Calcium sensor of the mitochondrial calcium uniporter (MCU) channel, which senses calcium level via its EF-hand domains (PubMed:24503055, PubMed:24560927, PubMed:26903221, PubMed:28615291, PubMed:30699349, PubMed:31397067, PubMed:32494073, PubMed:32667285, PubMed:32762847, PubMed:32790952). MICU1 and MICU2 form a disulfide- linked heterodimer that stimulates and inhibits MCU activity, depending on the concentration of calcium (PubMed:24560927, PubMed:26903221, PubMed:28615291, PubMed:30699349, PubMed:31397067, PubMed:32148862, PubMed:32494073, PubMed:32667285, PubMed:32762847, PubMed:32790952). At low calcium levels, MICU1 occludes the pore of the MCU channel, preventing mitochondrial calcium uptake (PubMed:32494073, PubMed:32667285, PubMed:32762847). At higher calcium levels, calcium- binding to MICU1 and MICU2 induces a conformational change that weakens MCU-MICU1 interactions and moves the MICU1-MICU2 heterodimer away from the pore, allowing calcium permeation through the MCU channel (PubMed:32494073, PubMed:32667285, PubMed:32762847). {ECO:0000269|PubMed:24503055, ECO:0000269|PubMed:24560927, ECO:0000269|PubMed:26903221, ECO:0000269|PubMed:28615291, ECO:0000269|PubMed:30699349, ECO:0000269|PubMed:31397067, ECO:0000269|PubMed:32148862, ECO:0000269|PubMed:32494073, ECO:0000269|PubMed:32667285, ECO:0000269|PubMed:32762847, ECO:0000269|PubMed:32790952}. This is the function of ENSG00000165487 (MICU2, mitochondrial calcium uptake 2).