Mechanism of Thiosulfate Oxidation in the SoxA Family of Cysteine-ligated Cytochromes
| Autor: | Bianca Eisel, Ben C. Berks, Susan M. Lea, Steven Johnson, Daniel B. Grabarczyk, Paul E. Chappell |
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| Rok vydání: | 2015 |
| Předmět: |
Cytochrome
Protein Conformation Stereochemistry Metalloenzyme Molecular Sequence Data Thiosulfates Bacterial Metabolism Heme Biochemistry Thiosulfate dehydrogenase Mass Spectrometry Electron Transport 03 medical and health sciences chemistry.chemical_compound Bacterial Proteins Thiosulfate Dehydrogenase Amino Acid Sequence Cysteine Sulfur Oxidizing Bacteria Molecular Biology DNA Primers 030304 developmental biology Tetrathionate Thiosulfate 0303 health sciences Bacteria Base Sequence Sequence Homology Amino Acid biology 030302 biochemistry & molecular biology Active site Thiosulfate binding Cell Biology 3. Good health Sox System chemistry Enzymology biology.protein Cytochromes Spectrophotometry Ultraviolet Oxidation-Reduction |
| Zdroj: | The Journal of Biological Chemistry |
| ISSN: | 0021-9258 |
| Popis: | Background: The hemoprotein TsdA catalyzes the oxidation of two thiosulfate molecules to form tetrathionate. Results: The mechanism of TsdA has been probed using biochemical and structural methods. Conclusion: The TsdA reaction proceeds via a cysteine S-thiosulfonate intermediate formed on a cysteine ligand to the active site heme. Significance: TsdA provides a catalytic model for other members of the SoxA enzyme family. Thiosulfate dehydrogenase (TsdA) catalyzes the oxidation of two thiosulfate molecules to form tetrathionate and is predicted to use an unusual cysteine-ligated heme as the catalytic cofactor. We have determined the structure of Allochromatium vinosum TsdA to a resolution of 1.3 Å. This structure confirms the active site heme ligation, identifies a thiosulfate binding site within the active site cavity, and reveals an electron transfer route from the catalytic heme, through a second heme group to the external electron acceptor. We provide multiple lines of evidence that the catalytic reaction proceeds through the intermediate formation of a S-thiosulfonate derivative of the heme cysteine ligand: the cysteine is reactive and is accessible to electrophilic attack; cysteine S-thiosulfonate is formed by the addition of thiosulfate or following the reverse reaction with tetrathionate; the S-thiosulfonate modification is removed through catalysis; and alkylating the cysteine blocks activity. Active site amino acid residues required for catalysis were identified by mutagenesis and are inferred to also play a role in stabilizing the S-thiosulfonate intermediate. The enzyme SoxAX, which catalyzes the first step in the bacterial Sox thiosulfate oxidation pathway, is homologous to TsdA and can be inferred to use a related catalytic mechanism. |
| Databáze: | OpenAIRE |
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