1. Biochemistry and Chemical Biology
  2. Structural Biology and Molecular Biophysics

Cryo-EM structure of the calcium release-activated calcium channel Orai in an open conformation

  1. Xiaowei Hou
  2. Ian R Outhwaite
  3. Leanne Pedi
  4. Stephen Barstow Long  Is a corresponding author
  1. Memorial Sloan Kettering Cancer Center, United States
https://doi.org/10.7554/eLife.62772
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  1. Xiaowei Hou
  2. Ian R Outhwaite
  3. Leanne Pedi
  4. Stephen Barstow Long
(2020)
Cryo-EM structure of the calcium release-activated calcium channel Orai in an open conformation
eLife 9:e62772.
https://doi.org/10.7554/eLife.62772
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Abstract

The calcium release-activated calcium channel Orai regulates Ca2+ entry into non-excitable cells and is required for proper immune function. While the channel typically opens following Ca2+ release from the endoplasmic reticulum, certain pathologic mutations render the channel constitutively open. Previously, using one such mutation (H206A), we obtained low (6.7 Å) resolution X-ray structural information on Drosophila melanogaster Orai in an open conformation (Hou, Burstein, & Long, 2018). Here, we present a structure of this open conformation at 3.3 Å resolution using fiducial-assisted cryo-EM. The improved structure reveals the conformations of amino acids in the open pore, which dilates by outward movements of subunits. A ring of phenylalanine residues repositions to expose previously shielded glycine residues to the pore without significant rotational movement of the associated helices. Together with other hydrophobic amino acids, the phenylalanines act as the channel's gate. Structured M1-M2 turrets, not evident previously, form the channel's extracellular entrance.

Data availability

The cryo-EM map and the atomic model have been deposited in the Electron Microscopy Data Bank (EMDB) and in the Protein Data Bank (PDB) with accession numbers EMD-23002 and 7KR5, respectively.

Article and author information

Author details

  1. Xiaowei Hou

    Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
    Competing interests
    The authors declare that no competing interests exist.

  2. Ian R Outhwaite

    Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-2037-3261

  3. Leanne Pedi

    Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
    Competing interests
    The authors declare that no competing interests exist.

  4. Stephen Barstow Long

    Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
    For correspondence
    longs@mskcc.org
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-8144-1398

Funding

National Institute of General Medical Sciences (R01GM094273)

  • Stephen Barstow Long

National Institute of General Medical Sciences (R35GM131921)

  • Stephen Barstow Long

National Cancer Institute (P30CA008748)

  • Stephen Barstow Long

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

Copyright

© 2020, Hou et al.

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.

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  1. Xiaowei Hou
  2. Ian R Outhwaite
  3. Leanne Pedi
  4. Stephen Barstow Long
(2020)
Cryo-EM structure of the calcium release-activated calcium channel Orai in an open conformation
eLife 9:e62772.
https://doi.org/10.7554/eLife.62772

Share this article

https://doi.org/10.7554/eLife.62772

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Further reading

    1. Biochemistry and Chemical Biology
    2. Structural Biology and Molecular Biophysics

    Structures reveal opening of the store-operated calcium channel Orai

    Xiaowei Hou, Shana R Burstein, Stephen Barstow Long
    Research Article Updated

    The store-operated calcium (Ca2+) channel Orai governs Ca2+ influx through the plasma membrane of many non-excitable cells in metazoans. The channel opens in response to the depletion of Ca2+ stored in the endoplasmic reticulum (ER). Loss- and gain-of-function mutants of Orai cause disease. Our previous work revealed the structure of Orai with a closed pore. Here, using a gain-of-function mutation that constitutively activates the channel, we present an X-ray structure of Drosophila melanogaster Orai in an open conformation. Well-defined electron density maps reveal that the pore is dramatically dilated on its cytosolic side in comparison to the slender closed pore. Cations and anions bind in different regions of the open pore, informing mechanisms for ion permeation and Ca2+ selectivity. Opening of the pore requires the release of cytosolic latches. Together with additional X-ray structures of an unlatched-but-closed conformation, we propose a sequence for store-operated activation.