The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Hans-erik Åkerlund - One of the best experts on this subject based on the ideXlab platform.
Laurdan fluorescence spectroscopy in the thylakoid bilayer: the effect of Violaxanthin to zeaxanthin conversion on the galactolipid dominated lipid environment.Biochimica et biophysica acta, 2007Co-Authors: Anna Szilágyi, Eva Selstam, Hans-erik ÅkerlundAbstract:
Laurdan (6-lauroyl-2-dimethylaminonaphthalene) fluorescence spectroscopy has been applied to probe the physical status of the thylakoid membrane upon conversion of Violaxanthin to zeaxanthin. So far, only phospholipid-dominated membranes have been studied by this method and hereby we report the first use of laurdan in mono- and digalactosyldiacylglycerol-dominated membrane systems. The generalised polarisation (GP) of laurdan was used as a measure of the structural effect of xanthophyll cycle pigments in isolated spinach (Spinacia oleracea) thylakoids and in model membrane vesicles composed of chloroplast galactolipids. Higher GP values indicate a membrane in a more ordered structure, whereas lower GP values point to a membrane in a less ordered fluid phase. The method was used to probe the effect of Violaxanthin and zeaxanthin in thylakoid membranes at different temperatures. At 4, 25 and 37 degrees C the GP values for dark-adapted thylakoids in the Violaxanthin-form were 0.55, 0.28 and 0.26. After conversion of Violaxanthin to zeaxanthin, at the same temperatures, the GP values were 0.62, 0.36 and 0.34, respectively. GP values increased gradually upon conversion of Violaxanthin to zeaxanthin. Similar results were obtained in the liposomal systems in the presence of these xanthophyll cycle pigments. We conclude from these results that the conversion of Violaxanthin to zeaxanthin makes the thylakoid membrane more ordered.
Membrane curvature stress controls the maximal conversion of Violaxanthin to zeaxanthin in the Violaxanthin cycle--influence of alpha-tocopherol, cetylethers, linolenic acid, and temperature.Biochimica et biophysica acta, 2007Co-Authors: Anna Szilágyi, Marianne Sommarin, Hans-erik ÅkerlundAbstract:
Zeaxanthin, an important component in protection against overexcitation in higher plants, is formed from Violaxanthin by the enzyme Violaxanthin de-epoxidase. We have investigated factors that may control the maximal degree of conversion in the Violaxanthin cycle. The conversion of Violaxanthin to zeaxanthin in isolated spinach thylakoids was followed at different temperatures and in the presence of lipid packing modifiers. The maximum degree of conversion was found to be 35%, 70% and 80% at 4 degrees C, 25 degrees C and 37 degrees C respectively. In the presence of membrane modifying agents, known to promote non-lamellar structures (H(II)), such as linolenic acid the conversion increased, and the maximal level of Violaxanthin de-epoxidation obtained was close to 100%. In contrast, substances promoting lamellar phases (L(alpha)), such as alpha-tocopherol and 8-cetylether (C(16)EO(8)), only 55% and 35% of the Violaxanthin was converted at 25 degrees C, respectively. The results are interpreted in light of the lipid composition of the thylakoid membrane, and we propose a model where a negative curvature elastic stress in the thylakoid lipid bilayer is required for Violaxanthin de-epoxidase activity. In this model zeaxanthin with its longer hydrophobic stretch is proposed to promote lamellar arrangements of the membrane. As a result, zeaxanthin relieves the curvature elastic stress, which in turn leads to inactivation of Violaxanthin de-epoxidase.
Violaxanthin de epoxidase the xanthophyll cycle enzyme requires lipid inverted hexagonal structures for its activityBiochemistry, 2004Co-Authors: Dariusz Latowski, Hans-erik Åkerlund, Kazimierz StrzalkaAbstract:
Bilayer-forming lipids were shown to be ineffective in sustaining the enzymatic activity of Violaxanthin de-epoxidase. On the other hand, non-bilayer-forming lipids, regardless of their different chemical character, ensured high activity of Violaxanthin de-epoxidase, resulting in conversion of Violaxanthin to zeaxanthin. Our data indicates that the presence of lipids forming reversed hexagonal structures is necessary for Violaxanthin de-epoxidase activity and this activity is dependent on the degree of unsaturation of the fatty acids. The significance of the reversed hexagonal phase domains in the conversion of Violaxanthin into zeaxanthin in model systems and in the native thylakoid membranes is discussed.
Changes in the quantities of Violaxanthin de-epoxidase, xanthophylls and ascorbate in spinach upon shift from low to high lightPhotosynthesis Research, 1998Co-Authors: Marie Eskling, Hans-erik ÅkerlundAbstract:
Zeaxanthin, a carotenoid in the xanthophyll cycle, has been suggested to play a role in the protection against photodestruction. We have studied the importance of the parameters involved in zeaxanthin formation by comparing spinach plants grown in low light (100 to 250 μmol m^-2 s^-1) to plants transferred to high light (950 μmol m^-2 s^-1). Different parameters were followed for a total of 11 days. Our experiments show that Violaxanthin de-epoxidase decreased between 15 and 30%, the quantity of xanthophyll cycle pigments doubled to 100 mmol (mol Chl)^-1, corresponding to 27 μmol m^-2, and the rate of Violaxanthin to zeaxanthin conversion was doubled. Lutein and neoxanthin increased from 50 to 71 μmol m^-2 and from 16 to 23 μmol m^-2, respectively. On a leaf area basis, chlorophyll and β-carotene levels first decreased and then after 4 days increased. The chlorophyll a/b ratio was unchanged. The quantity of ascorbate was doubled to 2 mmol m^-2, corresponding to an estimated increase in the chloroplasts from 25 to 50 mM. In view of our data, we propose that the increase in xanthophyll cycle pigments and ascorbate only partly explain the increased rate of conversion of Violaxanthin to zeaxanthin, but the most probable explanation of the faster conversion is an increased accessibility of Violaxanthin in the membrane.
Physiologia Plantarum, 1997Co-Authors: Marie Eskling, Perola Arvidsson, Hans-erik ÅkerlundAbstract:
During the last few years much interest has been focused on the photoprotective role of zeaxanthin. In excessive light zeaxanthin is rapidly formed in the xanthophyll cycle from Violaxanthin, via the intermediate antheraxanthin, a reaction reversed in the dark. The role of zeaxanthin and the xanthophyll cycle in photoprotection, is based on fluorescence quenching measurements, and in many studies a good correlation to the amount of zeaxanthin (and antheraxanthin) has been found. Other suggested roles for the xanthophylls involve, protection against oxidative stress of lipids, participation in the blue light response, modulation of the membrane fluidity and regulation of abscisic acid synthesis. The enzyme Violaxanthin de-epoxidase has recently been purified from spinach and lettuce as a 43-kDa protein. It was found as 1 molecule per 20-100 electron-transport chains. The gene has been cloned and sequenced from Lactuca sativa, Nicotiana tabacum and Arabidopsis thaliana. The transit peptide was characteristic of nuclear-encoded and lumen-localized proteins. The activity of Violaxanthin de-epoxidase is controlled by the lumen pH. Thus, below pH 6.6 the enzyme binds to the thylakoid membrane. In addition ascorbate becomes protonated to ascorbic acid (pKa= 4.2) the true substrate (Km= 0.1 mM) for the Violaxanthin de-epoxidase. We present arguments for an ascorbate transporter in the thylakoid membrane. The enzyme zeaxanthin epoxidase requires FAD as a cofactor and appears to use ferredoxin rather than NADPH as a reductant. The zeaxanthin epoxidase has not been isolated but the gene has been sequenced and a functional protein of 72.5 kDa has been expressed. The xanthophyll cycle pigments are almost evenly distributed in the thylakoid membrane and at least part of the pigments appears to be free in the lipid matrix where we conclude that the conversion by Violaxanthin de-epoxidase occurs.
Harry Y. Yamamoto - One of the best experts on this subject based on the ideXlab platform.
Planta, 2006Co-Authors: Harry Y. YamamotoAbstract:
Monogalactosyldiacylglyceride (MGDG) and digalactosyldiacylglyceride (DGDG) are the major membrane lipids of chloroplasts. The question of the specialized functions of these unique lipids has received limited attention. One function is to support Violaxanthin de-epoxidase (VDE) activity, an enzyme of the Violaxanthin cycle. To understand better the properties of this system, the effects of galactolipids and phosphatidylcholines on VDE activity were examined by two independent methods. The results show that the micelle-forming lipid (MGDG) and bilayer forming lipids (DGDG and phosphatidylcholines) support VDE activity differently. MGDG supported rapid and complete de-epoxidation starting at a threshold lipid concentration (10 μM) coincident with complete solubilization of Violaxanthin. In contrast, DGDG supported slow but nevertheless complete to nearly complete de-epoxidation at a lower lipid concentration (6.7 μM) that did not completely solubilize Violaxanthin. Phosphotidylcholines showed similar effects as DGDG except that de-epoxidation was incomplete. Since VDE requires solubilized Violaxanthin, aggregated Violaxanthin in DGDG at low concentration must become solubilized as de-epoxidation proceeds. High lipid concentrations had lower activity possibly due to formation of multilayered structures (liposomes) that restrict accessibility of Violaxanthin to VDE. MGDG micelles do not present such restrictions. The results indicate VDE operates throughout the lipid phase of the single bilayer thylakoid membrane and is not limited to putative MGDG micelle domains. Additionally, the results also explain the differential partitioning of Violaxanthin between the envelope and thylakoid as due to the relative solubilities of Violaxanthin and zeaxanthin in MGDG, DGDG and phospholipids. The Violaxanthin cycle is hypothesized to be a linked system of the thylakoid and envelope for signal transduction of light stress.
Biochimica et Biophysica Acta, 2000Co-Authors: Arleen D. Hieber, Robert C. Bugos, Harry Y. YamamotoAbstract:
Abstract Violaxanthin de-epoxidase and zeaxanthin epoxidase catalyze the interconversions between the carotenoids Violaxanthin, antheraxanthin and zeaxanthin in plants. These interconversions form the Violaxanthin or xanthophyll cycle that protects the photosynthetic system of plants against damage by excess light. These enzymes are the first reported lipocalin proteins identified from plants and are only the second examples of lipocalin proteins with enzymatic activity. This review summarizes the discovery and characterization of these two unique lipocalin enzymes and examines the possibility of other potential plant lipocalin proteins.
Antisense suppression of Violaxanthin de-epoxidase in tobacco does not affect plant performance in controlled growth conditions.Photosynthesis research, 2000Co-Authors: Sue-hwei Chang, Robert C. Bugos, Wen-hao Sun, Harry Y. YamamotoAbstract:
Violaxanthin de-epoxidase (VDE) catalyzes the de-epoxidation of Violaxanthin to antheraxanthin and zeaxanthin in the xanthophyll cycle. Tobacco was transformed with an antisense VDE construct under control of the cauliflower mosaic virus 35S promoter to determine the effect of reduced levels of VDE on plant growth. Screening of 40 independent transformants revealed 18 antisense lines with reduced levels of VDE activity with two in particular (TAS32 and TAS39) having greater than 95% reduction in VDE activity. Northern analysis demonstrated that these transformants had greatly suppressed levels of VDE mRNA. De-epoxidation of Violaxanthin was inhibited to such an extent that no zeaxanthin and only very low levels of antheraxanthin could be detected after exposure of leaves to high light (2000 μmol m−2 s−1 for 20 min) with no observable effect on levels of other carotenoids and chlorophyll. Non-photochemical quenching was greatly reduced in the antisense VDE tobacco, demonstrating that a significant level of the non-photochemical quenching in tobacco requires de-epoxidation of Violaxanthin. Although the antisense plants demonstrated a greatly impaired de-epoxidation of Violaxanthin, no effect on plant growth or photosynthetic rate was found when plants were grown at a photon flux density of 500 or 1000 μmol m−2 s−1 under controlled growth conditions as compared to wild-type tobacco.
Journal of Biological Chemistry, 1998Co-Authors: Robert C. Bugos, David A Hieber, Harry Y. YamamotoAbstract:
Abstract Violaxanthin de-epoxidase and zeaxanthin epoxidase catalyze the addition and removal of epoxide groups in carotenoids of the xanthophyll cycle in plants. The xanthophyll cycle is implicated in protecting the photosynthetic apparatus from excessive light. Two new sequences for Violaxanthin de-epoxidase from tobacco andArabidopsis are described. Although the mature proteins are well conserved, the transit peptides of these proteins are divergent, in contrast to transit peptides from other proteins targeted to the thylakoid lumen. Sequence analyses of both Violaxanthin de-epoxidase and zeaxanthin epoxidase establish the xanthophyll cycle enzymes as members of the lipocalin family of proteins. The lipocalin family is a diverse group of proteins that bind small hydrophobic (lipophilic) molecules and share a conserved tertiary structure of eight β-strands forming a barrel configuration. This is the first reported identification of lipocalin proteins in plants.
Photosynthesis: Mechanisms and Effects, 1998Co-Authors: Arleen D. Hieber, Robert C. Bugos, Harry Y. YamamotoAbstract:
Violaxanthin, antheraxanthin and zeaxanthin in thylakoids are components of a cyclical carotenoid pathway commonly referred to as the xanthophyll or Violaxanthin cycle (1). Two enzymes localized in different regions of the thylakoid catalyze the pathway. The forward half of the cycle, the de-epoxidation of Violaxanthin to zeaxanthin, is catalyzed by Violaxanthin de-epoxidase (VDE) localized in the lumen (2) whereas regeneration of Violaxanthin is catalyzed by zeaxanthin epoxidase (ZE) localized on the stromal side of the membrane (3,4). Antheraxanthin is a common intermediate in both halves of the cycle (1).
Krishna K. Niyogi - One of the best experts on this subject based on the ideXlab platform.
Chlamydomonas Xanthophyll Cycle Mutants ldentified by Video Imaging of Chlorophyll Fluorescence Quenching2013Co-Authors: Krishna K. Niyogi, Olle Bjorkman, Arthur R. GrossmanAbstract:
The photosynthetic apparatus in plants is protected against oxidative damage by processes that dissipate excess absorbed light energy as heat within the light-harvesting complexes. This dissipation of excitation energy is measured as nonphotochemical quenching of chlorophyll fluorescence. Nonphotochemical quenching depends primarily on the ApH that is generated by photosynthetic electron transport, and it is also correlated with the amounts of zeaxanthin and antheraxanthin that are formed from Violaxanthin by the operation of the xanthophyll cycle. To perform a genetic dissection of nonphotochemical quenching, we have isolated npq mutants of Chlamydomonas by using a digital videoimaging system. In excessive light, the npql mutant is unable to convert Violaxanthin to antheraxanthin and zeaxanthin; this reaction is catalyzed by Violaxanthin de-epoxidase. The npq2 mutant appears to be defective in zeaxanthin epoxidase activity, because it accumulates zeaxanthin and completely lacks antheraxanthin and Violaxanthin under all light conditions. Characterization of these mutants demonstrates that a component of nonphotochemical quenching that develops in vivo in Chlamydomonas depends on the accumulation of zeaxanthin and antheraxanthin via the xanthophyll cycle. However, observation of substantial, rapid, ApH-dependent nonphotochemical quenching in the npql mutant demonstrates that the formation of zeaxanthin and antheraxanthin via Violaxanthin de-epoxidase activity is not required for all ApH-dependent nonphotochemical quenching in this alga. Furthermore, the xanthophyll cycle is not required for survival of Chlamydomonas in excessive light
Plant physiology, 2002Co-Authors: Patricia Müller-moulé, Patricia L. Conklin, Krishna K. NiyogiAbstract:
As a response to high light, plants have evolved non-photochemical quenching (NPQ), mechanisms that lead to the dissipation of excess absorbed light energy as heat, thereby minimizing the formation of dangerous oxygen radicals. One component of NPQ is pH dependent and involves the formation of zeaxanthin from Violaxanthin. The enzyme responsible for the conversion of Violaxanthin to zeaxanthin is Violaxanthin de-epoxidase, which is located in the thylakoid lumen, is activated by low pH, and has been shown to use ascorbate (vitamin C) as its reductant in vitro. To investigate the effect of low ascorbate levels on NPQ in vivo, we measured the induction of NPQ in a vitamin C-deficient mutant of Arabidopsis, vtc2-2 . During exposure to high light (1,500 μmol photons m −2 s −1 ), vtc2-2 plants initially grown in low light (150 μmol photons m −2 s −1 ) showed lower NPQ than the wild type, but the same quantum efficiency of photosystem II. Crosses between vtc2-2 and Arabidopsis ecotype Columbia established that the ascorbate deficiency cosegregated with the NPQ phenotype. The conversion of Violaxanthin to zeaxanthin induced by high light was slower in vtc2-2 , and this conversion showed saturation below the wild-type level. Both the NPQ and the pigment phenotype of the mutant could be rescued by feeding ascorbate to leaves, establishing a direct link between ascorbate, zeaxanthin, and NPQ. These experiments suggest that ascorbate availability can limit Violaxanthin de-epoxidase activity in vivo, leading to a lower NPQ. The results also demonstrate the interconnectedness of NPQ and antioxidants, both important protection mechanisms in plants.
Proceedings of the National Academy of Sciences of the United States of America, 1999Co-Authors: Michel Havaux, Krishna K. NiyogiAbstract:
When light energy absorbed by plants becomes excessive relative to the capacity of photosynthesis, the xanthophyll Violaxanthin is reversibly deepoxidized to zeaxanthin (Violaxanthin cycle). The protective function of this phenomenon was investigated in a mutant of Arabidopsis thaliana, npq1, that has no functional Violaxanthin deepoxidase. Two major consequences of the npq1 mutation are the absence of zeaxanthin formation in strong light and the partial inhibition of the quenching of singlet excited chlorophylls in the photosystem II light-harvesting complexes. Prolonged exposure of whole plants to bright light resulted in a limited photoinhibition of photosystem II in both npq1 and wild-type leaves, although CO2 fixation and the linear electron transport in npq1 plants were reduced substantially. Lipid peroxidation was more pronounced in npq1 compared with the wild type, as measured by chlorophyll thermoluminescence, ethane production, and the total hydroperoxy fatty acids content. Lipid peroxidation was amplified markedly under chilling stress, and photooxidative damage ultimately resulted in leaf bleaching and tissue necrosis in npq1. The npq4 mutant, which possesses a normal Violaxanthin cycle but has a limited capacity of quenching singlet excited chlorophylls, was rather tolerant to lipid peroxidation. The double mutant, npq4 npq1, which differs from npq4 only by the absence of the Violaxanthin cycle, exhibited an increased susceptibility to photooxidative damage, similar to that of npq1. Our results demonstrate that the Violaxanthin cycle specifically protects thylakoid membrane lipids against photooxidation. Part of this protection involves a mechanism other than quenching of singlet excited chlorophylls.
altered xanthophyll compositions adversely affect chlorophyll accumulation and nonphotochemical quenching in arabidopsis mutantsProceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Barry J. Pogson, Olle Bjorkman, Krishna K. Niyogi, Dean DellapennaAbstract:
Collectively, the xanthophyll class of carotenoids perform a variety of critical roles in light harvesting antenna assembly and function. The xanthophyll composition of higher plant photosystems (lutein, Violaxanthin, and neoxanthin) is remarkably conserved, suggesting important functional roles for each. We have taken a molecular genetic approach in Arabidopsis toward defining the respective roles of individual xanthophylls in vivo by using a series of mutant lines that selectively eliminate and substitute a range of xanthophylls. The mutations, lut1 and lut2 (lut = lutein deficient), disrupt lutein biosynthesis. In lut2, lutein is replaced mainly by a stoichiometric increase in Violaxanthin and antheraxanthin. A third mutant, aba1, accumulates normal levels of lutein and substitutes zeaxanthin for Violaxanthin and neoxanthin. The lut2aba1 double mutant completely lacks lutein, Violaxanthin, and neoxanthin and instead accumulates zeaxanthin. All mutants were viable in soil and had chlorophyll a/b ratios ranging from 2.9 to 3.5 and near wild-type rates of photosynthesis. However, mutants accumulating zeaxanthin exhibited a delayed greening virescent phenotype, which was most severe and often lethal when zeaxanthin was the only xanthophyll present. Chlorophyll fluorescence quenching kinetics indicated that both zeaxanthin and lutein contribute to nonphotochemical quenching; specifically, lutein contributes, directly or indirectly, to the rapid rise of nonphotochemical quenching. The results suggest that the normal complement of xanthophylls, while not essential, is required for optimal assembly and function of the light harvesting antenna in higher plants.
On the Respective Roles of the Various Xanthophylls During Seedling Development and High Light Stress in ArabidopsisPhotosynthesis: Mechanisms and Effects, 1998Co-Authors: Barry J. Pogson, Olle Bjorkman, Krishna K. Niyogi, Dean DellapennaAbstract:
Six hundred different naturally occurring carotenoids have been identified to date and this diversity is reflected in the composition of the photosynthetic apparatus of different bacterial and algal classes. However, the carotenoid composition of the photosystems in green algae and higher plants is remarkably conserved (1). Lutein is the most abundant (up to 50% of total); with β-carotene, Violaxanthin and neoxanthin occurring in decreasing abundance (Fig. 1). β-carotene is essential for the assembly and photoprotection of PSII reaction centers and the xanthophylls, lutein, Violaxanthin and neoxanthin, are enriched in the LHCs where they contribute to assembly, light harvesting, and photoprotection (2). One of the many responses to high light is the reversible interconversion of Violaxanthin to zeaxanthin (the xanthophyll cycle)(3) which contributes to nonphotochemical quenching (NPQ) of chlorophyll fluorescence (4–6).
Alexander V Ruban - One of the best experts on this subject based on the ideXlab platform.
FEBS letters, 2016Co-Authors: Radek Kaňa, Eva Kotabova, Jana Kopecna, Eliska Trskova, Erica Belgio, Roman Sobotka, Alexander V RubanAbstract:
Non-photochemical quenching (NPQ) is a photoprotective mechanism in light-harvesting antennae. NPQ is triggered by chloroplast thylakoid lumen acidification and is accompanied by Violaxanthin de-epoxidation to zeaxanthin, which further stimulates NPQ. In the present study, we show that Violaxanthin can act in the opposite direction to zeaxanthin because an increase in the concentration of Violaxanthin reduced NPQ in the light-harvesting antennae of Chromera velia. The correlation overlapped with a similar relationship between Violaxanthin and NPQ as observed in isolated higher plant light-harvesting complex II. The data suggest that Violaxanthin in C. velia can act as an inhibitor of NPQ, indicating that Violaxanthin has to be removed from the vicinity of the protein to reach maximal NPQ.
changes in the energy transfer pathways within photosystem ii antenna induced by xanthophyll cycle activityJournal of Physical Chemistry B, 2013Co-Authors: Cristian Ilioaia, Christopher D P Duffy, Matthew P Johnson, Alexander V RubanAbstract:
: Energy transfer pathways between photosystem II (PSII) antenna complexes in intact thylakoid membranes have been studied using low-temperature (77 K) excitation fluorescence spectroscopy. The focus of this study was to see whether de-epoxidation of Violaxanthin into zeaxanthin causes any alterations in the energetic couplings between the core antenna complexes CP43 and CP47 and the peripheral light-harvesting antenna (LHCII). It was discovered that the appearance of zeaxanthin caused characteristic alterations in the PSII excitation fluorescence spectra in the Soret-band region. While in the dark Violaxanthin was found to be largely uncoupled from any emitting chlorophylls, its intensive de-epoxidation resulted in the appearance of two additional bands at 509 and 492 nm. The former was attributed to weak coupling of zeaxanthin to emitters in the CP43 and LHCII complexes and the latter to efficient coupling of Violaxanthin of the CP29 complex to emitters in the CP43, CP47, and LHCII complexes. The role of CP29-bound Violaxanthin is discussed in light of both its efficient energetic coupling and strong physical binding to this complex. The finding that zeaxanthin is energetically coupled to chlorophyll a emitters of the PSII antenna is discussed with respect to its suggested role as a quencher involved in photoprotective energy dissipation, or non-photochemical quenching (NPQ), in the photosynthetic membrane.
Carotenoid Specificity of Light-harvesting Complex II Binding Sites OCCURRENCE OF 9-CIS-Violaxanthin IN THE NEOXANTHIN-BINDING SITE IN THE PARASITIC ANGIOSPERM CUSCUTA REFLEXAThe Journal of biological chemistry, 2003Co-Authors: Alison M. Snyder, Bruno Robert, Alexander V Ruban, Bruce M. Clark, R. A. BungardAbstract:
The parasitic angiosperm Cuscuta reflexa has a highly unusual carotenoid composition in that it does not contain neoxanthin, an otherwise ubiquitous component of the major light-harvesting complex protein (LHCIIb) in all other higher plant species studied to date. Combined HPLC and mass spectrometric analysis has enabled us to detect in tissues of C. reflexa two new types of xanthophylls: lutein-5,6-epoxide and 9-cis-Violaxanthin. We have isolated the LHCIIb complex from thylakoids and analyzed chlorophyll and carotenoid composition. The data show that the 9-cis-Violaxanthin is present in amounts similar to that of neoxanthin in most plants. On the other hand, lutein-5,6-epoxide was found to be in substoichiometric quantities, suggesting a peripheral location similar to the loosely-associated all-trans-Violaxanthin and also enabling suitable accessibility for the de-epoxidase (VDE). Absorption spectroscopy revealed close similarities of the excited state energies of neoxanthin and 9-cis-Violaxanthin in vitro and in intact LHCIIb complex. Resonance Raman analysis clearly indicates a cis conformation of Violaxanthin in the complex, confirming the pigment analysis data and proving that not only does Violaxanthin replace neoxanthin as an intrinsic component of LHCIIb in C. reflexa but it also adopts the same 9-cis conformation of neoxanthin. These results suggest that the N1 binding site of LHCIIb preferentially binds 9-cis-5,6-epoxy carotenoids, which has implications for the features of this binding site and its role in the photosystem II antenna assembly and stability.
Journal of Biological Chemistry, 2002Co-Authors: Alexander V Ruban, A A Pascal, Bruno Robert, Peter HortonAbstract:
Abstract The molecular configuration of the xanthophyll cycle carotenoids, Violaxanthin and zeaxanthin, was studied in various isolated photosystem II antenna components in comparison to intact photosystem II membranes using resonance Raman combined with low-temperature absorption spectroscopy. The molecular configurations of zeaxanthin and Violaxanthin in thylakoids and isolated photosystem II membranes were found to be the same within an isolated oligomeric LHCII antenna, confirming our recent conclusion that these molecules are not freely located in photosynthetic membranes (Ruban, A. V., Pascal, A. A., Robert, B., and Horton, P. (2001) J. Biol. Chem. 276, 24862–24870). In contrast, xanthophyll cycle carotenoids bound to LHCII trimers had largely lost their in vivo configuration, suggesting their partial dissociation from the binding locus. Violaxanthin and zeaxanthin associated with the minor antenna complexes, CP26 and CP29, were also found to be in a relaxed configuration, similar to that of free pigment. The origin of the characteristic C–H vibrational bands of Violaxanthin and zeaxanthin in vivo is discussed by comparison with those of neoxanthin and lutein in oligomeric and trimeric LHCII respectively.
determination of the stoichiometry and strength of binding of xanthophylls to the photosystem ii light harvesting complexesJournal of Biological Chemistry, 1999Co-Authors: Alexander V Ruban, Andrew J. Young, Pamela J Lee, Mark Wentworth, Peter HortonAbstract:
Xanthophylls have a crucial role in the structure and function of the light harvesting complexes of photosystem II (LHCII) in plants. The binding of xanthophylls to LHCII has been investigated, particularly with respect to the xanthophyll cycle carotenoids Violaxanthin and zeaxanthin. It was found that most of the Violaxanthin pool was loosely bound to the major complex and could be removed by mild detergent treatment. Gentle solubilization of photosystem II particles and thylakoids allowed the isolation of complexes, including a newly described oligomeric preparation, enriched in trimers, that retained all of the in vivo Violaxanthin pool. It was estimated that each LHCII monomer can bind at least one Violaxanthin. The extent to which different pigments can be removed from LHCII indicated that the relative strength of binding was chlorophyll b > neoxanthin > chlorophyll a > lutein > zeaxanthin > Violaxanthin. The xanthophyll binding sites are of two types: internal sites binding lutein and peripheral sites binding neoxanthin and Violaxanthin. In CP29, a minor LHCII, both a lutein site and the neoxanthin site can be occupied by Violaxanthin. Upon activation of the Violaxanthin de-epoxidase, the highest de-epoxidation state was found for the main LHCII component and the lowest for CP29, suggesting that only Violaxanthin loosely bound to LHCII is available for de-epoxidation.
Wiesław I. Gruszecki - One of the best experts on this subject based on the ideXlab platform.
The xanthophyll cycle pigments, Violaxanthin and zeaxanthin, modulate molecular organization of the photosynthetic antenna complex LHCII.Archives of biochemistry and biophysics, 2016Co-Authors: Ewa Janik, Joanna Bednarska, Monika Zubik, Karol Sowinski, Rafal Luchowski, Wojciech Grudzinski, Dariusz Matosiuk, Wiesław I. GruszeckiAbstract:
The effect of Violaxanthin and zeaxanthin, two main carotenoids of the xanthophyll cycle, on molecular organization of LHCII, the principal photosynthetic antenna complex of plants, was studied in a model system based on lipid-protein membranes, by means of analysis of 77 K chlorophyll a fluorescence and "native" electrophoresis. Violaxanthin was found to promote trimeric organization of LHCII, contrary to zeaxanthin which was found to destabilize trimeric structures. Moreover, Violaxanthin was found to induce decomposition of oligomeric LHCII structures formed in the lipid phase and characterized by the fluorescence emission band at 715 nm. Both pigments promoted formation of two-component supramolecular structures of LHCII and xanthophylls. The Violaxanthin-stabilized structures were composed mostly of LHCII trimers while, the zeaxanthin-stabilized supramolecular structures of LHCII showed more complex organization which depended periodically on the xanthophyll content. The effect of the xanthophyll cycle pigments on molecular organization of LHCII was analyzed based on the results of molecular modeling and discussed in terms of a physiological meaning of this mechanism. Supramolecular structures of LHCII stabilized by Violaxanthin, prevent uncontrolled oligomerization of LHCII, potentially leading to excitation quenching, therefore can be considered as structures protecting the photosynthetic apparatus against energy loses at low light intensities.
Journal of Photochemistry and Photobiology B: Biology, 2010Co-Authors: Ewa Janik, Waldemar Maksymiec, Wiesław I. GruszeckiAbstract:
The influence of excess Cu ions and high light treatment on the function of photosystem II was investigated in order to examine how this heavy metal modifies the photoprotective mechanisms operating at the molecular level in Secale cereale plants. Thus, non-treated plants and those treated with 5 or 50 microM Cu, simultaneously illuminated with 150 micromol m(-2) s(-1) or 1200 micromol m(-2) s(-1) light intensity, were studied. To analyze the PSII reaction to the stress conditions, Chl a fluorescence induction was applied. An increase in the value of Phi(PSII) and R(fd) parameters indicated that the photosynthetic apparatus adapted to the high light condition by effective utilization of excitation energy in the light and dark phases of photosynthesis. This phenomenon was accompanied by dissipation of excitation energy within the antenna complexes. The xanthophyll cycle pigments in Secale cereale leaves were separated and quantified by the HPLC technique. The results showed that, under high light irradiance, both 5 and 50 microM Cu induced the process of Violaxanthin de-epoxidation and zeaxanthin accumulation. The significant zeaxanthin accumulation was found to be involved in photoprotective energy dissipation as heat, which was supported by correlation between the rate of Violaxanthin de-epoxidation and the value of SV parameters. Interestingly, Cu treatment caused Violaxanthin isomerization from its trans to 15-, 13- and 9-cis forms in proportional correlation to the metal concentration. This phenomenon was confirmed by a study of Cu-induced Violaxanthin isomerization in vitro, which suggests a direct metal-pigment molecule interaction. We also observed that the Violaxanthin trans-cis isomerization increased simultaneously with anteraxanthin content. On the basis of these findings, it can be speculated that Violaxanthin isomerization is the basic process responsible for the xanthophyll cycle operation.
Temperature-induced isomerization of Violaxanthin in organic solvents and in light-harvesting complex II.Journal of photochemistry and photobiology. B Biology, 2005Co-Authors: Dariusz M. Niedzwiedzki, Zbigniew Krupa, Wiesław I. GruszeckiAbstract:
Abstract Three main xanthophyll pigments are bound to the major photosynthetic pigment-protein complex of Photosystem II (LHCII): lutein, neoxanthin and Violaxanthin. Chromatographic analysis of the xanthophyll fraction of LHCII reveals that lutein appears mainly in the all-trans conformation, neoxanthin in the 9′-cis conformation and major fraction of Violaxanthin in the all-trans conformation. Nevertheless, a small fraction of Violaxanthin appears always in a cis conformation: 9-cis and 13-cis (approximately 4% and 2% in the darkness, respectively). Illumination of the isolated complex (5 min, 445 nm, 250 μmol m−2 s−1) results in the substantial increase in the concentration of the cis steric conformers of Violaxanthin: up to 6% of 9-cis and 4% of 13-cis. Similar effect can be obtained by dark incubation of the same preparation for 30 min at 60 °C. Heating-induced isomerization of the all-trans Violaxanthin can also be obtained in the organic solvent system but the formation of the 9-cis stereoisomer has not been observed under such conditions. The fact that the appearance of the 9-cis form of Violaxanthin is specific for the protein environment suggests that Violaxanthin may replace neoxanthin in LHCII in the N1 xanthophyll binding pocket and that the protein stabilizes this particular conformation. The analysis of the electronic absorption spectra of LHCII and the FTIR spectra of the protein in the Amid I band spectral region indicates that Violaxanthin isomerization is associated with the disaggregation of the complex. It is postulated that this reorganization of LHCII provides conditions for desorption of Violaxanthin from the pigment protein complexes, its diffusion within the thylakoid membrane and therefore, availability to the enzymatic deepoxidation within the xanthophyll cycle. It is also possible that Violaxanthin isomerization plays the role of a security valve, by consuming an energy of excessive excitations in the antenna pigment network (in particular, exchanged at the triplet state levels).
Interaction between chlorophyll a and Violaxanthin in different steric conformations: Model studies in monomolecular layersColloids and Surfaces B: Biointerfaces, 2003Co-Authors: Dariusz Niedźwiedzki, Wiesław I. GruszeckiAbstract:
Monomolecular layers of pure chlorophyll a (Chl a), Violaxanthin in the conformation all-trans, 9-cis, 13-cis and two-component monomolecular layers formed with Chl a and all isomers of Violaxanthin, at a stoichiometric ratio 1:1, were formed and compressed at the argon–water interface. The specific molecular areas of Chl a and the isomers of Violaxanthin in monomolecular layers were determined on the basis of the isotherms of compression. The isotherms of compression of the Chl a–Violaxanthin-all trans monolayers correspond well to the theoretical ones, calculated on the basis of the additivity rule. The theoretical isotherms of compression of monolayers formed with Chl a and Violaxanthin in conformations 9-cis and 13-cis are shifted towards higher molecular areas with respect to the experimental ones, indicating molecular interaction between components of the system. Monolayers were also deposited to a solid support by means of the Langmuir–Blodgett technique and subjected to spectroscopic studies: to quartz lamella in the case of electronic absorption and fluorescence spectroscopy and to ZnSe crystal in the case of Fourier Transform Infrared Spectroscopy (FTIR). The comparison of the absorption and Chl a fluorescence excitation spectra enabled to make a calculation of the rate of excitation energy transfer from Violaxanthin to Chl a. Efficiency of energy transfer from a carotenoid to Chl a was 32% in the case of Violaxanthin all-trans, 21% in the case of Violaxanthin 9-cis and 15% for Violaxanthin 13-cis. Such findings suggest a structural role of Violaxanthin in conformation 9-cis and 13-cis and an accessory role of Violaxanthin all-trans in the photosynthetic apparatus. The analysis of FTIR spectra reveals molecular interaction between Chl a and Violaxanthin in conformations cis via the hydroxyl groups of xanthophylls located in the C3 and C3′ positions.
Effect of 13-cis Violaxanthin on organization of light harvesting complex II in monomolecular layers.Biochimica et biophysica acta, 2001Co-Authors: W. Grudzinski, Jan Sielewiesiuk, Zbigniew Krupa, Magda Matuła, Peter Kernen, Wiesław I. GruszeckiAbstract:
Abstract Lutein, neoxanthin and Violaxanthin are the main xanthophyll pigment constituents of the largest light-harvesting pigment–protein complex of photosystem II (LHCII). High performance liquid chromatography analysis revealed photoisomerization of LHCII-bound Violaxanthin from the conformation all-trans to the conformation 13-cis and 9-cis. Maximally, the conversion of 15% of all-trans Violaxanthin to a cis form could be achieved owing to the light-driven reactions. The reactions were dark-reversible. The all-trans to cis isomerization was found to be driven by blue light, absorbed by chlorophylls and carotenoids, as well as by red light, absorbed exclusively by chlorophyll pigments. This suggests that the photoisomerization is a carotenoid triplet-sensitized reaction. The monomolecular layer technique was applied to study the effect of the 13-cis conformer of Violaxanthin and its de-epoxidized form, zeaxanthin, on the organization of LHCII as compared to the all-trans stereoisomers. The specific molecular areas of LHCII in the two-component system composed of protein and exogenous 13-cis Violaxanthin or 13-cis zeaxanthin show overadditivity, which is an indication of the xanthophyll-induced disassembly of the aggregated forms of the protein. Such an effect was not observed in the monomolecular layers of LHCII containing all-trans conformers of Violaxanthin and zeaxanthin. 77 K chlorophyll a fluorescence emission spectra recorded from the Langmuir–Blodgett (L–B) films deposited to quartz from monomolecular layers formed with LHCII and LHCII in the two-component systems with all-trans and 13-cis isomers of Violaxanthin and zeaxanthin revealed opposite effects of both conformers on the aggregation of the protein. The cis isomers of both xanthophylls were found to decrease the aggregation level of LHCII and the all-trans isomers increased the aggregation level. The calculated efficiency of excitation energy transfer to chlorophyll a from Violaxanthin assumed to remain in two steric conformations was analyzed on the basis of the chlorophyll a fluorescence excitation spectra and the mean orientation of Violaxanthin molecules in LHCII (71° with respect to the normal to the membrane), determined recently in the linear dichroism experiments [Gruszecki et al., Biochim. Biophys. Acta 1412 (1999) 173–183]. The calculated efficiency of excitation energy transfer from the Violaxanthin pool assumed to remain in conformation all-trans was found to be almost independent on the orientation angle within a variability range. In contrast the calculated efficiency of energy transfer from the form cis was found to be strongly dependent on the orientation and varied between 1.0 (at 67.48°) and 0 (at 70.89°). This is consistent with two essentially different, possible functions of the cis forms of Violaxanthin: as a highly efficient excitation donor (and possibly energy transmitter between other chromophores) or purely as a LHCII structure modifier.