Malignant hyperthermia-associated mutations in the S2-S3 cytoplasmic loop of type 1 ryanodine receptor calcium channel impair calcium-dependent inactivation

Am J Physiol Cell Physiol. 2016 Nov 1;311(5):C749-C757. doi: 10.1152/ajpcell.00134.2016. Epub 2016 Aug 24.

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.

Keywords: Ca2+-dependent inactivation; central core disease; centronuclear myopathy; malignant hyperthermia; type-1 ryanodine receptor.

MeSH terms

  • Amino Acid Sequence
  • Calcium / metabolism*
  • Cell Line
  • Cytoplasm / genetics
  • Cytoplasm / metabolism*
  • HEK293 Cells
  • Humans
  • Ion Transport / genetics
  • Magnesium / metabolism
  • Malignant Hyperthermia / genetics*
  • Malignant Hyperthermia / metabolism
  • Muscle, Skeletal / metabolism
  • Mutation / genetics*
  • Protein Binding / genetics
  • Protein Isoforms / genetics
  • Ryanodine Receptor Calcium Release Channel / genetics*
  • Ryanodine Receptor Calcium Release Channel / metabolism*

Substances

  • Protein Isoforms
  • Ryanodine Receptor Calcium Release Channel
  • Magnesium
  • Calcium