A 37-Amino Acid Sequence in the Skeletal Muscle Ryanodine Receptor Interacts with the Cytoplasmic Loop between Domains II and III in the Skeletal Muscle Dihydropyridine Receptor *

Interactions between the Ca 2+ release channel of skeletal muscle sarcoplasmic reticulum (ryanodine receptor or RyR1) and the loop linking domains II and III (II-III loop) of the skeletal muscle l -type Ca 2+ channel (dihydropyridine receptor or DHPR) are critical for excitation-contraction coupling in skeletal muscle. The DHPR II-III loop was fused to glutathione S -transferase- or His-peptide and used as a protein affinity column for 35 S-labeled in vitro translated fragments from the N-terminal three-fourths of RyR1. RyR1 residues Leu 922 –Asp 1112 bound specifically to the DHPR II-III loop column, but the corresponding fragment from the cardiac ryanodine receptor (RyR2) did not. The use of chimeras between RyR1 and RyR2 localized the interaction to 37 amino acids, Arg 1076 –Asp 1112, in RyR1. The RyR1 922–1112 fragment did not bind to the cardiac DHPR II-III loop but did bind to the skeletal muscle Na + channel II-III loop. The skeletal DHPR II-III loop double mutant K677E/K682E lost most of its capacity to interact with RyR1, suggesting that two positively charged residues are important in the interaction between RyR and DHPR.