Key result
The Ca2+ ATPase of the sarcoplasmic reticulum utilizes an extramembranous globular head and a membrane-bound region to sequentially bind and vectorially dissociate calcium ions against a gradient.
Experimental systems identify how phosphorylation influences Ca2+ binding in sarcoplasmic reticulum ATPase, hinting at transport mechanisms.
Three experimental systems are described including sarcoplasmic reticulum (SR) vesicles, reconstituted proteoliposomes, and recombinant protein obtained by gene transfer and expression in foreign cells. It is shown that the Ca(2+) ATPase of sarcoplasmic reticulum (SR) includes an extramembranous globular head which is connected through a stalk to a membrane bound region. Cooperative binding of two calcium ions occurs sequentially, within a channel formed by four clustered helices within the membrane bound region. Destabilization of the helical cluster is produced following enzyme phosphorylation by ATP at the catalytic site in the extramembranous region. The affinity and orientation of the Ca2+ binding site are thereby changed, permitting vectorial dissociation of bound Ca2+ against a concentration gradient. A long range linkage between phosphorylation and Ca2+ binding sites is provided by an intervening peptide segment that retains high homology in cation transport ATPases, and whose function is highly sensitive to mutational perturbations.
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Inesi et al. (1995) reported a review. The Ca2+ ATPase of the sarcoplasmic reticulum utilizes an extramembranous globular head and a membrane-bound region to sequentially bind and vectorially dissociate calcium ions against a gradient.
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