A 37-AMINO ACID SEQUENCE IN THE SKELETAL-MUSCLE RYANODINE RECEPTOR INTERACTS WITH THE CYTOPLASMIC LOOP BETWEEN DOMAIN-II AND DOMAIN-III IN THE SKELETAL-MUSCLE DIHYDROPYRIDINE RECEPTOR

Interactions between the Ca2+ release channel of skeletal muscle sarco plasmic reticulum (ryanodine receptor or RyR1) and the loop linking do mains II and III (II-III loop) of the skeletal muscle L-type Ca2+ chan nel (dihydropyridine receptor or DHPR) are critical for excitation-con traction coupling in skeletal muscle. The DHPR II-III loop was fused t o glutathione S-transferase-or His-peptide and used as a protein affin ity column for S-35-labeled in vitro translated fragments from the N-t erminal three-fourths of RyR1. RyR1 residues Leu(922)-Asp(1112) bound specifically to the DHPR II-III loop column, but the corresponding fra gment from the cardiac ryanodine receptor (RS RS) did not. The use of chimeras between RyR1 and RyR2 localized the interaction to 37 amino a cids, 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 mus cle Na+ channel II-III loop. The skeletal DHPR II-III loop double muta nt K677E/K682E lost most of its capacity to interact with RyR1, sugges ting that two positively charged residues are important in the interac tion between RyR and DHPR.