Omnitemporal choreographies of all five STIM/Orai and IP(3)Rs underlie the complexity of mammalian Ca(2+) signaling

Stromal-interaction molecules (STIM1/2) sense endoplasmic reticulum (ER) Ca(2+) depletion and activate Orai channels. However, the choreography of interactions between native STIM/Orai proteins under physiological agonist stimulation is unknown. We show that the five STIM1/2 and Orai1/2/3 proteins are non-redundant and function together to ensure the graded diversity of mammalian Ca(2+) signaling. Physiological Ca(2+) signaling requires functional interactions between STIM1/2, Orai1/2/3, and IP(3)Rs, ensuring that receptor-mediated Ca(2+) release is tailored to Ca(2+) entry and nuclear factor of activated T cells (NFAT) activation. The N-terminal Ca(2+)-binding ER-luminal domains of unactivated STIM1/2 inhibit IP(3)R-evoked Ca(2+) release. A gradual increase in agonist intensity and STIM1/2 activation relieves IP(3)R inhibition. Concomitantly, activated STIM1/2 C termini differentially interact with Orai1/2/3 as agonist intensity increases. Thus, coordinated and omnitemporal functions of all five STIM/Orai and IP(3)Rs translate the strength of agonist stimulation to precise levels of Ca(2+) signaling and NFAT induction, ensuring the fidelity of complex mammalian Ca(2+) signaling.