Plays a role in mediating store-operated Ca(2+) entry (SOCE), a Ca(2+) influx following depletion of intracellular Ca(2+) stores (By similarity). Acts as Ca(2+) sensor in the endoplasmic reticulum via its EF-hand domain. Upon Ca(2+) depletion, translocates from the endoplasmic reticulum to the plasma membrane where it activates the Ca(2+) release-activated Ca(2+) (CRAC) channel subunit ORAI1 (PubMed:16208375). Involved in enamel formation (By similarity). Activated following interaction with STIMATE, leading to promote STIM1 conformational switch (By similarity). Monomer in the presence of Ca(2+). It oligomerizes in absence of Ca(2+). Forms homooligomers and heterooligomers with STIM2. Interacts (via the transmembrane region and the SOAR/CAD domain) with SPPL3; the interaction promotes the binding of STIM1 to ORAI1. Interacts with ORAI1. Interacts with MAPRE1; probably required for targeting to the growing microtubule plus ends. Interacts with CRACR2A/EFCAB4B; the interaction is direct and takes place in absence of Ca(2+). Forms a complex with CRACR2A/EFCAB4B and ORAI1 at low concentration of Ca(2+), the complex dissociates at elevated Ca(2+) concentrations. Interacts with SARAF, promoting a slow inactivation of STIM1-dependent SOCE activity, possibly by facilitating the deoligomerization of STIM1 (By similarity). Interacts with EFHB; the interaction takes place upon Ca(2+)-store depletion and inhibits the association with SARAF (By similarity). Interacts with ASPH. Interacts with SLC35G1; intracellular Ca(2+)-dependent. May interact with ATP1A1, ATP2A2, ATP2B1, ATP2B4, KPNB1 and XPO1; through SLC35G1. Interacts with TMEM203. Interacts with STIMATE, promoting STIM1 conformational switch (By similarity). Interacts with TMEM178A (By similarity). Interacts with CASQ1 (via C-terminal end and preferentially with the monomeric form); this interaction increases in response to a depletion of intracellular Ca(2+), decreases both STIM1 aggregation and clustering, interaction of STIM1 with ORAI1 and store-operated Ca(2+) entry (SOCE) activity (By similarity). Interacts with ADCY8 (By similarity). Translocates from the endoplasmic reticulum to the cell membrane in response to a depletion of intracellular calcium and is detected at punctae corresponding to junctions between the endoplasmic reticulum and the cell membrane. Associated with the microtubule network at the growing distal tip of microtubules. Colocalizes with ORAI1 at the cell membrane. Colocalizes preferentially with CASQ1 at endoplasmic reticulum in response to a depletion of intracellular calcium (By similarity). The microtubule tip localization signal (MtLS) motif; mediates interaction with MAPRE1 and targeting to the growing microtubule plus ends. The STIM1 Orai1-activating region/CRAC-activating domain (SOAR/CAD) mediates interaction with ORAI1 to activate the channel. Glycosylation is required for cell surface expression. Phosphorylated predominantly on Ser residues.