The structure of the MICU1-MICU2 complex unveils the regulation of the mitochondrial calcium uniporter

TheMICU1-MICU2 heterodimer regulates the mitochondrial calcium uniporter (MCU) and mitochondrial calcium uptake. Herein, we present two crystal structures of theMICU1-MICU2 heterodimer, in which Ca2+-free and Ca2+-boundEF-hands are observed in both proteins, revealing both electrostatic and hydrophobic interfaces. Furthermore, we show thatMICU1 interacts withEMRE, another regulator ofMCU, through a Ca2+-dependent alkaline groove. Ca(2+)binding strengthens theMICU1-EMREinteraction, which in turn facilitates Ca(2+)uptake. Conversely, theMICU1-MCUinteraction is favored in the absence of Ca2+, thus inhibiting the channel activity. This Ca2+-dependent switch illuminates how calcium signals are transmitted from regulatory subunits to the calcium channel and the transition between gatekeeping and activation channel functions. Furthermore, competition with anEMREpeptide alters the uniporter threshold in resting conditions and elevates Ca(2+)accumulation in stimulated mitochondria, confirming the gatekeeper role of theMICU1-MICU2 heterodimer. Taken together, these structural and functional data provide new insights into the regulation of mitochondrial calcium uptake.