Endoplasmic reticulum and mitochondria-associated protein that probably functions as a regulator of cellular redox state and thereby regulates protein post-translational modification, protein folding and mitochondrial activity. Indirectly regulates neuronal proliferation, migration, and organization in the developing brain. Monomer (By similarity). Homodimer; disulfide-linked (By similarity). Occurs in both reduced and oxidized monomeric form (By similarity). Oxidative conditions increase homodimerization (By similarity). Interacts with CANX (By similarity). Interacts with ATP2A2 (By similarity). Localizes to endoplasmic reticulum mitochondria-associated membrane (MAMs) that connect the endoplasmic reticulum and the mitochondria. The thioredoxin domain lacks the 2 redox-active cysteines, suggesting that it lacks thioredoxin activity. The di-lysine motif confers endoplasmic reticulum localization for type I membrane proteins.