Journal
SCIENCE
Volume 304, Issue 5677, Pages 1672-1675Publisher
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.1099366
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A tight coupling between adenosine triphosphate (ATP) hydrolysis and vectorial ion transport has to be maintained by ATP-consuming ion pumps. We report two crystal structures of Ca2+-bound sarco(endo) plasmic reticulum Ca2+- adenosine triphosphatase (SERCA) at 2.6 and 2.9 angstrom resolution in complex with (i) a nonhydrolyzable ATP analog [adenosine (beta-gamma methylene) triphosphate] and (ii) adenosine diphosphate plus aluminum fluoride. SERCA reacts with ATP by an associative mechanism mediated by two Mg2+ ions to form an aspartyl-phosphorylated intermediate state (Ca-2- E1 similar to P). The conformational changes that accompany the reaction with ATP pull the transmembrane helices 1 and 2 and close a cytosolic entrance for Ca2+, thereby preventing backflow before Ca2+ is released on the other side of the membrane.
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