title: The N-terminus of the Qcr7 protein of the cytochrome bc(1) complex in S. cerevisiae may be involved in facilitating stability of the subcomplex with the Qcr8 protein and cytochrome b.
abstract: Subunit 7 or the Qcr7 protein of the cytochrome bc(1) complex in yeast is a nuclear-encoded 14-kDa protein and is essential for formation of a functional bc(1) complex and respiration. It was shown previously that the N-terminal region of the Qcr7 protein might play little role in import but may be essential for correct assembly of the bc(1) complex. To examine the role of the N-terminus in assembly of the bc(1) complex, various N-terminus deletion and point mutants of the QCR7 gene were expressed in yeast strains where the endogenous QCR7 gene has been inactivated. Deletion of the first 8-15 residues after methionine at the N-terminus of the Qcr7 protein was studied and it was shown that except for the Qcr7p-Delta7 mutant, the strains overexpressing deletion mutants (Qcr7p-Delta8 to Qcr7p-Delta14) displayed decreased steady-state levels of iron-sulfur protein (ISP) and 14-kDa (Qcr7) and 11-kDa (Qcr8) subunits, as well as a respiratory defect. It was shown that introducing mutations at the N-terminus of the QCR7 gene in the Delta7 context had more drastic effects on respiration and assembly than in the full-length context, suggesting that the first seven residues at the N-terminus have a role in increasing the stability of the holocomplex. This led to a respiratory-deficient phenotype and drastic decrease in the steady-state levels of Qcr7 (14-kDa) and Qcr8 (11-kDa) proteins. The mutants Qcr7p-Delta7 (R10I), Qcr7p-Delta7 (G12V), Qcr7p-Delta7 (D13G), Qcr7p-Delta7 (D13V), and Qcr7p-Delta7 (D13Y) showed decreases in the steady-state levels of ISP and 14- and 11-kDa subunits, as well as defects in respiration. These results are interpreted in the light of the X-ray crystal structure of the yeast bc(1) complex.
authors.affiliation: Metabolism Research Programme, University of Toronto, Toronto, Ontario, M5G 1X8, Canada.
authors.forename: S Y
authors.initials: SY
authors.lastname: Lee
authors.forename: C
authors.initials: C
authors.lastname: Hunte
authors.forename: S
authors.initials: S
authors.lastname: Malaney
authors.forename: B H
authors.initials: BH
authors.lastname: Robinson
mesh_terms: D003573:Cytochrome b Group / Q000378:metabolism*; D014450:Electron Transport Complex III / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004795:Enzyme Stability; D005656:Fungal Proteins / Q000378:metabolism*; D017353:Gene Deletion; D008970:Molecular Weight; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D003573:Cytochrome b Group; D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; C436959:Qcr7 protein, S cerevisiae; C436960:Qcr8 protein, S cerevisiae; D014450:Electron Transport Complex III