MICU1 controls spatial membrane potential gradients and guides Ca fluxes within mitochondrial substructures.

Mitochondrial ultrastructure represents a pinnacle of form and function, with the inner mitochondrial membrane (IMM) forming isolated pockets of cristae membrane (CM), separated from the inner-boundary membrane (IBM) by cristae junctions (CJ). Applying structured illumination and electron microscopy, a novel and fundamental function of MICU1 in mediating Ca control over spatial membrane potential gradients (SMPGs) between CM and IMS was identified. We unveiled alterations of SMPGs by transient CJ openings when Ca binds to MICU1 resulting in spatial cristae depolarization. This Ca/MICU1-mediated plasticity of the CJ further provides the mechanistic bedrock of the biphasic mitochondrial Ca uptake kinetics via the mitochondrial Ca uniporter (MCU) during intracellular Ca release: Initially, high Ca opens CJ via Ca/MICU1 and allows instant Ca uptake across the CM through constantly active MCU. Second, MCU disseminates into the IBM, thus establishing Ca uptake across the IBM that circumvents the CM. Under the condition of MICU1 methylation by PRMT1 in aging or cancer, UCP2 that binds to methylated MICU1 destabilizes CJ, disrupts SMPGs, and facilitates fast Ca uptake via the CM.