MICU1 Interacts with the D-Ring of the MCU Pore to Control Its Ca2+ Flux and Sensitivity to Ru360

Proper control of the mitochondrial CA²⁺ uniporter's pore (MCU) is required to allow CA²⁺-dependent activation of oxidative metabolism and to avoid mitochondrial CA²⁺ overload and cell death. The MCU's gatekeeping and cooperative activation is mediated by the CA²⁺-sensing MICU1 protein, which has been proposed to form dimeric complexes anchored to the EMRE scaffold of MCU. We unexpectedly find that MICU1 suppresses inhibition of MCU by ruthenium red/Ru360, which bind to MCU's DIME motif, the selectivity filter. This led us to recognize in MICU1's sequence a putative DIME interacting domain (DID), which is required for both gatekeeping and cooperative activation of MCU and for cell survival. Thus, we propose that MICU1 has to interact with the D-ring formed by the DIME domains in MCU to control the uniporter.