Structural Insight Into Ryanodine Receptor Channelopathies

Abstract

The ryanodine receptors (RyRs) are large cation-selective ligand-gated channels that are expressed in the sarcoplasmic reticulum (SR) membrane. They mediate the controlled release of Ca2+ from SR and play an important role in many cellular processes. The mutations in RyRs are associated with several skeletal muscle and cardiac conditions, including malignant hyperthermia (MH), central core disease (CCD), catecholaminergic polymorphic ventricular tachycardia (CPVT), and arrhythmogenic right ventricular dysplasia (ARVD). Recent breakthroughs in structural biology including cryo-electron microscopy (EM) and X-ray crystallography allowed the determination of a number of near-atomic structures of RyRs, including wildtype and mutant structures as well as the structures in complex with different modulating molecules. This allows us to comprehend the physiological gating and regulatory mechanisms of RyRs and the underlying pathological mechanisms of the disease-causing mutations. In this review, based on the insights gained from the available high-resolution structures of RyRs, we address several questions: 1) what are the gating mechanisms of different RyR isoforms; 2) how RyRs are regulated by multiple channel modulators, including ions, small molecules, and regulatory proteins; 3) how do disease-causing mutations affect the structure and function of RyRs; 4) how can these structural information aid in the diagnosis of the related diseases and the development of pharmacological therapies.

A dual-targeted drug inhibits cardiac ryanodine receptor Ca2+leak but activates SERCA2a Ca2+uptake

“…The RY1&2 domain was postulated to represent a second ATP binding site in addition to the C-terminal ATP-binding site binding site described at the mutual junction of the S6c (cytoplasmic extension of S6), the CTD (C-terminal domain), and TaF (thumb and forefingers domain) domain (des Georges et al, 2016). In detail, ARM210 reversed the destabilization of the bridging solenoid domain (Hadiatullah et al, 2022) of RyR2 induced by the CPVT-associated RyR2-R2474S mutation thereby stabilizing the closed channel conformation (Miotto et al, 2022). Overall, the mechanism of ARM210 binding to RY1&2 occurred cooperatively together with ATP and stabilized the closed state in the presence of activating ligands (Ca 2+ , ATP, and caffeine) (Melville et al, 2022).…”

Molecular Aspects Implicated in Dantrolene Selectivity with Respect to Ryanodine Receptor Isoforms

“…These mutations are mostly clustered in four hotspots: region I (roughly 80–470 residues), region II (roughly 2250–2550 residues), region III (roughly 3800–4200), and region IV (from around 4500 to the C-terminus) [ 58 , 65 ]. Despite such a strong clustering, the overall distribution pattern of RyR1 and RyR2 mutations appears to be similar (reviewed in [ 11 , 58 , 66 ]), suggesting similar modulatory mechanisms of RyR dysfunctions. The vast majority of almost 170 RyR2 mutations encode for catecholaminergic polymorphic ventricular tachycardia, type 1 (CPVT1) [ 67 , 68 ] and the remaining mutations are mainly associated with arrhythmogenic right ventricular dysplasia, type 2 (ARVC/D2) [ 69 , 70 ] and polymorphic ventricular tachycardia (PVT) [ 71 , 72 ].…”

“…From a structural point of view, a widely held hypothesis states that weakened N terminal-Helical domain1 interactions are a common point in RyR2 dysfunction [ 32 , 192 ]. Although this zipping/unzipping concept seems to be reasonable, more cryo-EM 3D structures of the RyR2 channel with CPVT1 mutations are needed to obtain a more comprehensive view of pathological mechanisms involved [ 66 , 193 ]. Presently, only two works reported conformational changes caused by the CPVT1 mutations R2474S (human numbering) [ 194 ] and R176Q (human numbering) [ 112 ].…”

“…Notably, cell-free studies listed in Table 1 clearly demonstrate that the dantrolene–RyR1 interaction also requires particular RyR1 conformations as the presence of ATP, cytosolic Mg 2+ , and calmodulin together with the increased temperature (35−37 °C) was found to fully drive the channel’s responsiveness to dantrolene. The binding locations of ATP and calmodulin were mapped to the close-transmembrane region and the lateral face of the cytosolic domain, respectively, in the cryo-EM 3D structures (reviewed in [ 66 ]). Apparently, these regions are located far away from the dantrolene-binding site, strongly suggesting that a long-range allosteric coupling is involved in a potentiation of dantrolene’s action.…”

Rapid small-scale nanobody-assisted purification of ryanodine receptors for cryo-EM

“…Ca 2+ release by RyRs is regulated and modulated by interaction with small molecules including Ca 2+ , ATP, caffein and ryanodine 36 , and interaction with proteins among which are FKBP, calmodulin, and S100A 37 . Many but not all of them were structurally mapped by cryo-EM and X-ray crystallography 38 .…”