Interspecies Variation in the Functional Consequences of Mutation of Cytochrome c

• Published in: PloS one Vol. 10; no. 6; p. e0130292
• Main Authors: Josephs, Tracy M, Hibbs, Moira E, Ong, Lily, Morison, Ian M, Ledgerwood, Elizabeth C
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 18.06.2015; Public Library of Science (PLoS)
• Subjects: Amino Acid Sequence; Amphibians; Animals; Apaf-1 protein; Apoptosis; Binding; Biochemistry; Blood platelets; Bone marrow; Caspase; Caspases - metabolism; Conservation; Cytochrome; Cytochrome c; Cytochromes c - genetics; Cytochromes c - metabolism; Electrostatic properties; Enzyme Activation; Gene Knock-In Techniques; Genetic aspects; Hematology; Hematopoiesis; Human performance; Humans; Mice, Inbred C57BL; Mice, Transgenic; Mitochondrial DNA; Molecular chains; Molecular Sequence Data; Mutation; Phenotypes; Platelet Count; Platelets; Proteins; Species; Species Specificity; Thrombocytopenia; New Zealand
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0130292

The naturally occurring human cytochrome c variant (G41S) is associated with a mild autosomal dominant thrombocytopenia (Thrombocytopenia Cargeeg) caused by dysregulation of platelet production. The molecular basis of the platelet production defect is unknown. Despite high conservation of cytochrome c between human and mouse (91.4% identity), introducing the G41S mutation into mouse cytochrome c in a knockin mouse (CycsG41S/G41S) did not recapitulate the low platelet phenotype of Thrombocytopenia Cargeeg. While investigating the cause of this disparity we found a lack of conservation of the functional impact of cytochrome c mutations on caspase activation across species. Mutation of cytochrome c at residue 41 has distinct effects on the ability of cytochrome c to activate caspases depending on the species of both the cytochrome c and its binding partner Apaf-1. In contrast to our previous results showing the G41S mutation increases the ability of human cytochrome c to activate caspases, here we find this activity is decreased in mouse G41S cytochrome c. Additionally unlike wildtype human cytochrome c, G41S cytochrome c is unable to activate caspases in Xenopus embryo extracts. Taken together these results demonstrate a previously unreported species-specific component to the interaction of cytochrome c with Apaf-1. This suggests that the electrostatic interaction between cytochrome c and Apaf-1 is not the sole determinant of binding, with additional factors controlling binding specificity and affinity. These results have important implications for studies of the effects of cytochrome c mutations on the intrinsic apoptosis pathway.