Mitochondrial nicotinamide adenine dinucleotide transporter SLC25A51
mitochondrial inner membrane
MCART1/SLC25A51 is required for mitochondrial NAD transport.
The nicotinamide adenine dinucleotide (NAD<sup>+</sup>/NADH) pair is a cofactor in redox reactions and is particularly critical in mitochondria as it connects substrate oxidation by the tricarboxylic acid (TCA) cycle to adenosine triphosphate generation by the electron transport chain (ETC) and oxidative phosphorylation. While a mitochondrial NAD<sup>+</sup> transporter has been identified in yeast, how NAD enters mitochondria in metazoans is unknown. Here, we mine gene essentiality data from human cell lines to identify <i>MCART1</i> (<i>SLC25A51</i>) as coessential with ETC components. <i>MCART1</i>-null cells have large decreases in TCA cycle flux, mitochondrial respiration, ETC complex I activity, and mitochondrial levels of NAD<sup>+</sup> and NADH. Isolated mitochondria from cells lacking or overexpressing <i>MCART1</i> have greatly decreased or increased NAD uptake in vitro, respectively. Moreover, <i>MCART1</i> and <i>NDT1</i>, a yeast mitochondrial NAD<sup>+</sup> transporter, can functionally complement for each other. Thus, we propose that MCART1 is the long sought mitochondrial transporter for NAD in human cells.