High Resolution Structure of the Membrane Embedded Skeletal Muscle Ryanodine Receptor

The type 1 ryanodine receptor (RyR1)/calcium release channel on the sarcoplasmic reticulum (SR) is required for skeletal muscle excitation-contraction coupling and is the largest known ion channel, comprised of four 565 kDa protomers. Cryogenic electron microscopy (cryoEM) studies of the RyR have primarily used detergent to solubilize the channel; in the present study, we have used cryoEM to solve high-resolution structures of the channel in liposomes using a gel-filtration approach with on-column detergent removal to form liposomes and incorporate the channel simultaneously, improving the incorporation rate by >20-fold compared to a dialysis-based approach. This allowed us to resolve the structure of the channel in the closed and open states at 3.36 and 3.98 A, respectively. This method offers validation for detergent-based structures of the RyR and offers a method for utilizing an electrochemical gradient mimicking the SR, where Ca2+ concentrations are millimolar in the lumen and nanomolar in the cytosol.