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PubMed2005

PsbS genotype in relation to coordinated function of PS II and PS I in Arabidopsis leaves.

Application of multiple probes to systems that carry specific mutations provides a powerful means for studying how known regulators of light utilization interact in vivo. Two lines of Arabidopsis thaliana were studied, each carrying a unique lesion in the nuclear psbS gene encoding a 22-kDa pigment-binding protein (PS II-S) essential for full expression of photoprotective, rapid-phase, nonphotochemical quenching of chlorophyll fluorescence (NPQ). The PS II-S protein is absent in line npq4-1 due to deletion of psbS. Line npq4-9 expresses normal levels of PS II-S but carries a single amino acid substitution that lowers NPQ capacity by about 50%. A prior report [Peterson RB and Havir EA (2001) Planta 214: 142-152] described an altered pattern of redox states of the acceptor side of Photosystem II (PS II) and donor side of Photosystem I (PS I) for npq4-9 suggesting that interphotosystem electron transport may be restricted by a higher transthylakoid DeltapH in this line. In vivo steady state fluorescence and absorbance measurements (820 nm) confirmed these earlier observations for line npq4-9 but not for npq4-1. Thus, the prior results cannot be correlated simply to a loss of NPQ capacity. Likewise, the kinetics of the 820-nm absorbance change did not indicate a substantial effect of psbS genotype on electron flow from plastoquinol to PS I. A simple model is proposed to relate linear electron transport rate (measured gasometrically) to a parameter (based on fluorescence) that provides a relative measure of the density of excitation available for photochemistry in PS II. Surprisingly, analyses using this model suggested that the in vivo midpoint potential of the primary quinone acceptor in PS II (Q(A)) is lowered in both psbS mutant lines. This heretofore-unsuspected role for PS II-S is discussed with regard to: (1) numerous prior reports indicating plasticity of the redox potential of Q(A) and (2) the basis for the contrasting regulation of quantum yields of PS I and II in npq4-1 and npq4-9.

Amino Acid Substitution↗

PubMed1998

Association of His117 in the D2 protein of photosystem II with a chlorophyll that affects excitation-energy transfer efficiency to the reaction center.

His117 of the D2 protein of photosystem II (PS II) is a conserved residue in the second transmembrane region of the protein and has been suggested to bind chlorophyll. Nine site-directed mutations were introduced at residue 117, using both photosystem I (PS I)-containing and PS I-less background strains of the cyanobacterium Synechocystis sp. PCC 6803. Of these nine, four (H117C, H117M, H117N, and H117T) were photoautotrophic in the PS I-containing background. The other mutants (H117F, H117L, H117P, H117R, and H117Y) did not accumulate appreciable amounts of PS II in their thylakoids. The type of residues that can functionally replace His117 support the notion of His117 serving as a chlorophyll ligand. The properties of the H117N and H117T mutants were characterized in more detail. Whereas the properties of the H117N mutant were close to those of wild type, in the H117T mutant the 77-K fluorescence emission spectrum shows a much smaller amplitude at 695 nm than expected on the basis of the amount of PS II that is present. Moreover, in H117T, the amount of light needed to half-saturate O2-evolution rates was twofold higher than in the control strain, and the variable fluorescence yield was quenched. However, O2 evolution rates at saturating light intensity and electron-transport kinetics were normal in the mutant. Also, the radical accessory chlorophyll (Chlz+) formed by donation of an electron to the PS-II reaction center could be generated normally by illumination at low temperature in the H117T mutant. We conclude that the chlorophyll associated with residue 117 of the D2 protein is important for efficient excitation transfer between the proximal antenna and the PS II reaction center. A possible mechanism involving a chlorophyll cation to explain the quenching in the H117T mutant is discussed.

Chlorophyll↗

PubMed2003

Probing connection of PBS with the photosystems in intact cells of Spirulina platensis by temperature-induced fluorescence fluctuation.

Temperature-dependent fluorescence for intact cells of cyanobacterium Spirulina platensis was detected to search for the connection of the phycobilisome (PBS) with Photosystem I (PSI) and Photosystem II (PSII). Some interesting results were obtained from the deconvoluted fluorescence components of C-phycocyanin (C-PC), allophycocyanin (APC), PSI and PSII as well as the fluorescence spectra of the intact cells at room temperature (RT=25 degrees C) and 0 degrees C. It was observed that, compared to those at RT, both of the fluorescence components for PSI and APC increased, whereas those for PSII and C-PC decreased at 0 degrees C with excitation at 580 nm, that is, the fluorescence for C-PC is not synchronous with that for APC, and the fluorescence fluctuation for PSI is not synchronous with that for PSII. On the other hand, the decrease in C-PC fluorescence is synchronous with the increase in PSI fluorescence, and the increase in APC fluorescence is synchronous with the decrease in PSII fluorescence. Therefore, it can be readily deduced that PBS should be coupled not only with PSII through the terminal acceptors in the APC core but also with PSI through C-PC in PBS rods at physiological condition, while at 0 degrees C, a migration of a PBS makes the APC partially detached from PSII but the C-PC more efficiently coupled with PSI. The results provide good evidences for "mobile PBS" model and "parallel connection" model but not for the "spillover" model.

Bacterial Proteins↗

PubMed1998

A thermal broadening study of the antenna chlorophylls in PSI-200, LHCI, and PSI core.

The intact photosystem I of maize containing its full antenna complement (PSI-200) has been purified and fractionated into the core and outer antenna (LHCI) components. It is demonstrated by absorption and fluorescence spectroscopy that at least 80% of the long wavelength absorbing antenna pigments (red forms) are located in LHCI. Absorption spectra in the Qy region of all three preparations were measured between 72 and 300 K and subjected to a thermal broadening analysis. Data are interpreted in the linear electron-phonon coupling assumption, and the average optical reorganization energy (Snum) for the bulk pigment band and the red absorption tail determined. A marked asymmetry in Snum values across the absorption band is demonstrated. The bulk pigments in all three preparations have rather low values, in the range of 15-25 cm-1, suggesting that Stokes shifts for the absorption forms are in the 1. 5-3 nm range. On the other hand the red forms have markedly greater reorganization energies. While a direct thermal analysis of the red tail indicates minimum Snum values of around 60 cm-1, when the contribution of the red tail of the bulk pigments is corrected for in LHCI, the more reliable value of 110 cm-1 is obtained. These high Snum values for the red pigment forms suggest that they have unusually wide homogeneously broadened absorption bands and large Stokes shifts (6-11 nm).

Carrier Proteins↗

PubMed2001

Thermodynamics of electron transfer in oxygenic photosynthetic reaction centers: volume change, enthalpy, and entropy of electron-transfer reactions in manganese-depleted photosystem II core complexes.

We have previously reported the thermodynamic data of electron transfer in photosystem I using pulsed time-resolved photoacoustics [Hou et al. (2001) Biochemistry 40, 7109-7116]. In the present work, using preparations of purified manganese-depleted photosystem II (PS II) core complexes from Synechocystis sp. PCC 6803, we have measured the DeltaV, DeltaH, and estimated TDeltaS of electron transfer on the time scale of 1 micros. At pH 6.0, the volume contraction of PS II was determined to be -9 +/- 1 A3. The thermal efficiency was found to be 52 +/- 5%, which corresponds to an enthalpy change of -0.9 +/- 0.1 eV for the formation of the state P680+Q(A-) from P680*. An unexpected volume expansion on pulse saturation of PS II was observed, which is reversible in the dark. At pH 9.0, the volume contraction, the thermal efficiency, and the enthalpy change were -3.4 +/- 0.5 A3, 37 +/- 7%, and -1.15 +/- 0.13 eV, respectively. The DeltaV of PS II, smaller than that of PS I and bacterial centers, is assigned to electrostriction and analyzed using the Drude-Nernst equation. To explain the small DeltaV for the formation of P680+Q(A-) or Y(Z*)Q(A-), we propose that fast proton transfer into a polar region is involved in this reaction. Taking the free energy of charge separation of PS II as the difference between the energy of the excited-state P680* and the difference in the redox potentials of the donor and acceptor, the apparent entropy change (TDeltaS) for charge separation of PS II is calculated to be negative, -0.1 +/- 0.1 eV at pH 6.0 (P680+Q(A-)) and -0.2 +/- 0.15 eV at pH 9.0 (Y(Z*)Q(A-)). The thermodynamic properties of electron transfer in PS II core reaction centers thus differ considerably from those of bacterial and PS I reaction centers, which have DeltaV of approximately -27 A3, DeltaH of approximately -0.4 eV, and TDeltaS of approximately +0.4 eV.

Cyanobacteria↗

PubMed2000

Mutations in the CD-loop region of the D2 protein in Synechocystis sp. PCC 6803 modify charge recombination pathways in photosystem II in vivo.

The lumenal CD-loop region of the D2 protein of photosystem II contains residues that interact with the primary electron donor P680 and the redox active tyrosyl residue Y(D). Photosystem II properties were studied in a number of photoautotrophic mutants of Synechocystis sp. PCC 6803, most of which carried combinatorial mutations in residues 164-170, 179-186, or 187-194 of the D2 protein. To facilitate characterization of photosystem II properties in the mutants, the CD-loop mutations were introduced into a photosystem I-less background. According to variable fluorescence decay measurements in DCMU-treated cells, charge recombination of Q(A)(-) with the donor side was faster in the majority of mutants (t(1/2) = 45-140 ms) than in the control (t(1/2) = 180 ms). However, in one mutant (named C7-3), the decay of Q(A)(-) was 2 times slower than in the control (t(1/2) = 360 ms). The decay half-time of each mutant correlated with the yield of the Q-band of thermoluminescence (TL) emitted due to S(2)Q(A)(-) charge recombination. The C7-3 mutant had the highest TL intensity, whereas no Q-band was detected in the mutants with fast Q(A)(-) decay (t(1/2) = 45-50 ms). The correlated changes in the rate of recombination and in TL yield in these strains suggest the existence of a nonradiative pathway of charge recombination between Q(A)(-) and the donor side. This may involve direct electron transfer from Q(A)(-) to P680(+) in a way not leading to formation of excited chlorophyll. Many mutations in the CD-loop appear to increase the equilibrium P680(+) concentration during the lifetime of the S(2)Q(A)(-) state, for example, by making the midpoint potential of the P680(+)/P680 redox couple more negative. The nonradiative charge recombination pathway involves a low activation energy and is less temperature-dependent than the formation of excited P680 that leads to TL emission. Therefore, during the TL measurements in these mutants, the S(2)Q(A)(-) state can recombine nonradiatively before temperatures are reached at which radiative charge recombination becomes feasible. The results presented here highlight the presence of two charge recombination pathways and the importance of the CD-loop of the D2 protein in determination of the energy gap between the P680(+)S(1) and P680S(2) states.

Amino Acid Sequence↗

PubMed2000

Minicircular plastid DNA in the dinoflagellate Amphidinium operculatum.

Plastid DNA was purified from the dinoflagellate Amphidinium operculatum. The genes atpB, petD, psaA, psbA and psbB have been shown to reside on single-gene minicircles of a uniform size of 2.3-2.4 kb. The psaA and psbB genes lack conventional initiation codons in the expected positions, and may use GTA for translation initiation. There are marked biases in codon preference. The predicted PsbA protein lacks the C-terminal extension which is present in all other photosynthetic organisms except Euglena gracilis, and there are other anomalies elsewhere in the predicted amino acid sequences. The non-coding regions of the minicircles contain a "core" region which includes a number of stretches that are highly conserved across all minicircles and modular regions that are conserved within subsets of the minicircles.

Amino Acid Sequence↗

PubMed2006

Lipids in photosynthetic reaction centres: structural roles and functional holes.

Photosynthetic proteins power the biosphere. Reaction centres, light harvesting antenna proteins and cytochrome b(6)f (or bc(1)) complexes are expressed at high levels, have been subjected to an intensive spectroscopic, biochemical and mutagenic analysis, and several have been characterised to an informatively high resolution by X-ray crystallography. In addition to revealing the structural basis for the transduction of light energy, X-ray crystallography has brought molecular insights into the relationships between these multicomponent membrane proteins and their lipid environment. Lipids resolved in the X-ray crystal structures of photosynthetic proteins bind light harvesting cofactors, fill intra-protein cavities through which quinones can diffuse, form an important part of the monomer-monomer interface in multimeric structures and may facilitate structural flexibility in complexes that undergo partial disassembly and repair. It has been proposed that individual lipids influence the biophysical properties of reaction centre cofactors, and so affect the rate of electron transfer through the complex. Lipids have also been shown to be important for successful crystallisation of photosynthetic proteins. Comparison of the three types of reaction centre that have been structurally characterised reveals interesting similarities in the position of bound lipids that may point towards a generic requirement to reinforce the structure of the core electron transfer domain. The crystallographic data are also providing new opportunities to find molecular explanations for observed effects of different types of lipid on the structure, mechanism and organisation of reaction centres and other photosynthetic proteins.

Binding Sites↗

PubMed2006

Protein composition and native state of pigments of thylakoid membrane of wheat genotypes differently tolerant to water stress.

Protein composition and native state of chlorophylls were analyzed in two wheat (Triticum durum L.) genotypes with different tolerance to drought, Barakatli-95 (drought-tolerant) and Garagylchyg-2 (drought-sensitive), during water deficit. It is shown that the plants subjected to water deficit appear to have a slight increase in alpha- and beta-subunits of CF1 ATP-synthase complex (57.5 and 55 kD, respectively) in Barakatli-95 and their lower content in Garagylchyg-2. Steady-state levels of the core antenna of PS II (CP47 and CP43) and light-harvesting Chl a/b-apoproteins (LHC) II in the 29.5-24 kD region remained more or less unchanged in both wheat genotypes. The synthesis of 36 kD protein and content of low-molecular-weight polypeptides (21.5, 16.5, and 14 kD) were noticeably increased in the tolerant genotype Barakatli-95. Drought caused significant changes in the carotenoid region of the spectrum (400-500 nm) in drought-sensitive genotype Garagylchyg-2 (especially in the content of pigments of the violaxanthin cycle). A shift of the main band from 740-742 to 738 nm is observed in the fluorescence spectra (77 K) of chloroplasts from both genotypes under water deficiency, and there is a stimulation of the ratio of fluorescence band intensity F687/F740.

Adaptation, Biological↗

PubMed2000

Functional analysis of the PsbX protein by deletion of the corresponding gene in Synechocystis sp. PCC 6803.

The psbX gene (sml0002) coding for a 4.1 kDa protein in Photosystem II of plants and cyanobacteria was deleted in both wild type and in a Photosystem I-less mutant of the cyanobacterium Synechocystis sp. PCC 6803. Polymerase chain reaction and sequencing analysis showed that the mutants had completely segregated. Deletion of the PsbX protein does not seem to influence growth rate, electron transport or water oxidation ability. Whereas a high light induction of the psbX mRNA could be observed in wild type, deletion of the gene did not lead to high light sensibility. Light saturation measurements and 77K fluorescence measurements indicated a minor disconnection of the antenna in the deletion mutant. Furthermore, fluorescence induction measurements as well as immuno-staining of the D1 protein showed that the amount of Photosystem II complexes in the mutants was reduced by 30%. Therefore, PsbX does not seem to be necessary for the Photosystem II electron transport, but directly or indirectly involved in the regulation of the amount of functionally active Photosystem II centres in Synechocystis sp. PCC 6803.

Algal Proteins↗

PubMed1976

The light-harvesting chlorpohyll-protein complex of photosystem II. Its location in the photosynthetic membrane.

We have investigated the structure of the photosynthetic membrane in a mutant of barley known to lack a chlorophyll-binding protein. This protein is thought to channel excitation energy to photosystem II, and is known as the "light-harvesting chlorophyll-protein complex." Extensive stacking of thylakoids into grana occurs in both mutant and wild-type chloroplasts. Examination of membrane internal structure by freeze-fracturing indicates that only slight differences exist between the fracture faces of mutant and wild-type membranes. These differences are slight reductions in the size of particles visible on the EFs fracture face, and in the number of particles seen on the PFs fracture face. No differences can be detected between mutant and wild-type on the etched out surface of the membrane. In contrast, tetrameric particles visible on the etched inner surface of wild-type thylakoids are extremely difficult to recognize on similar surfaces of the mutant. These particles can be recognized on inner surfaces of the mutant membranes when they are organized into regular lattices, but these lattices show a much closer particle-to-particle spacing than similar lattices in wild-type membranes. Although several interpretations of these data are possible, these observations are consistent with the proposal that the light-harvesting chlorophyll-protein complex of photosystem II is bound to the tetramer (which is visible on the EFs face as a single particle) near the inner surface of the membrane. The large tetramer, which other studies have shown to span the thylakoid membrane, may represent an assembly of protein, lipid, and pigment comprising all the elements of the photosystem II reaction. A scheme is presented which illustrates one possibility for the light reaction across the photosynthetic membrane.

Carrier Proteins↗

PubMed2005

The effect of norflurazon on protein composition and chlorophyll organization in pigment-protein complex of photosystem II.

The pyridazinone-type herbicide norflurazon SAN 9789 inhibiting the biosynthesis of long-chain carotenoids results in significant decrease in PS II core complexes and content of light-harvesting complex (LHC) polypeptides in the 29.5-21 kDa region. The Chl a forms at 668, 676, and 690 nm that belong to LHC and antenna part of PS I disappear completely after treatment. The intensity of the Chl b form at 648 nm is sharply decreased in treated seedlings grown under 30 or 100 lx light intensity. The bands of carotenoid absorption at 421, 448 (Chl a), 452, 480, 492, 496 (beta-carotene), and 508 nm also disappear. The band shift from 740 to 720 nm and decrease in its intensity relative to the 687 nm emission peak in the low-temperature fluorescence spectrum (77 K) suggests a disturbance of energy transfer from LHC to the Chl a form at 710-712 nm.

Carotenoids↗

PubMed1984

Chlorophyll-Protein Complexes of a Photosystem II Mutant of Maize : Evidence that Chlorophyll-Protein a-2 and a Chlorophyll-Protein Complex Derived from a Photosystem I Antennae System Comigrate on Polyacrylamide Gels.

Use of the octyl beta-d-glucopyranoside solubilization procedure of Camm and Green (1980 Plant Physiol 66: 428-432) reveals that thylakoid membranes of a photosystem (PS) II-deficient maize (Zea mays L.) mutant lack two chlorophyll protein (CP) complexes associated with PSII, i.e. CPa-1 and CPa-2. In contrast, when lithium dodecyl sulfate is used to solubilize the membranes of the mutant prior to electrophoretic separation, a CP complex is observed which has a mobility similar to that of CPa-2. Comparison of spectral characteristics and polypeptide composition of the green bands in this region taken from samples of the mutant, normal sibling control plants and from PSII preparations indicate that the CP complex observed in the mutant represents a portion of a light-harvesting complex of PSI (Mullet et al. 1980 Plant Physiol 65: 814-822). The green band observed in normal maize samples can contain both the CPa-2 complex as well as the CP complex derived from the PSI antennae system.

Journal Article↗

PubMed1997

Minor constituents of photosystem II core complexes: possible regulators of photosystem II protein kinase.

We recently identified a 58-kDa protein kinase, PS II-PK, closely associated in substoichiometric abundance with a core complex of photosystem II and capable of phosphorylating both the photosystem and its associated light-harvesting proteins. Oxidizing species, produced during aerobic illumination, inhibited the kinase, and the irreversibility of this process is now demonstrated. Other substoichiometric protein constituents of the core preparation were identified as probably originating in the grana margins. These include the cytochrome b6/f complex, the apocytochrome f precursor, and membrane-bound ferredoxin:NADP+ oxidoreductase. PS II-PK was successfully resolved from photosystem II cores and shown to be active in the absence of cytochrome complex.

Cell Compartmentation↗

PubMed1998

Implications of a developmental-stage-dependent thylakoid-bound protease in the stabilization of the light-harvesting pigment-protein complex serving photosystem II during thylakoid biogenesis in red kidney bean

Intact etioplasts of bean (Phaseolus vulgaris) plants exhibit proteolytic activity against the exogenously added apoprotein of the light-harvesting pigment-protein complex serving photosystem II (LHCII) that increases as etiolation is prolonged. The activity increases in the membrane fraction but not in the stroma, where it remains low and constant and is mainly directed against LHCII and protochlorophyllide oxidoreductase. The thylakoid proteolytic activity, which is low in etioplasts of 6-d-old etiolated plants, increases in plants pretreated with a pulse of light or exposed to intermittent-light (ImL) cycles, but decreases during prolonged exposure to continuous light, coincident with chlorophyll (Chl) accumulation. To distinguish between the control of Chl and/or development on proteolytic activity, we used plants exposed to ImL cycles of varying dark-phase durations. In ImL plants exposed to an equal number of ImL cycles with short or long dark intervals (i.e. equal Chl accumulation but different developmental stage) proteolytic activity increased with the duration of the dark phase. In plants exposed to ImL for equal durations to such light-dark cycles (i.e. different Chl accumulation but same developmental stage) the proteolytic activity was similar. These results suggest that the protease, which is free to act under limited Chl accumulation, is dependent on the developmental stage of the chloroplast, and give a clue as to why plants in ImL with short dark intervals contain LHCII, whereas those with long dark intervals possess only photosystem-unit cores and lack LHCII.

Journal Article↗

PubMed1995

Genetic analysis of the form and function of photosystem I and photosystem II.

Photosystem I (PSI) and photosystem II (PSII) are two multisubunit pigment-protein complexes in the thylakoid membranes in the chloroplasts of plants, algae, and in cyanobacteria. In recent years, directed mutagenesis has been used to specifically modify individual polypeptide components of both PSI and PSII in cyanobacteria and the green alga, Chlamydomonas. Biochemical and spectroscopic analyses of such mutants have produced a rich source of information regarding the structure and function of these two protein complexes. In addition, the natural transformation systems of certain cyanobacterial strains have been exploited to unravel novel genetic loci that regulate the biogenesis and function of these proteins. This review article discusses recent key findings in these areas.

Genes, Bacterial↗

PubMed1990

Amino-terminal sequence of the 21 kDa apoprotein of a minor light-harvesting pigment-protein complex of the Photosystem II antenna (LHC IId/CP24).

The 21 kDa apoprotein of LHC IId, a minor light-harvesting antenna component of Photosystem II, has been isolated and subjected to N-terminal protein sequencing. A sequence of 66 residues was obtained which contains regions of considerable homology to both those reported for LHC II and LHC I, but which is obviously distinct from them. The proposed occurrence of an identical 21 kDa LHC subunit in both photosystems I and II is shown to be incorrect.

Amino Acid Sequence↗

PubMedDate not supplied

[Kinetics and spectra of photo-induced changes in the absorption of pigment-protein complexes of photosystem 1 in a picosecond range].

The energy transfer from the light-harvesting antenna chlorophylls to the reaction center molecules and subsequent charge separation were investigated using a difference picosecond spectrophotometer with selective excitation. The objects were the pigment-protein complexes of photosystem 1 (Chl/P700 = 60) isolated from bean leaves. The difference absorption spectra of the excited states of light-harvesting antenna chlorophylls and the P700 photooxidation were measured. It was shown that the excited states of antenna chlorophylls were generated within 10 ps and deactivated with three-component kinetics: tau 1 = 20--45 ps, tau 2 = 100--300 ps, tau 3 greater than 500 ps. The process of the P700 photooxidation induced by the 650 nm exciting pulse was approximately monoexponential with tau equal to 15--30 ps. It is established that the P700 photooxidation is due to the efficient transfer of excitation energy from antenna chlorophylls to reaction centers.

Chlorophyll↗