title: Structural study of the X-ray-induced enzymatic reaction of octahaem cytochrome C nitrite reductase.
abstract: Octahaem cytochrome c nitrite reductase from the bacterium Thioalkalivibrio nitratireducens catalyzes the reduction of nitrite to ammonium and of sulfite to sulfide. The reducing properties of X-ray radiation and the high quality of the enzyme crystals allow study of the catalytic reaction of cytochrome c nitrite reductase directly in a crystal of the enzyme, with the reaction being induced by X-rays. Series of diffraction data sets with increasing absorbed dose were collected from crystals of the free form of the enzyme and its complexes with nitrite and sulfite. The corresponding structures revealed gradual changes associated with the reduction of the catalytic haems by X-rays. In the case of the nitrite complex the conversion of the nitrite ions bound in the active sites to NO species was observed, which is the beginning of the catalytic reaction. For the free form, an increase in the distance between the oxygen ligand bound to the catalytic haem and the iron ion of the haem took place. In the case of the sulfite complex no enzymatic reaction was detected, but there were changes in the arrangement of the active-site water molecules that were presumably associated with a change in the protonation state of the sulfite ions.
authors.affiliation: Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow 119991, Russian Federation.
authors.forename: A A
authors.initials: AA
authors.lastname: Trofimov
authors.affiliation: Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow 119991, Russian Federation.
authors.forename: K M
authors.initials: KM
authors.lastname: Polyakov
authors.affiliation: Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow 119991, Russian Federation.
authors.forename: V A
authors.initials: VA
authors.lastname: Lazarenko
authors.affiliation: European Synchrotron Radiation Facility, BP-220, 38043 Grenoble, France.
authors.forename: A N
authors.initials: AN
authors.lastname: Popov
authors.affiliation: Bach Institute of Biochemistry, Russian Academy of Sciences, Leninskii pr. 33, Moscow 119071, Russian Federation.
authors.forename: T V
authors.initials: TV
authors.lastname: Tikhonova
authors.affiliation: Bach Institute of Biochemistry, Russian Academy of Sciences, Leninskii pr. 33, Moscow 119071, Russian Federation.
authors.forename: A V
authors.initials: AV
authors.lastname: Tikhonov
authors.affiliation: Bach Institute of Biochemistry, Russian Academy of Sciences, Leninskii pr. 33, Moscow 119071, Russian Federation.
authors.forename: V O
authors.initials: VO
authors.lastname: Popov
mesh_terms: D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D045263:Cytochromes a1 / Q000737:chemistry* / Q000378:metabolism* / Q000528:radiation effects; D003575:Cytochromes c1 / Q000737:chemistry* / Q000378:metabolism* / Q000528:radiation effects; D042001:Ectothiorhodospiraceae / Q000201:enzymology* / Q000528:radiation effects; D006418:Heme / Q000737:chemistry*; D008958:Models, Molecular; D009565:Nitrate Reductases / Q000737:chemistry* / Q000378:metabolism* / Q000528:radiation effects; D009573:Nitrites / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D011485:Protein Binding; D011487:Protein Conformation / Q000528:radiation effects*; D011830:Radiation Effects; D013379:Substrate Specificity; D013447:Sulfites / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D014965:X-Rays
chemical_list: D009573:Nitrites; D013447:Sulfites; D006418:Heme; D045263:Cytochromes a1; D003575:Cytochromes c1; D009565:Nitrate Reductases; C054690:nitrate reductase (cytochrome)
keywords: Thioalkalivibrio nitratireducens; octahaem cytochrome c nitrite reductase