Coupling of RYR1 and L-type Calcium Channels via Calmodulin Binding Domains

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Abstract
In skeletal muscle the L-type Ca2+ channel directly controls the opening of the sarcoplasmic reticulum Ca2+ release channel (RYR1), and RYR1, in turn, prevents L-type Ca2+ channel inactivation. We demonstrate that the two proteins interact using calmodulin binding regions of both proteins. A recombinant protein representing amino acids 1393–1527 (D1393–1527) of the carboxyl-terminal tail of the skeletal muscle L-type voltage-dependent calcium channel binds Ca2+, Ca2+ calmodulin, and apocalmodulin. In the absence of calmodulin, D1393–1527 binds to both RYR1 and a peptide representing the calmodulin binding site of RYR1 (amino acids 3609–3643). In addition, biotinylated R3609–3643 peptide can be used with streptavidin beads to pull down [3H]PN200–110-labeled L-type channels from detergent-solubilized transverse tubule membranes. The binding of the L-type channel carboxyl-terminal tail to the calmodulin binding site on RYR1 may stabilize the contact between the two proteins, provide a mechanism for Ca2+ and/or calmodulin regulation of their interaction, or participate directly in functional signaling between these two proteins. A unique aspect of this study is the finding that calmodulin binding sequences can serve as specific binding motifs for proteins other than calmodulin.