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Structural changes in the calcium pump accompanying the dissociation of calcium


In skeletal muscle, calcium ions are transported (pumped) against a concentration gradient from the cytoplasm into the sarcoplasmic reticulum, an intracellular organelle. This causes muscle cells to relax after cytosolic calcium increases during excitation. The Ca2+ ATPase that carries out this pumping is a representative P-type ion-transporting ATPase. Here we describe the structure of this ion pump at 3.1 Å resolution in a Ca2+-free (E2) state, and compare it with that determined previously for the Ca2+-bound (E1Ca2+) state. The structure of the enzyme stabilized by thapsigargin, a potent inhibitor, shows large conformation differences from that in E1Ca2+. Three cytoplasmic domains gather to form a single headpiece, and six of the ten transmembrane helices exhibit large-scale rearrangements. These rearrangements ensure the release of calcium ions into the lumen of sarcoplasmic reticulum and, on the cytoplasmic side, create a pathway for entry of new calcium ions.

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Figure 1: Ribbon representation of SR Ca2+-ATPase in the Ca2+-bound form (E1Ca2+) and that (E2(TG)) in the absence of Ca2+ but in the presence of thapsigargin (TG).
Figure 2: Superimposition of the Ca2+-bound form (E1Ca2+, violet) and the thapsigargin-bound form (E2(TG), light green) of Ca2+-ATPase fitted with the transmembrane domain. α-Helices are represented by cylinders and β-strands by arrows.
Figure 3: Interface between the transmembrane helices (M3–M5) and the P domain of Ca2+-ATPase.
Figure 4: Rearrangement of transmembrane helices viewed from the rear (a), and a diagram illustrating the shift of M4 normal to the membrane by the tilting of M5 (b).
Figure 5: Conformation changes around the Ca2+-binding sites.
Figure 6: Thapsigargin (TG) binding site in Ca2+-ATPase.


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We thank H. Ogawa for help in data gathering, R. Yoshida for computations, and M. Nakasako for modelling. We also thank G. Inesi, P. Champeil, D. B. McIntosh and H. Suzuki for communicating unpublished results to us and for their help in improving the manuscript. Thanks are also due to E. Yamashita and all the staff at BL44XU of SPring-8. This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, the Japan New Energy and Industry Technology Development Organization, and the Human Frontier Science Program.

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Correspondence to Chikashi Toyoshima.

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Toyoshima, C., Nomura, H. Structural changes in the calcium pump accompanying the dissociation of calcium. Nature 418, 605–611 (2002).

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