Calcium-selective channel required to prevent calcium stores from overfilling, thereby playing a key role in calcium homeostasis. In response to endoplasmic reticulum (ER) overloading, assembles into a homotetramer, forming a functional calcium-selective channel, regulating the calcium content in endoplasmic reticulum store. Component of the multi-pass translocon (MPT) complex that mediates insertion of multi-pass membrane proteins into the lipid bilayer of membranes. The MPT complex takes over after the SEC61 complex: following membrane insertion of the first few transmembrane segments of proteins by the SEC61 complex, the MPT complex occludes the lateral gate of the SEC61 complex to promote insertion of subsequent transmembrane regions. Within the MPT complex, the GEL subcomplex may mediate insertion of transmembrane regions into the membrane.
Subcellular locations: Endoplasmic reticulum membrane, Golgi apparatus membrane
The first transmembrane region is required for localization to the endoplasmic reticulum.