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 ...
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 Ca(2+) 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 A resolution in a Ca(2+)-free (E2) state, and compare it with that determined previously for the Ca(2+)-bound (E1Ca(2+)) state. The structure of the enzyme stabilized by thapsigargin, a potent inhibitor, shows large conformation differences from that in E1Ca(2+). 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.
Related Citations:
Crystal structure of the calcium pump of sarcoplasmic reticulum at 2.6 A resolution Toyoshima, C., Nakasako, M., Nomura, H., Ogawa, H. (2000) Nature 405: 647
The crystal and molecular structure of the sesquiterpenoid silerin (trilobolide) Kutschabsky, L., Kretschmer, R.-G., Ripperger, H. (1986) Cryst Res Technol 21: 627
Sesquiterpenoids from Thapsia species and medicinal chemistry of the thapsigargins Christensen, S.B., Andersen, A., Smitt, U.W. (1997) Fortschr Chem Org Naturst 71: 129
Organizational Affiliation:
Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan. ct@iam.u-tokyo.ac.jp
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