Coupling of remote alternating-access transport mechanisms for protons and substrates in the multidrug efflux pump AcrB
Coupling of remote alternating-access transport mechanisms for protons and substrates in the multidrug efflux pump AcrB
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DOI：
10.7554/elife.03145
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发表时间：
2014-09-19
期刊：
影响因子：
7.7
通讯作者：
Pos, Klaas M.
中科院分区：
文献类型：
--
作者：
Eicher, Thomas;Seeger, Markus A.;Pos, Klaas M.
RND超家族的膜转运蛋白赋予病原菌多药耐药性，并且对人类胆固醇代谢和胚胎发育至关重要。我们使用高分辨率的X射线晶体学和计算方法来描述同源三聚体RND型质子/药物反向转运蛋白AcrB的机制，AcrB是大肠杆菌中主要外排系统AcrAB-TolC的活性成分，也是迄今为止已知的最复杂和最有趣的膜转运蛋白之一。野生型AcrB和四个功能不活跃的变体的分析揭示了一个前所未有的机制，涉及两个远程交替访问每个原聚体内的构象循环，即一个质子在跨膜区和另一个药物在周质域，50埃分开。这些循环中的每一个都需要两个结构重复的两种不同类型的集体运动，通过从膜上突出的侧翼a-螺旋耦合。此外，我们合理化如何在三聚界面的原聚体之间的串扰可能会导致一个更动力学有效的外排系统。
Membrane transporters of the RND superfamily confer multidrug resistance to pathogenic bacteria, and are essential for cholesterol metabolism and embryonic development in humans. We use high-resolution X-ray crystallography and computational methods to delineate the mechanism of the homotrimeric RND-type proton/drug antiporter AcrB, the active component of the major efflux system AcrAB-TolC in Escherichia coli, and one most complex and intriguing membrane transporters known to date. Analysis of wildtype AcrB and four functionally-inactive variants reveals an unprecedented mechanism that involves two remote alternating-access conformational cycles within each protomer, namely one for protons in the transmembrane region and another for drugs in the periplasmic domain, 50 angstrom apart. Each of these cycles entails two distinct types of collective motions of two structural repeats, coupled by flanking a-helices that project from the membrane. Moreover, we rationalize how the cross-talk among protomers across the trimerization interface might lead to a more kinetically efficient efflux system.