X-ray and cryo-EM structures of the mitochondrial calcium uniporter

Abstract

Mitochondrial calcium uptake is critical for regulating ATP production, intracellular calcium signalling, and cell death. This uptake is mediated by a highly selective calcium channel called the mitochondrial calcium uniporter (MCU). Here, we determined the structures of the pore-forming MCU proteins from two fungi by X-ray crystallography and single-particle cryo-electron microscopy. The stoichiometry, overall architecture, and individual subunit structure differed markedly from those described in the recent nuclear magnetic resonance structure of Caenorhabditis elegans MCU. We observed a dimer-of-dimer architecture across species and chemical environments, which was corroborated by biochemical experiments. Structural analyses and functional characterization uncovered the roles of key 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.

Why don't mice lacking the mitochondrial Ca2+ uniporter experience an energy crisis?

“…Most recently, cryo‐EM and X‐ray structures of fungi MCU indicate a tetrameric architecture (Fan et al . ; Nguyen et al . ; Yoo et al .…”

Redox Stability Controls the Cellular Uptake and Activity of Ruthenium‐Based Inhibitors of the Mitochondrial Calcium Uniporter (MCU)

“…It is well established that Ru265 and Ru360 inhibit mitochondrial Ca 2+ uptake effectively in permeabilized cells. We first sought to confirm that the observed MCU-inhibitory activity of these complexes arises from their intact forms, rather than likely impurities or decomposition products.T o consider this possibility,wetested the mitochondrial calcium uptake inhibition properties of several structurally related ruthenium compounds and starting materials.O ft hese compounds,K 3 6 ] 3+ are potential decomposition products or impurities that may arise during the syntheses of Ru360' and Ru265.…”

“…[1] Uptake of these ions by the mitochondria is mediated by the highly selective and inwardly rectifying channel known as the mitochondrial calcium uniporter (MCU). [2] This protein resides in the inner mitochondrial membrane (IMM) and forms atetrameric,dimer of dimers type of assembly, [3][4][5][6] with both the N-and C-terminal domains located within the mitochondrial matrix. [7,8] Although mitochondrial Ca 2+ uptake through the MCU is needed for proper cellular function, dysregulation of this process through mitochondrial calcium overload gives rise to cell damage and death.…”

Progress in understanding mitochondrial calcium uniporter complex‐mediated calcium signalling: A potential target for cancer treatment

“…They also indicate potential sites of channel regulation by other molecules within the mitochondrial matrix, besides the above listed MCU accessory proteins located at the IMM (Baradaran et al, 2018;Fan et al, 2018;Yoo et al, 2018). By using an N-terminal domain (NTD) dimer-of-dimers assembly manner, which is similar to that of ionotropic glutamate receptors, MCU forms the channel.…”

“…Trp 332 , Glu 336 , and Pro 337 stabilizes closely spaced carboxylate groups of the Glu 336 ring, which might contribute to the high-affinity binding and high selectivity of Ca 2+ (Fan et al, 2018). Although higher resolution is needed for further validation of the structure and functional mechanism of MCU, this approach will definitely accelerate the development of structure-based computer-aided drug design, such as the identification of novel molecules, hit-to-lead optimization of affinity, and selectivity.…”