title: Comparative structural and functional analysis of two octaheme nitrite reductases from closely related Thioalkalivibrio species.
abstract: Octaheme nitrite reductase from the haloalkaliphilic bacterium Thioalkalivibrio paradoxus was isolated and characterized. A comparative structural and functional analysis of two homologous octaheme nitrite reductases from closely related Thioalkalivibrio species was performed. It was shown that both enzymes have similar catalytic properties, owing to high structural similarity. Both enzymes are characterized by specific structural features distinguishing them from pentaheme cytochrome c nitrite reductases, such as the Tyr-Cys bond in the active site, the hexameric structure resulting in the formation of a void space inside the hexamer, and the product channel that opens into the void interior space of the hexamer. It is suggested that these specific structural features are responsible for the higher nitrite reductase activity, the greater preference for nitrite than for sulfite as a substrate, and the wider pH range of the catalytic activity of octaheme nitrite reductases than of pentaheme homologs.
  
  
  METHODS
  Nucleotide sequence data are available in the GenBank database under the accession number HQ665012.1. Structural data are available in the RCSB Protein Data Bank database under the accession numbers 3SXQ and 3TTB STRUCTURED DIGITAL ABSTRACT: TvPaR and TvPaR bind by x-ray crystallography (View interaction).
authors.affiliation: Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow, Russia. ttikhonova@inbi.ras.ru
authors.forename: Tamara
authors.initials: T
authors.lastname: Tikhonova
authors.forename: Alexey
authors.initials: A
authors.lastname: Tikhonov
authors.forename: Anton
authors.initials: A
authors.lastname: Trofimov
authors.forename: Konstantin
authors.initials: K
authors.lastname: Polyakov
authors.forename: Konstantin
authors.initials: K
authors.lastname: Boyko
authors.forename: Eugene
authors.initials: E
authors.lastname: Cherkashin
authors.forename: Tatiana
authors.initials: T
authors.lastname: Rakitina
authors.forename: Dmitry
authors.initials: D
authors.lastname: Sorokin
authors.forename: Vladimir
authors.initials: V
authors.lastname: Popov
mesh_terms: D002384:Catalysis; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D042001:Ectothiorhodospiraceae / Q000201:enzymology*; D006418:Heme / Q000737:chemistry*; D008958:Models, Molecular; D009572:Nitrite Reductases / Q000737:chemistry* / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D013379:Substrate Specificity; D013447:Sulfites / Q000378:metabolism*
chemical_list: D009573:Nitrites; D013447:Sulfites; D006418:Heme; D009572:Nitrite Reductases