Structure of the rabbit ryanodine receptor RyR1 at near-atomic resolution

Abstract

The ryanodine receptors (RyRs) are high-conductance intracellular Ca2+ channels that play a pivotal role in the excitation-contraction coupling of skeletal and cardiac muscles. RyRs are the largest known ion channels, with a homotetrameric organization and approximately 5000 residues in each protomer. Here we report the structure of the rabbit RyR1 in complex with its modulator FKBP12 at an overall resolution of 3.8 Å, determined by single-particle electron cryo-microscopy. Three previously uncharacterized domains, named Central, Handle, and Helical domains, display the armadillo repeat fold. These domains, together with the amino-terminal domain, constitute a network of superhelical scaffold for binding and propagation of conformational changes. The channel domain exhibits the voltage-gated ion channel superfamily fold with distinct features. A negative charge-enriched hairpin loop connecting S5 and the pore helix is positioned above the entrance to the selectivity filter vestibule. The four elongated S6 segments form a right-handed helical bundle that closes the pore at the cytoplasmic border of the membrane. Allosteric regulation of the pore by the cytoplasmic domains is mediated through extensive interactions between the Central domains and the channel domain. These structural features explain high ion conductance by RyRs and the long-range allosteric regulation of channel activities.

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.…”

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.…”

“…Here the answer highly depends on the vantage point, because Bai et al have shown that there are multiple possible conformations in the cytosolic cap for a closed channel [7]. Using the previously reported 3.8 Å structure of closed RyR1 as a reference [2], Wei et al describe the movements of the cap as a large breathing motion, with an increase in the width and height of the cytosolic cap (Figure 1). The socalled central domain plays the role of 'relay', linking these movements to the U-motif and thus the TM region.…”

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

“…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.…”