Neurological disease mutations compromise a C-terminal ion pathway in the Na+/K+-ATPase

Abstract

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 α-subunit carboxy terminus at the transmembrane domain1,2. 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 pump3,4,5, 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 diseases6,7. 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 Ca2+-ATPase.

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Figure 1: Structural indication of an ion pathway from the α C terminus to site III in the Na + /K + -ATPase.
Figure 2: The voltage dependence of transient currents of C-terminally mutated Na + /K + -ATPases.
Figure 3: Asp 930 is essential for ion shuttling.
Figure 4: Model for ion transport by the Na + /K + -ATPase in a simplified Post–Albers scheme.

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Acknowledgements

We acknowledge the Danish Center for Scientific Computing at the University of Southern Denmark, Odense, for computing resources. We thank D. Gadsby, N. Vedovato and A. Gulyas-Kovacs at the Rockefeller University, New York City, for technical advice and discussion, A. Skov Kristensen and M. H. Poulsen (University of Copenhagen) for supplies of oocytes, and M. J. Clausen, G. Hartvigsen and A. M. Nielsen for assistance with experimental procedures. We are grateful to C. Slayman and F. Ashcroft for discussions on electrogenic transport. H.P. was supported by a short-term travel fellowship from the European Molecular Biology Organisation, J.P.M. was supported by grants from the Carlsberg Foundation and the Lundbeck Foundation, and P.N. was supported by an Elite Researcher grant of the Danish Ministry of Science and Innovation and a Hallas-Møller stipend from the Novo Nordisk Foundation.

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H.P. designed experiments, performed the electrophysiological experiments, analysed the data and wrote the paper; H.K. designed, performed and analysed the molecular dynamics simulations; J.P.M. performed structural analyses and designed experiments, M.B. analysed the water-filled sarco-endoplasmic Ca2+-ATPase channel, O.G.M. supervised the molecular dynamics simulations, J.E. analysed the electrophysiological experiments, P.N. supervised the project, designed experiments and analysed the data. All authors commented on the paper.

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Correspondence to Hanne Poulsen or Poul Nissen.

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The authors declare no competing financial interests.

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Supplementary Information

The file contains Supplementary Figures 1-7 with legends, Supplementary Tables 1-2 and additional References. (PDF 908 kb)

Supplementary Movie 1

This movie shows the C-terminal cytoplasmic pathway of Na+,K+-ATPase (MOV 1121 kb)

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Poulsen, H., Khandelia, H., Morth, J. et al. Neurological disease mutations compromise a C-terminal ion pathway in the Na+/K+-ATPase. Nature 467, 99–102 (2010). https://doi.org/10.1038/nature09309

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