Modulation of the free energy of the primary quinone acceptor (Q A) in reaction centers from Rhodobacter sphaeroides

Contributions from the protein and protein-lipid(cardiolipin) interactions

Laszlo Rinyu, Erik W. Martin, Eiji Takahashi, P. Maróti, Colin A. Wraight

Research output: Article

38 Citations (Scopus)

Abstract

The redox midpoint potential (Em) of QA, the primary quinone of bacterial reaction centers, is substantially modulated by the protein environment. Quite subtle mutations in the QA binding site, e.g., at residues M218, M252 and M265, cause significant increases in the equilibrium constant for electron transfer to QB, which indicate relative lowering of the Em of QA. However, reports of functional linkage between the QA and QB sites make it difficult to partition such effects between QA and QB from purely relative changes. We report here measurements on the yield of delayed fluorescence emission from the primary donor (P) accompanying the thermally activated charge recombination of P+QA- to form the excited singlet state of the primary donor, P*. The results show that for mutations of the QA site residues, MetM218 and IleM265, essentially all the substantial thermodynamic effect is localized at QA, with no evidence for a significant effect of these residues on the properties of QB or the mutual influence (linkage) of QA and QB. We also report a significant lowering of the Em of QA by the native lipid, cardiolipin, which brings the Em in isolated reaction centers more in line with that seen in native membrane vesicles (chromatophores). Possible origins of this effect are discussed in the context of the QA binding site structure.

Original languageEnglish
Pages (from-to)93-101
Number of pages9
JournalBBA - Bioenergetics
Volume1655
Issue number1-3
DOIs
Publication statusPublished - ápr. 12 2004

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Rhodobacter sphaeroides
Cardiolipins
Free energy
Binding Sites
Modulation
Chromatophores
Lipids
Mutation
Equilibrium constants
Thermodynamics
Excited states
Genetic Recombination
Oxidation-Reduction
Proteins
Fluorescence
Electrons
Membranes
benzoquinone

ASJC Scopus subject areas

  • Biophysics

Cite this

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title = "Modulation of the free energy of the primary quinone acceptor (Q A) in reaction centers from Rhodobacter sphaeroides: Contributions from the protein and protein-lipid(cardiolipin) interactions",
abstract = "The redox midpoint potential (Em) of QA, the primary quinone of bacterial reaction centers, is substantially modulated by the protein environment. Quite subtle mutations in the QA binding site, e.g., at residues M218, M252 and M265, cause significant increases in the equilibrium constant for electron transfer to QB, which indicate relative lowering of the Em of QA. However, reports of functional linkage between the QA and QB sites make it difficult to partition such effects between QA and QB from purely relative changes. We report here measurements on the yield of delayed fluorescence emission from the primary donor (P) accompanying the thermally activated charge recombination of P+QA- to form the excited singlet state of the primary donor, P*. The results show that for mutations of the QA site residues, MetM218 and IleM265, essentially all the substantial thermodynamic effect is localized at QA, with no evidence for a significant effect of these residues on the properties of QB or the mutual influence (linkage) of QA and QB. We also report a significant lowering of the Em of QA by the native lipid, cardiolipin, which brings the Em in isolated reaction centers more in line with that seen in native membrane vesicles (chromatophores). Possible origins of this effect are discussed in the context of the QA binding site structure.",
keywords = "Cardiolipin, Delayed fluorescence, Electron transfer, Midpoint redox potential, Photosynthetic reaction center, Quinone",
author = "Laszlo Rinyu and Martin, {Erik W.} and Eiji Takahashi and P. Mar{\'o}ti and Wraight, {Colin A.}",
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T1 - Modulation of the free energy of the primary quinone acceptor (Q A) in reaction centers from Rhodobacter sphaeroides

T2 - Contributions from the protein and protein-lipid(cardiolipin) interactions

AU - Rinyu, Laszlo

AU - Martin, Erik W.

AU - Takahashi, Eiji

AU - Maróti, P.

AU - Wraight, Colin A.

PY - 2004/4/12

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N2 - The redox midpoint potential (Em) of QA, the primary quinone of bacterial reaction centers, is substantially modulated by the protein environment. Quite subtle mutations in the QA binding site, e.g., at residues M218, M252 and M265, cause significant increases in the equilibrium constant for electron transfer to QB, which indicate relative lowering of the Em of QA. However, reports of functional linkage between the QA and QB sites make it difficult to partition such effects between QA and QB from purely relative changes. We report here measurements on the yield of delayed fluorescence emission from the primary donor (P) accompanying the thermally activated charge recombination of P+QA- to form the excited singlet state of the primary donor, P*. The results show that for mutations of the QA site residues, MetM218 and IleM265, essentially all the substantial thermodynamic effect is localized at QA, with no evidence for a significant effect of these residues on the properties of QB or the mutual influence (linkage) of QA and QB. We also report a significant lowering of the Em of QA by the native lipid, cardiolipin, which brings the Em in isolated reaction centers more in line with that seen in native membrane vesicles (chromatophores). Possible origins of this effect are discussed in the context of the QA binding site structure.

AB - The redox midpoint potential (Em) of QA, the primary quinone of bacterial reaction centers, is substantially modulated by the protein environment. Quite subtle mutations in the QA binding site, e.g., at residues M218, M252 and M265, cause significant increases in the equilibrium constant for electron transfer to QB, which indicate relative lowering of the Em of QA. However, reports of functional linkage between the QA and QB sites make it difficult to partition such effects between QA and QB from purely relative changes. We report here measurements on the yield of delayed fluorescence emission from the primary donor (P) accompanying the thermally activated charge recombination of P+QA- to form the excited singlet state of the primary donor, P*. The results show that for mutations of the QA site residues, MetM218 and IleM265, essentially all the substantial thermodynamic effect is localized at QA, with no evidence for a significant effect of these residues on the properties of QB or the mutual influence (linkage) of QA and QB. We also report a significant lowering of the Em of QA by the native lipid, cardiolipin, which brings the Em in isolated reaction centers more in line with that seen in native membrane vesicles (chromatophores). Possible origins of this effect are discussed in the context of the QA binding site structure.

KW - Cardiolipin

KW - Delayed fluorescence

KW - Electron transfer

KW - Midpoint redox potential

KW - Photosynthetic reaction center

KW - Quinone

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