Structure and Reconstitution of an MCU-EMRE Mitochondrial Ca2+ Uniporter Complex

The proteins MCU and EMRE form the minimal functional unit of the mitochondria' calcium uniporter complex in metazoans, a highly selective and tightly controlled Ca2+ channel of the inner mitochondria' membrane that regulates cellular metabolism. Here we present functional reconstitution of an MCU-EMRE complex from the red flour beetle. Tribolium castaneum, and a cryo-EM structure of the complex at 3.5 angstrom resolution. Using a novel assay, we demonstrate robust Ca2+ uptake into proteoliposomes containing the purified complex. Uptake is dependent on EMRE and also on the mitochondrial lipid cardiolipin. The structure reveals a tetranneric channel with a single ion pore. EMRE is located at the periphery of the transmembrane domain and associates primarily with the first transmennbrane helix of MCU. Coiled-coil and juxtamembrane domains within the matrix portion of the complex adopt markedly different conformations than in a structure of a human MCU EMRE complex, suggesting that the structures represent different conformations of these functionally similar metazoan channels. (C) 2020 Elsevier Ltd. All rights reserved.