Drobnak Igor, Braselmann Esther, Clark Patricia L
From the Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556.
From the Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556
J Biol Chem. 2015 Apr 17;290(16):10104-16. doi: 10.1074/jbc.M114.629170. Epub 2015 Feb 10.
Autotransporter (AT) proteins are a broad class of virulence proteins from Gram-negative bacterial pathogens that require their own C-terminal transmembrane domain to translocate their N-terminal passenger across the bacterial outer membrane (OM). But given the unavailability of ATP or a proton gradient across the OM, it is unknown what energy source(s) drives this process. Here we used a combination of computational and experimental approaches to quantitatively compare proposed AT OM translocation mechanisms. We show directly for the first time that when translocation was blocked an AT passenger remained unfolded in the periplasm. We demonstrate that AT secretion is a kinetically controlled, non-equilibrium process coupled to folding of the passenger and propose a model connecting passenger conformation to secretion kinetics. These results reconcile seemingly contradictory reports regarding the importance of passenger folding as a driving force for OM translocation but also reveal that another energy source is required to initiate translocation.
自转运蛋白（AT）是革兰氏阴性细菌病原体中的一类广泛的毒力蛋白，它们需要自身的C末端跨膜结构域将其N末端乘客结构域转运穿过细菌外膜（OM）。但是，由于无法获得ATP或跨OM的质子梯度，驱动这一过程的能量来源尚不清楚。在这里，我们结合计算和实验方法，定量比较了提出的AT OM转运机制。我们首次直接表明，当转运受阻时，AT乘客结构域在周质中保持未折叠状态。我们证明，AT分泌是一个动力学控制的非平衡过程，与乘客结构域的折叠相关，并提出了一个将乘客结构域构象与分泌动力学联系起来的模型。这些结果调和了关于乘客结构域折叠作为OM转运驱动力的重要性的看似矛盾的报道，但也揭示了启动转运还需要另一种能量来源。
