1. Centre for Membrane Pumps in Cells and Disease—PUMPKIN, Danish National Research Foundation, and,
2. Department of Molecular Biology, University of Aarhus, Gustav Wieds Vej 10C, DK-8000 Aarhus C, Denmark
3. Institute of Physiology and Biophysics, University of Aarhus, Ole Worms Allé, Blg. 1160, DK-8000 Aarhus C, Denmark
4. Present address: Diamond Light Source Ltd, Diamond House, Chilton, Didcot, Oxfordshire, OX11 0DE, UK.
5. These authors contributed equally to this work.

Correspondence to: Bente Vilsen^1,3,5Poul Nissen^1,2,5 Correspondence and requests for materials should be addressed to P.N. (Email: pn@mb.au.dk) and B.V. (Email: bv@fi.au.dk).

Abstract

The Na⁺,K⁺-ATPase generates electrochemical gradients for sodium and potassium that are vital to animal cells, exchanging three sodium ions for two potassium ions across the plasma membrane during each cycle of ATP hydrolysis. Here we present the X-ray crystal structure at 3.5 Å resolution of the pig renal Na⁺,K⁺-ATPase with two rubidium ions bound (as potassium congeners) in an occluded state in the transmembrane part of the -subunit. Several of the residues forming the cavity for rubidium/potassium occlusion in the Na⁺,K⁺-ATPase are homologous to those binding calcium in the Ca²⁺-ATPase of sarco(endo)plasmic reticulum. The - and -subunits specific to the Na⁺,K⁺-ATPase are associated with transmembrane helices M7/M10 and M9, respectively. The -subunit corresponds to a fragment of the V-type ATPase c subunit. The carboxy terminus of the -subunit is contained within a pocket between transmembrane helices and seems to be a novel regulatory element controlling sodium affinity, possibly influenced by the membrane potential.

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