1. Centre for Membrane Pumps in Cells and Disease—PUMPKIN, Danish National Research Foundation, and,
2. Institute of Physiology and Biophysics, University of Aarhus, Ole Worms Alle, blg. 1185, DK - 8000 Aarhus C, Denmark
3. Department of Molecular Biology, University of Aarhus, Gustav Wieds Vej 10C, DK - 8000 Aarhus C, Denmark
4. Present address: Laboratoire de Cristallographie et RMN biologiques, UMR 8015 CNRS, Faculté de Pharmacie. Université Paris Descartes, 4 avenue de l'Observatoire, 75270 Paris Cedex 06, France.

Correspondence to: Jesper Vuust Møller^1,2Poul Nissen^1,3 Correspondence and requests for materials should be addressed to P.N. (Email: pn@mb.au.dk) and J.V.M. (Email: jvm@biophys.au.dk).

Abstract

The sarcoplasmic reticulum Ca²⁺-ATPase, a P-type ATPase, has a critical role in muscle function and metabolism. Here we present functional studies and three new crystal structures of the rabbit skeletal muscle Ca²⁺-ATPase, representing the phosphoenzyme intermediates associated with Ca²⁺ binding, Ca²⁺ translocation and dephosphorylation, that are based on complexes with a functional ATP analogue, beryllium fluoride and aluminium fluoride, respectively. The structures complete the cycle of nucleotide binding and cation transport of Ca²⁺-ATPase. Phosphorylation of the enzyme triggers the onset of a conformational change that leads to the opening of a luminal exit pathway defined by the transmembrane segments M1 through M6, which represent the canonical membrane domain of P-type pumps. Ca²⁺ release is promoted by translocation of the M4 helix, exposing Glu 309, Glu 771 and Asn 796 to the lumen. The mechanism explains how P-type ATPases are able to form the steep electrochemical gradients required for key functions in eukaryotic cells.

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