Comparison of Primary Charge Separation in the Photosystem II Reaction Center Complex Isolated from Wild-type and D1-130 Mutants of the Cyanobacterium Synechocystis PCC 6803

Upon exposure to low temperature under constant light conditions, the cyanobacterium Synechococcus sp. PCC 7942 exchanges the photosystem II reaction center D1 protein form 1 (D1:1) with D1 protein form 2 (D1:2). This exchange is only transient, and after acclimation to low temperature the cells revert back to D1:1, which is the preferred form in acclimated cells (Campbell, D., Zhou, G., Gustafsson, P., Ö quist, G., and Clarke, A. K. (1995) EMBO J. 14, 5457-5466). In the present work we use thermoluminescence to study charge recombination events between the acceptor and donor sides of photosystem II in relation to D1 replacement. The data indicate that in cold-stressed cells exhibiting D1:2, the redox potential of Q B becomes lower approaching that of Q A . This was confirmed by examining the Synechococcus sp. PCC 7942 inactivation mutants R2S2C3 and R2K1, which possess only D1:1 or D1:2, respectively. In contrast, the recombination of Q A ؊ with the S 2 and S 3 states did not show any change in their redox characteristics upon the shift from D1:1 to D1:2. We suggest that the change in redox properties of Q B results in altered charge equilibrium in favor of Q A . This would significantly increase the probability of Q A ؊ and P680 ؉ recombination. The resulting non-radiative energy dissipation within the reaction center of PSII may serve as a highly effective protective mechanism against photodamage upon excessive excitation. The proposed reaction center quenching is an important protective mechanism because antenna and zeaxanthin cycle-dependent quenching are not present in cyanobacteria. We suggest that lowering the redox potential of Q B by exchanging D1:1 for D1:2 imparts the increased resistance to high excitation pressure induced by exposure to either low temperature or high light.

Section: Discussionmentioning

confidence: 99%

A Transient Exchange of the Photosystem II Reaction Center Protein D1:1 with D1:2 during Low Temperature Stress ofSynechococcus sp. PCC 7942 in the Light Lowers the Redox Potential of QB

Sane

Ivanov

Sveshnikov

et al. 2002

“…PCC6803 was grown at 30°C in BG-11 medium (11) in liquid and solid (0.5% agar) media under continuous illumination with normal light (50 mol photons/m 2 s, white fluorescence lamp) or high light (1000 mol photons/m 2 s). Pigment Analysis-Pigments were extracted with 80% acetone and analyzed by high performance liquid chromatography (HPLC) with photodiode array detection (SPD-M20A, Shimadzu, Kyoto, Japan) on a reversed phase C18 column (150 ϫ 6 mm, Shim-pack CLC-ODS, Shimadzu) using the solvent (methanol/ethyl acetate ϭ 2:1 (v/v)) at the flow rate of 0.8 ml/min (12).…”

Section: Methodsmentioning

confidence: 99%

Identification of a Novel Vinyl Reductase Gene Essential for the Biosynthesis of Monovinyl Chlorophyll in Synechocystis sp. PCC6803

Itô¹,

Yokono²,

Tanaka

et al. 2008

112

The vast majority of oxygenic photosynthetic organisms use monovinyl chlorophyll for their photosynthetic reactions. For the biosynthesis of this type of chlorophyll, the reduction of the 8-vinyl group that is located on the B-ring of the macrocycle is essential. Previously, we identified the gene encoding 8-vinyl reductase responsible for this reaction in higher plants and termed it DVR. Among the sequenced genomes of cyanobacteria, only several Synechococcus species contain DVR homologues. Therefore, it has been hypothesized that many other cyanobacteria producing monovinyl chlorophyll should contain a vinyl reductase that is unrelated to the higher plant DVR. To identify the cyanobacterial gene that is responsible for monovinyl chlorophyll synthesis, we developed a bioinformatics tool, correlation coefficient calculation tool, which calculates the correlation coefficient between the distributions of a certain phenotype and genes among a group of organisms. The program indicated that the distribution of a gene encoding a putative dehydrogenase protein is best correlated with the distribution of the DVR-less cyanobacteria. We subsequently knocked out the corresponding gene (Slr1923) in Synechocystis sp. PCC6803 and characterized the mutant. The knock-out mutant lost its ability to synthesize monovinyl chlorophyll and accumulated 3,8-divinyl chlorophyll instead. We concluded that Slr1923 encodes the vinyl reductase or a subunit essential for monovinyl chlorophyll synthesis. The function and evolution of 8-vinyl reductase genes are discussed.Chlorophyll is an essential molecule that is utilized in photosynthetic reactions (1). Various chlorophyll species exist among photosynthetic organisms. Anoxygenic photosynthetic bacteria contain bacteriochlorophyll a, b, c, d, e, and g (2), and oxygenic photosynthetic organisms such as cyanobacteria, algae, and land plants produce chlorophyll a, b, c, d and 3,8-divinyl chlorophyll a 3 and b ( Fig. 1) (3, 4). Among them, the biosynthesis of chlorophyll a, b, c, d and all bacteriochlorophyll species requires the reduction of the 8-vinyl group (2). All of these chlorophyll molecules have a common backbone structure. Modification of the side chains on the common backbone structure gives rise to the diversity of chlorophylls (5, 6). Among the variety of chlorophyll species, bacteriochlorophyll a and monovinyl chlorophyll a (Fig. 1) are most commonly used for the photochemistry in photosynthetic organisms. The exceptions to this are a group of marine cyanobacteria, Prochlorococcus species (7), and a cyanobacterial symbiont, Acaryochloris marina (8), which use 3,8-divinyl chlorophyll a (Fig. 1) and chlorophyll d for their photochemistry, respectively. It is not clear why the majority of photosynthetic organisms prefer monovinyl chlorophylls instead of divinyl chlorophyll species. Akimoto et al. (9) recently suggested that the replacement of monovinyl chlorophylls by 3,8-divinyl chlorophylls in the dvr mutant of Arabidopsis thaliana significantly changed the antenna system and t...

“…1 for ring designation) carbonyl group and the protein. Significantly, only the pheophytin (active branch) that is hydrogen-bonded to glutamic acid 130 of polypeptide D1 (D1-E130 residue) via the ring V carbonyl group is reduced following charge separation (2). Site-directed mutagenesis coupled with spectroscopic techniques have proven to be extremely useful tools to characterize pigment-protein interactions.…”

Section: Photosystem II (Psii)mentioning

confidence: 99%

“…Modeling studies based on the sequence homology between the PSII D1 and D2 subunits and the bacterial reaction center L and M subunits have been carried out on C. reinhardtii, as well as on spinach, pea and Synechocystis (6,7). Mutagenesis studies on Synechocystis have also been carried out at the predicted pheophytin hydrogen bonding site (2). These modeling and mutagenesis studies supported the conclusion of the earlier spectroscopic studies that the pheophytin ring V carbonyl group in all PSII complexes is hydrogen-bonded.…”

Section: Photosystem II (Psii)mentioning

confidence: 99%

High Field EPR Study of the Pheophytin Anion Radical in Wild Type and D1-E130 Mutants of Photosystem II in Chlamydomonas reinhardtii

Dorlet

Xiong²,

Sayre³

et al. 2001

The intermediate electron acceptor in photosystem II is a pheophytin molecule. The radical anion of this molecule was studied using high field electron paramagnetic resonance in a series of Chlamydomonas reinhardtii mutants. Glutamic acid 130 of the D1 polypeptide is thought to hydrogen bond the ring V carbonyl group of this radical. Mutations at this site, designed to weaken or remove this hydrogen bond, strongly affected the g tensor of the radical. The upward shift of the g x component followed the decreasing hydrogen bonding capacity of the amino acid introduced. This behavior is similar to that of tyrosyl and semiquinone radicals. It is also consistent with the optical spectra of the pheophytin in similar mutants. Density functional calculations were used to calculate the g tensors and rationalize the observed trend in the variation of the g x value for pheophytin and bacteriopheophytin radical. The theoretical results support the experimental observations and demonstrate the sensitivity of g values to the electrostatic protein environment for these types of radicals. Photosystem II (PSII)1 is a large protein complex found in higher plants and green algae that catalyzes the oxidation of water. The structure of PSII has been very recently determined to 3.8 Å resolution (1). The primary electron acceptor in PSII is a pheophytin-a molecule. There are two symmetry-related pheophytins in PSII that differ with respect to the presence or absence of a hydrogen bonding interaction between the pheophytin ring V ( Fig. 1 for ring designation) carbonyl group and the protein. Significantly, only the pheophytin (active branch) that is hydrogen-bonded to glutamic acid 130 of polypeptide D1 (D1-E130 residue) via the ring V carbonyl group is reduced following charge separation (2). Site-directed mutagenesis coupled with spectroscopic techniques have proven to be extremely useful tools to characterize pigment-protein interactions. The resolution of the x-ray structure is currently insufficient to accurately determine such interactions. In this paper, we report on HF-EPR measurements of the Pheo . radical in spinach as well as wild type and site-specific mutants of Chlamydomonas reinhardtii, which can be used to more precisely characterize such interactions between radicals and neighboring protein residues.The pheophytins in photosynthetic reaction centers have been studied using a variety of methods. Comparative measurements of the carbonyl vibrational frequencies of the bacterial and plant reaction centers using resonance Raman (3) and differential Fourier transform infrared spectroscopy (4) suggested that the ring V carbonyl group was likely to be hydrogen bonded in PSII. Such a hydrogen bond was also inferred from electron nuclear double resonance studies by using deuterium exchange experiments and in vitro pheophytin models (5). Modeling studies based on the sequence homology between the PSII D1 and D2 subunits and the bacterial reaction center L and M subunits have been carried out on C. reinhardtii, as well as on spina...