title: Subcellular compartmentation and differential catalytic properties of the three human nicotinamide mononucleotide adenylyltransferase isoforms.
abstract: Nicotinamide mononucleotide adenylyltransferase (NMNAT) is the central enzyme of the NAD biosynthetic pathway. Three human NMNAT isoforms have recently been identified, but isoform-specific functions are presently unknown, although a tissue-specific role has been suggested. Analyses of the subcellular localization confirmed NMNAT1 to be a nuclear protein, whereas NMNAT2 and -3 were localized to the Golgi complex and the mitochondria, respectively. This differential subcellular localization points to an organelle-specific, nonredundant function of each of the three proteins. Comparison of the kinetic properties showed that particularly NMNAT3 exhibits a high tolerance toward substrate modifications. Moreover, as opposed to preferred NAD+ synthesis by NMNAT1, the other two isoforms could also form NADH directly from the reduced nicotinamide mononucleotide, supporting a hitherto unknown pathway of NAD generation. A variety of physiological intermediates was tested and exerted only minor influence on the catalytic activities of the NMNATs. However, gallotannin was found to be a potent inhibitor, thereby compromising its use as a specific inhibitor of poly-ADP-ribose glycohydrolase. The presence of substrate-specific and independent nuclear, mitochondrial, and Golgi-specific NAD biosynthetic pathways is opposed to the assumption of a general cellular NAD pool. Their existence appears to be consistent with important compartment-specific functions rather than to reflect simple functional redundance.
authors.affiliation: Freie Universität Berlin, Institut für Biochemie, Thielallee 63, 14195 Berlin, Germany.
authors.forename: Felicitas
authors.initials: F
authors.lastname: Berger
authors.forename: Corinna
authors.initials: C
authors.lastname: Lau
authors.forename: Mathias
authors.initials: M
authors.lastname: Dahlmann
authors.forename: Mathias
authors.initials: M
authors.lastname: Ziegler
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D002384:Catalysis; D020134:Catalytic Domain; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000737:chemistry; D006056:Golgi Apparatus / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047348:Hydrolyzable Tannins / Q000737:chemistry; D007700:Kinetics; D009612:Nicotinamide-Nucleotide Adenylyltransferase / Q000737:chemistry* / Q000502:physiology; D011065:Poly(ADP-ribose) Polymerases / Q000737:chemistry; D011487:Protein Conformation; D020033:Protein Isoforms; D013379:Substrate Specificity; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D018076:DNA, Complementary; D047348:Hydrolyzable Tannins; D020033:Protein Isoforms; D000255:Adenosine Triphosphate; D011065:Poly(ADP-ribose) Polymerases; C484007:NMNAT1 protein, human; C484008:NMNAT2 protein, human; C484009:NMNAT3 protein, human; D009612:Nicotinamide-Nucleotide Adenylyltransferase; D006026:Glycoside Hydrolases; C022407:poly ADP-ribose glycohydrolase