title: The crystal structure of the pentahaem c-type cytochrome NrfB and characterization of its solution-state interaction with the pentahaem nitrite reductase NrfA.
abstract: NrfB is a small pentahaem electron-transfer protein widely involved in the respiratory reduction of nitrite or nitric oxide to ammonia, processes that provide energy for anaerobic metabolism in many enteric bacteria and also serve to detoxify these reactive nitrogen species. The X-ray crystal structure of Escherichia coli NrfB is presented at 1.74 A (1 A=0.1 nm) resolution. The architecture of the protein is that of a 40 A 'nanowire' in which the five haems are positioned within 6 A of each other along a polypeptide scaffold. During nitrite reduction, the physiological role of NrfB is to mediate electron transfer to another pentahaem protein, NrfA, the enzyme that catalyses periplasmic nitrite or nitric oxide reduction. Protein-protein interaction studies suggest NrfA and NrfB can form a 20-haem NrfA2-NrfB2 heterotetrameric complex.
authors.affiliation: Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Clarke
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Cole
authors.forename: David J
authors.initials: DJ
authors.lastname: Richardson
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Hemmings
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000378:metabolism*; D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism*; D019281:Dimerization; D004926:Escherichia coli / Q000737:chemistry* / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D008027:Light; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009565:Nitrate Reductases / Q000378:metabolism*; D010084:Oxidation-Reduction; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012542:Scattering, Radiation; D012996:Solutions; D013050:Spectrometry, Fluorescence; D014461:Ultracentrifugation
chemical_list: D003574:Cytochrome c Group; D029968:Escherichia coli Proteins; C492974:NrfB protein, E coli; D012996:Solutions; D006418:Heme; D045304:Cytochromes c; C022302:cytochrome C-552; D009565:Nitrate Reductases