Gumbart James, Wiener Michael C, Tajkhorshid Emad
Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
Biophys J. 2007 Jul 15;93(2):496-504. doi: 10.1529/biophysj.107.104158. Epub 2007 Apr 20.
For the uptake of scarce yet essential organometallic compounds, outer membrane transporters of Gram-negative bacteria work in concert with an energy-generating inner membrane complex, thus spanning the periplasmic space to drive active transport. Here, we examine the interaction of TonB, an inner membrane protein, with an outer membrane transporter based upon a recent crystal structure of a TonB-transporter complex to characterize two largely unknown steps of the transport cycle: how energy is transmitted from TonB to the transporter and how energy transduction initiates transport. Simulations of TonB in complex with BtuB reveal that force applied to TonB is transmitted to BtuB without disruption of the very small connection between the two, supporting a mechanical mode of coupling. Based on the results of different pulling simulations, we propose that the force transduction instigates a partial unfolding of the pore-occluding luminal domain of the transporter, a potential step in the transport cycle. Furthermore, analysis of the electrostatic potentials and salt bridge interactions between the two proteins during the simulations hints at involvement of electrostatic forces in long-range interaction and binding of TonB and BtuB.
对于稀缺但必不可少的有机金属化合物的摄取,革兰氏阴性菌的外膜转运蛋白与产生能量的内膜复合物协同工作,从而跨越周质空间驱动主动运输。在此,我们基于最近的TonB-转运蛋白复合物晶体结构,研究内膜蛋白TonB与外膜转运蛋白的相互作用,以表征运输循环中两个很大程度上未知的步骤:能量如何从TonB传递到转运蛋白,以及能量转导如何启动运输。TonB与BtuB复合物的模拟结果表明,施加在TonB上的力传递到了BtuB,而没有破坏两者之间非常小的连接,这支持了一种机械偶联模式。基于不同拉动模拟的结果,我们提出力转导促使转运蛋白的孔封闭腔内结构域部分展开,这是运输循环中的一个潜在步骤。此外,模拟过程中对两种蛋白质之间静电势和盐桥相互作用的分析表明,静电力参与了TonB和BtuB的远程相互作用和结合。