Binding and Energetics of Electron Transfer between an Artificial Four-Helix Mn-Protein and Reaction Centers from Rhodobacter sphaeroides

Eduardo Espiritu, Tien L. Olson, Joann Williams, James Allen

    Research output: Contribution to journalArticle

    Abstract

    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.

    Original languageEnglish (US)
    Pages (from-to)6460-6469
    Number of pages10
    JournalBiochemistry
    Volume56
    Issue number49
    DOIs
    StatePublished - Dec 12 2017

    Fingerprint

    Rhodobacter sphaeroides
    Electrons
    Bacteriochlorophylls
    Proteins
    Dimers
    Cytochrome c Group
    Metalloproteins
    Photosynthetic Reaction Center Complex Proteins
    Proteobacteria
    Redox reactions
    Amino Acid Substitution
    Lighting
    Free energy
    Oxidation-Reduction
    Protons
    Spectrum Analysis
    Substitution reactions
    Metals
    Amino Acids
    Oxidation

    ASJC Scopus subject areas

    • Biochemistry

    Cite this

    Binding and Energetics of Electron Transfer between an Artificial Four-Helix Mn-Protein and Reaction Centers from Rhodobacter sphaeroides. / Espiritu, Eduardo; Olson, Tien L.; Williams, Joann; Allen, James.

    In: Biochemistry, Vol. 56, No. 49, 12.12.2017, p. 6460-6469.

    Research output: Contribution to journalArticle

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