Crystal structure of Haemophilus influenzae NADR protein. A bifunctional enzyme endowed with NMN adenylyltransferase and ribosylnicotinamide kinase activities

S. Kumar Singh, Oleg V. Kurnasov, Baozhi Chen, Howard Robinson, Nick V. Grishin, Andrei L. Osterman, Hong Zhang

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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.

Original languageEnglish (US)
Pages (from-to)33291-33299
Number of pages9
JournalJournal of Biological Chemistry
Issue number36
StatePublished - Sep 6 2002


ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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