May function in lipid transport from the endoplasmic reticulum and be involved in a wide array of cellular functions probably through regulation of the biogenesis of lipid microdomains at the plasma membrane. May regulate calcium efflux at the endoplasmic reticulum (By similarity). Homotrimer (By similarity). During interphase, detected at the inner and outer nuclear membrane and the endoplasmic reticulum. Detected on cytoplasmic vesicles during mitosis (By similarity). Targeted to lipid droplets, cholesterol and galactosylceramide-enriched domains of the endoplasmic reticulum (By similarity). The C-terminal helices form a flat, hydrophobic surface that is probably tightly associated with the cytosolic surface of the endoplasmic reticulum membrane. Sigma receptors are classified into two subtypes (Sigma-1 and Sigma-2) based on their different pharmacological profile. Belongs to the ERG2 family.