Ligand Dynamics in an Electron Transfer Protein
| Autor: | Marten H. Vos, Audrius Jasaitis, Gary Silkstone, Michael T. Wilson |
|---|---|
| Rok vydání: | 2007 |
| Předmět: |
0303 health sciences
biology Chemistry Ligand Cytochrome c Electron donor Cell Biology 010402 general chemistry Photochemistry 01 natural sciences Biochemistry Electron transport chain 0104 chemical sciences 03 medical and health sciences Electron transfer chemistry.chemical_compound Myoglobin 13. Climate action biology.protein Molecular Biology Heme 030304 developmental biology Carbon monoxide |
| Zdroj: | Journal of Biological Chemistry. 282:1638-1649 |
| ISSN: | 0021-9258 |
| Popis: | Substitution of the heme coordination residue Met-80 of the electron transport protein yeast iso-1-cytochrome c allows external ligands like CO to bind and thus increase the effective redox potential. This mutation, in principle, turns the protein into a quasi-native photoactivable electron donor. We have studied the kinetic and spectral characteristics of geminate recombination of heme and CO in a series of single M80X (X = Ala, Ser, Asp, Arg) mutants, using femtosecond transient absorption spectroscopy. In these proteins, all geminate recombination occurs on the picosecond and early nanosecond time scale, in a multiphasic manner, in which heme relaxation takes place on the same time scale. The extent of geminate recombination varies from >99% (Ala, Ser) to ∼70% (Arg), the latter value being in principle low enough for electron injection studies. The rates and extent of the CO geminate recombination phases are much higher than in functional ligand-binding proteins like myoglobin, presumably reflecting the rigid and hydrophobic properties of the heme environment, which are optimized for electron transfer. Thus, the dynamics of CO recombination in cytochrome c are a tool for studying the heme pocket, in a similar way as NO in myoglobin. We discuss the differences in the CO kinetics between the mutants in terms of the properties of the heme environment and strategies to enhance the CO escape yield. Experiments on double mutants in which Phe-82 is replaced by Asp or Gly as well as the M80D substitution indicate that such steric changes substantially increase the motional freedom-dissociated CO. |
| Databáze: | OpenAIRE |
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