Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
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Gene/Protein
Disease
Symptom
Drug
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Target Concepts:
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Query: UMLS:C0348321 (
Haemophilus
)
15,372
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
NAD is an indispensable redox cofactor in all organisms. Most of the genes required for NAD biosynthesis in various species are known. Ribosylnicotinamide kinase (RNK) was among the few unknown (missing) genes involved with NAD salvage and recycling pathways. Using a comparative genome analysis involving reconstruction of NAD metabolism from genomic data, we predicted and experimentally verified that bacterial RNK is encoded within the 3' region of the nadR gene. Based on these results and previous data, the full-size multifunctional NadR protein (as in Escherichia coli) is composed of (i) an N-terminal DNA-binding domain involved in the transcriptional regulation of NAD biosynthesis, (ii) a central
nicotinamide mononucleotide adenylyltransferase
(
NMNAT
) domain, and (iii) a C-terminal RNK domain. The RNK and
NMNAT
enzymatic activities of recombinant NadR proteins from Salmonella enterica serovar Typhimurium and
Haemophilus
influenzae were quantitatively characterized. We propose a model for the complete salvage pathway from exogenous N-ribosylnicotinamide to NAD which involves the concerted action of the PnuC transporter and NRK, followed by the
NMNAT
activity of the NadR protein. Both the pnuC and nadR genes were proven to be essential for the growth and survival of H. influenzae, thus implicating them as potential narrow-spectrum drug targets.
...
PMID:Ribosylnicotinamide kinase domain of NadR protein: identification and implications in NAD biosynthesis. 1244 41
NadR is a bifunctional enzyme that converts nicotinamide riboside (NR) into nicotinamide mononucleotide (NMN), which is then converted into nicotinamide adenine dinucleotide (NAD). Although a crystal structure of the enzyme from the Gram-negative bacterium
Haemophilus
influenzae
is known, structural understanding of its catalytic mechanism remains unclear. Here, we purified the NadR enzyme from
Lactococcus lactis
and established an assay to determine the combined activity of this bifunctional enzyme. The conversion of NR into NAD showed hyperbolic dependence on the NR concentration, but sigmoidal dependence on the ATP concentration. The apparent cooperativity for ATP may be explained because both reactions catalyzed by the bifunctional enzyme (phosphorylation of NR and adenylation of NMN) require ATP. The conversion of NMN into NAD followed simple Michaelis-Menten kinetics for NMN, but again with the sigmoidal dependence on the ATP concentration. In this case, the apparent cooperativity is unexpected since only a single ATP is used in the
NMN adenylyltransferase
catalyzed reaction. To determine the possible structural determinants of such cooperativity, we solved the crystal structure of NadR from
L. lactis
(NadR
Ll
). Co-crystallization with NAD, NR, NMN, ATP, and AMP-PNP revealed a 'sink' for adenine nucleotides in a location between two domains. This sink could be a regulatory site, or it may facilitate the channeling of substrates between the two domains.
...
PMID:Structural and Functional Characterization of NadR from
Lactococcus lactis
. 3233 17
