Conformational change and human cytochrome c function: Mutation of residue 41 modulates caspase activation and destabilizes Met-80 coordination

Tracy M. Josephs, Matthew D. Liptak, Gillian Hughes, Alexandra Brazinova, Rebecca M. Smith, Sigurd M. Wilbanks, Kara L. Bren, Elizabeth C Ledgerwood

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Cytochrome c is a highly conserved protein, with 20 residues identical in all eukaryotic cytochromes c. Gly-41 is one of these invariant residues, and is the position of the only reported naturally occurring mutation in cytochrome c (human G41S). The basis, if any, for the conservation of Gly-41 is unknown. The mutation of Gly-41 to Ser enhances the apoptotic activity of cytochrome c without altering its role in mitochondrial electron transport. Here we have studied additional residue 41 variants and determined their effects on cytochrome c functions and conformation. A G41T mutation decreased the ability of cytochrome c to induce caspase activation and decreased the redox potential, whereas a G41A mutation had no impact on caspase induction but the redox potential increased. All residue 41 variants decreased the pK a of a structural transition of oxidized cytochrome c to the alkaline conformation, and this correlated with a destabilization of the interaction of Met-80 with the heme iron(III) at physiological pH. In reduced cytochrome c the G41T and G41S mutations had distinct effects on a network of hydrogen bonds involving Met-80, and in G41T the conformational mobility of two Ω-loops was altered. These results suggest the impact of residue 41 on the conformation of cytochrome c influences its ability to act in both of its physiological roles, electron transport and caspase activation.

Original languageEnglish
Pages (from-to)289-297
Number of pages9
JournalJournal of Biological Inorganic Chemistry
Issue number3
Publication statusPublished - Mar 2013
Externally publishedYes


  • Alkaline transition
  • Apoptosis
  • Cytochrome c
  • NMR
  • Redox potential

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