Related Experiment Video
Updated: Jul 1, 2025
Exploring Caspase Mutations and Post-Translational Modification by Molecular Modeling Approaches
Published on: October 13, 2022
Altered conformational dynamics contribute to species-specific effects of cytochrome c mutations on caspase
Thomas C Chin1, Sigurd M Wilbanks1, Elizabeth C Ledgerwood2
1Biochemistry Department, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand.
Insights
The G41S mutation in human cytochrome c (CYCS) increases protein mobility, enhancing apoptosome activation. This explains why the mutation causes thrombocytopenia in humans but not mice, despite sequence conservation.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Cytochrome c (CYCS) gene variants are linked to autosomal dominant thrombocytopenia.
- The G41S mutation's effects on CYCS function and phenotype differ between humans and mice.
- Cytochrome c's apoptotic activities are modulated by protein conformational dynamics.
Purpose of the Study:
- To investigate the molecular basis for the differing effects of the G41S CYCS mutation in humans and mice.
- To understand how protein dynamics influence cytochrome c's role in apoptosis and disease.
Main Methods:
- Computational simulations to analyze protein dynamics and conformational changes.
- In vitro assays to assess cytochrome c peroxidase and apoptosome activation activities.
- Comparative analysis of human and mouse G41S cytochrome c variants.
Main Results:
- The G41S mutation increases entropy and main chain mobility in human, but not mouse, cytochrome c.
- Human G41S cytochrome c exhibits decreased protein-heme hydrogen bond occupancy.
- Apoptosome activation is enhanced by increased mobility in human G41S cytochrome c, while peroxidase activity is unaffected.
Conclusions:
- Increased protein mobility, driven by the G41S mutation, enhances human cytochrome c's ability to trigger apoptosome formation.
- Differential protein dynamics explain the species-specific phenotype of the G41S CYCS mutation.
- Cytochrome c's role in apoptosis is sensitive to subtle changes in protein conformational dynamics.
Abstract:
Variants in the gene encoding human cytochrome c (CYCS) cause mild autosomal dominant thrombocytopenia. Despite high sequence conservation between mouse and human cytochrome c, this phenotype is not recapitulated in mice for the sole mutant (G41S) that has been investigated. The effect of the G41S mutation on the in vitro activities of cytochrome c is also not conserved between human and mouse. Peroxidase activity is increased in both mouse and human G41S variants, whereas apoptosome activation is increased for human G41S cytochrome c but decreased for mouse G41S cytochrome c. These apoptotic activities of cytochrome c are regulated at least in part by conformational dynamics of the main chain. Here we use computational and in vitro approaches to understand why the impact of the G41S mutation differs between mouse and human cytochromes c. The G41S mutation increases the inherent entropy and main chain mobility of human but not mouse cytochrome c. Exclusively in human G41S cytochrome c this is accompanied by a decrease in occupancy of H-bonds between protein and heme during simulations. These data demonstrate that binding of cytochrome c to Apaf-1 to trigger apoptosome formation, but not the peroxidase activity of cytochrome c, is enhanced by increased mobility of the native protein conformation.
Related Concept Videos
01:24Caspases
01:31The Intrinsic Apoptotic Pathway
01:19Allosteric Proteins-ATCase
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis...