photosystem (PSII) Dotaz Zobrazit nápovědu
Formation of the multi-subunit oxygen-evolving photosystem II (PSII) complex involves a number of auxiliary protein factors. In this study we compared the localization and possible function of two homologous PSII assembly factors, Psb28-1 and Psb28-2, from the cyanobacterium Synechocystis sp. PCC 6803. We demonstrate that FLAG-tagged Psb28-2 is present in both the monomeric PSII core complex and a PSII core complex lacking the inner antenna CP43 (RC47), whereas Psb28-1 preferentially binds to RC47. When cells are exposed to increased irradiance, both tagged Psb28 proteins additionally associate with oligomeric forms of PSII and with PSII-PSI supercomplexes composed of trimeric photosystem I (PSI) and two PSII monomers as deduced from electron microscopy. The presence of the Psb27 accessory protein in these complexes suggests the involvement of PSI in PSII biogenesis, possibly by photoprotecting PSII through energy spillover. Under standard culture conditions, the distribution of PSII complexes is similar in the wild type and in each of the single psb28 null mutants except for loss of RC47 in the absence of Psb28-1. In comparison with the wild type, growth of mutants lacking Psb28-1 and Psb27, but not Psb28-2, was retarded under high-light conditions and, especially, intermittent high-light/dark conditions, emphasizing the physiological importance of PSII assembly factors for light acclimation.
- MeSH
- bakteriální proteiny genetika metabolismus MeSH
- fotosystém I - proteinový komplex genetika metabolismus účinky záření MeSH
- fotosystém II - proteinový komplex genetika metabolismus účinky záření MeSH
- mutace MeSH
- světlo * MeSH
- Synechocystis genetika metabolismus účinky záření MeSH
- vazba proteinů MeSH
- Publikační typ
- časopisecké články MeSH
Photosynthetic carbon fixation by Chromophytes is one of the significant components of a carbon cycle on the Earth. Their photosynthetic apparatus is different in pigment composition from that of green plants and algae. In this work we report structural maps of photosystem I, photosystem II and light harvesting antenna complexes isolated from a soil chromophytic alga Xanthonema debile (class Xanthophyceae). Electron microscopy of negatively stained preparations followed by single particle analysis revealed that the overall structure of Xanthophytes' PSI and PSII complexes is similar to that known from higher plants or algae. Averaged top-view projections of Xanthophytes' light harvesting antenna complexes (XLH) showed two groups of particles. Smaller ones that correspond to a trimeric form of XLH, bigger particles resemble higher oligomeric form of XLH.
- MeSH
- chlorofyl analýza metabolismus MeSH
- elektronová mikroskopie MeSH
- fluorescenční spektrometrie MeSH
- fotosyntéza MeSH
- fotosystém I - proteinový komplex chemie ultrastruktura MeSH
- fotosystém II - proteinový komplex chemie ultrastruktura MeSH
- Heterokontophyta chemie ultrastruktura MeSH
- multimerizace proteinu MeSH
- půda MeSH
- půdní mikrobiologie MeSH
- světlosběrné proteinové komplexy chemie ultrastruktura MeSH
- tylakoidy chemie MeSH
- vysokoúčinná kapalinová chromatografie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
In photosynthetic electron transport, large multiprotein complexes are connected by small diffusible electron carriers, the mobility of which is challenged by macromolecular crowding. For thylakoid membranes of higher plants, a long-standing question has been which of the two mobile electron carriers, plastoquinone or plastocyanin, mediates electron transport from stacked grana thylakoids where photosystem II (PSII) is localized to distant unstacked regions of the thylakoids that harbor PSI. Here, we confirm that plastocyanin is the long-range electron carrier by employing mutants with different grana diameters. Furthermore, our results explain why higher plants have a narrow range of grana diameters since a larger diffusion distance for plastocyanin would jeopardize the efficiency of electron transport. In the light of recent findings that the lumen of thylakoids, which forms the diffusion space of plastocyanin, undergoes dynamic swelling/shrinkage, this study demonstrates that plastocyanin diffusion is a crucial regulatory element of plant photosynthetic electron transport.
- MeSH
- biologické modely MeSH
- fotosystém I - proteinový komplex metabolismus MeSH
- fotosystém II - proteinový komplex metabolismus MeSH
- Magnoliopsida fyziologie MeSH
- plastocyanin metabolismus MeSH
- počítačová simulace MeSH
- regulace genové exprese u rostlin fyziologie MeSH
- transport elektronů MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
Cytochrome b(559) (cyt b(559)) is a heme-bridged protein heterodimer in photosystem II (PSII) of all oxygenic photosynthetic organisms. In spite of the fact that cyt b(559) is strictly required for proper function of PSII, it is not involved in the linear electron transport chain from water to plastoquinone. Instead of that the participation of cyt b(559) in the cyclic electron transport around PSII has been proposed mainly based on the ability of the heme iron to accept and donate an electron form the electron acceptor and to the electron donor side of PSII, respectively. In addition to the involvement of cyt b(559) in the cyclic electron transport around PSII, several lines of evidence have been provided on the enzymatic function of cyt b(559). The ability of oxygenic photosynthetic organisms to oxidize water and reduce plastoquinone is connected to the formation of reactive oxygen species (ROS) and thus required to develop an effective antioxidant defense system against ROS. The review attempts to summarize a recent progress on the role of cyt b(559) as oxygen reductase, superoxide reductase, superoxide oxidase and plastoquinol oxidase. The focus is mainly given on the characterization of redox, redox potential and acid-base properties of the heme iron in the putative enzymatic cycles. The possible oxidase and reductase enzymatic activity of cyt b(559) in protection from photoinhibition is discussed.
Photosystem II (PSII) is a multi-subunit pigment-protein complex and is one of several protein assemblies that function cooperatively in photosynthesis in plants and cyanobacteria. As more structural data on PSII become available, new questions arise concerning the nature of the charge separation in PSII reaction center (RC). The crystal structure of PSII RC from cyanobacteria Thermosynechococcus vulcanus was selected for the computational study of conformational changes in photosystem II associated to the charge separation process. The parameterization of cofactors and lipids for classical MD simulation with Amber force field was performed. The parametrized complex of PSII was embedded in the lipid membrane for MD simulation with Amber in Gromacs. The conformational behavior of protein and the cofactors directly involved in the charge separation were studied by MD simulations and QM/MM calculations. This study identified the most likely mechanism of the proton-coupled reduction of plastoquinone QB. After the charge separation and the first electron transfer to QB, the system undergoes conformational change allowing the first proton transfer to QB- mediated via Ser264. After the second electron transfer to QBH, the system again adopts conformation allowing the second proton transfer to QBH-. The reduced QBH2 would then leave the binding pocket.
Plants, algae and cyanobacteria grow because of their ability to use sunlight to extract electrons from water. This vital reaction is catalysed by the Photosystem II (PSII) complex, a large multi-subunit pigment-protein complex embedded in the thylakoid membrane. Recent results show that assembly of PSII occurs in a step-wise fashion in defined regions of the membrane system, involves conserved auxiliary factors and is closely coupled to chlorophyll biosynthesis. PSII is also repaired following damage by light. FtsH proteases play an important role in selectively removing damaged proteins from the complex, both in chloroplasts and cyanobacteria, whilst undamaged subunits and pigments are recycled. The chloroplastic Deg proteases play a supplementary role in PSII repair.
- MeSH
- bakteriální proteiny metabolismus MeSH
- biologické modely MeSH
- chloroplasty metabolismus MeSH
- fotosyntéza účinky záření MeSH
- fotosystém II - proteinový komplex metabolismus MeSH
- rostlinné proteiny metabolismus MeSH
- rostliny metabolismus MeSH
- sinice metabolismus MeSH
- světlo MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
N-(Alkoxyphenyl)-2-hydroxynaphthalene-1-carboxamides (series A) and N-(alkoxyphenyl)-1-hydroxynaphthalene-2-carboxamides (series B) affecting photosystem (PS) II inhibited photosynthetic electron transport (PET) in spinach chloroplasts. Their inhibitory activity depended on the compound lipophilicity as well as on the position of the alkoxy substituent. The most potent PET inhibitors were 2-hydroxy-N-phenylnaphthalene-1-carboxamide and N-[3-(but-2-yloxy)phenyl]-2-hydroxynaphthalene-1-carboxamide within series A (IC50=28.9 and 42.5µM, respectively) and 1-hydroxy-N-(3-propoxyphenyl)naphthalene-2-carboxamide and 1-hydroxy-N-(3-ethoxyphenyl)-naphthalene-2-carboxamide (IC50=2.0 and 3.1µM, respectively) within series B. The inhibitory activity of C'(3) or C'(4) alkoxy substituted compounds of series B was considerably higher than that of C'(2) ones within series A. The PET-inhibiting activities of both series were compared with the PET inhibition of isomeric N-alkoxyphenyl-3-hydroxynaphthalene-2-carboxamides (series C) reported recently. Interactions of the studied compounds with chlorophyll a and aromatic amino acids present in pigment-protein complexes mainly in PS II were documented by fluorescence spectroscopy. The section between P680 and plastoquinone QB in the PET chain occurring on the acceptor side of PSII can be suggested as the site of action of the compounds.
- MeSH
- antibakteriální látky chemie metabolismus MeSH
- fotosystém II - proteinový komplex antagonisté a inhibitory metabolismus MeSH
- naftaleny chemie metabolismus MeSH
- rostlinné proteiny antagonisté a inhibitory metabolismus MeSH
- Spinacia oleracea účinky léků metabolismus MeSH
- transport elektronů účinky léků MeSH
- Publikační typ
- časopisecké články MeSH
Gymnosperms, unlike angiosperms, are able to synthesize chlorophyll and form photosystems in complete darkness. Photosystem I (PSI) formed under such conditions is fully active, but photosystem II (PSII) is present in its latent form with inactive oxygen evolving complex (OEC). In this work we have studied light-induced gradual changes in PSII function in dark-grown cotyledons of Norway spruce (Picea abies) via the measurement of chlorophyll a fluorescence rise, absorption changes at 830 nm, thermoluminescence glow curves (TL) and protein analysis. The results indicate that in dark-grown cotyledons, alternative reductants were able to act as electron donors to PSII with inactive OEC. Illumination of cotyledons for 5 min led to partial activation of PSII, which was accompanied by detectable oxygen evolution, but still a substantial number of PSII centers remained in the so called PSII-Q(B)-non-reducing form. Interestingly, even 24 h long illumination was not sufficient for the full activation of PSII centers. This was evidenced by a weak attachment of PsbP protein and the absence of PsbQ protein in PSII particles, the absence of PSII supercomplexes, the suboptimal maximum yield of PSII photochemistry, the presence of C band in TL curve and also the presence of up-shifted Q band in TL in DCMU-treated cotyledons. This slow light-induced activation of PSII in dark-grown cotyledons could contribute to the prevention of PSII overexcitation before the light-induced increase in PSI/PSII ratio allows effective operation of linear electron flow.
- MeSH
- chlorofyl chemie metabolismus MeSH
- fotosyntéza účinky záření MeSH
- fotosystém I - proteinový komplex metabolismus MeSH
- fotosystém II - proteinový komplex metabolismus MeSH
- kotyledon růst a vývoj metabolismus účinky záření MeSH
- kyslík metabolismus MeSH
- luminiscenční měření metody MeSH
- rostlinné proteiny metabolismus MeSH
- semenáček růst a vývoj metabolismus účinky záření MeSH
- smrk růst a vývoj metabolismus účinky záření MeSH
- světlo * MeSH
- teplota MeSH
- tma * MeSH
- transport elektronů účinky záření MeSH
- tylakoidy metabolismus účinky záření MeSH
- western blotting MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Photosystem II (PSII) is a multisubunit protein complex in cyanobacteria, algae and plants that use light energy for oxidation of water and reduction of plastoquinone. The conversion of excitation energy absorbed by chlorophylls into the energy of separated charges and subsequent water-plastoquinone oxidoreductase activity are inadvertently coupled with the formation of reactive oxygen species (ROS). Singlet oxygen is generated by the excitation energy transfer from triplet chlorophyll formed by the intersystem crossing from singlet chlorophyll and the charge recombination of separated charges in the PSII antenna complex and reaction center of PSII, respectively. Apart to the energy transfer, the electron transport associated with the reduction of plastoquinone and the oxidation of water is linked to the formation of superoxide anion radical, hydrogen peroxide and hydroxyl radical. To protect PSII pigments, proteins and lipids against the oxidative damage, PSII evolved a highly efficient antioxidant defense system comprising either a non-enzymatic (prenyllipids such as carotenoids and prenylquinols) or an enzymatic (superoxide dismutase and catalase) scavengers. It is pointed out here that both the formation and the scavenging of ROS are controlled by the energy level and the redox potential of the excitation energy transfer and the electron transport carries, respectively. The review is focused on the mechanistic aspects of ROS production and scavenging by PSII. This article is part of a Special Issue entitled: Photosystem II.
- MeSH
- fotosystém II - proteinový komplex chemie metabolismus MeSH
- molekulární modely MeSH
- oxidace-redukce MeSH
- přenos energie MeSH
- reaktivní formy kyslíku metabolismus MeSH
- scavengery volných radikálů metabolismus MeSH
- transport elektronů MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
Plant photosystem II (PSII) is organized into large supercomplexes with variable levels of membrane-bound light-harvesting proteins (LHCIIs). The largest stable form of the PSII supercomplex involves four LHCII trimers, which are specifically connected to the PSII core dimer via monomeric antenna proteins. The PSII supercomplexes can further interact in the thylakoid membrane, forming PSII megacomplexes. So far, only megacomplexes consisting of two PSII supercomplexes associated in parallel have been observed. Here we show that the forms of PSII megacomplexes can be much more variable. We performed single particle electron microscopy (EM) analysis of PSII megacomplexes isolated from Arabidopsis thaliana using clear-native polyacrylamide gel electrophoresis. Extensive image analysis of a large data set revealed that besides the known PSII megacomplexes, there are distinct groups of megacomplexes with non-parallel association of supercomplexes. In some of them, we have found additional LHCII trimers, which appear to stabilize the non-parallel assemblies. We also performed EM analysis of the PSII supercomplexes on the level of whole grana membranes and successfully identified several types of megacomplexes, including those with non-parallel supercomplexes, which strongly supports their natural origin. Our data demonstrate a remarkable ability of plant PSII to form various larger assemblies, which may control photochemical usage of absorbed light energy in plants in a changing environment.
- MeSH
- Arabidopsis metabolismus MeSH
- elektronová mikroskopie MeSH
- fotosystém II - proteinový komplex chemie metabolismus ultrastruktura MeSH
- konformace proteinů MeSH
- molekulární modely MeSH
- multimerizace proteinu MeSH
- proteiny huseníčku metabolismus ultrastruktura MeSH
- světlosběrné proteinové komplexy chemie metabolismus ultrastruktura MeSH
- tylakoidy metabolismus ultrastruktura MeSH
- vazba proteinů MeSH
- Publikační typ
- časopisecké články MeSH
