The sigma-1 receptor, one of two sigma receptor subtypes, is a chaperone protein at the endoplasmic reticulum that modulates calcium signaling through the IP3 receptor. In humans, the σ₁ receptor is encoded by the SIGMAR1 gene.
The σ₁ receptor is a transmembrane protein expressed in many different tissue types. It is particularly concentrated in certain regions of the central nervous system. From Wikipedia
