The thioreduction component CcmG confers efficiency and the heme ligation component CcmH ensures stereo-specificity during cytochrome c maturation
Open accessAbstract
In many Gram-negative bacteria, including Rhodobacter capsulatus, cytochrome c maturation (Ccm) is carried out by a membrane-integral machinery composed of nine proteins (CcmA to I). During this process, the periplasmic thiol-disulfide oxidoreductase DsbA is thought to catalyze the formation of a disulfide bond between the Cys residues at the apocytochrome c heme-binding site (C XX CH). Subsequently, a Ccm-specific thioreductive pathway involving CcmG and CcmH reduces this disulfide bond to allow covalent heme ligation. Currently, the sequence of thioredox reactions occurring between these components and apocytochrome c and the identity of their active Cys residues are unknown. In this work, we first investigated protein–protein interactions among the apocytochrome c, CcmG, and the heme-ligation components CcmF, CcmH, and CcmI. We found that they all interact with each other, forming a CcmFGHI–apocytochrome c complex. Using purified wild-type CcmG, CcmH, and apocytochrome c, as well as their respective Cys mutant variants, we determined the rates of thiol-disulfide exchange reactions between selected pairs of Cys residues from these proteins. We established that CcmG can efficiently reduce the disulfide bond of apocytochrome c and also resolve a mixed disulfide bond formed between apocytochrome c and CcmH. We further show that Cys-45 of CcmH and Cys-34 of apocytochrome c are most likely to form this mixed disulfide bond, which is consistent with the stereo-specificity of the heme–apocytochrome c ligation reaction. We conclude that CcmG confers efficiency, and CcmH ensures stereo-specificity during Ccm and present a comprehensive model for thioreduction reactions that lead to heme–apocytochrome c ligation.
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CcmFGH covalently attaches the heme to nascent cytochrome c-type proteins.
“Subsequently, CcmFGH covalently attaches the heme to nascent cytochrome c-type proteins45,46.”
From AF2Complex predicts direct physical interactions in multimeric proteins with deep learning (2022) · cites this paper as [46]
After entering the reaction groove, apocyt c is first reduced by Cys80 and Cys83 of CcmG.
“Of the previously proposed mechanisms46, our model supports the following: after entering the reaction groove, apocyt c is first reduced by Cys80 and Cys83 of CcmG.”
From AF2Complex predicts direct physical interactions in multimeric proteins with deep learning (2022) · cites this paper as [46]
The reduction of a mixed disulfide between the CXXC motifs of CcmG and H as proposed in an alternate mechanism is unlikely according to these models.
“and hence the reduction of a mixed disulfide between these two motifs as proposed in an alternate mechanism46 is unlikely according to these models.”
From AF2Complex predicts direct physical interactions in multimeric proteins with deep learning (2022) · cites this paper as [46]
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- Authors
- Verissimo, A. F., Khalfaoui-Hassani, B., Hwang, J., Steimle, S., Selamoglu, N., Sanders, C., Khatchikian, C. E., & Daldal, F.
- Affiliations
- University of Pennsylvania (US)
- Kutztown University (US)
- The University of Texas at El Paso (US)
- Corresponding author
- Daldal, Fevzi
- Venue
- Journal of Biological Chemistry
- Publisher
- Elsevier BV
- Published
- 2017-08
- Volume
- 292
- Issue
- 32
- Pages
- 13154-13167
- ISSN
- 0021-9258 (ISSN-L)
- PMC
- PMC5555179
- OpenAlex
- W2629863205
- Cited by
- 21
- References
- 52
- Citations by year
- 2025: 4 · 2023: 4 · 2022: 2 · 2021: 6 · 2020: 1 · 2019: 1 · 2018: 2 · 2017: 1
- FWCI
- 0.56
- Type
- journal article
- Language
- en
- Open access
- hybrid
- doi.org
- Licence
- Locations
- Journal of Biological Chemistry (publishedVersion, cc-by)
- Europe PMC (PubMed Central) (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) (submittedVersion)
- HAL (submittedVersion)
- Funders
- U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences (DOE DE-FG02–91ER20052)
- Office of Extramural Research, National Institutes of Health (GM 38237, 5G12MD007592)
- Topics
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Redox biology and oxidative stress
- Physical Sciences › Energy › Renewable Energy, Sustainability and the Environment › Metalloenzymes and iron-sulfur proteins
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Bacterial Genetics and Biotechnology
- Keywords
- cytochrome c maturation, apocytochrome c, heme ligation, disulfide bond reduction, thiol-disulfide exchange, protein-protein interaction, Rhodobacter capsulatus, DsbA
- MeSH terms
- Apoenzymes, Bacterial Outer Membrane Proteins, Bacterial Proteins, Binding Sites, Cysteine, Cystine, Heme, Models, Biological, Mutation, Oxidation-Reduction, Peptide Fragments, Protein Disulfide Reductase (Glutathione), Recombinant Fusion Proteins, Recombinant Proteins, Stereoisomerism, Rhodobacter capsulatus, Amino Acid Substitution, Cytochromes c, Protein Interaction Domains and Motifs, Protein Multimerization
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