Tryptophan at position 181 of the D2 protein of photosystem II confers quenching of variable fluorescence of chlorophyll

Implications for the mechanism of energy-dependent quenching

Dmitrii V. Vavilin, Svetlana Y. Ermakova-Gerdes, Anna T. Keilty, Willem Vermaas

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

The lumenal CD loop region of the D2 protein of photosystem II contains residues that interact with a reaction center chlorophyll and the redox- active TyrD. Using combinatorial mutagenesis. photoautotrophic mutants of Synechocystis sp. PCC 6803 have been generated with multiple amino acid changes in this region. The CD loop mutations were transferred into a photosystem I-less Synechocystis strain to facilitate characterization of photosystem II properties in the mutants. Most of the combinatorial photosystem I-less mutants obtained had a high yield of variable fluorescence, Fv. However, in three mutants, which shared a replacement of Phe181 by Trp, the F(V) yield was dramatically reduced although a high rate of oxygen evolution was maintained. A site-directed F181W D2 mutant shared similar properties. Picosecond time-resolved fluorescence measurements revealed that in the combinatorial F181W mutants the fluorescence lifetimes in closed and open photosystem II centers were essentially identical and were similar to the fluorescence lifetime in open centers of the control strain. These results are explained by quenching of variable fluorescence in the mutants by charge separation between Trp181 and excited reaction center chlorophyll. This reaction competes efficiently with fluorescence and nonradiative decay in closed photosystem II centers, where the lifetime of the excitation in the chlorophyll antenna is long. Thermodynamic considerations favor the formation of oxidized tryptophan and reduced chlorophyll in the quenching reaction, presumably followed by charge recombination. A possible role of tryptophan-chlorophyll charge separation in the mechanism of energy-dependent quenching of excitations in photosynthesis is discussed.

Original languageEnglish (US)
Pages (from-to)14690-14696
Number of pages7
JournalBiochemistry
Volume38
Issue number44
DOIs
StatePublished - Nov 2 1999

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Photosystem II Protein Complex
Chlorophyll
Tryptophan
Quenching
Fluorescence
Synechocystis
Photosystem I Protein Complex
Proteins
Strain control
Mutagenesis
Photosynthesis
Thermodynamics
Genetic Recombination
Oxidation-Reduction
Antennas
Oxygen
Amino Acids
Mutation

ASJC Scopus subject areas

  • Biochemistry

Cite this

Tryptophan at position 181 of the D2 protein of photosystem II confers quenching of variable fluorescence of chlorophyll : Implications for the mechanism of energy-dependent quenching. / Vavilin, Dmitrii V.; Ermakova-Gerdes, Svetlana Y.; Keilty, Anna T.; Vermaas, Willem.

In: Biochemistry, Vol. 38, No. 44, 02.11.1999, p. 14690-14696.

Research output: Contribution to journalArticle

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abstract = "The lumenal CD loop region of the D2 protein of photosystem II contains residues that interact with a reaction center chlorophyll and the redox- active TyrD. Using combinatorial mutagenesis. photoautotrophic mutants of Synechocystis sp. PCC 6803 have been generated with multiple amino acid changes in this region. The CD loop mutations were transferred into a photosystem I-less Synechocystis strain to facilitate characterization of photosystem II properties in the mutants. Most of the combinatorial photosystem I-less mutants obtained had a high yield of variable fluorescence, Fv. However, in three mutants, which shared a replacement of Phe181 by Trp, the F(V) yield was dramatically reduced although a high rate of oxygen evolution was maintained. A site-directed F181W D2 mutant shared similar properties. Picosecond time-resolved fluorescence measurements revealed that in the combinatorial F181W mutants the fluorescence lifetimes in closed and open photosystem II centers were essentially identical and were similar to the fluorescence lifetime in open centers of the control strain. These results are explained by quenching of variable fluorescence in the mutants by charge separation between Trp181 and excited reaction center chlorophyll. This reaction competes efficiently with fluorescence and nonradiative decay in closed photosystem II centers, where the lifetime of the excitation in the chlorophyll antenna is long. Thermodynamic considerations favor the formation of oxidized tryptophan and reduced chlorophyll in the quenching reaction, presumably followed by charge recombination. A possible role of tryptophan-chlorophyll charge separation in the mechanism of energy-dependent quenching of excitations in photosynthesis is discussed.",
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AB - The lumenal CD loop region of the D2 protein of photosystem II contains residues that interact with a reaction center chlorophyll and the redox- active TyrD. Using combinatorial mutagenesis. photoautotrophic mutants of Synechocystis sp. PCC 6803 have been generated with multiple amino acid changes in this region. The CD loop mutations were transferred into a photosystem I-less Synechocystis strain to facilitate characterization of photosystem II properties in the mutants. Most of the combinatorial photosystem I-less mutants obtained had a high yield of variable fluorescence, Fv. However, in three mutants, which shared a replacement of Phe181 by Trp, the F(V) yield was dramatically reduced although a high rate of oxygen evolution was maintained. A site-directed F181W D2 mutant shared similar properties. Picosecond time-resolved fluorescence measurements revealed that in the combinatorial F181W mutants the fluorescence lifetimes in closed and open photosystem II centers were essentially identical and were similar to the fluorescence lifetime in open centers of the control strain. These results are explained by quenching of variable fluorescence in the mutants by charge separation between Trp181 and excited reaction center chlorophyll. This reaction competes efficiently with fluorescence and nonradiative decay in closed photosystem II centers, where the lifetime of the excitation in the chlorophyll antenna is long. Thermodynamic considerations favor the formation of oxidized tryptophan and reduced chlorophyll in the quenching reaction, presumably followed by charge recombination. A possible role of tryptophan-chlorophyll charge separation in the mechanism of energy-dependent quenching of excitations in photosynthesis is discussed.

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