MICU 1 and MICU 2 play nonredundant roles in the regulation of the mitochondrial calcium uniporter

The mitochondrial uniporter is a selective Ca 2+ channel regulated by MICU 1, an EF hand‐containing protein in the organelle's intermembrane space. MICU 1 physically associates with and is co‐expressed with a paralog, MICU 2. To clarify the function of MICU 1 and its relationship to MICU 2, we used gene knockout ( KO ) technology. We report that HEK ‐293T cells lacking MICU 1 or MICU 2 lose a normal threshold for Ca 2+ intake, extending the known gating function of MICU 1 to MICU 2. Expression of MICU 1 or MICU 2 mutants lacking functional Ca 2+ ‐binding sites leads to a striking loss of Ca 2+ uptake, suggesting that MICU 1/2 disinhibit the channel in response to a threshold rise in [Ca 2+ ]. MICU 2's activity and physical association with the pore require the presence of MICU 1, though the converse is not true. We conclude that MICU 1 and MICU 2 are nonredundant and together set the [Ca 2+ ] threshold for uniporter activity.