Mitochondrial NAD⁺ gradient sustained by membrane potential and transport

Area of Science:

• Mitochondrial biology
• Molecular transport
• Bioenergetics

Background:

• Nicotinamide adenine dinucleotide (NAD+) is vital for cellular energy metabolism.
• Mammalian mitochondria require a continuous supply of NAD+ for respiration and ATP synthesis.
• The precise mechanism by which SLC25A51 imports NAD+ into the mitochondrial matrix against its gradient remains unclear.

Purpose of the Study:

• To elucidate the mechanism of NAD+ import into mitochondria mediated by SLC25A51.
• To understand how mitochondrial membrane potential and charged residues contribute to NAD+ transport.
• To identify conserved transport mechanisms within the mitochondrial carrier family.

Main Methods:

• Site-directed mutagenesis of SLC25A51.
• Development and utilization of localized NAD+ biosensors.
• Measurement of mitochondrial membrane potential (ΔΨm).
• Comparative analysis with yeast mitochondrial NAD+ carrier (ScNdt1p).

Main Results:

• Mitochondrial membrane potential (ΔΨm) and charged residues within SLC25A51's pore are essential for sustained NAD+ import.
• Disruption of ΔΨm or mutation of key residues abolishes the NAD+ gradient across the inner mitochondrial membrane.
• The findings suggest a conserved mechanism of electrogenic transport and charge compensation in mitochondrial carriers, including ATP transporters.

Conclusions:

• SLC25A51 utilizes mitochondrial membrane potential and specific charged residues to import NAD+ against its electrochemical gradient.
• This mechanism is critical for maintaining mitochondrial NAD+ levels necessary for cellular respiration and ATP production.
• Conserved principles of electrogenic transport and charge compensation operate across different mitochondrial carrier family members.