Variable Assembly of EMRE and MCU Creates Functional Channels with Distinct Gatekeeping Profiles

• Published in: iScience Vol. 23; no. 4; p. 101037
• Main Authors: Payne, Riley, Li, Carmen, Foskett, J. Kevin
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 24.04.2020; Elsevier
• Subjects: Molecular Biology; Molecular Structure; Molecular Biology; Molecular Structure
• ISSN: 2589-0042; 2589-0042
• DOI: 10.1016/j.isci.2020.101037

MCU is a Ca2+-selective channel that mediates mitochondrial Ca2+ influx. The human channel contains tetrameric pore-forming MCU, regulatory subunits MICU1/2, and EMRE that is required both for channel function and MICU1/2-mediated Ca2+ regulation. A structure of MCU with EMRE revealed a 4:4 stoichiometry, but the stoichiometry in vivo is unknown. Expression of tagged EMRE and MCU at a 1:10 ratio in cells lacking EMRE and MCU restored channel activity but not full channel gatekeeping. Increasing EMRE expression enhanced gatekeeping, raising the cytoplasmic Ca2+ concentration ([Ca2+]c) threshold for channel activation. MCU-EMRE concatemers creating channels with 1EMRE:4MCU restored Ca2+ uptake in cells, whereas cells expressing concatemers that enforced a 4EMRE:4MCU stoichiometry demonstrated enhanced channel gatekeeping. Concatemers enforcing 2EMRE/4MCU recapitulated the activity, gatekeeping, and size of endogenous channels. Thus, MCU does not require four EMRE, with most endogenous channels containing two, but complexes with 1–4 EMRE have activity with full or partial gatekeeping. [Display omitted] •Mitochondrial Ca2+ uptake is mediated by the MCU Ca2+ ion channel•EMRE is required for MCU activity and for MCU interactions with MICU proteins•The EMRE:MCU stoichiometry of an MCU channel in vivo is unknown•MCU does not require four EMRE, with most endogenous channels containing two Molecular Biology; Molecular Structure