Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 2.792
Filtrar
1.
Proc Natl Acad Sci U S A ; 119(37): e2122032119, 2022 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-36067315

RESUMO

Photosynthetic organisms have developed a regulation mechanism called state transition (ST) to rapidly adjust the excitation balance between the two photosystems by light-harvesting complex II (LHCII) movement. Though many researchers have assumed coupling of the dynamic transformations of the thylakoid membrane with ST, evidence of that remains elusive. To clarify the above-mentioned coupling in a model organism Chlamydomonas, here we used two advanced microscope techniques, the excitation-spectral microscope (ESM) developed recently by us and the superresolution imaging based on structured-illumination microscopy (SIM). The ESM observation revealed ST-dependent spectral changes upon repeated ST inductions. Surprisingly, it clarified a less significant ST occurrence in the region surrounding the pyrenoid, which is a subcellular compartment specialized for the carbon-fixation reaction, than that in the other domains. Further, we found a species dependence of this phenomenon: 137c strain showed the significant intracellular inhomogeneity of ST occurrence, whereas 4A+ strain hardly did. On the other hand, the SIM observation resolved partially irreversible fine thylakoid transformations caused by the ST-inducing illumination. This fine, irreversible thylakoid transformation was also observed in the STT7 kinase-lacking mutant. This result revealed that the fine thylakoid transformation is not induced solely by the LHCII phosphorylation, suggesting the highly susceptible nature of the thylakoid ultrastructure to the photosynthetic light reactions.


Assuntos
Chlamydomonas , Complexos de Proteínas Captadores de Luz , Complexo de Proteína do Fotossistema II , Tilacoides , Chlamydomonas/enzimologia , Chlamydomonas/efeitos da radiação , Luz , Complexos de Proteínas Captadores de Luz/química , Fosforilação , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema II/química , Tilacoides/enzimologia , Tilacoides/efeitos da radiação
2.
Cells ; 11(17)2022 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-36078087

RESUMO

It is well established that plant thylakoid membranes (TMs), in addition to a bilayer, contain two isotropic lipid phases and an inverted hexagonal (HII) phase. To elucidate the origin of non-bilayer lipid phases, we recorded the 31P-NMR spectra of isolated spinach plastoglobuli and TMs and tested their susceptibilities to lipases and proteases; the structural and functional characteristics of TMs were monitored using biophysical techniques and CN-PAGE. Phospholipase-A1 gradually destroyed all 31P-NMR-detectable lipid phases of isolated TMs, but the weak signal of isolated plastoglobuli was not affected. Parallel with the destabilization of their lamellar phase, TMs lost their impermeability; other effects, mainly on Photosystem-II, lagged behind the destruction of the original phases. Wheat-germ lipase selectively eliminated the isotropic phases but exerted little or no effect on the structural and functional parameters of TMs-indicating that the isotropic phases are located outside the protein-rich regions and might be involved in membrane fusion. Trypsin and Proteinase K selectively suppressed the HII phase-suggesting that a large fraction of TM lipids encapsulate stroma-side proteins or polypeptides. We conclude that-in line with the Dynamic Exchange Model-the non-bilayer lipid phases of TMs are found in subdomains separated from but interconnected with the bilayer accommodating the main components of the photosynthetic machinery.


Assuntos
Bicamadas Lipídicas , Tilacoides , Lipase/metabolismo , Bicamadas Lipídicas/metabolismo , Espectroscopia de Ressonância Magnética , Peptídeo Hidrolases/metabolismo , Tilacoides/metabolismo
3.
Biophys J ; 121(18): 3411-3421, 2022 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-35986519

RESUMO

The inner membrane-associated protein of 30 kDa (IM30) is essential in chloroplasts and cyanobacteria. The spatio-temporal cellular localization of the protein appears to be highly dynamic and triggered by internal as well as external stimuli, mainly light intensity. The soluble fraction of the protein is localized in the cyanobacterial cytoplasm or the chloroplast stroma, respectively. Additionally, the protein attaches to the thylakoid membrane as well as to the chloroplast inner envelope or the cyanobacterial cytoplasmic membrane, respectively, especially under conditions of membrane stress. IM30 is involved in thylakoid membrane biogenesis and/or maintenance, where it either stabilizes membranes and/or triggers membrane-fusion processes. These apparently contradicting functions have to be tightly controlled and separated spatiotemporally in chloroplasts and cyanobacteria. IM30's fusogenic activity depends on Mg2+ binding to IM30; yet, it still is unclear how Mg2+-loaded IM30 interacts with membranes and promotes membrane fusion. Here, we show that the interaction of Mg2+ with IM30 results in increased binding of IM30 to native, as well as model, membranes. Via atomic force microscopy in liquid, IM30-induced bilayer defects were observed in solid-supported bilayers in the presence of Mg2+. These structures differ dramatically from the membrane-stabilizing carpet structures that were previously observed in the absence of Mg2+. Thus, Mg2+-induced alterations of the IM30 structure switch the IM30 activity from a membrane-stabilizing to a membrane-destabilizing function, a crucial step in membrane fusion.


Assuntos
Synechocystis , Cloroplastos/metabolismo , Fusão de Membrana , Proteínas de Membrana/química , Synechocystis/metabolismo , Tilacoides/química
4.
Plant Cell Environ ; 45(10): 2954-2971, 2022 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-35916195

RESUMO

Photosynthetic light reactions require strict regulation under dynamic environmental conditions. Still, depending on environmental constraints, photoinhibition of Photosystem (PSII) or PSI occurs frequently. Repair of photodamaged PSI, in sharp contrast to that of PSII, is extremely slow and leads to a functional imbalance between the photosystems. Slow PSI recovery prompted us to take advantage of the PSI-specific photoinhibition treatment and investigate whether the imbalance between functional PSII and PSI leads to acclimation of photosynthesis to PSI-limited conditions, either by short-term or long-term acclimation mechanisms as tested immediately after the photoinhibition treatment or after 24 h recovery in growth conditions, respectively. Short-term acclimation mechanisms were induced directly upon inhibition, including thylakoid protein phosphorylation that redirects excitation energy to PSI as well as changes in the feedback regulation of photosynthesis, which relaxed photosynthetic control and excitation energy quenching. Longer-term acclimation comprised reprogramming of the stromal redox system and an increase in ATP synthase and Cytochrome b6 f abundance. Acclimation to PSI-limited conditions restored the CO2 assimilation capacity of plants without major PSI repair. Response to PSI inhibition demonstrates that plants efficiently acclimate to changes occurring in the photosynthetic apparatus, which is likely a crucial component in plant acclimation to adverse environmental conditions.


Assuntos
Complexo de Proteína do Fotossistema I , Complexo de Proteína do Fotossistema II , Aclimatação , Transporte de Elétrons , Luz , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Plantas/metabolismo , Tilacoides/metabolismo
5.
Plant Cell Physiol ; 63(9): 1205-1214, 2022 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-35792507

RESUMO

Higher plants acclimate to changes in light conditions by adjusting the thylakoid membrane ultrastructure. Additionally, excitation energy transfer between photosystem II (PSII) and photosystem I (PSI) is balanced in a process known as state transition. These modifications are mediated by reversible phosphorylation of Lhcb1 and Lhcb2 proteins in different pools of light-harvesting complex (LHCII) trimers. Our recent study demonstrated that chloroplast acetyltransferase NUCLEAR SHUTTLE INTERACTING (NSI)/GNAT2 (general control non-repressible 5 (GCN5)-related N-acetyltransferase 2) is also needed for the regulation of light harvesting, evidenced by the inability of the gnat2 mutant to perform state transitions although there are no defects in LHCII phosphorylation. Here, we show that despite contrasting phosphorylation states of LHCII, grana packing in the gnat2 and state transition 7 (stn7) mutants possesses similar features, as the thylakoid structure of the mutants does not respond to the shift from darkness to light, which is in striking contrast to wild type (Wt). Circular dichroism and native polyacrylamide gel electrophoresis analyses further revealed that the thylakoid protein complex organization of gnat2 and stn7 resembles each other, but differ from that of Wt. Also, the location of the phosphorylated Lhcb2 as well as the LHCII antenna within the thylakoid network in gnat2 mutant is different from that of Wt. In gnat2, the LHCII antenna remains largely in grana stacks, where the phosphorylated Lhcb2 is found in all LHCII trimer pools, including those associated with PSII. These results indicate that in addition to phosphorylation-mediated regulation through STN7, the GNAT2 enzyme is involved in the organization and dynamics of thylakoid structure, probably through the regulation of chloroplast protein acetylation.


Assuntos
Arabidopsis , Tilacoides , Acetiltransferases/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Cloroplastos/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Fosforilação , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Tilacoides/metabolismo
6.
G3 (Bethesda) ; 12(9)2022 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-35788847

RESUMO

The stromal and thylakoid membrane-bound ascorbate peroxidase isoforms are produced by the alternative splicing event of the 3'-terminal region of the APXII gene in spinach (Spinacia oleracea) and tobacco (Nicotiana tabacum), but not in Arabidopsis (Arabidopsis thaliana). However, all alternative splicing variants were detected in APXII gene-transformed Arabidopsis, indicating the occurrence of its regulatory mechanisms in Arabidopsis. The efficiency of this alternative splicing event in producing thylakoid membrane-bound ascorbate peroxidase mRNA is regulated by a splicing regulatory cis element, but trans splicing regulatory factor(s) for alternative splicing remain unclear. To identify this factor, we conducted a forward genetic screen using Arabidopsis in combination with a luciferase reporter system to evaluate the alternative splicing efficiency of thylakoid membrane-bound ascorbate peroxidase mRNA production. We isolated 9 mutant lines that showed low efficiency of the AS in producing thylakoid membrane-bound ascorbate peroxidase mRNA compared with that in the control plants. From one mutant [APXII alternative splicing inhibition (apsi1)], the causal gene responsible for the phenotype, AT5G38890 (oligonucleotide/oligosaccharide-binding-fold protein, APSI1), was identified. The levels of thylakoid membrane-bound ascorbate peroxidase mRNA from the transformed APXII gene decreased and increased in APSI1 knockout and APSI1-overexpressing plants, respectively. APSI1 was localized to the nucleus and specifically bound to the splicing regulatory cis element sequence. Tobacco plants that disrupted the closest homologs of APSI1 showed low levels of endogenous thylakoid membrane-bound ascorbate peroxidase mRNA. These results indicate that APSI1 is an enhancing component of the alternative splicing event of APXII.


Assuntos
Proteínas de Arabidopsis , Arabidopsis , Processamento Alternativo , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Ascorbato Peroxidases/genética , Ascorbato Peroxidases/metabolismo , Proteínas de Transporte/genética , Cloroplastos/genética , Regulação da Expressão Gênica de Plantas , Oligonucleotídeos , Oligossacarídeos/metabolismo , Peroxidases/genética , Plantas/genética , RNA Mensageiro/genética , Spinacia oleracea/genética , Spinacia oleracea/metabolismo , Tilacoides/metabolismo , Tabaco/genética , Tabaco/metabolismo
7.
Nat Plants ; 8(7): 840-855, 2022 07.
Artigo em Inglês | MEDLINE | ID: mdl-35798975

RESUMO

Non-photochemical quenching (NPQ) plays an important role for phototrophs in decreasing photo-oxidative damage. qH is a sustained form of NPQ and depends on the plastid lipocalin (LCNP). A thylakoid membrane-anchored protein SUPPRESSOR OF QUENCHING1 (SOQ1) prevents qH formation by inhibiting LCNP. SOQ1 suppresses qH with its lumen-located thioredoxin (Trx)-like and NHL domains. Here we report structural data, genetic modification and biochemical characterization of Arabidopsis SOQ1 lumenal domains. Our results show that the Trx-like and NHL domains are associated together, with the cysteine motif located at their interface. Residue E859, required for SOQ1 function, is pivotal for maintaining the Trx-NHL association. Importantly, the C-terminal region of SOQ1 forms an independent ß-stranded domain that has structural homology to the N-terminal domain of bacterial disulfide bond protein D and is essential for negative regulation of qH. Furthermore, SOQ1 is susceptible to cleavage at the loops connecting the neighbouring lumenal domains both in vitro and in vivo, which could be a regulatory process for its suppression function of qH.


Assuntos
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Plastídeos/metabolismo , Tilacoides/metabolismo
8.
Funct Plant Biol ; 49(10): 917-925, 2022 09.
Artigo em Inglês | MEDLINE | ID: mdl-35821662

RESUMO

The current hypotheses for the mechanisms of photosystem II (PSII) photodamage in vivo remain split on the primary damage site. However, most researchers have considered that PSII is inhibited by a sole mechanism and that the photoinhibited PSII consists of one population. In this perspective, we propose 'the mixed population hypothesis', in which there are four PSII populations: PSII with active/inactive Mn4 CaO5 oxygen-evolving complex respectively with functional/damaged primary quinone (QA ) reduction activity. This hypothesis provides a new insight into not only the PSII photoinhibition/photoprotection studies but also the repair process. We discuss our new data implying that the repair rate differs in the respective PSII populations.


Assuntos
Luz , Complexo de Proteína do Fotossistema II , Fluorescência , Tilacoides
9.
Biochim Biophys Acta Bioenerg ; 1863(7): 148589, 2022 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-35779585

RESUMO

In diatoms, light-harvesting processes take place in a specific group of proteins, called fucoxanthin chlorophyll a/c proteins (FCP). This group includes many members and represents the major characteristic of the diatom photosynthetic apparatus, with specific pigments bound (chlorophyll c, fucoxanthin, diadino- and diatoxanthin besides chlorophyll a). In thylakoids, FCP and photosystems (PS) form multimeric supercomplexes. In this study, we compared the biochemical properties of PS supercomplexes isolated from Thalassiosira pseudonana cells grown under low light or high light conditions, respectively. High light acclimation changed the molecular features of the PS and their ratio in thylakoids. In PSII, no obvious changes in polypeptide composition were observed, whereas for PSI changes in one specific group of FCP proteins were detected. As reported before, the amount of xanthophyll cycle pigments and their de-epoxidation ratio was increased in PSI under HL. In PSII, however, no additional xanthophyll cycle pigments occurred, but the de-epoxidation ratio was increased as well. This comparison suggests how mechanisms of photoprotection might take place within and in the proximity of the PS, which gives new insights into the capacity of diatoms to adapt to different conditions and in different environments.


Assuntos
Diatomáceas , Clorofila A/metabolismo , Diatomáceas/metabolismo , Tilacoides/metabolismo , Xantofilas/metabolismo
10.
Nat Commun ; 13(1): 4045, 2022 07 13.
Artigo em Inglês | MEDLINE | ID: mdl-35831297

RESUMO

The conversion of light energy to chemical energy by photosynthesis requires the concerted action of large protein complexes in the thylakoid membrane. Recent work has provided fundamental insights into the three-dimensional structure of these complexes, but how they are assembled from hundreds of parts remains poorly understood. Particularly little is known about the biogenesis of the cytochrome b6f complex (Cytb6f), the redox-coupling complex that interconnects the two photosystems. Here we report the identification of a factor that guides the assembly of Cytb6f in thylakoids of chloroplasts. The protein, DE-ETIOLATION-INDUCED PROTEIN 1 (DEIP1), resides in the thylakoid membrane and is essential for photoautotrophic growth. Knock-out mutants show a specific loss of Cytb6f, and are defective in complex assembly. We demonstrate that DEIP1 interacts with the two cytochrome subunits of the complex, PetA and PetB, and mediates the assembly of intermediates in Cytb6f biogenesis. The identification of DEIP1 provides an entry point into the study of the assembly pathway of a crucial complex in photosynthetic electron transfer.


Assuntos
Arabidopsis , Complexo Citocromos b6f , Arabidopsis/genética , Arabidopsis/metabolismo , Complexo Citocromos b6f/genética , Complexo Citocromos b6f/metabolismo , Citocromos b/metabolismo , Estiolamento , Fotossíntese , Tilacoides/metabolismo
11.
Plant Physiol Biochem ; 185: 144-154, 2022 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-35696889

RESUMO

High temperature can induce a substantial adverse effect on plant photosynthesis. This study addressed the impact of moderately high temperature (35 °C) on photosynthetic efficiency and thylakoid membrane organization in Pisum sativum. The Chl a fluorescence curves showed a significant change, indicating a reduction in photosynthetic efficiency when pea plants were exposed to moderate high-temperature stress. The pulse-amplitude modulation measurements showed decreased non-photochemical quenching while the non-regulated energy dissipation increased in treated compared to control and recovery plants. Both parameters indicated that the photosystem (PS)II was prone to temperature stress. The PSI donor side limitation increased in treated and recovery plants compared to control, suggesting the donor side of PSI is hampered in moderate-high temperature. Further, the PSI acceptor side increased in recovery plants compared to control, suggesting that the cyclic electron transport is repressed after temperature treatment but revert back to normal in recovery conditions. Also, the content of photoprotective carotenoid pigments like lutein and xanthophylls increased in temperature-treated leaves. These results indicate the alteration of macro-organization of thylakoid membranes under moderately elevated temperature, whereas supercomplexes restored to the control levels under recovery conditions. Further, the light harvesting complex (LHC)II trimers, and monomers were significantly decreased in temperature-treated plants. Furthermore, the amount of PSII reaction center proteins D1, D2, PsbO, and Cyt b6 was reduced under moderate temperature, whereas the content of LHC proteins of PSI was stable. These observations suggest that moderately high temperature can alter supercomplexes, which leads to change in the pigment-protein organization.


Assuntos
Ervilhas , Tilacoides , Clorofila/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Ervilhas/metabolismo , Fotossíntese , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/metabolismo , Temperatura , Tilacoides/metabolismo
12.
Sci Rep ; 12(1): 10982, 2022 06 29.
Artigo em Inglês | MEDLINE | ID: mdl-35768472

RESUMO

Plant growth under spectrally-enriched low light conditions leads to adjustment in the relative abundance of the two photosystems in an acclimatory response known as photosystem stoichiometry adjustment. Adjustment of photosystem stoichiometry improves the quantum efficiency of photosynthesis but how this process perceives light quality changes and how photosystem amount is regulated remain largely unknown. By using a label-free quantitative mass spectrometry approach in Arabidopsis here we show that photosystem stoichiometry adjustment is primarily driven by the regulation of photosystem I content and that this forms the major thylakoid proteomic response under light quality. Using light and redox signaling mutants, we further show that the light quality-responsive accumulation of photosystem I gene transcripts and proteins requires phytochrome B photoreceptor but not plastoquinone redox signaling as previously suggested. In far-red light, the increased acceptor side limitation might deplete active photosystem I pool, further contributing to the adjustment of photosystem stoichiometry.


Assuntos
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Luz , Oxirredução , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Proteômica , Tilacoides/metabolismo
13.
New Phytol ; 236(1): 86-98, 2022 10.
Artigo em Inglês | MEDLINE | ID: mdl-35715975

RESUMO

The nucleotides guanosine tetraphosphate and pentaphosphate (or (p)ppGpp) are implicated in the regulation of chloroplast function in plants. (p)ppGpp signalling is best understood in the model vascular plant Arabidopsis thaliana in which it acts to regulate plastid gene expression to influence photosynthesis, plant development and immunity. However, little information is known about the conservation or diversity of (p)ppGpp signalling in other land plants. We studied the function of ppGpp in the moss Physcomitrium (previously Physcomitrella) patens using an inducible system for triggering ppGpp accumulation. We used this approach to investigate the effects of ppGpp on chloroplast function, photosynthesis and growth. We demonstrate that ppGpp accumulation causes a dramatic drop in photosynthetic capacity by inhibiting chloroplast gene expression. This was accompanied by the unexpected reorganisation of the thylakoid system into super grana. Surprisingly, these changes did not affect gametophore growth, suggesting that bryophytes and vascular plants may have different tolerances to defects in photosynthesis. Our findings point to the existence of both highly conserved and more specific targets of (p)ppGpp signalling in the land plants that may reflect different growth strategies.


Assuntos
Arabidopsis , Bryopsida , Arabidopsis/metabolismo , Bryopsida/metabolismo , Cloroplastos/metabolismo , Genes de Cloroplastos , Guanosina Pentafosfato/metabolismo , Guanosina Tetrafosfato/metabolismo , Tilacoides/metabolismo
14.
Microb Cell Fact ; 21(1): 94, 2022 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-35643504

RESUMO

BACKGROUND: NADPH is used as a reductant in various biosynthetic reactions. Cell-free bio-systems have gained considerable attention owing to their high energy utilization and time efficiency. Efforts have been made to continuously supply reducing power to the reaction mixture in a cyclical manner. The thylakoid membrane (TM) is a promising molecular energy generator, producing NADPH under light. Thus, TM sustainability is of major relevance for its in vitro utilization. RESULTS: Over 70% of TMs prepared from Synechocystis sp. PCC6803 existed in a sealed vesicular structure, with the F1 complex of ATP synthase facing outward (right-side-out), producing NADPH and ATP under light. The NADPH generation activity of TM increased approximately two-fold with the addition of carbonyl cyanide-p-(trifluoromethoxy) phenylhydrazone (FCCP) or removal of the F1 complex using EDTA. Thus, the uncoupling of proton translocation from the electron transport chain or proton leakage through the Fo complex resulted in greater NADPH generation. Biosilicified TM retained more than 80% of its NADPH generation activity after a week at 30°C in the dark. However, activity declined sharply to below 30% after two days in light. The introduction of engineered water-forming NADPH oxidase (Noxm) to keep the electron transport chain of TM working resulted in the improved sustainability of NADPH generation activity in a ratio (Noxm to TM)-dependent manner, which correlated with the decrease of singlet oxygen generation. Removal of reactive oxygen species (ROS) by catalase further highlighted the sustainable NADPH generation activity of up to 80% in two days under light. CONCLUSION: Reducing power generated by light energy has to be consumed for TM sustainability. Otherwise, TM can generate singlet oxygen, causing oxidative damage. Thus, TMs should be kept in the dark when not in use. Although NADPH generation activity by TM can be extended via silica encapsulation, further removal of hydrogen peroxide results in an improvement of TM sustainability. Therefore, as long as ROS formation by TM in light is properly handled, it can be used as a promising source of reducing power for in vitro biochemical reactions.


Assuntos
Synechocystis , Trifosfato de Adenosina , NADP , Prótons , Espécies Reativas de Oxigênio , Oxigênio Singlete , Tilacoides
15.
J Phys Chem Lett ; 13(24): 5683-5691, 2022 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-35709359

RESUMO

The major photosystem II light-harvesting antenna (LHCII) is the most abundant membrane protein in nature and plays an indispensable role in light harvesting and photoprotection in the plant thylakoid. Here, we show that "pseudothylakoid characteristics" can be observed in artificial LHCII membranes. In our proteoliposomal system, at high LHCII densities, the liposomes become stacked, mimicking the in vivo thylakoid grana membranes. Furthermore, an unexpected, unstructured emission peak at ∼730 nm appears, similar in appearance to photosystem I emission, but with a clear excimeric character that has never been previously reported. These states correlate with the increasing density of LHCII in the membrane and a decrease in its average fluorescence lifetime. The appearance of these low-energy states can also occur in natural plant membrane structures, which has unique consequences for the interpretation of the spectroscopic and physiological properties of the photosynthetic membrane.


Assuntos
Complexos de Proteínas Captadores de Luz , Tilacoides , Complexos de Proteínas Captadores de Luz/química , Complexo de Proteína do Fotossistema I/química , Complexo de Proteína do Fotossistema II/metabolismo , Proteolipídeos
16.
Biochem J ; 479(13): 1487-1503, 2022 07 15.
Artigo em Inglês | MEDLINE | ID: mdl-35726684

RESUMO

In oxygenic photosynthesis, the cytochrome b6f (cytb6f) complex links the linear electron transfer (LET) reactions occurring at photosystems I and II and generates a transmembrane proton gradient via the Q-cycle. In addition to this central role in LET, cytb6f also participates in a range of processes including cyclic electron transfer (CET), state transitions and photosynthetic control. Many of the regulatory roles of cytb6f are facilitated by auxiliary proteins that differ depending upon the species, yet because of their weak and transient nature the structural details of these interactions remain unknown. An apparent key player in the regulatory balance between LET and CET in cyanobacteria is PetP, a ∼10 kDa protein that is also found in red algae but not in green algae and plants. Here, we used cryogenic electron microscopy to determine the structure of the Synechocystis sp. PCC 6803 cytb6f complex in the presence and absence of PetP. Our structures show that PetP interacts with the cytoplasmic side of cytb6f, displacing the C-terminus of the PetG subunit and shielding the C-terminus of cytochrome b6, which binds the heme cn cofactor that is suggested to mediate CET. The structures also highlight key differences in the mode of plastoquinone binding between cyanobacterial and plant cytb6f complexes, which we suggest may reflect the unique combination of photosynthetic and respiratory electron transfer in cyanobacterial thylakoid membranes. The structure of cytb6f from a model cyanobacterial species amenable to genetic engineering will enhance future site-directed mutagenesis studies of structure-function relationships in this crucial ET complex.


Assuntos
Complexo Citocromos b6f , Synechocystis , Microscopia Crioeletrônica , Complexo Citocromos b6f/química , Complexo Citocromos b6f/metabolismo , Complexo Citocromos b6f/fisiologia , Transporte de Elétrons/fisiologia , Fotossíntese , Synechocystis/metabolismo , Synechocystis/fisiologia , Tilacoides/genética , Tilacoides/metabolismo
17.
Biochim Biophys Acta Biomembr ; 1864(10): 183981, 2022 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-35690100

RESUMO

The advent of improved structural biology protocols and bioinformatics methodologies have provided paradigm-shifting insights on metabolic or physiological processes catalyzed by homo-/hetero- proteins (super)complexes embedded in phospholipid membranes of cells/organelles. In this panoramic review, we succinctly elucidate the structural features of select redox proteins from four systems: hepatocyte/adrenal cortex endoplasmic reticulum (microsomes), inner mitochondrial membrane (cristae), thylakoid membrane (grana), and in the flattened disks of rod/cone cells (in retina). Besides catalyzing fast/crucial (photo)chemical reactions, these proteins utilize the redox-active diatomic gaseous molecule of oxygen, the elixir of aerobic life. Quite contrary to extant perceptions that invoke primarily deterministic affinity-binding or conformation-change based "proton-pump"/"serial electron-relay" type roles, we advocate murzyme functions for the membrane-embedded proteins in these systems. Murzymes are proteins that generate/stabilize/utilize diffusible reactive (oxygen) species (DRS/DROS) based activities. Herein, we present a brief compendium of the recently revealed wealth of structural information and mechanistic concepts on how the membrane proteins use DRS/DROS to aid 'effective charge separation' and facilitate trans-membrane dynamics of diverse species in milieu, thereby enabling the cells to function as 'simple chemical engines'.


Assuntos
Retículo Endoplasmático , Fosfolipídeos , Retículo Endoplasmático/metabolismo , Oxigênio/metabolismo , Fosfolipídeos/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Tilacoides/metabolismo
18.
Commun Biol ; 5(1): 460, 2022 05 13.
Artigo em Inglês | MEDLINE | ID: mdl-35562408

RESUMO

Different intensities of high temperatures affect the growth of photosynthetic cells in nature. To elucidate the underlying mechanisms, we cultivated the unicellular green alga Chlamydomonas reinhardtii under highly controlled photobioreactor conditions and revealed systems-wide shared and unique responses to 24-hour moderate (35°C) and acute (40°C) high temperatures and subsequent recovery at 25°C. We identified previously overlooked unique elements in response to moderate high temperature. Heat at 35°C transiently arrested the cell cycle followed by partial synchronization, up-regulated transcripts/proteins involved in gluconeogenesis/glyoxylate-cycle for carbon uptake and promoted growth. But 40°C disrupted cell division and growth. Both high temperatures induced photoprotection, while 40°C distorted thylakoid/pyrenoid ultrastructure, affected the carbon concentrating mechanism, and decreased photosynthetic efficiency. We demonstrated increased transcript/protein correlation during both heat treatments and hypothesize reduced post-transcriptional regulation during heat may help efficiently coordinate thermotolerance mechanisms. During recovery after both heat treatments, especially 40°C, transcripts/proteins related to DNA synthesis increased while those involved in photosynthetic light reactions decreased. We propose down-regulating photosynthetic light reactions during DNA replication benefits cell cycle resumption by reducing ROS production. Our results provide potential targets to increase thermotolerance in algae and crops.


Assuntos
Chlamydomonas reinhardtii , Carbono/metabolismo , Chlamydomonas reinhardtii/genética , Temperatura Alta , Plantas/metabolismo , Temperatura , Tilacoides/metabolismo
19.
J Exp Bot ; 73(9): 2751-2764, 2022 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-35560204

RESUMO

Fibrillins (FBNs) are a family of genes in cyanobacteria, algae, and plants. The proteins they encode possess a lipid-binding motif, exist in various types of plastids, and are associated with lipid bodies called plastoglobules, implicating them in lipid metabolism. FBNs present in the thylakoid and stroma are involved in the storage, transport, and synthesis of lipid molecules for photoprotective functions against high-light stress. In this review, the diversity of subplastid locations in the evolution of FBNs, regulation of FBNs expression by various stresses, and the role of FBNs in plastid lipid metabolism are comprehensively summarized and directions for future research are discussed.


Assuntos
Plastídeos , Tilacoides , Fibrilinas/metabolismo , Lipídeos/análise , Plantas/genética , Plastídeos/metabolismo , Tilacoides/metabolismo
20.
ACS Appl Mater Interfaces ; 14(19): 22216-22224, 2022 May 18.
Artigo em Inglês | MEDLINE | ID: mdl-35511069

RESUMO

The light-dependent reactions of photosynthesis use light energy to generate photoelectrons traveling through the thylakoid membranes (TMs). Extracting the photoelectrons from the TMs to form bioanodes can have various applications. Most studies focus on modifying the electrode materials to increase the collected photocurrent. Seldom studies have investigated how the orientation of the TMs influences photocurrent collection. In addition, the formation of reactive oxygen species (ROS) during photosynthesis is a challenge for stable photocurrent generation. Here, we enhanced the photoelectron transfer from the TMs to electrodes by depositing expanded thylakoids as planar supported membranes onto an electrode. The high contact area between the external electrodes and TMs per unit mass of thylakoid allows the thylakoid to more effectively transfer electrons to the electrodes, thereby reducing the free electrons available for the ROS generation. We expanded the naturally stacked thylakoids into liposomes through osmotic pressure and dropcasted them onto an Au electrode. The electrochemical impedance measurement showed that the supported membrane bioanode formed by the expanded liposomes had a lower photoelectron transfer resistance. Additionally, we observed that the expanded TM bioanode provided a higher photocurrent and was more durable to air/water interfacial tension. These results suggest that the effective contact between the expanded TM and electrodes can lead to more efficient electron transfer and increase the system robustness. The photo fuel cell (PFC) made by the expanded TM bioanode had a higher open-circuit voltage than the one made by the stacked TM bioanode. Interestingly, we found that PFCs made of high-load TM bioanodes had fast photocurrent decay under continuous operation at high cell voltages. The poor contact of large numbers of TMs with the electrodes at the high-load TM bioanodes could cause more ROS accumulation and therefore decreased the operational stability, supporting the importance of effective contact between TMs and the electrodes.


Assuntos
Elétrons , Tilacoides , Eletrodos , Transporte de Elétrons , Lipossomos/metabolismo , Espécies Reativas de Oxigênio/metabolismo
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...