The nuclear ABC1 gene is essential for the correct conformation and functioning of the cytochrome bc1 complex and the neighbouring complexes II and IV in the mitochondrial respiratory chain.
The nuclear ABC1 gene was isolated as a multicopy suppressor of a cytochrome b mRNA translation defect. Its inactivation leads to a respiratory deficiency suggesting a block in the bc1 segment of the respiratory chain [Bousquet, I., Dujardin, G. & Slonimski, P. P. (1991) EMBO J. 10, 2023-2031]. In the present study, we established that deleting the ABC1 chromosomal gene from Saccharomyces cerevisiae does not prevent the assembly of the bc1 complex (complex III) but markedly impairs the kinetics of its high-potential electron transfer pathway occurring on the positive, outer, side of the membrane, which results in reduced activity of the bc1 complex. In addition, the activity of complex II and its cytochrome b560 decrease drastically and complex IV activity is halved. It is also observed that the binding of the quinol to the bc1 complex ubiquinol oxidation site is affected and that adding exogenous quinones partially compensates for the respiratory deficiency in vitro, although the quinone content of mutant and wild-type mitochondria are similar. Lastly, complexes II, III and IV are found to be thermosensitive and the bc1 complex exhibits greater sensitivity than the wild-type strain to center N and P inhibitors, suggesting that the three multisubunit complexes have undergone structural modifications. The data suggest that the ABC1 gene product acts as a chaperone-like protein essential for the proper conformation and efficient functioning of the bc1 complex and the effects of the Abc1 protein on the complexes II and IV might result from interactions with the modified bc1 complex.
Brasseur
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Laboratoire de Bioénergetique et Ingéniérie des protéines, UPR9036,Institut de Biologie Structurale et Microbiologie, CNRS, Marseille, France.
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Dujardin
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Slonimski
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Brivet-Chevillotte
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D003573:Cytochrome b Group / Q000378:metabolism; D004579:Electron Transport; D042967:Electron Transport Complex I; D042963:Electron Transport Complex II; D014450:Electron Transport Complex III / Q000737:chemistry / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004795:Enzyme Stability; D029968:Escherichia coli Proteins; D005656:Fungal Proteins / Q000235:genetics* / Q000502:physiology; D005800:Genes, Fungal; D016153:Genes, Suppressor; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009245:NADH Dehydrogenase / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism*; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D017384:Sequence Deletion; D013384:Succinate Cytochrome c Oxidoreductase / Q000378:metabolism; D013385:Succinate Dehydrogenase / Q000378:metabolism*; D013696:Temperature; D014451:Ubiquinone / Q000031:analogs & derivatives / Q000378:metabolism
C099891:COQ8 protein, S cerevisiae; D003573:Cytochrome b Group; D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; D005656:Fungal Proteins; D018832:Molecular Chaperones; D009097:Multienzyme Complexes; D029701:Saccharomyces cerevisiae Proteins; D014451:Ubiquinone; C017850:cytochrome b562, E coli; D010088:Oxidoreductases; D013384:Succinate Cytochrome c Oxidoreductase; D042963:Electron Transport Complex II; D013385:Succinate Dehydrogenase; D009247:NADH, NADPH Oxidoreductases; D009245:NADH Dehydrogenase; D003576:Electron Transport Complex IV; D042967:Electron Transport Complex I; D014450:Electron Transport Complex III; C003741:ubiquinol