title: Localization and function of the membrane-bound riboflavin in the Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) from Vibrio cholerae.
abstract: The sodium ion-translocating NADH:quinone oxidoreductase (Na(+)-NQR) from the human pathogen Vibrio cholerae is a respiratory membrane protein complex that couples the oxidation of NADH to the transport of Na(+) across the bacterial membrane. The Na(+)-NQR comprises the six subunits NqrABCDEF, but the stoichiometry and arrangement of these subunits are unknown. Redox-active cofactors are FAD and a 2Fe-2S cluster on NqrF, covalently attached FMNs on NqrB and NqrC, and riboflavin and ubiquinone-8 with unknown localization in the complex. By analyzing the cofactor content and NADH oxidation activity of subcomplexes of the Na(+)-NQR lacking individual subunits, the riboflavin cofactor was unequivocally assigned to the membrane-bound NqrB subunit. Quantitative analysis of the N-terminal amino acids of the holo-complex revealed that NqrB is present in a single copy in the holo-complex. It is concluded that the hydrophobic NqrB harbors one riboflavin in addition to its covalently attached FMN. The catalytic role of two flavins in subunit NqrB during the reduction of ubiquinone to ubiquinol by the Na(+)-NQR is discussed.
authors.affiliation: Department of Neuropathology, Breisacherstrasse 64, University of Freiburg, 79106 Freiburg, Germany.
authors.forename: Marco S
authors.initials: MS
authors.lastname: Casutt
authors.affiliation: Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland.
authors.forename: Tamara
authors.initials: T
authors.lastname: Huber
authors.affiliation: Functional Genomics Centre Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors.forename: René
authors.initials: R
authors.lastname: Brunisholz
authors.affiliation: Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland.
authors.forename: Minli
authors.initials: M
authors.lastname: Tao
authors.affiliation: Department of Neuropathology, Breisacherstrasse 64, University of Freiburg, 79106 Freiburg, Germany.
authors.forename: Günter
authors.initials: G
authors.lastname: Fritz
authors.affiliation: Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland. Electronic address: julia.steuber@uni-hohenheim.de.
authors.forename: Julia
authors.initials: J
authors.lastname: Steuber
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D020134:Catalytic Domain; D002462:Cell Membrane / Q000201:enzymology* / Q000235:genetics; D003067:Coenzymes / Q000235:genetics / Q000378:metabolism; D005486:Flavin Mononucleotide / Q000235:genetics / Q000378:metabolism; D005182:Flavin-Adenine Dinucleotide / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism*; D009243:NAD / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D011808:Quinone Reductases / Q000235:genetics / Q000378:metabolism*; D012256:Riboflavin / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D014451:Ubiquinone / Q000235:genetics / Q000378:metabolism; D014734:Vibrio cholerae / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D003067:Coenzymes; D007506:Iron-Sulfur Proteins; D009243:NAD; D014451:Ubiquinone; D005182:Flavin-Adenine Dinucleotide; D005486:Flavin Mononucleotide; D012964:Sodium; D011808:Quinone Reductases; D012256:Riboflavin