A proapoptotic mutation in human cytochrome c associated with abnormal platelet production

• Published in: The FASEB journal Vol. 20; no. 5; p. LB71
• Main Authors: Ledgerwood, Elizabeth, Cheong, Anthony, Lo, Alexandra, Cramer, Elisabeth, Morison, Ian
• Format: Journal Article
• Language: English
• Published: Federation of American Societies for Experimental Biology 01-03-2006
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fasebj.20.5.LB71-c

Cytochrome c is a highly conserved protein with dual roles in mitochondrial electron transport and apoptosis. We have identified the first known mutation in cytochrome c. The autosomal dominant mutation is in a New Zealand family with low levels of circulating platelets. To determine the functional effect of the mutation we have carried out a series of in vitro investigations. We have expressed and purified recombinant wildtype and mutant human cytochrome c in E. coli. When analysed by circular dichroism spectroscopy the structure of the mutant cytochrome c is indistinguishable from wildtype. In addition the mutant binds haem and has a reduction potential the same as wildtype, suggesting that the redox function of cytochrome c is unaffected by the mutation. In a cell‐free apoptosis assay the mutant has a significantly increased ability to activate caspases. Analysis of platelet production in the heterozygous family members shows that the low platelet phonotype is characterised by premature megakaryocyte apoptosis, resulting in platelet destruction in the bone marrow. Taken together these observations indicate that increased apoptotic activity of the mutant cytochrome c is responsible for the low platelet phenotype in the family. Surprisingly the family are otherwise healthy, active and long‐lived with no other obvious apoptotic abnormalities. This suggests that tight regulation of the cytochrome c‐mediated apoptotic pathway may not be necessary for normal development.
This research is supported by the Lottery Grants Board and Health Research Council of New Zealand.