Mitochondria take up Ca 2+ through the mitochondrial calcium uniporter complex to regulate energy production, cytosolic Ca 2+ signaling, and cell death 1 , 2 . In mammals, the uniporter complex (u Show more
Mitochondria take up Ca 2+ through the mitochondrial calcium uniporter complex to regulate energy production, cytosolic Ca 2+ signaling, and cell death 1 , 2 . In mammals, the uniporter complex (uniplex) contains four core components: the pore-forming MCU, gatekeeper MICU1 and MICU2, and an auxiliary EMRE subunit essential for Ca 2+ transport 3 – 8 . To prevent detrimental Ca 2+ overload, the activity of MCU must be tightly regulated by MICUs, which sense the changes in cytosolic Ca 2+ concentrations to switch MCU on and off 9 , 10 . Here, we report cryo-EM structures of human mitochondrial calcium uniporter holocomplex in inhibited and Ca 2+ -activated states. These structures define the architecture of this multi-component Ca 2+ uptake machinery and reveal the gating mechanism by which MICUs control uniporter activity. This work provides a framework for understanding regulated Ca 2+ uptake in mitochondria and lends clues to modulate uniporter activity for treating mitochondrial Ca 2+ overload-related diseases. Show less
Mitochondrial calcium uptake plays critical roles in regulating ATP
production, intracellular calcium signaling, and cell death. This uptake is
mediated by a highly selective calcium channel called th Show more
Mitochondrial calcium uptake plays critical roles in regulating ATP
production, intracellular calcium signaling, and cell death. This uptake is
mediated by a highly selective calcium channel called the mitochondrial calcium
uniporter. Here, we determined the structures of the pore-forming MCU proteins
by X-ray crystallography and single-particle cryo-electron microscopy. The
stoichiometry, overall architecture, and individual subunit structure differed
markedly from those in the recent nuclear magnetic resonance structure of the
Caenorhabditis elegans MCU. In our studies, we observed a dimer-of-dimer
architecture across species and chemical environments, which was corroborated by
biochemical experiments. Structural analyses and functional characterizations
uncovered the roles of critical residues in the pore. These results reveal a new
ion channel architecture, provide insights into calcium coordination,
selectivity, and conduction, and establish a structural framework for
understanding the mechanism of mitochondrial calcium uniporter function. Show less