Structural determinants for activation or inhibition of ryanodine receptors by basic residues in the dihydropyridine receptor II-III loop

The structures of peptide A, and six other 7-20 amino acid peptides corresp onding to sequences in the A region (Thr(671) - Leu(690)) of the skeletal m uscle dihydropyridine receptor II-III loop have been examined, and are corr elated with the ability of the peptides to activate or inhibit skeletal rya nodine receptor calcium release channels. The peptides adopted either rando m coil or nascent helix-like structures, which depended upon the polarity o f the terminal residues as well as the presence and ionisation state of two glutamate residues. Enhanced activation of Ca2+ release from sarcoplasmic reticulum, and activation of current flow through single ryanodine receptor channels (at -40 mV), was seen with peptides containing the basic residues (681)Arg Lys Arg Arg Lys(685), and was strongest when the residues were a part of an alpha -helix. Inhibition of channels (at +40 mV) was also seen w ith peptides containing the five positively charged residues, but was not e nhanced in helical peptides. These results confirm the hypothesis that acti vation of ryanodine receptor channels by the II-III loop peptides requires both the basic residues and their participation in helical structure, and s how for the first time that inhibition requires the basic residues, but is not structure-dependent. These findings imply that activation and inhibitio n result from peptide binding to separate sites on the ryanodine receptor.