Forcing Calcium Through

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Science  23 Jun 2000:
Vol. 288, Issue 5474, pp. 2097
DOI: 10.1126/science.288.5474.2097b

Cells excel at interconverting types of energy under mild and controlled conditions; for example, the uphill transport of calcium from the cytoplasm into the sarcoplasmic reticulum of muscle cells is driven by the hydrolysis of ATP. Toyoshima et al. provide a high-resolution view of the enzyme responsible for this activity, the Ca2+-ATPase. The salient features are a bundle of ten transmembrane α-helices and a cytoplasmic trio of domains that together bind one molecule of ATP and couple the energy released by hydrolysis to the movement of two calcium ions through the helical bundle. Although structural characterization of reaction intermediates lies ahead, the cytoplasmic domains appear to re-orient and coalesce during catalysis, which may result in lever-like movement of the helices and extrusion of the ions much as air is expelled from a hand bellows.—GJC

Nature405, 647 (2000).

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