Both the STIM1-Orai1 interaction as well as the molecular rearrangements in Orai1 are altered by two powerful modulators of CRAC channel activity: extracellular Ca(2+) and 2-APB.     ///    These studies identify a STIM1-dependent conformational change in Orai1 during the activation of CRAC channels and reveal that STIM1-Orai1 interaction and the downstream Orai1 conformational change can be independently modulated to fine-tune CRAC channel activity..     ///    STIM1-Orai1 interactions and Orai1 conformational changes revealed by live-cell FRET microscopy.. 