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Nature. 2009 May 21;459(7245):446-50. doi: 10.1038/nature07939.

Crystal structure of the sodium-potassium pump at 2.4 A resolution.

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Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.


Sodium-potassium ATPase is an ATP-powered ion pump that establishes concentration gradients for Na(+) and K(+) ions across the plasma membrane in all animal cells by pumping Na(+) from the cytoplasm and K(+) from the extracellular medium. Such gradients are used in many essential processes, notably for generating action potentials. Na(+), K(+)-ATPase is a member of the P-type ATPases, which include sarcoplasmic reticulum Ca(2+)-ATPase and gastric H(+), K(+)-ATPase, among others, and is the target of cardiac glycosides. Here we describe a crystal structure of this important ion pump, from shark rectal glands, consisting of alpha- and beta-subunits and a regulatory FXYD protein, all of which are highly homologous to human ones. The ATPase was fixed in a state analogous to E2.2K(+).P(i), in which the ATPase has a high affinity for K(+) and still binds P(i), as in the first crystal structure of pig kidney enzyme at 3.5 A resolution. Clearly visualized now at 2.4 A resolution are coordination of K(+) and associated water molecules in the transmembrane binding sites and a phosphate analogue (MgF(4)(2-)) in the phosphorylation site. The crystal structure shows that the beta-subunit has a critical role in K(+) binding (although its involvement has previously been suggested) and explains, at least partially, why the homologous Ca(2+)-ATPase counter-transports H(+) rather than K(+), despite the coordinating residues being almost identical.

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