The function of MCUB (mitochondrial calcium uniporter dominant negative subunit beta, Ensembl gene identifier ENSG00000005059) is as follows. Negative regulator of the mitochondrial calcium uniporter (MCU), a channel that mediates calcium uptake into the mitochondrial matrix (PubMed:31533452). MCUB is required to limit mitochondrial calcium overload during stress (PubMed:31533452). Acts as a dominant- negative regulator that displaces MCU from the functional uniplex complex and thereby decreases the association of calcium sensors MICU1 and MICU2, preventing channel gating (PubMed:31533452). Mitochondrial calcium homeostasis plays key roles in mitochondrial metabolism (PubMed:31533452). Acts as an important regulator of mitochondrial metabolism in response to stress in muscle cells: induced in response to fasting, leading to restrict mitochondrial calcium uptake, resulting in reprogramming of mitochondria toward fatty acid oxidation preference (By similarity). Acts as a regulator of macrophage polarization during skeletal muscle regeneration: inhibition of mitochondrial calcium uptake drives differentiation of macrophages with anti-inflammatory profile, promoting the differentiation and fusion of satellite cells (By similarity). {ECO:0000250|UniProtKB:Q810S1, ECO:0000269|PubMed:31533452}.