Quinolinate Salvage and Insights for Targeting NAD Biosynthesis in Group A Streptococci

Abstract

eThe essential coenzyme NAD plays important roles in metabolic reactions and cell regulation in all organisms. As such, NAD synthesis has been investigated as a source for novel antibacterial targets. Cross-species genomics-based reconstructions of NAD metabolism in group A streptococci (GAS), combined with focused experimental testing in Streptococcus pyogenes, led to a better understanding of NAD metabolism in the pathogen. The predicted niacin auxotrophy was experimentally verified, as well as the essential role of the nicotinamidase PncA in the utilization of nicotinamide (Nm). PncA is dispensable in the presence of nicotinate (Na), ruling it out as a viable antibacterial target. The function of the "orphan" NadC enzyme, which is uniquely present in all GAS species despite the absence of other genes of NAD de novo synthesis, was elucidated. Indeed, the quinolinate (Qa) phosphoribosyltransferase activity of NadC from S. pyogenes allows the organism to sustain growth when Qa is present as a sole pyridine precursor. Finally, the redundancy of functional upstream salvage pathways in GAS species narrows the choice of potential drug targets to the two indispensable downstream enzymes of NAD synthesis, nicotinate adenylyltransferase (NadD family) and NAD synthetase (NadE family). Biochemical characterization of NadD confirmed its functional role in S. pyogenes, and its potential as an antibacterial target was supported by inhibition studies with previously identified class I inhibitors of the NadD enzyme family. One of these inhibitors efficiently inhibited S. pyogenes NadD (sp.NadD) in vitro (50% inhibitory concentration [IC 50 ], 15 M), exhibiting a noncompetitive mechanism with a K i of 8 M.

Biological Activities of the Essential Oil from Erigeron floribundus

“…NadD has been recognized as a promising new target for developing novel antibiotics due to its crucial role in synthesizing NAD + [17][18][19][20]. Another attractive aspect of targeting NadD is that it is highly conserved in the overwhelming majority of bacterial species including most pathogens.…”

A Key Enzyme of the NAD + Salvage Pathway in Thermus thermophilus: Characterization of Nicotinamidase and the Impact of Its Gene Deletion at High Temperatures

“…Many organisms possess distinct types of pathways for the salvage synthesis of NAD ϩ , in which chemical and/or enzymatic degradants of NAD ϩ (e.g., nicotinamide and nicotinate) can be directly utilized as building blocks of the cofactor resynthesis (2,6). Some nicotinate-auxotrophic yeasts (22) and pathogenic microorganisms (23)(24)(25) are known to grow even without a de novo synthetic pathway for NAD ϩ , indicating the importance of the salvage pathway in these organisms. In addition, the growth of thermophiles also appears to be highly dependent on the salvage pathway because of the thermally unstable nature of NAD ϩ .…”

Cytosine chemoreceptor McpC in Pseudomonas putida F1 also detects nicotinic acid

“…Many human, animal and plant pathogens lack pathways for de novo biosynthesis of NAD, and are nicotinic acid or nicotinamide auxotrophs; a few examples include Shigella species, enteroinvasive E. coli strains, Salmonella enterica (serovar Dublin), group A streptococci and Erwinia amylovora (Bergthorsson & Roth, 2005;Paternoster et al, 2010;Prunier et al, 2007;Sorci et al, 2013). The use of nicotinic acid-degrading strains of Pseudomonas rhizosphaerae and Pseudomonas fluorescens as biocontrol agents to protect plants from the plant pathogen Erwinia amylovora, a nicotinic acid auxotroph, was reported recently (Paternoster et al, 2010).…”