Structural characterization of the N-terminal domain of the Dictyostelium discoideum mitochondrial calcium uniporter

AbstractThe mitochondrial calcium uniporter (MCU) plays a critical role in the mitochondrial calcium uptake into the matrix. In metazoans, the uniporter is a tightly regulated multi-component system including the pore-forming subunit MCU and several regulators (MICU1, MICU2, EMRE). The calcium-conducting activity of metazoan MCU requires the single-transmembrane protein EMRE. Dictyostelium discoideum (Dd), however, developed a simplified uniporter for which the pore-forming MCU (DdMCU) alone is necessary and sufficient for calcium influx. Here, we report a crystal structure of the N-terminal domain (NTD) of DdMCU at 1.7 Å resolution. The DdMCU-NTD contains four helices and two strands arranged in a fold that is completely different from the known structures of other MCU-NTD homologs. Biochemical and biophysical analyses of DdMCU-NTD in solution indicated that the domain exists as oligomers, most probably as a pentamer or hexamer. Mutagenesis showed that the acidic residues Asp60, Glu72 and Glu74, which appeared to mediate the parallel interface as observed in the crystal structure, participated in the self-assembly of DdMCU-NTD. Intriguingly, the oligomeric complex readily dissociated to lower-order oligomers in the presence of calcium. We propose that the calcium-triggered dissociation of NTD regulates the channel activity of DdMCU by a yet unknown mechanism.

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Structural Characterization of the N-Terminal Domain of the Dictyostelium discoideum Mitochondrial Calcium Uniporter

ACS Omega ◽

10.1021/acsomega.9b04045 ◽

2020 ◽

Vol 5 (12) ◽

pp. 6452-6460 ◽

Cited By ~ 1

Author(s):

Yuan Yuan ◽

Chan Cao ◽

Maorong Wen ◽

Min Li ◽

Ying Dong ◽

...

Keyword(s):

Dictyostelium Discoideum ◽

Structural Characterization ◽

Mitochondrial Calcium ◽

Mitochondrial Calcium Uniporter ◽

Terminal Domain ◽

Calcium Uniporter

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Abstract 513: Emre Regulates the Mitochondrial Calcium Uniporter in vivo

Circulation Research ◽

10.1161/res.127.suppl_1.513 ◽

2020 ◽

Vol 127 (Suppl_1) ◽

Author(s):

Julia C Liu ◽

Nicole Syder ◽

Nima Ghorashi ◽

Thomas B Willingham ◽

Randi J Parks ◽

...

Keyword(s):

Ischemia Reperfusion Injury ◽

Transmembrane Protein ◽

Ischemia Reperfusion ◽

Strenuous Exercise ◽

Mitochondrial Calcium ◽

Mitochondrial Calcium Uniporter ◽

Isolated Mitochondria ◽

Mendelian Genetics ◽

Calcium Uniporter

Mitochondrial uptake of Ca 2+ plays critical roles in cardiac energy production as well as cell death. The mitochondrial calcium uniporter in mice and humans is a multi-protein complex that includes the channel-forming protein MCU and several other subunit proteins, including EMRE. EMRE is a single transmembrane protein that is conserved among metazoan species and is known to be essential for mitochondrial Ca 2+ uptake in cell culture. To investigate EMRE’s role in organismal physiology, we generated a mouse model of global germline EMRE deletion. We show that EMRE is indeed required for mitochondrial calcium uniporter function in isolated mitochondria from multiple tissues. Although the birth rate of Emre -/- mice is lower than expected by Mendelian genetics (~5-10% instead of ~25%), the mice that are born are viable and appear healthy. Oxygen consumption in isolated mitochondria and cells is not significantly affected by loss of EMRE, and similarly the mice do not exhibit overt metabolic impairment, even under strenuous exercise. No significant differences between Emre -/- and wild-type ( WT ) cardiac function at baseline and after isoproterenol stimulation are evident by echocardiography. Moreover, Emre -/ - hearts are not protected from ischemia/reperfusion injury in a Langendorff perfusion model (mean infarct area 61% in Emre -/- hearts; 57% in WT ). Collectively, these data and their similarities to results found via germline Mcu deletion demonstrate that EMRE is indeed essential for mitochondrial Ca 2+ uptake in vivo. Furthermore, we find evidence that EMRE protein expression is elevated in some mouse muscular dystrophy models, suggesting that modulation of EMRE levels may play a role in regulating uniporter activity in conditions of stress or disease. We therefore further explore whether and how EMRE expression changes with isoproterenol-induced cardiac hypertrophy in mice and in samples from human patients with heart failure. Understanding of how uniporter components such as EMRE can regulate MCU in a diseased state can inform better therapeutic strategies aimed at restoring mitochondrial metabolic homeostasis.

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