Figure 2. Cryo-EM structure of the human MCU-EMRE super-complex.

A. Dimer of functional MCU tetrameric channels. Each MCU tetramer (cyan) is in complex with four EMRE peptides (blue). The individual MCU channels dimerize via interactions between the N-terminal domains (MCU-NTD; pink). The Asp261 (red sticks) and Glu264 (red sticks) of the DIME motif (indicated) are located closest to the intermembrane space side of each channel. The juxtamembrane loop (magenta spheres) is located on the matrix side of each channel. The residues making up MRAP within each MCU-NTD (red spheres) are localized only between MCU-NTDs within one channel. B. Top view (from the intermembrane space) of a single MCU channel highlighting the pore entrance. The Asp261 and Glu264 sidechains (red sticks) of the DIME motif are directed to the centre axis of the channel. Coordination of a single Ca²⁺ (yellow sphere) is primarily mediated by the Glu264 side chain in this structure. The inner surface of the channel is lined with the TM2 helices, while the TM1 helices pack on the outside of each TM2 helix. Four EMRE peptides are oriented at the periphery of each channel. C. Bottom view (from the matrix) of a single MCU channel highlighting the pore exit. The juxtamembrane loop (magenta spheres) forms an exit pore constriction. In the presence of EMRE, the juxtamembrane loop does not obstruct the pore exit due to interactions between the N-terminal region of EMRE and CC2 of MCU. In (A – C), the MCU and EMRE protein backbone is represented as a cartoon ribbon. TM1/2, transmembrane 1/2 (cyan); CC1/2, coiled-coil-1/2 (cyan); MCU-NTD, MCU Nterminal domain (pink); MRAP, MCU regulating acidic patch (red); Ca²⁺, calcium ion (yellow); DIME, Asp-Ile-Met-Glu motif; EMRE, essential MCU regulator (blue); MCU, mitochondrial Ca²⁺ uniporter; N, amino terminus; C, carboxyl terminus. The structure images were rendered in PyMOL (Schrodinger, LLC) using the 6O58.pdb coordinates.