title: Characterization of the iron-sulfur cluster N7 (N1c) in the subunit NuoG of the proton-translocating NADH-quinone oxidoreductase from Escherichia coli.
abstract: The proton-pumping NADH-quinone oxidoreductase from Escherichia coli houses nine iron-sulfur clusters, eight of which are found in its mitochondrial counterpart, complex I. The extra putative iron-sulfur cluster binding site with a CXXCXXXCX(27)C motif in the NuoG subunit has been assigned to ligate a [2Fe-2S] (N1c). However, we have shown previously that the Thermus thermophilus N1c fragment containing this motif ligates a [4Fe-4S] (Nakamaru-Ogiso, E., Yano, T., Ohnishi, T., and Yagi, T. (2002) J. Biol. Chem. 277, 1680-1688). In the current study, we individually inactivated four sets of the iron-sulfur binding motifs in the E. coli NuoG subunit by replacing all four ligands with Ala. Each mutant subunit, designated Delta N1b, Delta N1c, Delta N4, and Delta N5, was expressed as maltose-binding protein fusion proteins. After in vitro reconstitution, all mutant subunits were characterized by EPR. Although EPR signals from cluster N1b were not detected in any preparations, we detected two [4Fe-4S] EPR signals with g values of g(x,y,z) = 1.89, 1.94, and 2.06, and g(x,y,z) = 1.91, 1.94, and 2.05 at 6-20 K in wild type, Delta N1b, and Delta N5. The former signal was assigned to cluster N4, and the latter signal was assigned to cluster N1c because of their disappearance in Delta N4 and Delta N1c. Confirming that a [4Fe-4S] cluster ligates to the N1c motif, we propose to replace its misleading [2Fe-2S] name, N1c, with "cluster N7." In addition, because these mutations differently affected the assembly of peripheral subunits by in trans complementation analysis with the nuoG knock-out strain, the implicated structural importance of the iron-sulfur binding domains is discussed.
authors.affiliation: Division of Biochemistry, Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: Eiko
authors.initials: E
authors.lastname: Nakamaru-Ogiso
authors.forename: Takahiro
authors.initials: T
authors.lastname: Yano
authors.forename: Takao
authors.initials: T
authors.lastname: Yagi
authors.forename: Tomoko
authors.initials: T
authors.lastname: Ohnishi
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D021122:Protein Subunits; D011808:Quinone Reductases / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D029968:Escherichia coli Proteins; D007506:Iron-Sulfur Proteins; D021122:Protein Subunits; C041831:NADH dehydrogenase (quinone); D011808:Quinone Reductases