Abstract
STIM1 and STIM2 are dynamic transmembrane endoplasmic reticulum Ca(2+) sensors, coupling directly to activate plasma membrane Orai Ca(2+) entry channels. Despite extensive sequence homology, the STIM proteins are functionally distinct. We reveal that the short variable N-terminal random coil sequences of STIM1 and STIM2 confer profoundly different activation properties. Using Orai1-expressing HEK293 cells, chimeric replacement of the 43-amino-acid STIM1 N terminus with that of STIM2 attenuates Orai1-mediated Ca(2+) entry and drastically slows store-induced Orai1 channel activation. Conversely, the 55-amino-acid STIM2 terminus substituted within STIM1 strikingly enhances both Orai1-mediated Ca(2+) entry and constitutive coupling to activate Orai1 channels. Hence, STIM N termini are powerful coupling modifiers, functioning in STIM2 to "brake" the otherwise constitutive activation of Orai1 channels afforded by its high sensitivity to luminal Ca(2+).
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Blotting, Western
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Calcium / metabolism
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Calcium Channels / genetics
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Calcium Channels / physiology*
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Cell Adhesion Molecules / chemistry
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Cell Adhesion Molecules / genetics
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Cell Adhesion Molecules / metabolism*
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Cell Line
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Humans
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Kinetics
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Membrane Potentials
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Membrane Proteins / chemistry
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Membrane Proteins / genetics
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Membrane Proteins / metabolism*
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Neoplasm Proteins / chemistry
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Neoplasm Proteins / genetics
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Neoplasm Proteins / metabolism*
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ORAI1 Protein
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Patch-Clamp Techniques
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Stromal Interaction Molecule 1
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Stromal Interaction Molecule 2
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Transfection
Substances
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Calcium Channels
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Cell Adhesion Molecules
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Membrane Proteins
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Neoplasm Proteins
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ORAI1 Protein
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ORAI1 protein, human
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Recombinant Fusion Proteins
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STIM1 protein, human
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STIM2 protein, human
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Stromal Interaction Molecule 1
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Stromal Interaction Molecule 2
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Calcium