Key regulator of mitochondrial calcium uniporter (MCU) required to limit calcium uptake by MCU when cytoplasmic calcium is low (PubMed:23409044, PubMed:24560927). MICU1 and MICU2 form a disulfide-linked heterodimer that stimulate and inhibit MCU activity, depending on the concentration of calcium (PubMed:24560927). MICU2 acts as a gatekeeper of MCU that senses calcium level via its EF-hand domains: prevents channel opening at resting Ca(2+), avoiding energy dissipation and cell-death triggering (PubMed:24560927). Heterodimer; disulfide-linked; heterodimerizes with MICU1 (PubMed:23409044, PubMed:24560927). Interacts with MCU (PubMed:23409044). The heterodimer formed with MICU1 associates with MCU at low calcium concentration and dissociates from MCU at high calcium level (By similarity). Component of the uniplex complex, composed of MCU, MCUB, MICU1, MICU2 and EMRE/SMDT1. Predominantly expressed in stomach, intestine, skeletal muscle, kidney, heart, testis, prostate and uterus. The EF-hand domains have high affinity for calcium and act as sensors of mitochondrial matrix calcium levels (PubMed:24560927). It is unclear which EF-hand binds calcium as none of the 4 EF-hand domains seem to contain a canonical calcium-binding site. Belongs to the MICU1 family. MICU2 subfamily.