Key regulator of mitochondrial calcium uniporter (MCU) required for calcium entry into mitochondrion. Plays a direct role in uniporter-mediated calcium uptake via a direct interaction with MCU. Probably involved in the assembly of the membrane components of the uniporter complex (uniplex). Interacts (via coiled coil regions) with MCU; the interaction is direct. Interacts with SMDT1/EMRE; the interaction is direct. Interacts with PPIF. Conditional knockout mice lacking Mcur1 in cardiomyocytes and endothelial cells are viable and are born at the expected Mendelian. They however show impaired mitochondrial calcium uptake and mitochondrial calcium uniporter (MCU) current. Belongs to the CCDC90 family.