Structure and function of P-type ATPase cation pumps
Abstract
P-type ATPases encompass the cation pumps like Na+,K+-ATPase and Ca2+-ATPase. They couple the transport and countertransport of ions, through a membrane spanning domain, to ATP hydrolysis via formation and breakdown of a phosphoenzyme intermediate at cytoplasmic domains. The enzymes undergo large conformational changes where half-channels open and close, and where the ion binding sites at the middle of the membrane switch their specificity and orientation (Møller et al. 2010, Palmgren & Nissen 2011). Worth noting, these large-scale movements take place in close interaction with the membrane.
In favourable crystal forms of Ca2+-ATPase we have observed electron density for lipid-detergent bilayers between molecules and we have used this experimental basis to validate molecular dynamics simulations and to interpret biochemical/biophysical data on the protein-lipid interactions of a working transport undergoing large conformational changes in a membrane (Sonntag et al., 2011).
Na+,K+-ATPase is of key importance in animal cells and physiology. The enzyme transports three sodium ions out and two potassium ions in per ATPase cycle. From the crystal structure of the pig kidney enzyme in the potassium-bound form - further probed by mutagenesis and electrophysiology - we pinpointed a key role of the alpha subunit C-terminus on sodium binding (Morth et al. 2007) with significant implications to neurological diseases (Poulsen et al. 2010). Furthermore, a low resolution crystal structure of the phosphorylated E2P form of the Na+,K+-ATPase in complex with the cardiotonic steroid ouabain shows conformational changes that not only explain the mechanism of cardiotonic steroid inhibition, but also hint at the possible role of these steroids in signalling, i.e. with Na+,K+-ATPase as a receptor (Yatime et al. 2011).
Furthermore we have determined structures of the Cu+-ATPase CopA, which reveal novel mechanisms of transport associated with the P-type ATPase scaffold as well as a use of general mechanisms of the protein family (Gourdon et al., 2011)
References
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Poulsen H, Khandelia H, Morth JP, Bublitz M, Mouritsen OG, Egebjerg J, Nissen P (2010). Neurological disease mutations compromise a C-terminal ion pathway in the Na(+)/K(+)-ATPase. Nature 467, 99-102
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Yatime L, Laursen M, Morth JP, Esmann M, Nissen P, Fedosova NU (2011). Structural insights into the high affinity binding of cardiotonic steroids to the Na(+),K(+)-ATPase. J. Struct. Biol. 174, 296-30.
