Phosphoryl Moiety Closes the Hatch

Science  24 Dec 2004:
Vol. 306, Issue 5705, pp. 2160
DOI: 10.1126/science.306.5705.2160i

The calcium-dependent adenosine triphosphatase (ATPase) of the sarcoplasmic reticulum is one of the best studied ion pumps, and the structural description of two of the intermediate states in the reaction cycle helped to define the calcium ion binding sites within the transmembrane region of the enzyme. A recent series of crystal structures of the enzyme trapped at other stages in the reaction cycle is now capped by Olesen et al. (p. 2251), who identify the binding sites for the counter-transported protons. They also found that phosphoryl transfer from ATP to the enzyme closes the entry hatch to the calcium-binding site and that the release of adenosine diphosphate opens the exit hatch and allows the exchange of calcium for protons. Phosphoryl transfer from the enzyme to water and closes the exit hatch. Finally, release of phosphate opens the entry hatch and allows the exchange of protons for calcium.

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