The Ca2+-Dependent Release of the Mia40-Induced MICU1-MICU2 Dimer from MCU Regulates Mitochondrial Ca2+ Uptake

Abstract

The essential oxidoreductase Mia40/CHCHD4 mediates disulfide bond formation and protein folding in the mitochondrial intermembrane space. Here, we investigated the interactome of Mia40 thereby revealing links between thiol-oxidation and apoptosis, energy metabolism, and Ca(2+) signaling. Among the interaction partners of Mia40 is MICU1-the regulator of the mitochondrial Ca(2+) uniporter (MCU), which transfers Ca(2+) across the inner membrane. We examined the biogenesis of MICU1 and find that Mia40 introduces an intermolecular disulfide bond that links MICU1 and its inhibitory paralog MICU2 in a heterodimer. Absence of this disulfide bond results in increased receptor-induced mitochondrial Ca(2+) uptake. In the presence of the disulfide bond, MICU1-MICU2 heterodimer binding to MCU is controlled by Ca(2+) levels: the dimer associates with MCU at low levels of Ca(2+) and dissociates upon high Ca(2+) concentrations. Our findings support a model in which mitochondrial Ca(2+) uptake is regulated by a Ca(2+)-dependent remodeling of the uniporter complex.

The EF-Hand Ca2+ Binding Protein MICU Choreographs Mitochondrial Ca2+ Dynamics in Arabidopsis

“…The role of MCUC components in regulating intracellular Ca 2+ levels has been investigated in several studies employing forward and reverse genetics in mammalian cells (Mallilankaraman et al, 2012a;Csordás et al, 2013;Pan et al, 2013;Logan et al, 2014;Patron et al, 2014;Petrungaro et al, 2015). Nevertheless, the critical step toward the bona fide in vivo situation, i.e., assessing Ca 2+ responses in the intact tissue of a multicellular organism such as a living, anesthetized mouse (Breckwoldt et al, 2014), has not been made.…”

“…Upon a rise in free Ca 2+ levels of the cytosol/IMS, specific EF-hands of MICU bind Ca 2+ ( Figures 1C and 1D). This may partially overcome the inhibitory effect of MICU on the pore by a conformational change and/or by dissociation (Petrungaro et al, 2015). In the absence of MICU, the pore lacks stringent sealing, resulting in steady leakage of Ca 2+ from the IMS into the matrix.…”

“…This inhibitory function that sets a threshold for flux through the MCU pore has since been refined and is now specifically attributed to the MICU1 paralog MICU2 Patron et al, 2014). The impact of MICU1 on baseline Ca 2+ levels may be due to the fact that MICU1 forms a heterodimer, stabilizing MICU2 and mediating its interaction with the MCU pore multimer (Harrington and Murphy, 2015;Petrungaro et al, 2015). Thus, increased matrix Ca 2+ levels upon loss of MICU in Arabidopsis (Figures 5 and 6) resemble the functional impact of either MICU1 or MICU2 removal in mammalian cells.…”

Mitochondrial Proteins Containing Coiled-Coil-Helix-Coiled-Coil-Helix (CHCH) Domains in Health and Disease

“…In human cells, the import of MICU1 in the IMS 379 requires an N-terminal targeting sequence while its interaction with CHCHD4 and cysteine 380 oxidation are secondary to its membrane potential-dependent import [130]. This latter 381 example underscores the versatile implication of the Mia40/CHCHD4 system in multiple 382 distinct import pathways.…”

“…Yet another type of Mia40/CHCHD4 substrate is represented by MICU1, a mitochondrial 378 regulator of the Ca 2+ uniporter (MCU) [130]. In human cells, the import of MICU1 in the IMS 379 requires an N-terminal targeting sequence while its interaction with CHCHD4 and cysteine 380 oxidation are secondary to its membrane potential-dependent import [130].…”