MICU1 controls cristae junction and spatially anchors mitochondrial Ca2+ uniporter complex

Abstract

Recently identified core proteins (MICU1, MCU, EMRE) forming the mitochondrial Ca 2+ uniporter complex propelled investigations into its physiological workings. Here, we apply structured illumination microscopy to visualize and localize these proteins in living cells. Our data show that MICU1 localizes at the inner boundary membrane (IBM) due to electrostatic interaction of its polybasic domain. Moreover, this exclusive localization of MICU1 is important for the stability of cristae junctions (CJ), cytochrome c release and mitochondrial membrane potential. In contrast to MICU1, MCU and EMRE are homogeneously distributed at the inner mitochondrial membrane under resting conditions. However, upon Ca 2+ elevation MCU and EMRE dynamically accumulate at the IBM in a MICU1-dependent manner. Eventually, our findings unveil an essential function of MICU1 in CJ stabilization and provide mechanistic insights of how sophistically MICU1 controls the MCU-Complex while maintaining the structural mitochondrial membrane framework.

Visualization of Sirtuin 4 Distribution between Mitochondria and the Nucleus, Based on Bimolecular Fluorescence Self-Complementation

“…We observed similar patterns of fluorescent mitochondria with a dark lumen upon expression of a super-enhanced cyan FP (seCFP) variant fused to an efficient OMM targeting peptide, derived from outer mitochondrial protein 25 (OMP25, Supplementary Figure S2b) [73]. Co-staining of cells expressing Sirt4-sfGFP with MitoTracker TM Red FM, which integrates into the inner mitochondrial membrane (IMM) [74], resulted in low levels of colocalization between the green and red mitochondrial fluorescence, respectively (Supplementary Figure S2c). These data indicate the localization of Sirt4-sfGFP exclusively at the OMM but not in the mitochondrial matrix.…”

Strongly coupled transmembrane mechanisms control MCU-mediated mitochondrial Ca2+uptake

“…Whereas transient elevations of [Ca 2+ ]m promote enhanced ATP production to support cellular energy demands, failure to maintain low matrix [Ca 2+ ] may trigger DYm depolarization, and opening of the permeability transition pore (PTP) that can result in cell death. Thus, mitochondrial Ca 2+ uptake must be tightly controlled, but how mitochondrial Ca 2+ uptake through MCU is regulated is controversial (2,3). The MCU channel in metazoans exists as a protein complex comprised of MCU as the tetrameric channel pore-forming subunit (4,5), EMRE, a single-pass transmembrane protein that is essential for channel activity (6)(7)(8), and IMS-localized (but see (9)) Ca 2+ -binding EF hand domain-containing MICU1/2 heterodimers (10-13) that associate with the channel complex by interactions with the carboxyl-terminus of EMRE (14) and with MCU (15,16).…”

“…The MCU channel in metazoans exists as a protein complex comprised of MCU as the tetrameric channel pore-forming subunit (4,5), EMRE, a single-pass transmembrane protein that is essential for channel activity (6)(7)(8), and IMS-localized (but see (9)) Ca 2+ -binding EF hand domain-containing MICU1/2 heterodimers (10-13) that associate with the channel complex by interactions with the carboxyl-terminus of EMRE (14) and with MCU (15,16). In a current model of MCU regulation (but see (2)), MICU1/2 promotes cooperative channel activation in response to Ca 2+ binding by their EF hands, whereas apo-MICU1/2 imposes a threshold [Ca 2+ ]i below which MCU channel activity is inhibited, so-called channel gatekeeping (13,(17)(18)(19)(20)(21).…”

The mRNA Decay Factor CAR-1/LSM14 Regulates Axon Regeneration via Mitochondrial Calcium Dynamics

“…We find that this [Ca 2+ ] mt uptake is completely dependent on MCU-1 and is regulated in complex ways by MICU-1. In cultured mammalian cells, MICU1 localizes to mitochondria [31,[57][58][59] and inhibits MCU function at low [Ca 2+ ] c levels (known as ''gatekeeping''), but at higher [Ca 2+ ] c levels, Ca 2+ binds to MICU1 to stimulate MCU1 opening [33,34,59]. MICU1 therefore can inhibit or promote MCU function depending on the [Ca 2+ ] c level.…”