Rearrangement of MICU1 multimers for activation of MCU is solely controlled by cytosolic Ca2+

Abstract

Mitochondrial Ca2+ uptake is a vital process that controls distinct cell and organelle functions. Mitochondrial calcium uptake 1 (MICU1) was identified as key regulator of the mitochondrial Ca2+ uniporter (MCU) that together with the essential MCU regulator (EMRE) forms the mitochondrial Ca2+ channel. However, mechanisms by which MICU1 controls MCU/EMRE activity to tune mitochondrial Ca2+ signals remain ambiguous. Here we established a live-cell FRET approach and demonstrate that elevations of cytosolic Ca2+ rearranges MICU1 multimers with an EC 50 of 4.4 μM, resulting in activation of mitochondrial Ca2+ uptake. MICU1 rearrangement essentially requires the EF-hand motifs and strictly correlates with the shape of cytosolic Ca2+ rises. We further show that rearrangements of MICU1 multimers were independent of matrix Ca2+ concentration, mitochondrial membrane potential, and expression levels of MCU and EMRE. Our experiments provide novel details about how MCU/EMRE is regulated by MICU1 and an original approach to investigate MCU/EMRE activation in intact cells.