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Protonation of key acidic residues is critical for the K+-selectivity of the Na/K pump

Abstract

The sodium-potassium (Na/K) pump is a P-type ATPase that generates Na+ and K+ concentration gradients across the cell membrane. For each hydrolyzed ATP molecule, the pump extrudes three Na+ and imports two K+ by alternating between outward- and inward-facing conformations that preferentially bind K+ or Na+, respectively. Remarkably, the selective K+ and Na+ binding sites share several residues, and how the pump is able to achieve the selectivity required for the functional cycle is unclear. Here, free energy–perturbation molecular dynamics (FEP/MD) simulations based on the crystal structures of the Na/K pump in a K+-loaded state (E2·Pi) reveal that protonation of the high-field acidic side chains involved in the binding sites is crucial to achieving the proper K+ selectivity. This prediction is tested with electrophysiological experiments showing that the selectivity of the E2P state for K+ over Na+ is affected by extracellular pH.

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Figure 1: Superposition of instantaneous configurations from MD simulations of the Na/K pump.
Figure 2: Electrophysiological experiments on the Na/K pump expressed in Xenopus oocytes.

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Acknowledgements

This work was supported by US National Institutes of Health grant GM062342 (H.Y. and B.R.) and by American Heart Association grant BGIA2140172 (P.A.).

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H.Y. and B.R. designed the computations, and H.Y. carried out the computations; P.A. and B.R. set the overall aim of the experiments; the electrophysiological experiments were designed by P.A. and carried out by I.R. and P.A.; H.Y., P.A. and B.R. wrote the manuscript.

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Correspondence to Benoît Roux.

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The authors declare no competing financial interests.

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Supplementary Figs 1-9, Supplementary Tables 1-3 and Supplementary Methods (PDF 1954 kb)

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Yu, H., Ratheal, I., Artigas, P. et al. Protonation of key acidic residues is critical for the K+-selectivity of the Na/K pump. Nat Struct Mol Biol 18, 1159–1163 (2011). https://doi.org/10.1038/nsmb.2113

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