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Proc Natl Acad Sci U S A. 2009 Aug 18;106(33):13742-7. doi: 10.1073/pnas.0907054106. Epub 2009 Aug 3.

Crystal structure of the sodium-potassium pump (Na+,K+-ATPase) with bound potassium and ouabain.

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


The sodium-potassium pump (Na(+),K(+)-ATPase) is responsible for establishing Na(+) and K(+) concentration gradients across the plasma membrane and therefore plays an essential role in, for instance, generating action potentials. Cardiac glycosides, prescribed for congestive heart failure for more than 2 centuries, are efficient inhibitors of this ATPase. Here we describe a crystal structure of Na(+),K(+)-ATPase with bound ouabain, a representative cardiac glycoside, at 2.8 A resolution in a state analogous to E2.2K(+).Pi. Ouabain is deeply inserted into the transmembrane domain with the lactone ring very close to the bound K(+), in marked contrast to previous models. Due to antagonism between ouabain and K(+), the structure represents a low-affinity ouabain-bound state. Yet, most of the mutagenesis data obtained with the high-affinity state are readily explained by the present crystal structure, indicating that the binding site for ouabain is essentially the same. According to a homology model for the high affinity state, it is a closure of the binding cavity that confers a high affinity.

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