title: Crystal structure of Haemophilus influenzae NadR protein. A bifunctional enzyme endowed with NMN adenyltransferase and ribosylnicotinimide kinase activities.
abstract: 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.
authors.affiliation: Department of Biochemistry and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
authors.forename: S Kumar
authors.initials: SK
authors.lastname: Singh
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Kurnasov
authors.forename: Baozhi
authors.initials: B
authors.lastname: Chen
authors.forename: Howard
authors.initials: H
authors.lastname: Robinson
authors.forename: Nick V
authors.initials: NV
authors.lastname: Grishin
authors.forename: Andrei L
authors.initials: AL
authors.lastname: Osterman
authors.forename: Hong
authors.initials: H
authors.lastname: Zhang
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001665:Binding Sites; D018360:Crystallography, X-Ray; D006193:Haemophilus influenzae / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015233:Models, Statistical; D008969:Molecular Sequence Data; D009612:Nicotinamide-Nucleotide Adenylyltransferase / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; C117105:NadR protein, bacteria; D012097:Repressor Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor); C061783:nicotinamide riboside kinase; D009612:Nicotinamide-Nucleotide Adenylyltransferase