TY - JOUR TI - Ca2+ inactivation of the mammalian ryanodine receptor type 1 in a lipidic environment revealed by cryo-EM AU - Nayak, Ashok R AU - Samsó, Montserrat A2 - Colecraft, Henry M A2 - Aldrich, Richard W VL - 11 PY - 2022 DA - 2022/03/08 SP - e75568 C1 - eLife 2022;11:e75568 DO - 10.7554/eLife.75568 UR - https://doi.org/10.7554/eLife.75568 AB - Activation of the intracellular Ca2+ channel ryanodine receptor (RyR) triggers a cytosolic Ca2+ surge, while elevated cytosolic Ca2+ inhibits the channel in a negative feedback mechanism. Cryogenic electron microscopy of rabbit RyR1 embedded in nanodiscs under partially inactivating Ca2+ conditions revealed an open and a closed-inactivated conformation. Ca2+ binding to the high-affinity site engages the central and C-terminal domains into a block, which pries the S6 four-helix bundle open. Further rotation of this block pushes S6 toward the central axis, closing (inactivating) the channel. Main characteristics of the Ca2+-inactivated conformation are downward conformation of the cytoplasmic assembly and tightly knit subunit interface contributed by a fully occupied Ca2+ activation site, two inter-subunit resolved lipids, and two salt bridges between the EF hand domain and the S2–S3 loop validated by disease-causing mutations. The structural insight illustrates the prior Ca2+ activation prerequisite for Ca2+ inactivation and provides for a seamless transition from inactivated to closed conformations. KW - rabbit KW - ryanodine receptor KW - inactivation KW - calcium KW - excitation-contraction coupling KW - cryo-electron microscopy JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -