title: Ubiquinone accumulates in the mitochondria of yeast mutated in the ubiquinone binding protein, Qcr8p.
abstract: In Saccharomyces cerevisiae, the trans-membrane helix of Qcr8p, the ubiquinone binding protein of complex III, contributes to the Q binding site. In wild-type cells, residue 62 of the helix is non-polar (proline). Substitution of proline 62 with a polar, uncharged residue does not impair the ability of the cells to respire, complex III assembly is unaffected, ubiquinone occupancy of the Q binding site is unchanged, and mitochondrial ubiquinone levels are in the wild-type range. Substitution with a +1 charged residue is associated with partial respiratory competence, impaired complex III assembly, and loss of cytochrome b. Although ubiquinone occupancy of the Q binding site is similar to wild-type, total mitochondrial ubiquinone doubled in these mutants. Mutants with a +2 charged substitution at position 62 are unable to respire. These results suggest that the accumulation of ubiquinone in the mitochondria may be a compensatory mechanism for impaired electron transport at cytochrome b.
authors.affiliation: School of Biological Sciences, University of Texas at Austin, Austin, TX 78712, USA. rhagerman@mail.utexas.edu
authors.forename: Ruth A
authors.initials: RA
authors.lastname: Hagerman
authors.forename: Natashya J
authors.initials: NJ
authors.lastname: Waring
authors.forename: Richard A
authors.initials: RA
authors.lastname: Willis
authors.forename: Ann E
authors.initials: AE
authors.lastname: Hagerman
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001665:Binding Sites; D014450:Electron Transport Complex III / Q000235:genetics*; D008928:Mitochondria / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D011392:Proline / Q000737:chemistry / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics*; D014451:Ubiquinone / Q000032:analysis / Q000378:metabolism*
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D014451:Ubiquinone; D011392:Proline; C436960:Qcr8 protein, S cerevisiae; D014450:Electron Transport Complex III