Dataset Information

Orai channel pore properties and gating by STIM: implications from the Orai crystal structure.

ABSTRACT: The Orai channels are unusual, yet prominent, calcium (Ca2+) signal mediators in most cell types. Orai proteins are structurally unique, having little sequence homology with other ion channels. They are also functionally unique with exceedingly high selectivity for Ca2+, mediating both short-term Ca2+ homeostasis and long-term Ca2+ signals important for transcriptional control. Operating in the plasma membrane (PM), Orai channel regulation is unprecedented among ion channels; channel gating occurs through an elaborate intermembrane coupling with stromal interaction molecule (STIM) proteins in the endoplasmic reticulum (ER). STIM proteins function as sensors of Ca2+ stored in the ER lumen and translocate into ER-PM junctions to tether and activate Orai channels when ER Ca2+ concentration decreases. Crystallization studies reveal an unexpected hexameric structure for the Orai channel and provide important insights into the pore architecture, the structural basis of its unusual cation selectivity, and how channel gating occurs through its coupling with STIM proteins.

SUBMITTER: Rothberg BS

PROVIDER: S-EPMC4746713 | biostudies-literature | 2013 Mar

REPOSITORIES: biostudies-literature

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Orai channel pore properties and gating by STIM: implications from the Orai crystal structure.

Rothberg Brad S BS Wang Youjun Y Gill Donald L DL

Science signaling 20130319 267

The Orai channels are unusual, yet prominent, calcium (Ca2+) signal mediators in most cell types. Orai proteins are structurally unique, having little sequence homology with other ion channels. They are also functionally unique with exceedingly high selectivity for Ca2+, mediating both short-term Ca2+ homeostasis and long-term Ca2+ signals important for transcriptional control. Operating in the plasma membrane (PM), Orai channel regulation is unprecedented among ion channels; channel gating occu ...[more]

PMID: 23512988

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Project description:Ca(2+)-release-activated Ca(2+) (CRAC) channels underlie sustained Ca(2+) signalling in lymphocytes and numerous other cells after Ca(2+) liberation from the endoplasmic reticulum (ER). RNA interference screening approaches identified two proteins, Stim and Orai, that together form the molecular basis for CRAC channel activity. Stim senses depletion of the ER Ca(2+) store and physically relays this information by translocating from the ER to junctions adjacent to the plasma membrane, and Orai embodies the pore of the plasma membrane calcium channel. A close interaction between Stim and Orai, identified by co-immunoprecipitation and by Förster resonance energy transfer, is involved in the opening of the Ca(2+) channel formed by Orai subunits. Most ion channels are multimers of pore-forming subunits surrounding a central channel, which are preassembled in the ER and transported in their final stoichiometry to the plasma membrane. Here we show, by biochemical analysis after cross-linking in cell lysates and intact cells and by using non-denaturing gel electrophoresis without cross-linking, that Orai is predominantly a dimer in the plasma membrane under resting conditions. Moreover, single-molecule imaging of green fluorescent protein (GFP)-tagged Orai expressed in Xenopus oocytes showed predominantly two-step photobleaching, again consistent with a dimeric basal state. In contrast, co-expression of GFP-tagged Orai with the carboxy terminus of Stim as a cytosolic protein to activate the Orai channel without inducing Ca(2+) store depletion or clustering of Orai into punctae yielded mostly four-step photobleaching, consistent with a tetrameric stoichiometry of the active Orai channel. Interaction with the C terminus of Stim thus induces Orai dimers to dimerize, forming tetramers that constitute the Ca(2+)-selective pore. This represents a new mechanism in which assembly and activation of the functional ion channel are mediated by the same triggering molecule.

Dataset Information

Orai channel pore properties and gating by STIM: implications from the Orai crystal structure.

Publications

Orai channel pore properties and gating by STIM: implications from the Orai crystal structure.

Similar Datasets

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