必须跨越周质空间，在细胞质膜和外膜受体之间提供联系。基于这些数据以及其他实验室发表的数据，我们提出了一个模型，其中TonB作为一种“机械”连接，通过将蛋白质构象变化从细胞质膜传递穿过周质空间，作为将能量耦合到外膜转运过程的一种方式。这种机制对蛋白质内部和蛋白质之间的信号转导具有普遍意义。
