TonB is an essential component of an energy-generating system that powers active transport across the outer membrane (OM) of compounds that are too large or too scarce to diffuse through porins. The TonB-dependent OM transport proteins (TBDTs) consist of β barrels forming pores that are closed by plugs. The binding of TonB to TBDTs elicits plug movement, which opens the pores and enables nutrient translocation from the cell surface into the periplasm. TonB is also involved in the uptake of certain proteins, particularly toxins, through OM proteins that differ structurally from TBDTs. TonB binds to a sequence of five residues, designated as the TonB box, which is conserved in all TBDTs. Energy from the proton motive force (pmf) of the cytoplasmic membrane is transmitted to TonB by two proteins, ExbB and ExbD. These proteins form an energy-transmitting protein complex consisting of five ExbB proteins, forming a pore that encloses the ExbD dimer. This review discusses the structural changes that occur in TBDTs upon interaction with TonB, as well as the interaction of ExbB-ExbD with TonB, which is required to transmit the energy of the pmf and thereby open TBDT pores. TonB facilitates import of a wide range of substrates.

中文翻译：

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TonB 依赖性外膜转运蛋白的底物摄取


TonB 是能量产生系统的重要组成部分，该系统为太大或太稀少而无法通过孔蛋白扩散的化合物穿过外膜 （OM） 的主动运输提供动力。TonB 依赖性 OM 转运蛋白 （TBDT） 由β桶组成，这些桶形成由塞子封闭的孔。TonB 与 TBDT 的结合会引发栓子运动，从而打开孔隙并使营养物质从细胞表面转移到周质中。TonB 还通过结构上与 TBDT 不同的 OM 蛋白参与某些蛋白质（尤其是毒素）的摄取。TonB 与五个残基的序列结合，称为 TonB 盒，在所有 TBDT 中都是保守的。来自细胞质膜质子动力 （pmf） 的能量通过两种蛋白质传递到 TonB， ExbB 和 ExbD。这些蛋白质形成一个由五个 ExbB 蛋白组成的能量传递蛋白复合物，形成一个包围 ExbD 二聚体的孔。本文讨论了 TBDT 与 TonB 相互作用时发生的结构变化，以及 ExbB-ExbD 与 TonB 的相互作用，这是传递 pmf 能量并因此打开 TBDT 孔所必需的。TonB 有助于导入各种基材。