Conformations of NhaA, the Na/H Exchanger from Escherichia coli, in the pH-Activated and Ion-Translocating States
Conformations of NhaA, the Na/H Exchanger from Escherichia coli, in the pH-Activated and Ion-Translocating States
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DOI：
10.1016/j.jmb.2008.12.042
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发表时间：
2009-02-20
影响因子：
5.6
通讯作者：
Kuehlbrandt, Werner
中科院分区：
文献类型：
--
作者：
Appel, Matthias;Hizlan, Dilem;Kuehlbrandt, Werner
NhaA是大肠杆菌内膜中主要的钠-质子交换剂，调节细胞内H和Na的浓度。它在酸性pH下无活性，在pH 6和pH 7之间变得有活性，并在pH 8时达到最大活性。通过低温电子显微镜的二维晶体生长在pH 4和在更高的pH值下孵育，我们确定了两个连续的构象变化的蛋白质在响应pH值或底物离子。第一个变化是由pH从6上升到7引起的，标志着从非活性状态到pH活化状态的转变。pH活化，这之前的离子诱导的构象变化，是伴随着NhaA单体的整体扩张和局部排序的N-末端。第二个构象变化是由底物离子Na和Li在pH高于7时引起的，涉及螺旋IVp的7埃位移。这种移动将导致离子结合位点处的电荷不平衡，这可能触发底物离子的释放并打开周质出口通道。(C)2008爱思唯尔有限公司保留所有权利。
NhaA, the main sodium-proton exchanger in the inner membrane of Escherichia coli, regulates the cytosolic concentrations of H and Na. It is inactive at acidic pH, becomes active between pH 6 and pH 7, and reaches maximum activity at pH 8. By cryo-electron microscopy of two-dimensional crystals grown at pH 4 and incubated at higher pH, we identified two sequential conformational changes in the protein in response to pH or substrate ions. The first change is induced by a rise in pH from 6 to 7 and marks the transition from the inactive state to the pH-activated state. pH activation, which precedes the ion-induced conformational change, is accompanied by an overall expansion of the NhaA monomer and a local ordering of the N-terminus. The second conformational change is induced by the substrate ions Na and Li at pH above 7 and involves a 7-angstrom displacement of helix IVp. This movement would cause a charge imbalance at the ion-binding site that may trigger the release of the substrate ion and open a periplasmic exit channel. (C) 2008 Elsevier Ltd. All rights reserved.