Key regulator of mitochondrial calcium uniporter (MCU) required to limit calcium uptake by MCU when cytoplasmic calcium is low (PubMed:24503055, PubMed:24560927, PubMed:26903221). 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 calcium, avoiding energy dissipation and cell-death triggering (PubMed:24560927). Heterodimer; disulfide-linked; heterodimerizes with MICU1 (PubMed:24560927). Interacts with MCU (PubMed:26341627). The heterodimer formed with MICU1 associates with MCU at low calcium concentration and dissociates from MCU at high calcium level (PubMed:26387864). Component of the uniplex complex, composed of MCU, MCUB, MICU1, MICU2 and EMRE/SMDT1 (PubMed:24231807). The EF-hand domains have high affinity for calcium and act as sensors of mitochondrial matrix calcium levels (PubMed:24503055). 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. Truncated N-terminus.