Structure of the calcium pump from sarcoplasmic reticulum at 8-A resolution.
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.
Zhang
P
P
Skirball Institute of Biomolecular Medicine, New York University Medical Center, New York 10016, USA.
Toyoshima
C
C
Yonekura
K
K
Green
N M
NM
Stokes
D L
DL
D000595:Amino Acid Sequence; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000737:chemistry*; D003461:Crystallography; D007091:Image Processing, Computer-Assisted; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011817:Rabbits; D051381:Rats; D012441:Saccharomyces cerevisiae; D012519:Sarcoplasmic Reticulum / Q000737:chemistry*; D012756:Sheep
D000252:Calcium-Transporting ATPases