title: Subunit IV of cytochrome bc1 complex from Rhodobacter sphaeroides. Localization of regions essential for interaction with the three-subunit core complex.
abstract: Recombinant subunit IV mutants which identify the regions essential for restoration of bc(1) activity to the three-subunit core complex of Rhodobacter sphaeroides were generated and characterized. Four C-terminal truncated mutants: IV(1-109), IV(1-85), IV(1-76), and IV(1-40) had 100, 0, 0, and 0% of reconstitutive activity of the wild-type IV, indicating that residues 86-109 are essential. IV(1-109) is associated with the core complex in the same manner as the wild-type IV while mutants IV(1-85), IV(1-76), and IV(1-40) do not associate with the core complex, indicating that subunit IV requires its transmembrane helix region (residues 86-109) for assembly into the bc(1) complex. Since GST-IV(86-109) fusion protein has little reconstitutive activity, some region(s) in residues 1-85 are required for bc(1) activity restoration after subunit IV is incorporated into the complex through the transmembrane helix, presumably by interaction with cytochrome b in the core complex. The interacting regions are identified as residues 41-53 and 77-85, since mutants IV(21-109), IV(41-109), IV(54-109), and IV(77-109) had 95, 98, 53, and 53% of the reconstitutive activity of the wild-type IV. These two interacting regions are on the cytoplasmic side of the chromatophore membrane and closed to the DE loop and helix G of cytochrome b, respectively.
authors.affiliation: Department of Biochemistry & Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Tso
authors.forename: S K
authors.initials: SK
authors.lastname: Shenoy
authors.forename: B N
authors.initials: BN
authors.lastname: Quinn
authors.forename: L
authors.initials: L
authors.lastname: Yu
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003001:Cloning, Molecular; D003573:Cytochrome b Group / Q000737:chemistry / Q000378:metabolism; D014450:Electron Transport Complex III / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000201:enzymology* / Q000235:genetics; D017384:Sequence Deletion
chemical_list: D003573:Cytochrome b Group; D046911:Macromolecular Substances; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D014450:Electron Transport Complex III