Structure of a mammalian ryanodine receptor

Abstract

Ryanodine receptors (RyRs) mediate 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 MDa complex of the rabbit skeletal muscle type 1 RyR (RyR1), solved by single-particle cryo-electron microscopy at an overall resolution of 4.8 Å. We fitted a polyalanine-level model to all 3939 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 (6TM) 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+.

Ryanodine receptor fragmentation and sarcoplasmic reticulum Ca 2+ leak after one session of high-intensity interval exercise

“…Similarly, FDB fibers displayed decreased, but not absent, SR Ca 2+ release in response to tetanic stimulation at the time when RyR1 was severely fragmented. The channel pore region of RyR1 is located close to the C-terminal of the protein, and even the smallest major fragments (60 kDa) observed 24 h after the HIIT exercise would include the pore (47,48). Our immunostaining experiments on dissociated mouse FDB fibers showed a striated pattern of RyR1 staining at the time of fragmentation, hence indicating the continued presence of functional RyR1 Ca 2+ pores in the SR membrane.…”

The EF-hand Ca2+ Binding Domain Is Not Required for Cytosolic Ca2+ Activation of the Cardiac Ryanodine Receptor

“…On the basis of the near-atomic resolution three-dimensional structure of RyR1, it has been proposed recently that the EF-hand Ca 2ϩ binding domain (Fig. 9) encompasses a Ca 2ϩ sensor or conformational switch that is important for the activation of RyR1 by cytosolic Ca 2ϩ (13)(14)(15). However, the significance of the EF-hand domain in the cytosolic Ca 2ϩ activation of the RyR2 channel is unclear.…”

“…Similarly, Gomez and Yamaguchi (11) have also shown that the EF-hand Ca 2ϩ binding domain in RyR1 is involved in Ca 2ϩ -dependent inactivation. Furthermore, a peptide that encompasses the EF1 and EF2 motifs has been found to bind to the intact RyR1 channel and altered the Ca 2ϩ dependence of [ 3 H]ryanodine binding (12 Recently, the three-dimensional structure of RyR1 has been solved at near-atomic resolutions by using cryo-electron microscopy and single particle analysis (13)(14)(15). These highresolution structures have provided unprecedented insights into the structure-function relationship of Ca 2ϩ regulation of RyR.…”

“…The EF-hand Ca 2ϩ binding domain is located in the central domain. This central domain interacts with the C-terminal domain believed to be involved in channel gating (13)(14)(15). On the basis of the three-dimensional structure of RyR1, it has been proposed that the paired EF-hand Ca 2ϩ binding motifs in RyR1 may function as a Ca 2ϩ sensor or conformational switch important for the activation of RyR1 by cytosolic Ca 2ϩ and, therefore, the mechanism of CICR (13,14 …”

How to open a Ryanodine Receptor

“…With continued improvements in technology, these have culminated in three reports on RyR1 in closed states between 6.1 and 3.8 Å, allowing up to 70% of the structure to be built [2][3][4]. RyRs are clear members of the superfamily of six-transmembrane (6-TM) ion channels, containing a transmembrane region with a pore-forming domain with inner (S5) and outer helices (S6), and a 4-helix bundle (S1-S4) that resembles voltage-sensing domains in voltagegated channels.…”