Binding and Energetics of Electron Transfer between an Artificial Four-Helix Mn-Protein and Reaction Centers from Rhodobacter sphaeroides
| Autor: | Joann Williams, James P. Allen, Eduardo Espiritu, Tien L. Olson |
|---|---|
| Rok vydání: | 2017 |
| Předmět: |
Protein Conformation
alpha-Helical 0301 basic medicine Photosynthetic reaction centre Photosynthetic Reaction Center Complex Proteins Rhodobacter sphaeroides 010402 general chemistry Photochemistry 01 natural sciences Biochemistry Electron Transport 03 medical and health sciences Electron transfer chemistry.chemical_compound Bacterial Proteins Bacteriochlorophylls chemistry.chemical_classification Manganese biology Electron acceptor biology.organism_classification Electron transport chain Binding constant 0104 chemical sciences Dissociation constant Kinetics 030104 developmental biology chemistry Bacteriochlorophyll Oxidation-Reduction Protein Binding |
| Zdroj: | Biochemistry. 56:6460-6469 |
| ISSN: | 1520-4995 0006-2960 |
| DOI: | 10.1021/acs.biochem.7b00978 |
| Popis: | The ability of an artificial four-helix bundle Mn-protein, P1, to bind and transfer an electron to photosynthetic reaction centers from the purple bacterium Rhodobacter sphaeroides was characterized using optical spectroscopy. Upon illumination of reaction centers, an electron is transferred from P, the bacteriochlorophyll dimer, to QA, the primary electron acceptor. The P1 Mn-protein can bind to the reaction center and reduce the oxidized bacteriochlorophyll dimer, P+, with a dissociation constant of 1.2 μM at pH 9.4, comparable to the binding constant of c-type cytochromes. Amino acid substitutions of surface residues on the Mn-protein resulted in increases in the dissociation constant to 8.3 μM. The extent of reduction of P+ by the P1 Mn-protein was dependent on the P/P+ midpoint potential and the pH. Analysis of the free energy difference yielded a midpoint potential of approximately 635 mV at pH 9.4 for the Mn cofactor of the P1 Mn-protein, a value similar to those found for other Mn cofactors in proteins. The linear dependence of -56 mV/pH is consistent with one proton being released upon Mn oxidation, allowing the complex to maintain overall charge neutrality. These outcomes demonstrate the feasibility of designing four-helix bundles and other artificial metalloproteins to bind and transfer electrons to bacterial reaction centers and establish the usefulness of this system as a platform for designing sites to bind novel metal cofactors capable of performing complex oxidation-reduction reactions. |
| Databáze: | OpenAIRE |
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