title: Malignant hyperthermia-associated mutations in the S2-S3 cytoplasmic loop of type 1 ryanodine receptor calcium channel impair calcium-dependent inactivation.
abstract: Channel activities of skeletal muscle ryanodine receptor (RyR1) are activated by micromolar Ca2+and inactivated by higher (∼1 mM) Ca2+To gain insight into a mechanism underlying Ca2+-dependent inactivation of RyR1 and its relationship with skeletal muscle diseases, we constructed nine recombinant RyR1 mutants carrying malignant hyperthermia or centronuclear myopathy-associated mutations and determined RyR1 channel activities by [3H]ryanodine binding assay. These mutations are localized in or near the RyR1 domains which are responsible for Ca2+-dependent inactivation of RyR1. Four RyR1 mutations (F4732D, G4733E, R4736W, and R4736Q) in the cytoplasmic loop between the S2 and S3 transmembrane segments (S2-S3 loop) greatly reduced Ca2+-dependent channel inactivation. Activities of these mutant channels were suppressed at 10-100 μM Ca2+, and the suppressions were relieved by 1 mM Mg2+The Ca2+- and Mg2+-dependent regulation of S2-S3 loop RyR1 mutants are similar to those of the cardiac isoform of RyR (RyR2) rather than wild-type RyR1. Two mutations (T4825I and H4832Y) in the S4-S5 cytoplasmic loop increased Ca2+affinities for channel activation and decreased Ca2+affinities for inactivation, but impairment of Ca2+-dependent inactivation was not as prominent as those of S2-S3 loop mutants. Three mutations (T4082M, S4113L, and N4120Y) in the EF-hand domain showed essentially the same Ca2+-dependent channel regulation as that of wild-type RyR1. The results suggest that nine RyR1 mutants associated with skeletal muscle diseases were differently regulated by Ca2+and Mg2+Four malignant hyperthermia-associated RyR1 mutations in the S2-S3 loop conferred RyR2-type Ca2+- and Mg2+-dependent channel regulation.
authors: Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, South Carolina; and.|Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina, and Clemson University, Charleston, South Carolina.
authors: Angela C
authors: AC
authors: Gomez
authors: Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, South Carolina; and.|Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina, and Clemson University, Charleston, South Carolina.
authors: Timothy W
authors: TW
authors: Holford
authors: Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, South Carolina; and yamaguch@musc.edu.|Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina, and Clemson University, Charleston, South Carolina.
authors: Naohiro
authors: N
authors: Yamaguchi
mesh_terms: D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D017136:Ion Transport / Q000235:genetics; D008274:Magnesium / Q000378:metabolism; D008305:Malignant Hyperthermia / Q000235:genetics* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D011485:Protein Binding / Q000235:genetics; D020033:Protein Isoforms / Q000235:genetics; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics* / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D019837:Ryanodine Receptor Calcium Release Channel; D008274:Magnesium; D002118:Calcium
keywords: Ca2+-dependent inactivation; central core disease; centronuclear myopathy; malignant hyperthermia; type-1 ryanodine receptor