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Longevity researchSelected research

NAD+

The oxidized form of a dinucleotide redox cofactor, resolved bound in enzyme crystal structures, consumed by sirtuins and ADP-ribosyltransferases, and measured as free concentrations inside separate subcellular compartments.

For in-vitro research only.Reviewed 2026-09-20

Key findings

  • Crystal structures of a human flavoprotein show the nicotinamide moiety held away from the flavin when the oxidized cofactor is bound and stacked directly on the isoalloxazine ring when the reduced form is bound, so the two oxidation states occupy the site differently. [1]
  • A bacterial Nudix hydrolase resolved with the intact cofactor and with its cleavage product strongly prefers the RNA-linked form of the cofactor over the free dinucleotide, which separates the free molecule from the RNA cap species. [2]
  • A genetically encoded fluorescent biosensor put free cofactor concentrations in nucleus, cytoplasm and mitochondria close to the Michaelis constants of the sirtuins and ADP-ribosyltransferases resident in each compartment. [3]
  • In cells engineered to overconsume the cofactor in one compartment at a time, the lowered concentration kinetically restricted consumption while the biosynthesis rate stayed unchanged, and mitochondria buffered the shortfall by import through SLC25A51. [4]

Identity and structure

Role
A redox cofactor and an enzymatic substrate, consumed by sirtuins and poly ADP-ribose polymerases that sit in nucleus, cytosol and mitochondria [3][5]
Oxidation state
The oxidized and reduced forms bind the same enzyme site in different conformations and are not interchangeable reagents [1]
RNA-linked form
The same dinucleotide occurs attached to small regulatory bacterial RNAs in a cap-like manner, which a Nudix hydrolase cleaves in preference to the free molecule [2]
Reaction products
Sirtuin turnover of the cofactor with an acetyllysine substrate yields lysine, 2'-O-acetyl-ADP-ribose and nicotinamide [5]
Form as supplied
Dry crystalline or lyophilized powder

Mechanism as studied

Sirtuin chemistry is resolved in two stages. A ternary structure with a nonhydrolyzable analogue places the nicotinamide group in a pocket of conserved residues where a strictly conserved asparagine is positioned to stabilize the proposed oxocarbenium intermediate, and comparison with the ADP-ribose complex shows the cofactor ribose and a conserved protein loop rearranging between nicotinamide cleavage and ADP-ribose transfer. [5]

Structures of human SIRT2 taken with the native cofactor extend that sequence upstream. They capture a zinc-binding domain shift as the cofactor enters, a water-mediated hydrogen bond that disrupts nicotinamide aromaticity before cleavage, and the first reaction intermediate, with two mutants showing which residues hold the cofactor in a productive conformation. [6]

Enzymatic consumption is not limited to deacylases. A TIR domain protein binds double-stranded DNA through lysine residues and, once bound, degrades the cofactor in a sequence-independent way, giving a route by which cytosolic DNA lowers the cellular pool. [7]

Research findings

Structural
System
Human dihydrolipoamide dehydrogenase crystallized in the presence of the oxidized cofactor or of its reduced form, at 2.5 and 2.1 angstrom resolution
Measured
Overall fold against the yeast enzyme, the position of the nicotinamide moiety relative to the bound flavin, and the locations of mutation sites associated with enzyme deficiency
Reported
With the oxidized cofactor bound the nicotinamide moiety is not proximal to the flavin, while with the reduced form the nicotinamide base stacks directly on the isoalloxazine ring. The authors report this as the first observation of that mechanistically required conformation in this enzyme from any species, and place the deficiency mutations at the dimer interface, the active site and the cofactor binding sites. [1]
Structural
System
Escherichia coli NudC in complex with the intact cofactor as substrate and with the NMN cleavage product, plus mutational and RNA binding assays
Measured
Catalytic residues lining the binding pocket, the requirement for a homodimer, strand and nucleotide preference, and relative activity on the RNA-linked cofactor against the free molecule
Reported
The structures resolve the recognition of substrate and product and identify the conserved Nudix motif as the catalytic center, with the pocket built from residues of both monomers. The enzyme is single-strand specific with a purine preference at the 5' terminal nucleotide, strongly prefers the RNA-linked form over the free cofactor and binds cellular RNAs without sequence specificity. [2]
Structural
System
Yeast Hst2 in ternary complex with an acetyllysine histone H4 peptide and the nonhydrolyzable analogue carba-NAD, so the resolved cofactor is an analogue rather than the native molecule, plus an analogous complex with ADP-ribose
Measured
High resolution ternary structures, the contacts stabilizing the nicotinamide group, the position of the conserved asparagine N116, and the rearrangements of the cofactor ribose and the beta1-alpha2 loop between complexes
Reported
The nicotinamide group is stabilized in a pocket of conserved residues, and the conserved asparagine sits where it can stabilize the proposed oxocarbenium intermediate preceding nicotinamide hydrolysis. Comparison across the complexes shows the ribose ring and the conserved loop rearranging to order nicotinamide cleavage before ADP-ribose transfer. [5]
Structural
System
Six crystal structures of human SIRT2 with native myristoylated peptides and the native cofactor, plus the F96A and H187A mutants
Measured
The structural sequence from cofactor entry to the first reaction intermediate, the zinc-binding domain position, hydrogen bonding at the nicotinamide, and the effect of each mutation on cofactor conformation
Reported
The structures show a zinc-binding domain shift during cofactor entry, a water-mediated hydrogen bond that disrupts nicotinamide aromaticity before cleavage, and the formation of the first intermediate. The two mutants demonstrate the residues that hold the cofactor in a productive conformation. [6]
In vitro
System
Cells expressing a genetically encoded fluorescent biosensor targeted to nucleus, cytoplasm or mitochondria, with systematic depletion of the enzymes catalyzing the last biosynthetic step
Measured
Free cofactor concentration in each compartment, compared against the Michaelis constants of the sirtuins and ADP-ribosyltransferases resident there, and the effect of each depletion on the mitochondrial pool
Reported
Free concentrations in all three compartments approximate the Michaelis constants of the consuming enzymes in the same compartment. Depletion of the terminal biosynthetic enzymes revealed cell-specific routes for maintaining the mitochondrial concentration. [3]
In vitro
System
Cell lines stably expressing ADP-ribosyltransferase activity targeted to mitochondria, cytosol, endoplasmic reticulum or peroxisomes, with isotope tracer flux measurement and mathematical modelling
Measured
Cellular cofactor concentration under chronic compartment-specific overconsumption, consumption and biosynthesis fluxes, tolerance of the deficiency, and the contributions of SLC25A51 import and of NMNAT3
Reported
Concentrations fell by up to 50 percent. The lowered concentration kinetically restricted consumption to match an unchanged biosynthesis rate. The deficiency was tolerated unless mitochondria were targeted directly, and mitochondria maintained their pool by SLC25A51 import and by reversibly cleaving the cofactor to nicotinamide mononucleotide and ATP where NMNAT3 was present. [4]
In vitro
System
SARM1 protein and cells carrying transfected or chemotherapy-derived cytosolic double-stranded DNA, with SARM1 knockout and DNA-binding residue mutants as controls
Measured
Binding of double-stranded DNA by the TIR domain and the contribution of its lysine residues, colocalization of DNA with the protein, cofactor degradation and cell death
Reported
Double-stranded DNA bound and activated the protein, which then degraded the cofactor without sequence specificity. Binding ran through the TIR domain with lysine residues contributing, and both the degradation and the cell death were abolished by knockout or by mutating the DNA-binding residues. [7]
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Handling for in-vitro work

Analogue in cited work
Structural work on sirtuin chemistry used the nonhydrolyzable analogue carba-NAD in place of the native cofactor to trap the pre-cleavage state [5]
Oxidation state
The oxidized and reduced forms are distinct reagents and were crystallized separately in the cited flavoprotein work [1]
Storage
Dry powder at -20 °C, dark and dry; solutions prepared fresh and kept cold

Open questions

  • Compartment concentrations in the cited work are free cofactor measured by a sensor, not total cofactor, so protein-bound pools are not counted.
  • The enzymes resolved with the cofactor in the cited structures are bacterial, yeast and human proteins in separate studies, and the cited work does not compare binding geometry across them systematically.
  • The cited work establishes what consumes the cofactor inside cells; it does not address what happens to the molecule supplied to an experimental system from outside.
  • The identity and oxidation state of a supplied material should be confirmed analytically, since the oxidized and reduced forms behave differently in the cited enzyme structures.

A large clinical and ageing literature discusses this cofactor and its precursors; it concerns finished formulations and is out of scope for a research material profile.

Lot records

Check the record for the exact material you order. A published paper and a batch certificate answer different questions.

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References

  1. Brautigam CA, Chuang JL, Tomchick DR, et al. Crystal structure of human dihydrolipoamide dehydrogenase: NAD+/NADH binding and the structural basis of disease-causing mutations. Journal of molecular biology. 2005.

    PubMed 15946682 · doi:10.1016/j.jmb.2005.05.014

  2. Höfer K, Li S, Abele F, et al. Structure and function of the bacterial decapping enzyme NudC. Nature chemical biology. 2016.

    PubMed 27428510 · doi:10.1038/nchembio.2132

  3. Cambronne XA, Stewart ML, Kim D, et al. Biosensor reveals multiple sources for mitochondrial NAD⁺. Science (New York, N.Y.). 2016.

    PubMed 27313049 · doi:10.1126/science.aad5168

  4. Høyland LE, VanLinden MR, Niere M, et al. Subcellular NAD+ pools are interconnected and buffered by mitochondrial NAD. Nature metabolism. 2024.

    PubMed 39702414 · doi:10.1038/s42255-024-01174-w

  5. Zhao K, Harshaw R, Chai X, et al. Structural basis for nicotinamide cleavage and ADP-ribose transfer by NAD(+)-dependent Sir2 histone/protein deacetylases. Proceedings of the National Academy of Sciences of the United States of America. 2004.

    PubMed 15150415 · doi:10.1073/pnas.0401057101

  6. Zhang N, Pow KC, Chen L, et al. Structural basis of SIRT2 pre-catalysis NAD+ binding dynamics and mechanism. RSC chemical biology. 2025.

    PubMed 40963517 · doi:10.1039/d5cb00169b

  7. Wang L, Liu Q, Li S, et al. SARM1 senses dsDNA to promote NAD+ degradation and cell death. Cell. 2025.

    PubMed 41138726 · doi:10.1016/j.cell.2025.09.026

Publication records fetched from PubMed on 2026-09-20. Profile text reviewed 2026-09-20.