title: Nicotinamide mononucleotide synthetase is the key enzyme for an alternative route of NAD biosynthesis in Francisella tularensis.
abstract: Enzymes involved in the last 2 steps of nicotinamide adenine dinucleotide (NAD) cofactor biosynthesis, which catalyze the adenylylation of the nicotinic acid mononucleotide (NaMN) precursor to nicotinic acid dinucleotide (NaAD) followed by its amidation to NAD, constitute promising drug targets for the development of new antibiotics. These enzymes, NaMN adenylyltransferase (gene nadD) and NAD synthetase (gene nadE), respectively, are indispensable and conserved in nearly all bacterial pathogens. However, a comparative genome analysis of Francisella tularensis allowed us to predict the existence of an alternative route of NAD synthesis in this category A priority pathogen, the causative agent of tularaemia. In this route, the amidation of NaMN to nicotinamide mononucleotide (NMN) occurs before the adenylylation reaction, which converts this alternative intermediate to the NAD cofactor. The first step is catalyzed by NMN synthetase, which was identified and characterized in this study. A crystal structure of this enzyme, a divergent member of the NadE family, was solved at 1.9-A resolution in complex with reaction products, providing a rationale for its unusual substrate preference for NaMN over NaAD. The second step is performed by NMN adenylyltransferase of the NadM family. Here, we report validation of the predicted route (NaMN --> NMN --> NAD) in F. tularensis including mathematical modeling, in vitro reconstitution, and in vivo metabolite analysis in comparison with a canonical route (NaMN --> NaAD --> NAD) of NAD biosynthesis as represented by another deadly bacterial pathogen, Bacillus anthracis.
authors.affiliation: Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Sorci
authors.forename: Dariusz
authors.initials: D
authors.lastname: Martynowski
authors.forename: Dmitry A
authors.initials: DA
authors.lastname: Rodionov
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Eyobo
authors.forename: Xhavit
authors.initials: X
authors.lastname: Zogaj
authors.forename: Karl E
authors.initials: KE
authors.lastname: Klose
authors.forename: Evgeni V
authors.initials: EV
authors.lastname: Nikolaev
authors.forename: Giulio
authors.initials: G
authors.lastname: Magni
authors.forename: Hong
authors.initials: H
authors.lastname: Zhang
authors.forename: Andrei L
authors.initials: AL
authors.lastname: Osterman
mesh_terms: D001408:Bacillus anthracis / Q000201:enzymology; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003198:Computer Simulation; D005604:Francisella tularensis / Q000201:enzymology* / Q000235:genetics; D016680:Genome, Bacterial / Q000235:genetics; D007700:Kinetics; D008958:Models, Molecular; D009243:NAD / Q000096:biosynthesis*; D009537:Nicotinamide Mononucleotide / Q000096:biosynthesis*; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
chemical_list: D001426:Bacterial Proteins; D009243:NAD; D009537:Nicotinamide Mononucleotide