Abstract
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 (Cycs G41S/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.
Highlights
Thrombocytopenia Cargeeg (THC4; OMIM 612004) is one of two autosomal dominant thrombocytopenias associated with the only known mutations of the human cytochrome c gene (CYCS) [1,2]
We have previously reported that human G41S cytochrome c has up to 2-fold increased caspase-inducing activity compared to human WT cytochrome c [1,5] (S2A Fig)
Our results demonstrate that the well described electrostatic interaction between cytochrome c and apoptotic protease activating factor-1 (Apaf-1) is modulated by additional species-specific factors
Summary
Thrombocytopenia Cargeeg (THC4; OMIM 612004) is one of two autosomal dominant thrombocytopenias associated with the only known mutations of the human cytochrome c gene (CYCS) [1,2]. Cytochrome c is an essential electron carrier in the mitochondrial respiratory chain and is a critical mediator of the intrinsic apoptosis pathway. In response to PLOS ONE | DOI:10.1371/journal.pone.0130292. Species-Specific Activity of Cytochrome c in Apoptosis role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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