Fig. 2.

The mitochondrial Ca²⁺ uniporter is a complex composed of pore-forming proteins (comprising the channel subunit MCU, the dominant-negative subunit of the channel MCUb, and the short transmembrane regulator EMRE) and of regulatory proteins (MICU1 and MICU2). Both MICU1 and MICU2 contain EF-hand domains facing the intermembrane space. By sensing IMS [Ca²⁺], MICU1 and MICU2 coordinately regulate both the threshold and the cooperativity of channel opening