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

Riley Payne; Carmen Li; J Kevin Foskett

doi:10.1016/j.isci.2020.101037

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

iScience. 2020 Apr 24;23(4):101037. doi: 10.1016/j.isci.2020.101037. Epub 2020 Apr 10.

Authors

Riley Payne¹, Carmen Li¹, J Kevin Foskett²

Affiliations

¹ Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
² Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address: foskett@pennmedicine.upenn.edu.

Abstract

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.

Keywords: Molecular Biology; Molecular Structure.

Abstract

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