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1.
Proc Natl Acad Sci U S A ; 117(16): 9101-9111, 2020 04 21.
Artigo em Inglês | MEDLINE | ID: mdl-32245810

RESUMO

In eukaryotic photosynthetic organisms, the conversion of solar into chemical energy occurs in thylakoid membranes in the chloroplast. How thylakoid membranes are formed and maintained is poorly understood. However, previous observations of vesicles adjacent to the stromal side of the inner envelope membrane of the chloroplast suggest a possible role of membrane transport via vesicle trafficking from the inner envelope to the thylakoids. Here we show that the model plant Arabidopsis thaliana has a chloroplast-localized Sec14-like protein (CPSFL1) that is necessary for photoautotrophic growth and vesicle formation at the inner envelope membrane of the chloroplast. The cpsfl1 mutants are seedling lethal, show a defect in thylakoid structure, and lack chloroplast vesicles. Sec14 domain proteins are found only in eukaryotes and have been well characterized in yeast, where they regulate vesicle budding at the trans-Golgi network. Like the yeast Sec14p, CPSFL1 binds phosphatidylinositol phosphates (PIPs) and phosphatidic acid (PA) and acts as a phosphatidylinositol transfer protein in vitro, and expression of Arabidopsis CPSFL1 can complement the yeast sec14 mutation. CPSFL1 can transfer PIP into PA-rich membrane bilayers in vitro, suggesting that CPSFL1 potentially facilitates vesicle formation by trafficking PA and/or PIP, known regulators of membrane trafficking between organellar subcompartments. These results underscore the role of vesicles in thylakoid biogenesis and/or maintenance. CPSFL1 appears to be an example of a eukaryotic cytosolic protein that has been coopted for a function in the chloroplast, an organelle derived from endosymbiosis of a cyanobacterium.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiologia , Proteínas de Transferência de Fosfolipídeos/metabolismo , Fotossíntese , Tilacoides/metabolismo , Proteínas de Arabidopsis/genética , Microscopia Eletrônica de Transmissão , Mutação , Ácidos Fosfatídicos/metabolismo , Fosfatos de Fosfatidilinositol/metabolismo , Proteínas de Transferência de Fosfolipídeos/genética , Plantas Geneticamente Modificadas , Domínios Proteicos , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Plântula , Homologia de Sequência de Aminoácidos , Tilacoides/ultraestrutura
3.
Nat Commun ; 11(1): 1361, 2020 03 13.
Artigo em Inglês | MEDLINE | ID: mdl-32170184

RESUMO

Grana are a characteristic feature of higher plants' thylakoid membranes, consisting of stacks of appressed membranes enriched in Photosystem II (PSII) and associated light-harvesting complex II (LHCII) proteins, together forming the PSII-LHCII supercomplex. Grana stacks undergo light-dependent structural changes, mainly by reorganizing the supramolecular structure of PSII-LHCII supercomplexes. LHCII is vital for grana formation, in which also PSII-LHCII supercomplexes are involved. By combining top-down and crosslinking mass spectrometry we uncover the spatial organization of paired PSII-LHCII supercomplexes within thylakoid membranes. The resulting model highlights a basic molecular mechanism whereby plants maintain grana stacking at changing light conditions. This mechanism relies on interactions between stroma-exposed N-terminal loops of LHCII trimers and Lhcb4 subunits facing each other in adjacent membranes. The combination of light-dependent LHCII N-terminal trimming and extensive N-terminal α-acetylation likely affects interactions between pairs of PSII-LHCII supercomplexes across the stromal gap, ultimately mediating membrane folding in grana stacks.


Assuntos
Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Plantas/metabolismo , Proteínas Quinases/metabolismo , Tilacoides/metabolismo , Proteínas de Ligação à Clorofila/metabolismo , Embriófitas , Luz , Complexos de Proteínas Captadores de Luz/química , Espectrometria de Massas/métodos , Modelos Moleculares , Complexo de Proteína do Fotossistema II/química , Proteínas de Plantas/metabolismo , Conformação Proteica , Proteínas Quinases/química , Proteômica
4.
Environ Pollut ; 262: 114274, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32135430

RESUMO

The impact of nanoplastics (NP) using model polystyrene nanoparticles amine functionalized (PS-NH2) has been investigated on pigment and lipid compositions of the marine diatom Chaetoceros neogracile, at two growth phases using a low (0.05 µg mL-1) and a high (5 µg mL-1) concentrations for 96 h. Results evidenced an impact on pigment composition associated to the light-harvesting function and photoprotection mainly at exponential phase. NP also impacted lipid composition of diatoms with a re-adjustment of lipid classes and fatty acids noteworthy. Main changes upon NP exposure were observed in galactolipids and triacylglycerol's at both growth phases affecting the thylakoids membrane structure and cellular energy reserve of diatoms. Particularly, exponential cultures exposed to high NP concentration showed an impairment of long chain fatty acids synthesis. Changes in pigment and lipid content of diatom' cells revealed that algae physiology is determinant in the way cells adjust their thylakoid membrane composition to cope with NP contamination stress. Compositions of reserve and membrane lipids are proposed as sensitive markers to assess the impact of NP exposure, including at potential predicted environmental doses, on marine organisms.


Assuntos
Diatomáceas , Organismos Aquáticos , Lipídeos , Poliestirenos , Tilacoides
5.
Biochim Biophys Acta Bioenerg ; 1861(5-6): 148183, 2020 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-32173384

RESUMO

Photosynthetic organisms are frequently exposed to excess light conditions and hence to photo-oxidative stress. To counteract photo-oxidative damage, land plants and most algae make use of non- photochemical quenching (NPQ) of excess light energy, in particular the rapidly inducible and relaxing qE-mechanism. In vascular plants, the constitutively active PsbS protein is the key regulator of qE. In the green algae C. reinhardtii, however, qE activation is only possible after initial high-light (HL) acclimation for several hours and requires the synthesis of LHCSR proteins which act as qE regulators. The precise function of PsbS, which is transiently expressed during HL acclimation in C. reinhardtii, is still unclear. Here, we investigated the impact of different PsbS amounts on HL acclimation characteristics of C. reinhardtii cells. We demonstrate that lower PsbS amounts negatively affect HL acclimation at different levels, including NPQ capacity, electron transport characteristics, antenna organization and morphological changes, resulting in an overall increased HL sensitivity and lower vitality of cells. Contrarily, higher PsbS amounts do not result in a higher NPQ capacity, but nevertheless provide higher fitness and tolerance towards HL stress. Strikingly, constitutively expressed PsbS protein was found to be degraded during HL acclimation. We propose that PsbS is transiently required during HL acclimation for the reorganization of thylakoid membranes and/or antenna proteins along with the activation of NPQ and adjustment of electron transfer characteristics, and that degradation of PsbS is essential in the fully HL acclimated state.


Assuntos
Proteínas de Algas/metabolismo , Chlamydomonas reinhardtii/metabolismo , Chlamydomonas reinhardtii/efeitos da radiação , Transferência de Energia , Luz , Substâncias Protetoras/metabolismo , Proteínas de Algas/ultraestrutura , Chlamydomonas reinhardtii/ultraestrutura , Processos Fotoquímicos , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Tilacoides/metabolismo
6.
Nat Commun ; 11(1): 1460, 2020 03 19.
Artigo em Inglês | MEDLINE | ID: mdl-32193383

RESUMO

Since the discovery of quantum beats in the two-dimensional electronic spectra of photosynthetic pigment-protein complexes over a decade ago, the origin and mechanistic function of these beats in photosynthetic light-harvesting has been extensively debated. The current consensus is that these long-lived oscillatory features likely result from electronic-vibrational mixing, however, it remains uncertain if such mixing significantly influences energy transport. Here, we examine the interplay between the electronic and nuclear degrees of freedom (DoF) during the excitation energy transfer (EET) dynamics of light-harvesting complex II (LHCII) with two-dimensional electronic-vibrational spectroscopy. Particularly, we show the involvement of the nuclear DoF during EET through the participation of higher-lying vibronic chlorophyll states and assign observed oscillatory features to specific EET pathways, demonstrating a significant step in mapping evolution from energy to physical space. These frequencies correspond to known vibrational modes of chlorophyll, suggesting that electronic-vibrational mixing facilitates rapid EET over moderately size energy gaps.


Assuntos
Transferência de Energia , Complexos de Proteínas Captadores de Luz/química , Teoria Quântica , Elétrons , Complexos de Proteínas Captadores de Luz/metabolismo , Modelos Químicos , Folhas de Planta/citologia , Análise Espectral , Tilacoides/metabolismo
7.
Proc Natl Acad Sci U S A ; 117(12): 6918-6927, 2020 03 24.
Artigo em Inglês | MEDLINE | ID: mdl-32161131

RESUMO

Singlet oxygen (1O2), the major reactive oxygen species (ROS) produced in chloroplasts, has been demonstrated recently to be a highly versatile signal that induces various stress responses. In the fluorescent (flu) mutant, its release causes seedling lethality and inhibits mature plant growth. However, these drastic phenotypes are suppressed when EXECUTER1 (EX1) is absent in the flu ex1 double mutant. We identified SAFEGUARD1 (SAFE1) in a screen of ethyl methanesulfonate (EMS) mutagenized flu ex1 plants for suppressor mutants with a flu-like phenotype. In flu ex1 safe1, all 1O2-induced responses, including transcriptional rewiring of nuclear gene expression, return to levels, such as, or even higher than, those in flu Without SAFE1, grana margins (GMs) of chloroplast thylakoids (Thys) are specifically damaged upon 1O2 generation and associate with plastoglobules (PGs). SAFE1 is localized in the chloroplast stroma, and release of 1O2 induces SAFE1 degradation via chloroplast-originated vesicles. Our paper demonstrates that flu-produced 1O2 triggers an EX1-independent signaling pathway and proves that SAFE1 suppresses this signaling pathway by protecting GMs.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crescimento & desenvolvimento , Estresse Oxidativo , Substâncias Protetoras/metabolismo , Plântula/crescimento & desenvolvimento , Oxigênio Singlete/toxicidade , Tilacoides/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Cloroplastos/efeitos dos fármacos , Cloroplastos/metabolismo , Cloroplastos/patologia , Regulação da Expressão Gênica de Plantas , Luz , Mutação , Espécies Reativas de Oxigênio/metabolismo , Plântula/genética , Plântula/metabolismo , Tilacoides/efeitos dos fármacos , Tilacoides/patologia
8.
Biochim Biophys Acta Bioenerg ; 1861(4): 148039, 2020 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-31228404

RESUMO

The higher plant chloroplast thylakoid membrane system performs the light-dependent reactions of photosynthesis. These provide the ATP and NADPH required for the fixation of CO2 into biomass by the Calvin-Benson cycle and a range of other metabolic reactions in the stroma. Land plants are frequently challenged by fluctuations in their environment, such as light, nutrient and water availability, which can create a mismatch between the amounts of ATP and NADPH produced and the amounts required by the downstream metabolism. Left unchecked, such imbalances can lead to the production of reactive oxygen species that damage the plant and harm productivity. Fortunately, plants have evolved a complex range of regulatory processes to avoid or minimize such deleterious effects by controlling the efficiency of light harvesting and electron transfer in the thylakoid membrane. Generally the regulation of the light reactions has been studied and conceptualised at the microscopic level of protein-protein and protein-ligand interactions, however in recent years dynamic changes in the thylakoid macrostructure itself have been recognised to play a significant role in regulating light harvesting and electron transfer. Here we review the evidence for the involvement of macrostructural changes in photosynthetic regulation and review the techniques that brought this evidence to light.


Assuntos
Fotossíntese , Tilacoides/metabolismo , Aclimatação/efeitos da radiação , Luz , Fotossíntese/efeitos da radiação , Tilacoides/efeitos da radiação , Tilacoides/ultraestrutura
9.
Biochim Biophys Acta Mol Cell Res ; 1867(2): 118606, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-31733260

RESUMO

We have established an experimental system for the functional analysis of thylakoidal TatB, a component of the membrane-integral TatBC receptor complex of the thylakoidal Twin-arginine protein transport (Tat) machinery. For this purpose, the intrinsic TatB activity of isolated pea thylakoids was inhibited by affinity-purified antibodies and substituted by supplementing the assays with TatB protein either obtained by in vitro translation or purified after heterologous expression in E. coli. Tat transport activity of such reconstituted thylakoids, which was analysed with the authentic Tat substrate pOEC16, reached routinely 20-25% of the activity of mock-treated thylakoid vesicles analysed in parallel. In contrast, supplementation of the assays with the purified antigen comprising all but the N-terminal transmembrane helix of thylakoidal TatB did not result in Tat transport reconstitution which confirms that transport relies strictly on the activity of the TatB protein added and is not due to restoration of the intrinsic TatB activity by antibody release. Unexpectedly, even a mutated TatB protein (TatB,E10C) assumed to be incapable of assembling into the TatBC receptor complex showed low but considerable transport reconstitution underlining the sensitivity of the approach and its suitability for further functional analyses of protein variants. Finally, quantification of TatB demand suggests that TatA and TatB are required in approximately equimolar amounts to achieve Tat-dependent thylakoid transport.


Assuntos
Proteínas de Escherichia coli/metabolismo , Proteínas de Membrana Transportadoras/metabolismo , Tilacoides/metabolismo , Escherichia coli/metabolismo , Proteínas de Escherichia coli/genética , Proteínas de Membrana Transportadoras/genética , Transporte Proteico , Proteínas Recombinantes/biossíntese , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação
10.
Biochim Biophys Acta Bioenerg ; 1861(2): 148141, 2020 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-31825808

RESUMO

Hetero-oligomeric membrane protein complexes form the electron transport chain (ETC) of oxygenic photosynthesis. The ETC complexes undertake the light-driven vectorial electron and proton transport reactions, which generate energy-rich ATP and electron-rich NADPH molecules for carbon fixation. The rate of photosynthetic electron transport depends on the availability of photons and the relative abundance of electron transport complexes. The relative abundance of the two photosystems, critical for the quantum efficiency of photosynthesis in changing light quality conditions, has been determined successfully by optical methods. Due to the lack of spectroscopic signatures, however, relatively little is known about the stoichiometry of other non-photosystem complexes in plant photosynthetic membrane. Here we determine the ratios of all major thylakoid-bound ETC complexes in Arabidopsis by a label-free quantitative mass spectrometry technique. The calculated stoichiometries are consistent with known subunit composition of complexes and current estimates of photosystem and cytochrome b6f concentrations. The implications of these stoichiometries for photosynthetic light harvesting and the partitioning of electrons between the linear and cyclic electron transport pathways of photosynthesis are discussed.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimologia , Complexo Citocromos b6f/metabolismo , Fotossíntese/fisiologia , Tilacoides/enzimologia
11.
Biochim Biophys Acta Bioenerg ; 1861(2): 148135, 2020 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-31821793

RESUMO

In forests, understory plants are usually exposed to sunflecks on timescales of seconds or minutes. However, it is unclear how understory plants acclimate to fluctuating light. In this study, we compared chlorophyll fluorescence, PSI redox state and the electrochromic shift signal under fluctuating light between an understory plant Paris polyphylla (Liliaceae) and a light-demanding plant Bletilla striata (Orchidaceae). Within the first seconds after transition from low to high light, PSI was highly oxidized in P. polyphylla but was highly reduced in B. striata, although both species could not generate a sufficient trans-thylakoid proton gradient (ΔpH). Furthermore, the outflow of electrons from PSI to O2 was not significant in P. polyphylla, as indicated by the P700 redox kinetics upon dark-to-light transition. Therefore, the different responses of PSI to fluctuating light between P. polyphylla and B. striata could not be explained by ΔpH formation or alternative electron transport. In contrast, upon a sudden transition from low to high light, electron flow from PSII was much lower in P. polyphylla than in B. striata, suggesting that the rapid oxidation of PSI in P. polyphylla was largely attributed to the lower PSII activity. We propose, for the first time, that down-regulation of PSII activity is an important strategy used by some understory angiosperms to cope with sunflecks.


Assuntos
Luz , Melanthiaceae/enzimologia , Complexo de Proteína do Fotossistema II/metabolismo , Força Próton-Motriz/fisiologia , Tilacoides/enzimologia , Transporte de Elétrons/fisiologia , Orchidaceae/enzimologia , Oxigênio/metabolismo
12.
Biochim Biophys Acta Bioenerg ; 1861(4): 148035, 2020 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-31226317

RESUMO

Proper assembly of plant photosystem II, in the appressed region of thylakoids, allows for both efficient light harvesting and the dissipation of excitation energy absorbed in excess. The core moiety of wild type supercomplex is associated with monomeric antennae that, in turn, bind peripheral trimeric LHCII complexes. Acclimation to light environment dynamics involves structural plasticity within PSII-LHCs supercomplexes, including depletion in LHCII and CP24. Here, we report on the acclimation of NoM, an Arabidopsis mutant lacking monomeric LHCs but retaining LHCII trimer. Lack of monomeric LHCs impaired the operation of both photosynthetic electron transport and state transitions, despite the fact that NoM underwent a compensatory over-accumulation of the LHCII complement compared to the wild type. Mutant plants displayed stunted growth compared to the wild type when probed over a range of light conditions. When exposed to short-term excess light, NoM showed higher photosensitivity and enhanced singlet oxygen release than the wild type, whereas long-term acclimation under stress conditions was unaffected. Analysis of pigment-binding supercomplexes showed that the absence of monomeric LHCs did affect the macro-organisation of photosystems: large PSI-LHCII megacomplexes were more abundant in NoM, whereas the assembly of PSII-LHCs supercomplexes was impaired. Observation by electron microscopy (EM) and image analysis of thylakoids highlighted impaired granal stacking and membrane organisation, with a heterogeneous distribution of PSII and LHCII compared to the wild type. It is concluded that monomeric LHCs are critical for the structural and functional optimisation of the photosynthetic apparatus.


Assuntos
Transferência de Energia , Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Tilacoides/metabolismo , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Arabidopsis/efeitos da radiação , Biomassa , Luz , Mutação/genética , Oxirredução/efeitos da radiação , Fotossíntese/efeitos da radiação , Pigmentos Biológicos/metabolismo , Espectrometria de Fluorescência , Tilacoides/efeitos da radiação , Tilacoides/ultraestrutura
13.
Int J Vitam Nutr Res ; 90(1-2): 169-178, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30829138

RESUMO

Nowadays, overweight and obesity are major epidemic health problems that can bring about some other health issues such as cardiovascular disease which is the first cause of mortality worldwide. Thylakoids are disc-like membranes responsible for photosynthetic light reactions in chloroplasts of green plants. Although only a few animal and human studies have been conducted regarding the impact of thylakoids on overweight- and obesity-related factors, all of them have resulted in positive outcomes. These outcomes are as follows: increment of satiety response; suppression of hunger sensations, particularly hedonic hunger; reduction of body weight and fat; promotion of glucose homeostasis; decrease in serum lipids; attenuation of oxidative stress and inflammation; and modulation of gut microbiota, notably by increasing some helpful bacteria such as Lactobacillus reuteri. It seems that some of these useful effects are related to retarded absorption of dietary fat and carbohydrate caused by thylakoids. There is still a need for more well-designed studies.


Assuntos
Obesidade , Tilacoides , Animais , Peso Corporal , Suplementos Nutricionais , Humanos , Obesidade/dietoterapia , Obesidade/tratamento farmacológico , Sobrepeso , Tilacoides/química
14.
Biochim Biophys Acta Bioenerg ; 1861(4): 148027, 2020 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-31153887

RESUMO

Besides the so-called 'green lineage' of eukaryotic photosynthetic organisms that include vascular plants, a huge variety of different algal groups exist that also harvest light by means of membrane intrinsic light harvesting proteins (Lhc). The main taxa of these algae are the Cryptophytes, Haptophytes, Dinophytes, Chromeridae and the Heterokonts, the latter including diatoms, brown algae, Xanthophyceae and Eustigmatophyceae amongst others. Despite the similarity in Lhc proteins between vascular plants and these algae, pigmentation is significantly different since no Chl b is bound, but often replaced by Chl c, and a large diversity in carotenoids functioning in light harvesting and/or photoprotection is present. Due to the presence of Chl c in most of the taxa the name 'Chl c-containing organisms' has become common, however, Chl b-less is more precise since some harbour Lhc proteins that only bind one type of Chl, Chl a. In recent years huge progress has been made about the occurrence and function of Lhc in diatoms, so-called fucoxanthin chlorophyll proteins (FCP), where also the first molecular structure became available recently. In addition, especially energy transfer amongst the unusual pigments bound was intensively studied in many of these groups. This review summarises the present knowledge about the molecular structure, the arrangement of the different Lhc in complexes, the excitation energy transfer abilities and the involvement in photoprotection of the different Lhc systems in the so-called Chl c-containing organisms. This article is part of a Special Issue entitled Light harvesting, edited by Dr. Roberta Croce.


Assuntos
Clorofila/metabolismo , Eucariotos/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Carotenoides/química , Clorofila/química , Eucariotos/genética , Genes de Plantas , Tilacoides/metabolismo
15.
ACS Appl Mater Interfaces ; 11(50): 47625-47634, 2019 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-31794177

RESUMO

DNA release from an electrode surface was stimulated by application of a mild electrical potential (0 V vs Ag/AgCl). The release process was activated by interfacial pH increase originating from H+ consumption during O2 reduction bio-electrocatalyzed by bilirubin oxidase immobilized at the electrode surface. The pH increase resulted in a change of the electrical charge from positive to negative at the surface of SiO2 nanoparticles (200 nm) associated with the electrode surface and functionalized with trigonelline and boronic acid. While the negatively charged DNA molecules were electrostatically bound to the positively charged surface, the negative charge produced upon O2 reduction resulted in the DNA repulsion and release from the modified interface. The small electrical potential for O2 reduction resulting in the interface recharge was allowed due to the bio-electrocatalysis using bilirubin oxidase enzyme. While, in the first set of experiments, the potential was applied on the modified electrode from an electrochemical instrument, later it was generated in situ by biocatalytic or photo-biocatalytic processes at a connected electrode. A multistep biocatalytic cascade generating NADH or photosynthetic process in thylakoid membranes was used to produce in situ a small potential to stimulate the DNA release catalyzed by bilirubin oxidase. The designed system can be used for different release processes triggered by various signals (electrical, biomolecular, and light signals, etc.), thus representing a general interfacial platform for the controlled release of different biomolecules and nanosize species.


Assuntos
Técnicas Biossensoriais , Enzimas Imobilizadas/química , NAD/isolamento & purificação , Oxirredutases atuantes sobre Doadores de Grupo CH-CH/química , Biocatálise , DNA/química , Eletrodos , Hidrogênio/química , Concentração de Íons de Hidrogênio , NAD/química , Nanopartículas/química , Oxigênio/química , Propriedades de Superfície , Tilacoides/química
16.
Phys Rev E ; 100(5-1): 050601, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31869924

RESUMO

Motivated by biological membrane-containing organelles in plants and photosynthetic bacteria, we study charge regulation in a model membrane stack. Considering (de)protonation as the simplest mechanism of charge equilibration between the membranes and with the bathing environment, we uncover a symmetry-broken charge state in the stack with a quasiperiodic effective charge sequence. In the case of a monovalent bathing salt solution our model predicts complex, inhomogeneous charge equilibria depending on the strength of the (de)protonation reaction, salt concentration, and membrane size. Our results shed light on the basic reorganization mechanism of thylakoid membrane stacks.


Assuntos
Modelos Moleculares , Eletricidade Estática , Tilacoides/química , Termodinâmica
17.
J Plant Physiol ; 243: 153048, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31639536

RESUMO

Investigations of the luminal immunophilin AtCYP38 (cyclophilin 38) in Arabidopsis thaliana (At), the orthologue of the complex immunophilin TLP40 from Spinacia oleracea, revealed its involvement in photosystem II (PSII) repair and assembly, biogenesis of PSII complex, and cellular signalling. However, the main physiological roles of AtCYP38 and TLP40 are related to regulation of thylakoid PP2A-type phosphatase involved in PSII core protein dephosphorylation, and chaperone function during protein folding. Here we further investigate physiological roles of AtCYP38 and analyse the ultrastructure of chloroplasts from cyp38-2 plants. Transmission electron microscopy followed by quantitative micrography revealed modifications in thylakoid stacking. We also confirm that the depletion of AtCYP38 influences PSII performance, which leads to stunted phenotype of cyp38-2 plants.


Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Ciclofilinas/genética , Complexo de Proteína do Fotossistema II/metabolismo , Tilacoides/metabolismo , Arabidopsis/enzimologia , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Cloroplastos/ultraestrutura , Ciclofilinas/metabolismo , Microscopia Eletrônica de Transmissão
18.
Nat Plants ; 5(11): 1177-1183, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31659240

RESUMO

In nature, plants experience large fluctuations in light intensity and they need to balance the absorption and utilization of this energy appropriately. Non-photochemical quenching (NPQ) is a rapidly switchable mechanism that protects plants from photodamage caused by high light exposure by dissipating the excess absorbed energy as heat. It is triggered by the pH gradient across the thylakoid membrane and requires the protein PsbS and the xanthophyll zeaxanthin. However, the site and mechanism of the quencher(s) remain unknown. Here, we constructed a mutant of Arabidopsis thaliana that lacks light-harvesting complex II (LHCII), the main antenna complex of plants, to verify its contribution to NPQ. The mutant plant has normally stacked thylakoid membranes, displays no upregulation of other LHCs but shows a relative decrease in Photosystem I (PSI), which compensates for the decrease of the PSII antenna. The mutant plant exhibits a reduction in NPQ of about 60% and the remaining NPQ resembles that of mutant plants lacking chlorophyll (Chl) b, which lack all PSII peripheral antenna complexes. We thus report that PsbS-dependent NPQ occurs mainly in LHCII, but there is an additional quenching site in the PSII core.


Assuntos
Arabidopsis/metabolismo , Complexo de Proteína do Fotossistema II/fisiologia , Arabidopsis/genética , Mutação , Processos Fotoquímicos , Complexo de Proteína do Fotossistema II/genética , Tilacoides/metabolismo
19.
Proc Natl Acad Sci U S A ; 116(44): 22366-22375, 2019 10 29.
Artigo em Inglês | MEDLINE | ID: mdl-31611387

RESUMO

Plant photosynthetic (thylakoid) membranes are organized into complex networks that are differentiated into 2 distinct morphological and functional domains called grana and stroma lamellae. How the 2 domains join to form a continuous lamellar system has been the subject of numerous studies since the mid-1950s. Using different electron tomography techniques, we found that the grana and stroma lamellae are connected by an array of pitch-balanced right- and left-handed helical membrane surfaces of different radii and pitch. Consistent with theoretical predictions, this arrangement is shown to minimize the surface and bending energies of the membranes. Related configurations were proposed to be present in the rough endoplasmic reticulum and in dense nuclear matter phases theorized to exist in neutron star crusts, where the right- and left-handed helical elements differ only in their handedness. Pitch-balanced helical elements of alternating handedness may thus constitute a fundamental geometry for the efficient packing of connected layers or sheets.


Assuntos
Alface/ultraestrutura , Tilacoides/ultraestrutura , Tomografia com Microscopia Eletrônica , Retículo Endoplasmático/ultraestrutura , Alface/metabolismo , Fotossíntese
20.
Proc Natl Acad Sci U S A ; 116(43): 21907-21913, 2019 10 22.
Artigo em Inglês | MEDLINE | ID: mdl-31594847

RESUMO

In oxygenic photosynthetic organisms, photosystem II (PSII) is a unique membrane protein complex that catalyzes light-driven oxidation of water. PSII undergoes frequent damage due to its demanding photochemistry. It must undergo a repair and reassembly process following photodamage, many facets of which remain unknown. We have discovered a PSII subcomplex that lacks 5 key PSII core reaction center polypeptides: D1, D2, PsbE, PsbF, and PsbI. This pigment-protein complex does contain the PSII core antenna proteins CP47 and CP43, as well as most of their associated low molecular mass subunits, and the assembly factor Psb27. Immunoblotting, mass spectrometry, and ultrafast spectroscopic results support the absence of a functional reaction center in this complex, which we call the "no reaction center" complex (NRC). Analytical ultracentrifugation and clear native PAGE analysis show that NRC is a stable pigment-protein complex and not a mixture of free CP47 and CP43 proteins. NRC appears in higher abundance in cells exposed to high light and impaired protein synthesis, and genetic deletion of PsbO on the PSII luminal side results in an increased NRC population, indicative that NRC forms in response to photodamage as part of the PSII repair process. Our finding challenges the current model of the PSII repair cycle and implies an alternative PSII repair strategy. Formation of this complex may maximize PSII repair economy by preserving intact PSII core antennas in a single complex available for PSII reassembly, minimizing the risk of randomly diluting multiple recycling components in the thylakoid membrane following a photodamage event.


Assuntos
Complexo de Proteína do Fotossistema II/fisiologia , Células Cultivadas , Clorofila/fisiologia , Fotoquímica , Fotossíntese , Complexo de Proteína do Fotossistema II/isolamento & purificação , Tilacoides/fisiologia
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