Function of the IsiA pigment–protein complex in vivo

Photosynthesis Research - The acclimation of cyanobacterial photosynthetic apparatus to iron deficiency is crucial for their performance under limiting conditions. In many cyanobacterial species,...     

Interaction of pigment—protein complexes within aggregates stimulates dissipation of excess energy

Pigment—protein complexes in photosynthetic membranes exist mainly as aggregates that are functionally active as monomers but more stable due to their ability to dissipate excess energy. Dissipation of energy in the photosystem I (PSI) trimers of cyanobacteria takes place with a contribution of the long-wavelength chlorophylls whose excited state is quenched by cation radical of P700 or P700 in its triplet state. If P700 in one of the monomer complexes within a PSI trimer is oxidized, energy migration from antenna of other monomer complexes to cation radical of P700 via peripherally localized long-wave-length chlorophylls results in energy dissipation, thus protecting PSI complex of cyanobacteria against photodestruction. It is suggested that dissipation of excess absorbed energy in aggregates of the light-harvesting complex LHCII of higher plants takes place with a contribution of peripherally located chlorophylls and carotenoids.Translated from Biokhimiya, Vol. 69, No. 11, 2004, pp. 1592–1599.Original Russian Text Copyright © 2004 by Karapetyan     

Photoactive pigment—enzyme complexes of chlorophyll precursor in plant leaves

This review summarizes contemporary data on structure and function of photoactive pigment--enzyme complexes of the chlorophyll precursor that undergoes photochemical transformation to chlorophyllide. The properties and functions of the complex and its principal components are considered including the pigment (protochlorophyllide), the hydrogen donor (NADPH), and the photoenzyme protochlorophyllide oxidoreductase (POR) that catalyzes the photochemical production of chlorophyllide. Chemical variants of the chlorophyll precursor are described (protochlorophyllide, protochlorophyll, and their mono- and divinyl forms). The nature and photochemical activity of spectrally distinct native protochlorophyllide forms are discussed. Data are presented on structural organization of the photoenzyme POR, its substrate specificity, localization in etioplasts, and heterogeneity. The significance of different POR forms (PORA, PORB, and PORC) in adaptation of chlorophyll biosynthesis to various illumination conditions is considered. Attention is paid to structural and functional interactions of three main constituents of the photoactive complex and to possible existence of additional components associated with the pigment-enzyme complex. Historical aspects of the problem and the prospects of further investigations are outlined.     

Structurally flexible macro-organization of the pigment–protein complexes of the diatom Phaeodactylum tricornutum

By means of circular dichroism (CD) spectroscopy, we have characterized the organization of the photosynthetic complexes of the diatom Phaeodactylum tricornutum at different levels of structural complexity: in intact cells, isolated thylakoid membranes and purified fucoxanthin chlorophyll protein (FCP) complexes. We found that the CD spectrum of whole cells was dominated by a large band at (+)698 nm, accompanied by a long tail from differential scattering, features typical for psi-type (polymerization or salt-induced) CD. The CD spectrum additionally contained intense (−)679 nm, (+)445 nm and (−)470 nm bands, which were also present in isolated thylakoid membranes and FCPs. While the latter two bands were evidently produced by excitonic interactions, the nature of the (−)679 nm band remained unclear. Electrochromic absorbance changes also revealed the existence of a CD-silent long-wavelength (∼545 nm) absorbing fucoxanthin molecule with very high sensitivity to the transmembrane electrical field. In intact cells the main CD band at (+)698 nm appeared to be associated with the multilamellar organization of the thylakoid membranes. It was sensitive to the osmotic pressure and was selectively diminished at elevated temperatures and was capable of undergoing light-induced reversible changes. In isolated thylakoid membranes, the psi-type CD band, which was lost during the isolation procedure, could be partially restored by addition of Mg-ions, along with the maximum quantum yield and the non-photochemical quenching of singlet excited chlorophyll a, measured by fluorescence transients.     

A model of the protein–pigment baseplate complex in chlorosomes of photosynthetic green bacteria

In contrast to photosynthetic reaction centers, which share the same structural architecture, more variety is found in the light-harvesting antenna systems of phototrophic organisms. The largest antenna system described, so far, is the chlorosome found in anoxygenic green bacteria, as well as in a recently discovered aerobic phototroph. Chlorosomes are the only antenna system, in which the major light-harvesting pigments are organized in self-assembled supramolecular aggregates rather than on protein scaffolds. This unique feature is believed to explain why some green bacteria are able to carry out photosynthesis at very low light intensities. Encasing the chlorosome pigments is a protein-lipid monolayer including an additional antenna complex: the baseplate, a two-dimensional paracrystalline structure containing the chlorosome protein CsmA and bacteriochlorophyll a (BChl a). In this article, we review current knowledge of the baseplate antenna complex, which physically and functionally connects the chlorosome pigments to the reaction centers via the Fenna–Matthews–Olson protein, with special emphasis on the well-studied green sulfur bacterium Chlorobaculum tepidum (previously Chlorobium tepidum). A possible role for the baseplate in the biogenesis of chlorosomes is discussed. In the final part, we present a structural model of the baseplate through combination of a recent NMR structure of CsmA and simulation of circular dichroism and optical spectra for the CsmA–BChl a complex.     

The effect of illumination on the pigment composition of the ζ-carotenic mutant,PG1, of Scenedesmus obliquus

Dark grown Scenedesmus obliquus strain PG1 accumulated -carotene and phytoene as its major carotenoids. On illumination of dark-grown cultures in air/CO₂, cyclic carotenes and xanthophylls were formed, apparently at the expense of the accumulated phytoene and -carotene. This interconversion of carotenoids was accompanied by chlorophyll synthesis. In an atmosphere of nitrogen/CO₂ the light-induced changes occurred more slowly and in nitrogen alone the changes were incomplete. No massive production of cyclic carotenes from the accumulated -carotene was observed in cultures illuminated under anaerobic conditions.     

Why are higher plants green? Evolution of the higher plant photosynthetic pigment complement

The physiological reason that higher plants are green is unknown. Other photosynthetic organisms utilize pigments that strongly absorb green light; therefore, there must have been natural forces that ‘selected’ the photosynthetic pigments found in higher plants. Based on previously published data and our recent findings about green light and photosynthesis within leaves (Sun et al.), a specific functional role is described for the primary photosynthetic pigments of higher plants, that were derived from green algal progenitors. The particular absorptive characteristics of chlorophylls a and b appear to perform two contradictory, but necessary functions in higher plants. Firstly, chlorophylls a and b absorb light for maximum utilization under non‐saturating conditions, a function that is well understood. Secondly, they can act as protective pigments under over‐saturating light conditions, when absorbed light is dissipated as heat. Under such conditions, a significant portion of light can also be efficiently utilized, especially in the bottom portion of the leaf, that is mainly illuminated by green light and not down‐regulated. The second function may have been the selective force that gave rise to the extremely successful terrestrial plants, that evolved from green algae.     

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 (β-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 Chla form at 710–712 nm.     

Production of phycocyanin—a pigment with applications in biology, biotechnology, foods and medicine

C-phycocyanin (C-PC) is a blue pigment in cyanobacteria, rhodophytes and cryptophytes with fluorescent and antioxidative properties. C-PC is presently extracted from open pond cultures of the cyanobacterium Arthrospira platensis although these cultures are not very productive and open for contaminating organisms. C-PC is considered a healthy ingredient in cyanobacterial-based foods and health foods while its colouring, fluorescent or antioxidant properties are utilised only to a minor extent. However, recent research and developments in C-PC synthesis and functionality have expanded the potential applications of C-PC in biotechnology, diagnostics, foods and medicine: The productivity of C-PC has been increased in heterotrophic, high cell density cultures of the rhodophyte Galdieria sulphuraria that are grown under well-controlled and axenic conditions. C-PC purification protocols based on various chromatographic principles or novel two-phase aqueous extraction methods have expanded in numbers and improved in performance. The functionality of C-PC as a fluorescent dye has been improved by chemical stabilisation of C-PC complexes, while protein engineering has also introduced increased stability and novel biospecific binding sites into C-PC fusion proteins. Finally, our understanding of the physiological functions of C-PC in humans has been improved by a mechanistic hypothesis that links the chemical properties of the phycocyanobilin chromophores of C-PC to the natural antioxidant, bilirubin, and may explain the observed health benefits of C-PC intake. This review outlines how C-PC is produced and utilised and discusses the novel C-PC synthesis procedures and applications.     

Stimulatory role of smoke–water and karrikinolide on the photosynthetic pigment and phenolic contents of micropropagated ‘Williams’ bananas

At low concentrations, smoke–water (SW) and smoke-derived karrikinolide (KAR₁) are compounds with potential cytokinin and auxin-like activity. Their roles on the growth, photosynthetic pigment and phenolic contents of micropropagated ‘Williams’ bananas were investigated in comparison with meta-topolin (mT). Explants were cultured on modified Murashige and Skoog basal media supplemented with either SW (1:125; 1:250; 1:500; 1:1,000; 1:2,000 dilutions) or KAR₁ at four concentrations ranging from 4.8?×?10^?22 to 3.3?×?10^?12?M. After 42?days, growth parameters were measured while the photosynthetic pigments and phenolic contents were quantified using spectrophotometric methods. Chlorophyll a, b and total carotenoid contents were significantly enhanced by KAR₁ (4.8?×?10^?22?M) and SW (1:125 and 1:1,000 dilutions). The pigments in KAR₁-treated plantlets were approximately two-fold to three-fold higher than those in the control and mT-treated plants, respectively. Total phenolic content was highest with KAR₁ at 1.0?×?10^?19?M in the leaves and 7.8?×?10^?17?M in the roots. Furthermore, KAR₁-treated plants at 1.0?×?10^?19?M yielded the highest level of total phenolics (leaves) and proanthocyanidins (roots). At 1:500 dilutions, SW stimulated the highest total flavonoid content in the leaves across all the treatments. Combining mT with either SW (1:500) or KAR₁ (4.8?×?10^?22?M) significantly increased the quantity of secondary metabolites. However, the growth parameters and pigment contents were not improved. Based on the significant role of photosynthetic pigments and phenolic compounds on the defense and survival strategies of plants, current findings will have practical significance for important processes such as acclimatization and survival of micropropagated plants. These results are also demonstrating the potential of SW and KAR₁ as an eliciting agent for secondary metabolite production.     

Extraction and quantitative analysis of the blue-green pigment “marennine” synthesized by the diatom Haslea ostrearia

This study reports further information on mareninne, awater-soluble blue-green pigment synthesized by the diatom Hasleaostrearia, which is essential to the greening of maturing oysters inFrench production areas. The extraction process is reported, as well aspreliminary characterization of a partially purified marennine extract,including quantitative spectrophotometric analysis of intracellular pigment. Amean specific extinction coefficient, E ^1% _1cm = 17.2 at 669 nm, is proposed. Results forquantitative determination of marennine accumulated in cells during batchcultures are presented, and their importance for pigment production isconsidered in relation to potential industrial applications.     

Effect of protein aggregation on the spectroscopic properties and excited state kinetics of the LHCII pigment–protein complex from green plants

Steady-state and time-resolved absorption and fluorescence spectroscopic experiments have been carried out at room and cryogenic temperatures on aggregated and unaggregated monomeric and trimeric LHCII complexes isolated from spinach chloroplasts. Protein aggregation has been hypothesized to be one of the mechanistic factors controlling the dissipation of excess photo-excited state energy of chlorophyll during the process known as nonphotochemical quenching. The data obtained from the present experiments reveal the role of protein aggregation on the spectroscopic properties and dynamics of energy transfer and excited state deactivation of the protein-bound chlorophyll and carotenoid pigments.     

Changes in pigment content of the diatom Navicula pelliculosa (Bréb.) Hilse in silicon-starvation synchrony

Summary Exponentially grown cells of the freshwater diatom Navicula pelliculosa (Bréb) Hilse, contained chlorophyll a, chlorophyll c, fucoxanthin, diadinoxanthin, diatoxanthin, neofucoxanthin, -carotene, and an unknown pigment, the absorption spectrum of which is reported. Changes in amounts of chlorophyll a, fucoxanthin and diadinoxanthin were determined during the course of silicon-starvation synchrony carried out in the light or dark. Changes in the rate of chlorophyll a and fucoxanthin syntheses were similar. Synthesis ceased after 5–7 hr of silicon starvation, but recommenced in cultures kept in the light, once silicon was re-introduced. In cultures kept in the dark no significant synthesis was observed after re-introduction of silicon. Diadinoxanthin synthesis continued in the light at all times, although at a lower rate during the silicon-starvation period. In the dark, synthesis of this pigment ceased when cell division stopped, and the amount per unit volume of culture decreased. These results are discussed in relation both to the effect of silicon on the metabolism of the diatom and to the possible function of the carotenoids.Dedicated to Prof. C. B. van Niel on the occasion of his 70th birthday.     

Formation of amyloid-like fibrillar structures and destruction of fibroblasts of the Tenon’s capsule in progressive myopia due to resistance of the pigment epithelium-derived factor to restricted proteolysis

We have previously shown that, normally, two forms of the pigment epithelium-derived factor (PEDF) with molecular weights of 50 and 45 kDa are present in the Tenon??s capsule in equal amounts. These forms represent the full-length protein and a product of restricted proteolysis of PEDF. In persons with myopia, the full-length uncleaved factor was predominantly detected, which correlated with the disturbance of collagen fiber formation. An immunohistochemical study of the Tenon??s capsule using polyclonal antibodies to PEDF showed that, in the control group, the factor is localized solely inside fibroblasts, whereas in patients with myopia, PEDF is distributed outside the cell as a halo around destroyed fibroblasts. It was shown in the present work using atomic force microscopy and immunodot assay with antibodies specific to amyloid fibrils that only the full-length PEDF is capable of forming amyloid-like fibrillar structures. The accumulation of fibrils leads to the destruction of fibroblasts and is a cause of changes in the biochemical composition and morphological structure of the Tenon??s capsule in myopia.