A calcium pump made visible

The first high-resolution structure of a P-type ATPase, that of the Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum, was published in 2000. This structure has provided many clues to how the Ca2+-ATPase might work, but no complete answers. The Ca2+-ATPase structure reveals no clear pathway from the cytoplasmic side of the membrane to the pair of high-affinity binding sites for Ca2+ located in the transmembrane region of the ATPase and no clear pathway from these sites to the lumenal side of the membrane. The ATPase is therefore very unlike an ion channel in its construction. It is unclear from the crystal structure of the Ca2+-ATPase exactly how the protein sits within the lipid bilayer that surrounds it in the membrane. The Ca2+-ATPase is implicated in thermogenesis in some types of muscle; this could involve processes of slippage and leak modulated by interaction between the Ca2+-ATPase and sarcolipin