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首页> 外文期刊>Journal of Molecular Biology >Conformations of NhaA, the Na/H exchanger from Escherichia coli, in the pH-activated and ion-translocating states.
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Conformations of NhaA, the Na/H exchanger from Escherichia coli, in the pH-activated and ion-translocating states.

机译：NhaA（来自大肠杆菌的Na / H交换剂）的构型处于pH活化和离子转运状态。

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摘要

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-A 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.
机译：NhaA是大肠杆菌内膜中的主要钠质子交换剂，它调节H和Na的胞质浓度。它在酸性pH下无活性，在pH 6和pH 7之间有活性，并在pH 8下达到最大活性。通过在pH 4下生长并在较高pH下孵育的二维晶体的冷冻电子显微镜观察，我们确定了两个连续的构象变化响应于pH或底物离子中的蛋白质。第一个变化是由pH值从6升高到7引起的，标志着从非活性状态到pH活化状态的转变。在离子诱导的构象变化之前发生pH活化，伴随着NhaA单体的整体膨胀和N末端的局部排列。第二种构象变化是由pH值高于7的底物离子Na和Li诱导的，涉及螺旋IVp的7-A置换。这种运动将导致离子结合位点的电荷失衡，这可能触发底物离子的释放并打开周质出口通道。

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