1. Centre for Membrane Pumps in Cells and Disease—PUMPKIN. Danish National Research Foundation,
2. Department of Molecular Biology, University of Aarhus, Gustav Wieds Vej 10C, DK-8000 Aarhus, Denmark
3. Plant Physiology and Anatomy Laboratory, Department of Plant Biology, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg, Denmark
4. These authors contributed equally to this work.

Correspondence to: Michael G. Palmgren^1,3Poul Nissen^1,2 Correspondence and requests for materials should be addressed to P.N. (Email: pn@mb.au.dk) and M.G.P. (Email: palmgren@life.ku.dk).

Abstract

A prerequisite for life is the ability to maintain electrochemical imbalances across biomembranes. In all eukaryotes the plasma membrane potential and secondary transport systems are energized by the activity of P-type ATPase membrane proteins: H⁺-ATPase (the proton pump) in plants and fungi^{1, 2, 3}, and Na⁺,K⁺-ATPase (the sodium–potassium pump) in animals⁴. The name P-type derives from the fact that these proteins exploit a phosphorylated reaction cycle intermediate of ATP hydrolysis⁵. The plasma membrane proton pumps belong to the type III P-type ATPase subfamily, whereas Na⁺,K⁺-ATPase and Ca²⁺-ATPase are type II⁶. Electron microscopy has revealed the overall shape of proton pumps⁷, however, an atomic structure has been lacking. Here we present the first structure of a P-type proton pump determined by X-ray crystallography. Ten transmembrane helices and three cytoplasmic domains define the functional unit of ATP-coupled proton transport across the plasma membrane, and the structure is locked in a functional state not previously observed in P-type ATPases. The transmembrane domain reveals a large cavity, which is likely to be filled with water, located near the middle of the membrane plane where it is lined by conserved hydrophilic and charged residues. Proton transport against a high membrane potential is readily explained by this structural arrangement.

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