Mitochondrial cytochromes c and c1 are core components of the respiratory chain of all oxygen-respiring eukaryotes. These proteins contain haem, covalently bound to the polypeptide in a catalysed post-translational modification. In all eukaryotes, except members of the protist phylum Euglenozoa, haem attachment is to the cysteine residues of a CxxCH haem-binding motif. In the Euglenozoa, which include medically relevant trypanosomatid parasites, haem attachment is to a single cysteine residue in an AxxCH haem-binding motif. Moreover, genes encoding known c-type cytochrome biogenesis machineries are all absent from trypanosomatid genomes, indicating the presence of a novel biosynthetic apparatus. In the present study, we investigate expression and maturation of cytochrome c with a typical CxxCH haem-binding motif in the trypanosomatids Crithidia fasciculata and Trypanosoma brucei. Haem became attached to both cysteine residues of the haem-binding motif, indicating that, in contrast with previous hypotheses, nothing prevents formation of a CxxCH cytochrome c in euglenozoan mitochondria. The cytochrome variant was also able to replace the function of wild-type cytochrome c in T. brucei. However, the haem attachment to protein was not via the stereospecifically conserved linkage universally observed in natural c-type cytochromes, suggesting that the trypanosome cytochrome c biogenesis machinery recognized and processed only the wild-type single-cysteine haem-binding motif. Moreover, the presence of the CxxCH cytochrome c resulted in a fitness cost in respiration. The level of cytochrome c biogenesis in trypanosomatids was also found to be limited, with the cells operating at close to maximum capacity.
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Research Article|
November 07 2012
Probing why trypanosomes assemble atypical cytochrome c with an AxxCH haem-binding motif instead of CxxCH
Michael L. Ginger;
Michael L. Ginger
*Faculty of Health and Medicine, Division of Biomedical and Life Sciences, Lancaster University, Lancaster LA1 4YQ, U.K.
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Katharine A. Sam;
Katharine A. Sam
†Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K.
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James W. A. Allen
James W. A. Allen
1
†Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K.
1To whom correspondence should be addressed (email jwaallen1@gmail.com).
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Publisher: Portland Press Ltd
Received:
May 09 2012
Revision Received:
August 13 2012
Accepted:
August 28 2012
Accepted Manuscript online:
August 28 2012
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© The Authors Journal compilation © 2012 Biochemical Society
2012
Biochem J (2012) 448 (2): 253–260.
Article history
Received:
May 09 2012
Revision Received:
August 13 2012
Accepted:
August 28 2012
Accepted Manuscript online:
August 28 2012
Citation
Michael L. Ginger, Katharine A. Sam, James W. A. Allen; Probing why trypanosomes assemble atypical cytochrome c with an AxxCH haem-binding motif instead of CxxCH. Biochem J 1 December 2012; 448 (2): 253–260. doi: https://doi.org/10.1042/BJ20120757
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