Module 3: Figure SOC signalling components
Molecular components of store-operated (SOC) Ca2+ entry.
The best characterized store-operated entry channel is Orai1, which has four transmembrane regions with the N- and C-termini facing the membrane where they participate in the conformation-coupling process. The STIM1 protein located in the endoplasmic reticulum (ER) has an EF-hand domain that monitors the level of Ca2+ within the ER lumen. The cytoplasmic domain of STIM1 has a variety of domains that may function in conformational coupling. In response to an increase in inositol 1,4,5-trisphosphate (InsP3) the store empties and STIM1 migrates towards the ER regions facing the plasma membrane where it initiates Ca2+ entry. Some of the proposed coupling mechanisms are described in Module 3: Figure STIM-induced Ca2+ entry.