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Abstract

Here we present the determination of the three-dimensional structure of the skeletal muscle Ca²⁺-release channel in an open state using electron cryomicroscopy and angular reconstitution. In contrast to our reconstruction of the channel in its closed state, the density map of the channel driven towards its open state, by the presence of Ca²⁺ and ryanodine, features a central opening in the transmembrane region—the likely passageway for Ca²⁺ ions from the sarcoplasmic reticulum to the cytosol. The opening of the channel is associated with a 4° rotation of its transmembrane region with respect to its cytoplasmic region, and with significant mass translocations within the entire cytoplasmic region of the channel tetramer.