Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0348321 (Haemophilus)
 15,372 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Haemophilus influenzae NadR protein (hiNadR) has been shown to be a bifunctional enzyme possessing both NMN adenylytransferase (NMNAT; EC ) and ribosylnicotinamide kinase (RNK; EC ) activities. Its function is essential for the growth and survival of H. influenzae and thus may present a new highly specific anti-infectious drug target. We have solved the crystal structure of hiNadR complexed with NAD using the selenomethionine MAD phasing method. The structure reveals the presence of two distinct domains. The N-terminal domain that hosts the NMNAT activity is closely related to archaeal NMNAT, whereas the C-terminal domain, which has been experimentally demonstrated to possess ribosylnicotinamide kinase activity, is structurally similar to yeast thymidylate kinase and several other P-loop-containing kinases. There appears to be no cross-talk between the two active sites. The bound NAD at the active site of the NMNAT domain reveals several critical interactions between NAD and the protein. There is also a second non-active-site NAD molecule associated with the C-terminal RNK domain that adopts a highly folded conformation with the nicotinamide ring stacking over the adenine base. Whereas the RNK domain of the hiNadR structure presented here is the first structural characterization of a ribosylnicotinamide kinase from any organism, the NMNAT domain of hiNadR defines yet another member of the pyridine nucleotide adenylyltransferase family.
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PMID:Crystal structure of Haemophilus influenzae NadR protein. A bifunctional enzyme endowed with NMN adenyltransferase and ribosylnicotinimide kinase activities. 1206 16

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 (NadRLl). 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.
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PMID:Structural and Functional Characterization of NadR from Lactococcus lactis. 3233 17