Molecular determinants of fast Ca2+-dependent inactivation and gating of the Orai channels.
Ca(2+) influx by store-operated Ca(2+) influx channels (SOCs) mediates many cellular functions regulated by Ca(2+), and excessive SOC-mediated Ca(2+) influx is cytotoxic and associated with disease. One form of SOC is the CRAC current that is mediated by Orai channels activated by STIM1. A fundamental property of the native CRAC and of the Orais is fast Ca(2+)-dependent inactivation, which limits Ca(2+) influx to guard against cellular damage. The molecular mechanism of this essential regulatory mechanism is unknown. We report here the fast Ca(2+)-dependent inactivation is mediated by three conserved glutamates in the C termini (CT) of Orai2 and Orai3, which show prominent fast Ca(2+)-dependent inactivation compared with Orai1. Transfer of the CT between the Orais transfers both the extent of channel opening and the mode of fast Ca(2+)-dependent inactivation. Fast Ca(2+)-dependent inactivation of the Orais also requires a domain of STIM1; fragments of STIM1 that efficiently open Orai channels do not evoke fast inactivation unless they include an anionic sequence that is C-terminal to the STIM1-Orai activating region (SOAR). Our studies suggest that Orai CT are necessary and sufficient to control pore opening and uncover the molecular mechanism of fast Ca(2+)-dependent inactivation that has implications for Ca(2+) influx by SOC in physiological and pathological states.
Lee
Kyu Pil
KP
Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
Yuan
Joseph P
JP
Zeng
Weizhong
W
So
Insuk
I
Worley
Paul F
PF
Muallem
Shmuel
S
D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D005971:Glutamates / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D015640:Ion Channel Gating / Q000235:genetics / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018613:Microscopy, Confocal; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D000071740:ORAI1 Protein; D000071741:ORAI2 Protein; D000071737:Stromal Interaction Molecule 1; D014162:Transfection
D015220:Calcium Channels; D005971:Glutamates; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; D000071741:ORAI2 Protein; C514506:ORAI2 protein, human; C522867:Orai3 protein, human; C103530:STIM1 protein, human; D000071737:Stromal Interaction Molecule 1; D049452:Green Fluorescent Proteins; D002118:Calcium
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