Search

RYR1 encodes the type 1 ryanodine receptor, an intracellular calcium release channel (RyR1) on the skeletal muscle sarcoplasmic reticulum (SR). Pathogenic RYR1 variations can destabilize RyR1 leading to calcium leak causing oxidative overload and myopathy. However, the effect of RyR1 leak has not been established in individuals with RYR1-related myopathies (RYR1-RM), a broad spectrum of rare neuromuscular disorders. We sought to determine whether RYR1-RM affected individuals exhibit pathologic, leaky RyR1 and whether variant location in the channel structure can predict pathogenicity. Skeletal muscle biopsies were obtained from 17 individuals with RYR1-RM. Mutant RyR1 from these individuals exhibited pathologic SR calcium leak and increased activity of calcium-activated proteases. The increased calcium leak and protease activity were normalized by ex-vivo treatment with S107, a RyR stabilizing Rycal molecule. Using the cryo-EM structure of RyR1 and a new dataset of > 2200 suspected RYR1-RM affected individuals we developed a method for assigning pathogenicity probabilities to RYR1 variants based on 3D co-localization of known pathogenic variants. This study provides the rationale for a clinical trial testing Rycals in RYR1-RM affected individuals and introduces a predictive tool for investigating the pathogenicity of RYR1 variants of uncertain significance. [ABSTRACT FROM AUTHOR]

Ryanodine receptors (RyRs) mediate the rapid release of calcium (Ca2+) from intracellular stores into the cytosol, which is essential for numerous cellular functions including excitation-contraction coupling in muscle. Lack of sufficient structural detail has impeded understanding of RyR gating and regulation. Here we report the closed-state structure of the 2.3-megadalton complex of the rabbit skeletal muscle type 1 RyR (RyR1), solved by single-particle electron cryomicroscopy at an overall resolution of 4.8 Å. We fitted a polyalanine-level model to all 3,757 ordered residues in each protomer, defining the transmembrane pore in unprecedented detail and placing all cytosolic domains as tertiary folds. The cytosolic assembly is built on an extended α-solenoid scaffold connecting key regulatory domains to the pore. The RyR1 pore architecture places it in the six-transmembrane ion channel superfamily. A unique domain inserted between the second and third transmembrane helices interacts intimately with paired EF-hands originating from the α-solenoid scaffold, suggesting a mechanism for channel gating by Ca2+. [ABSTRACT FROM AUTHOR]

Key points Under conditions of acute adrenergic stress (i.e. fight or flight response), the contractile force of muscle is enhanced, a phenomenon known as inotropy., The molecular determinant of the inotropic mechanism is poorly understood but involves potentiated release of calcium within the muscle cell., Here we report that adrenergic receptor-dependent phosphorylation of a single amino acid in the calcium release channel (ryanodine receptor 1) mediates the increased calcium and force that is seen in the muscle following acute stress., These findings further our understanding of the molecular mechanisms of muscular force regulation, and the importance for exercise physiology and muscle weakness (dynopenia)., Abstract Enhancement of contractile force (inotropy) occurs in skeletal muscle following neuroendocrine release of catecholamines and activation of muscle β-adrenergic receptors. Despite extensive study, the molecular mechanism underlying the inotropic response in skeletal muscle is not well understood. Here we show that phosphorylation of a single serine residue (S2844) in the sarcoplasmic reticulum (SR) Ca2+ release channel/ryanodine receptor type 1 (RyR1) by protein kinase A (PKA) is critical for skeletal muscle inotropy. Treating fast twitch skeletal muscle from wild-type mice with the β-receptor agonist isoproterenol (isoprenaline) increased RyR1 PKA phosphorylation, twitch Ca2+ and force generation. In contrast, the enhanced muscle Ca2+, force and in vivo muscle strength responses following isoproterenol stimulation were abrogated in RyR1-S2844A mice in which the serine in the PKA site in RyR1 was replaced with alanine. These data suggest that the molecular mechanism underlying skeletal muscle inotropy requires enhanced SR Ca2+ release due to PKA phosphorylation of S2844 in RyR1. [ABSTRACT FROM AUTHOR]

A response from the authors of the article "Stress-induced increase in skeletal muscle force requires protein kinase A phosphorylation of the ryanodine receptor" in a 2012 issue of the journal is presented.

Age-dependent loss of body wall muscle function and impaired locomotion occur within 2 weeks in Caenorhabditis elegans (C. elegans); however, the underlying mechanism has not been fully elucidated. In humans, age-dependent loss of muscle function occurs at about 80 years of age and has been linked to dysfunction of ryanodine receptor (RyR)/intracellular calcium (Ca2+) release channels on the sarcoplasmic reticulum (SR). Mammalian skeletal muscle RyR1 channels undergo age-related remodeling due to oxidative overload, leading to loss of the stabilizing subunit calstabin1 (FKBP12) from the channel macromolecular complex. This destabilizes the closed state of the channel resulting in intracellular Ca2+ leak, reduced muscle function, and impaired exercise capacity. We now show that the C. elegans RyR homolog, UNC-68, exhibits a remarkable degree of evolutionary conservation with mammalian RyR channels and similar age-dependent dysfunction. Like RyR1 in mammals, UNC-68 encodes a protein that comprises a macromolecular complex which includes the calstabin1 homolog FKB-2 and is immunoreactive with antibodies raised against the RyR1 complex. Furthermore, as in aged mammals, UNC-68 is oxidized and depleted of FKB-2 in an age-dependent manner, resulting in 'leaky' channels, depleted SR Ca2+ stores, reduced body wall muscle Ca2+ transients, and age-dependent muscle weakness. FKB-2 (ok3007)-deficient worms exhibit reduced exercise capacity. Pharmacologically induced oxidization of UNC-68 and depletion of FKB-2 from the channel independently caused reduced body wall muscle Ca2+ transients. Preventing FKB-2 depletion from the UNC-68 macromolecular complex using the Rycal drug S107 improved muscle Ca2+ transients and function. Taken together, these data suggest that UNC-68 oxidation plays a role in age-dependent loss of muscle function. Remarkably, this age-dependent loss of muscle function induced by oxidative overload, which takes ~2 years in mice and ~80 years in humans, occurs in less than 2-3 weeks in C. elegans, suggesting that reduced antioxidant capacity may contribute to the differences in lifespan among species. [ABSTRACT FROM AUTHOR]

The ryanodine receptor (RyR)/calcium release channel on the sarcoplasmic reticulum (SR) is required for excitation-contraction coupling in skeletal and cardiac muscle. Inherited mutations and stress-induced post-translational modifications result in an SR Ca2+ leak that causes skeletal myopathies, heart failure, and exercise-induced sudden death. A class of therapeutics known as Rycals prevent the RyR-mediated leak, are effective in preventing disease progression and restoring function in animal models, and are in clinical trials for patients with muscle and heart disorders. Using cryogenic-electron microscopy, we present a model of RyR1 with a 2.45-Å resolution before local refinement, revealing a binding site in the RY1&2 domain (3.10 Å local resolution), where the Rycal ARM210 binds cooperatively with ATP and stabilizes the closed state of RyR1. [Display omitted] • High-resolution structure of RyR1 reveals second binding site for ATP • ATP and ARM210 bound simultaneously in binding site located in cytosolic shell • Binding of ARM210 is dependent on ATP and stabilizes closed state of the channel • Unique binding modes between ATP and ADP suggest role as metabolic sensor Melville et al. show the cryo-EM structure of the ARM210-bound ryanodine receptor. The Rycal compound (ARM210) binds cooperatively with ATP in a second ATP-binding site and stabilizes the closed state of the channel. This site may be a metabolic sensor as it binds two ADP but only one ATP. [ABSTRACT FROM AUTHOR]