MICU1 imparts the mitochondrial uniporter with the ability to discriminate between Ca2+ and Mn2+

The mitochondrial uniporter is a Ca2+-activated Ca2+ channel complex that displays exceptionally high conductance and selectivity. Here, we report cellular metal toxicity screens highlighting the uniporter's role in Mn2+ toxicity. Cells lacking the pore-forming uniporter subunit, MCU, are more resistant to Mn2+ toxicity, while cells lacking the Ca2+-sensing inhibitory subunit, MICU1, are more sensitive than the wild type. Consistent with these findings, Caenorhabditis elegans lacking the uniporter's pore have increased resistance to Mn2+ toxicity. The chemical-genetic interaction between uniporter machinery and Mn2+ toxicity prompted us to hypothesize that Mn2+ can indeed be transported by the uniporter's pore, but this transport is prevented by MICU1. To this end, we demonstrate that, in the absence of MICU1, both Mn2+ and Ca2+ can pass through the uniporter, as evidenced by mitochondrial Mn2+ uptake assays, mitochondrial membrane potential measurements, and mitoplast electrophysiology. We show that Mn2+ does not elicit the conformational change in MICU1 that is physiologically elicited by Ca2+, preventing Mn2+ from inducing the pore opening. Our work showcases a mechanism by which a channel's auxiliary subunit can contribute to its apparent selectivity and, furthermore, may have implications for understanding how manganese contributes to neurodegenerative disease.