Braun Volkmar
Max-Planck-Institute of Biology, Tübingen, Germany.
Mol Microbiol. 2024 Dec;122(6):929-947. doi: 10.1111/mmi.15332. Epub 2024 Dec 3.
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.
托蛋白B是一种能量产生系统的重要组成部分，该系统为那些因太大或太稀少而无法通过孔蛋白扩散穿过外膜（OM）的化合物的主动运输提供动力。托蛋白B依赖的外膜运输蛋白（TBDTs）由形成孔道的β桶组成，这些孔道被塞子封闭。托蛋白B与TBDTs的结合引发塞子移动，从而打开孔道并使营养物质从细胞表面转运到周质中。托蛋白B还通过结构上不同于TBDTs的外膜蛋白参与某些蛋白质，特别是毒素的摄取。托蛋白B与一段由五个残基组成的序列结合，该序列被称为托蛋白B框，在所有TBDTs中都保守。细胞质膜质子动力（pmf）的能量通过两种蛋白质ExbB和ExbD传递给托蛋白B。这些蛋白质形成一个能量传递蛋白复合物，由五个ExbB蛋白组成，形成一个包围ExbD二聚体的孔道。本文综述了TBDTs与托蛋白B相互作用时发生的结构变化，以及ExbB-ExbD与托蛋白B的相互作用，这是传递pmf能量从而打开TBDT孔道所必需的。托蛋白B促进多种底物的导入。
