Key result
Cryo-electron microscopy revealed that apoCaM and Ca2+-CaM bind to distinct but neighboring locations on the ryanodine receptor, suggesting a direct role in excitation-contraction coupling.
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The distinct but neighboring binding locations of apoCaM and Ca2+-CaM on RyR1 provide a structural basis for efficient switching during muscle relaxation/contraction cycles.
Calmodulin (CaM) binds to the ryanodine receptor/calcium release channel of skeletal muscle (RyR1), both in the absence and presence of Ca(2+), and regulates the activity of the channel activity by activating and inhibiting it, respectively. Using cryo-electron microscopy and three-dimensional reconstruction, we found that one apoCaM binds per RyR1 subunit along the sides of the cytoplasmic assembly of the receptor. This location is distinct from but close to the location found for Ca(2+)-CaM, providing a structural basis for efficient switching of CaM between these two positions with the oscillating intracellular Ca(2+) concentration that generates muscle relaxation/contraction cycles. The locations of apoCaM and Ca(2+)-CaM at a critical region for RYR1-dihydropyridine receptor interaction are suggestive of a direct role for CaM in the mechanism of excitation-contraction coupling.
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Samsó et al. (2002) studied Skeletal muscle ryanodine receptor (RyR1) structure. ApoCaM and Ca2+-CaM binding was evaluated on Binding locations on the ryanodine receptor. Cryo-electron microscopy revealed that apoCaM and Ca2+-CaM bind to distinct but neighboring locations on the ryanodine receptor, suggesting a direct role in excitation-contraction coupling.
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