Sandbox Reserved 970: Difference between revisions
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== Biological Function and Localisation == | == Biological Function and Localisation == | ||
The pumps exist in two major conformational states : E1 and E2. When the pump is in the E1 state, it has high calcium affinity and interacts with calcium at one side of the membrane. In the E2 state, the enzyme has a lower calcium affinity and that leads to the release of the ion at the opposite side. | |||
Recently, some structural work on the SERCA pump has shown that the mechanism of the pump is a little bit more complex. When the calcium pump is unphosphorylated, two of the helices are disrupted, forming a cavity accessible from the cytosol. This cavity binds two calcium ions. When ATP binds to the pump, it allows the phosphorylation of the enzyme on its phosphorylation domain. The hydrolysis of ATP causes conformational changes that bring the nucleotide binding domain and the phosphorylation domain of the enzyme into close proximity. The activator domain rotates and the transmembrane helices 4 and 6 rearrange. Calcium is released into the lumen of the sarcoplasmic reticulum. | |||
More recent structural work on the SERCA pump has increased the complexity of the conformational transitions that occur during the catalytic cycle. Upon binding of Ca2+, a series of structural changes occur that involve both the protruding cytoplasmic sector and the transmembrane domains, permitting the phosphorylation of the catalytic D-residue by the γ-phosphate of ATP. The dissociation of Ca2+ from the enzyme follows the transition of the high Ca2+ affinity E1∼P(Ca2+) enzyme to the lower affinity E2-P enzyme, the hydrolysis of which then regenerates the Ca2+-free E2 ATPase, completing the catalytic cycle. | |||
== Regulations == | == Regulations == | ||
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Marisa Brini and Ernesto Carafoli, 2010 - ''The Plasma Membrane Ca2+ ATPase and the Plasma Membrane Sodium Calcium Exchanger Cooperate in the Regulation of Cell Calcium'' - Cold Spring Harbor Perspectives in Biology | Marisa Brini and Ernesto Carafoli, 2010 - ''The Plasma Membrane Ca2+ ATPase and the Plasma Membrane Sodium Calcium Exchanger Cooperate in the Regulation of Cell Calcium'' - Cold Spring Harbor Perspectives in Biology | ||
Marisa Brini and Ernesto Carafoli, 2009 - ''Calcium Pumps in Health and Disease''- Physiological Reviews | |||
Thomas D.Pollard and William C. Earnshaw, - '' '' - Cell Biology (second edition), p. | Thomas D.Pollard and William C. Earnshaw, - '' '' - Cell Biology (second edition), p. | ||
