A calmodulin binding domain of RyR increases activation of spontaneous Ca2+ sparks in frog skeletal muscle.
The calmodulin C lobe binding region (residues 3614-3643) on the sarcoplasmic reticulum Ca2+ release channel (RyR1) is thought to be a region of contact between subunits within RyR1 homotetramer Ca2+ release channels. To determine whether the 3614-3643 region is a regulatory site/interaction domain within RyR in muscle fibers, we have investigated the effect of a synthetic peptide corresponding to this region (R3614-3643) on Ca2+ sparks in frog skeletal muscle fibers. R3614-3643 (0.2-3.0 microM) promoted the occurrence of Ca2+ sparks in a highly cooperative dose-dependent manner, with a half-maximal activation at 0.47 microM and a maximal increase in frequency of approximately 5-fold. A peptide with a single amino acid substitution within R3614-3643 (L3624D) retained the ability to bind Ca(2+)-free calmodulin but did not increase Ca2+ spark frequency, suggesting that R3614-3643 does not modulate Ca2+ sparks by removal of endogenous calmodulin. Our data support a model in which the calmodulin binding domain of RyR1 modulates channel activity by at least two mechanisms: direct binding of calmodulin as well as interactions with other regions of RyR.
Rodney
George G
GG
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
Wilson
Gerald M
GM
Schneider
Martin F
MF
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism*; D011894:Rana pipiens; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry* / Q000502:physiology; D013329:Structure-Activity Relationship
D002147:Calmodulin; D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium