Involved in the regulation of endoplasmic reticulum (ER)-mitochondria coupling. Negatively regulates the ER-mitochondria distance and Ca(2+) transfer from ER to mitochondria possibly implicating it in the regulation of apoptosis. May collaborate with RNF183 to restrain BIK protein levels thus regulating apoptotic signaling. Interacts with BIK and RNF183. Interacts with IMMT/MIC60and EMD. Localized to specific membrane structures termed mitochondria-associated membranes (MAMs) which connect the endoplasmic reticulum (ER) and the mitochondria. Also associated with the outer surface of mitochondria at sites that are not in close contact with the ER. The human, porcine and bovine orthologs have a longer N-terminal part.