PUMPKIN - Centre for Membrane Pumps in Cells and Disease, Danish National Research Foundation, Department of Molecular Biology, Aarhus University, DK-8000 Aarhus C, Denmark.
Nature. 2010 Sep 2;467(7311):99-102. doi: 10.1038/nature09309. Epub 2010 Aug 15.
The Na(+)/K(+)-ATPase pumps three sodium ions out of and two potassium ions into the cell for each ATP molecule that is split, thereby generating the chemical and electrical gradients across the plasma membrane that are essential in, for example, signalling, secondary transport and volume regulation in animal cells. Crystal structures of the potassium-bound form of the pump revealed an intimate docking of the alpha-subunit carboxy terminus at the transmembrane domain. Here we show that this element is a key regulator of a previously unrecognized ion pathway. Current models of P-type ATPases operate with a single ion conduit through the pump, but our data suggest an additional pathway in the Na(+)/K(+)-ATPase between the ion-binding sites and the cytoplasm. The C-terminal pathway allows a cytoplasmic proton to enter and stabilize site III when empty in the potassium-bound state, and when potassium is released the proton will also return to the cytoplasm, thus allowing an overall asymmetric stoichiometry of the transported ions. The C terminus controls the gate to the pathway. Its structure is crucial for pump function, as demonstrated by at least eight mutations in the region that cause severe neurological diseases. This novel model for ion transport by the Na(+)/K(+)-ATPase is established by electrophysiological studies of C-terminal mutations in familial hemiplegic migraine 2 (FHM2) and is further substantiated by molecular dynamics simulations. A similar ion regulation is likely to apply to the H(+)/K(+)-ATPase and the Ca(2+)-ATPase.
钠钾泵（Na(+)/K(+)-ATPase）每分解一个 ATP 分子，就会将三个钠离子泵出细胞，将两个钾离子泵入细胞，从而在质膜两侧产生电化学梯度。这些梯度对于动物细胞的信号转导、次级转运和体积调节等过程至关重要。泵的钾结合构象的晶体结构揭示了α亚基羧基末端与跨膜结构域的紧密对接。在这里，我们表明该元件是一个以前未被识别的离子通道的关键调节剂。目前的 P 型 ATP 酶模型采用单一的离子通道通过泵，但我们的数据表明，在钠钾泵中，在离子结合位点和细胞质之间存在另一种离子通道。C 端途径允许质子进入并在钾结合状态下空的情况下稳定 III 位，当钾释放时，质子也将返回细胞质，从而允许转运离子的总体不对称计量。C 端控制着通往该途径的门。该结构对于泵的功能至关重要，该区域的至少 8 个突变导致严重的神经疾病。该模型通过家族性偏瘫偏头痛 2（FHM2）的 C 端突变的电生理研究得到确立，并通过分子动力学模拟进一步证实。类似的离子调节可能适用于 H(+)/K(+)-ATPase 和 Ca(2+)-ATPase。
