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D1' centers are less efficient than normal photosystem II centers.
C Funk1, R Wiklund, W P Schröder
1Department of Biochemistry and Biophysics, The Arrhenius Laboratories, Stockholm University, Sweden. christiane@dbb.su.se
FEBS Letters
|September 15, 2001
Summary
The photosystem II (PSII) D1' protein in Synechocystis 6803, with leucine replacing phenylalanine at position 186, reduces chlorophyll fluorescence. This mutation affects charge recombination but not oxygen evolution in PSII centers.
Area of Science:
- Photosynthesis research
- Molecular biology of cyanobacteria
- Protein engineering
Background:
- Photosystem II (PSII) is crucial for oxygenic photosynthesis.
- The D1 protein is a core component of the PSII reaction center.
- Synechocystis 6803 possesses a D1 variant (D1') with a phenylalanine to leucine substitution at position 186 (Phe-186).
Purpose of the Study:
- To investigate the functional impact of the D1' protein and Phe-186 substitutions on PSII activity.
- To analyze how altering the D1 protein affects light-dependent reactions in Synechocystis 6803.
Main Methods:
- Analysis of Synechocystis 6803 mutants expressing D1' or engineered D1 proteins with Phe-186 substitutions.
- Utilized 77 K fluorescence emission spectra.
- Measured chlorophyll a fluorescence induction yield and decay kinetics.
- Assessed flash-induced oxygen evolution.
Main Results:
- PSII centers containing D1' showed a 50% reduction in variable chlorophyll a fluorescence yield compared to normal D1 centers.
- Flash-induced oxygen evolution patterns remained unaffected in D1' centers.
- Mutants with Phe-186 substitutions exhibited perturbed P680(+)/Q(A)(-) recombination and altered oxygen oscillation patterns.
Conclusions:
- The substitution of Phe-186 with leucine in the D1 protein significantly impacts the photophysical properties of the PSII reaction center.
- Altered D1 protein structure affects charge recombination dynamics within PSII.
- While oxygen evolution is robust, modifications in D1 influence electron transfer efficiency and stability.