The pore structure of the closed RyR1 channel.

Using single particle electron cryomicroscopy, several helices in the membrane-spanning region of RyR1, including an inner transmembrane helix, a short pore helix, and a helix parallel to the membrane on the cytoplasmic side, have been clearly resolved. Our model places a highly conserved glycine (G4934) at the hinge position of the bent inner helix and two rings of negative charges at the luminal and cytoplasmic mouths of the pore. The kinked inner helix closely resembles the inner helix of the open MthK channel, suggesting that kinking alone does not open RyR1, as proposed for K+ channels.