Structure of the calcium pump from sarcoplasmic reticulum at 8-Angstrom resolution

• Published in: Nature (London) Vol. 392; no. 6678; pp. 835 - 839
• Main Authors: Zhang, Peijun, Toyoshima, Chikashi, Yonekura, Koji, Green, N Michael, Stokes, David L
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 23.04.1998
• Subjects: ATP; Calcium; Cellular biology; Crystals; Hydrolysis; Membranes; Pumps; Topology
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/33959

The calcium pump from sarcoplasmic reticulum (Ca2+-ATPase) is typical of the large family of P-type cation pumps. These couple ATP hydrolysis with cation transport, generating cation gradients across membranes. Ca2+-ATPase specifically maintains the low cytoplasmic calcium concentration of resting muscle by pumping calcium into the sarcoplasmic reticulum; subsequent release is used to initiate contraction. No high-resolution structure of a P-type pump has yet been determined, although a 14-A structure of Ca2+-ATPase, obtained by electron microscopy of frozen-hydrated, tubular crystals, showed a large cytoplasmic head connected to the transmembrane domain by a narrow stalk. We have now improved the resolution to 8A and can discern ten transmembrane alpha-helices, four of which continue into the stalk On the basis of constraints from transmembrane topology, site-directed mutagenesis and disulphide crosslinking, we have made tentative assignments for these alpha-helices within the amino-acid sequence. A distinct cavity leads to the putative calcium-binding site, providing a plausible path for calcium release to the lumen of the sarcoplasmic reticulum.