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Wang X , Wang Y , Zhou Y , Hendron E , Mancarella S , Andrake MD , Rothberg BS , Soboloff J , Gill DL
Distinct Orai-coupling domains in STIM1 and STIM2 define the Orai-activating site
Nat Commun. 2014 Feb 4;5 :3183
PMID: 24492416    PMCID: PMC 3995141   
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STIM1 and STIM2 are widely expressed endoplasmic reticulum (ER) Ca(2+) sensor proteins able to translocate within the ER membrane to physically couple with and gate plasma membrane Orai Ca(2+) channels. Although they are structurally similar, we reveal critical differences in the function of the short STIM-Orai-activating regions (SOAR) of STIM1 and STIM2. We narrow these differences in Orai1 gating to a strategically exposed phenylalanine residue (Phe-394) in SOAR1, which in SOAR2 is substituted by a leucine residue. Remarkably, in full-length STIM1, replacement of Phe-394 with the dimensionally similar but polar histidine head group prevents both Orai1 binding and gating, creating an Orai1 non-agonist. Thus, this residue is critical in tuning the efficacy of Orai activation. While STIM1 is a full Orai1-agonist, leucine-replacement of this crucial residue in STIM2 endows it with partial agonist properties, which may be critical for limiting Orai1 activation stemming from its enhanced sensitivity to store-depletion.
Wang, Xizhuo Wang, Youjun Zhou, Yandong Hendron, Eunan Mancarella, Salvatore Andrake, Mark D Rothberg, Brad S Soboloff, Jonathan Gill, Donald L England Nat Commun. 2014 Feb 4;5:3183. doi: 10.1038/ncomms4183.