Mutations in the tether region of the iron-sulfur protein affect the activity and assembly of the cytochrome bc1 complex of yeast mitochondria

Victor H. Obungu, Yudong Wang, Suzelle M. Amyot, Christian B. Gocke, Diana S. Beattie

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29 Scopus citations


Resolution of the crystal structure of the mitochondrial cytochrome bc1 complex has indicated that the extra-membranous extrinsic domain of the iron- sulfur protein containing the 2Fe2S cluster is connected by a tether to the transmembrane helix that anchors the iron-sulfur protein to the complex. To investigate the role of this tether in the cytochrome bc1 complex, we have mutated the conserved amino acid residues Ala-86, Ala-90, Ala-92, Lys-93 and Glu-95 and constructed deletion mutants ΔVLA(88-90) and ΔAMA(90-92) and an insertion mutant I87AAA88 in the iron-sulfur protein of the yeast, Saccharomyces cerevisiae. In cells grown at 30°C, enzymatic activities of the bc1 complex were reduced 22-56% in mutants A86L, A90I, A92C, A92R and E95R, and the deletion mutants, ΔVLA(88-90) and ΔAMA(90-92), while activity of the insertion mutant was reduced 90%. No loss of cytochromes b or c-c1, detected spectrally, or the iron-sulfur protein, determined by quantitative immunoblotting, was observed in these mutants with the exception of the mutants of Ala-92 in which the loss of activity paralleled a loss in the amount of the iron-sulfur protein. EPR spectroscopy revealed no changes in the iron-sulfur cluster of mutants A86L, A90I, A92R or the deletion mutant ΔVLA(88-90). Greater losses of both protein and activity were observed in all of the mutants of Ala-92 as well as in A90F grown at 37°C. suggesting that these conserved alanine residues may be involved in maintaining the stability of the iron-sulfur protein and its assembly into the bc1 complex. By contrast, no significant loss of iron-sulfur protein was observed in the mutants of Ala-86 in cells grown at either 30°C or 37°C despite the 50-70% loss of enzymatic activity suggesting that Ala-86 may play a critical role in catalysis in the bc1 complex.

Original languageEnglish (US)
Pages (from-to)36-44
Number of pages9
JournalBiochimica et Biophysica Acta - Bioenergetics
Issue number1-2
StatePublished - Feb 24 2000
Externally publishedYes


  • Cytochrome bc
  • Iron-sulphur protein
  • Mitochondria
  • Yeast

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology


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