Ca2+-inactivation of the mammalian ryanodine receptor type 1 in a lipidic environment revealed by cryo-EM

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Abstract

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. Cryo-EM 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 seamless transition from inactivated to closed conformations.

Data availability

The cryo-EM maps and models are available in the EMDB and PDB databases.

The following data sets were generated

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Ashok R Nayak

Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, United States

Competing interests
The authors declare that no competing interests exist.
Montserrat Samsó

Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, United States

For correspondence
montserrat.samso@vcuhealth.org

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-2788-3283

Funding

National Institutes of Health (R01 AR068431)

Montserrat Samsó

Muscular Dystrophy Association (MDA 352845)

Montserrat Samsó

National Institutes of Health (U24 GM116790)

Montserrat Samsó

National Institutes of Health (HSSN261200800001E)

Montserrat Samsó

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Ethics

Animal experimentation: This study was performed in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. All of the animals were handled according to approved institutional animal care and use committee (IACUC) protocol #AD10001029 of Virginia Commonwealth. Animals were deeply anesthetized for tissue harvesting, and every effort was made to minimize suffering.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.