Ca²⁺ flux across the mitochondrial inner membrane regulates bioenergetics, cytoplasmic Ca²⁺ signals and activation of cell death pathways¹. Mitochondrial Ca²⁺ uptake occurs at regions of close apposition with intracellular Ca²⁺ release sites driven by the inner membrane voltage generated by oxidative phosphorylation and mediated by a Ca²⁺ selective ion channel called the uniporter^2,3. Mitochondrial calcium uniporter (MCU) was recently identified as an ion-conducting pore⁴. MCUR1 (mitochondrial calcium uniporter regulator 1), belongs to the CCDC90 family, an integral membrane protein required for MCU-dependent mitochondrial Ca²⁺ uptake. MCUR1 binds to MCU and regulates ruthenium-red-sensitive MCU-dependent Ca²⁺ uptake⁵.

MCUR1 contains two transmembrane helices, where the N- and the short C-termini are exposed to the inter-membrane space⁵.

MCUR1 is ubiquitously expressed in mammalian tissues including: skeletal muscle, brain, heart, lung, liver, kidney, large intenstine and spleen⁵.

It was found that cells depleted of MCUR1 have abnormal bioenergetic properties similar to those observed in cells in which Ca²⁺ uptake is blocked. Thus, MCUR1 is necessary for MCU to efficiently promote mitochondrial Ca²⁺ uptake and to ensure normal mitochondrial bioenergetics⁵.