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1.
Int J Mol Sci ; 22(6)2021 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-33804002

RESUMO

Antenna protein aggregation is one of the principal mechanisms considered effective in protecting phototrophs against high light damage. Commonly, it is induced, in vitro, by decreasing detergent concentration and pH of a solution of purified antennas; the resulting reduction in fluorescence emission is considered to be representative of non-photochemical quenching in vivo. However, little is known about the actual size and organization of antenna particles formed by this means, and hence the physiological relevance of this experimental approach is questionable. Here, a quasi-single molecule method, fluorescence correlation spectroscopy (FCS), was applied during in vitro quenching of LHCII trimers from higher plants for a parallel estimation of particle size, fluorescence, and antenna cluster homogeneity in a single measurement. FCS revealed that, below detergent critical micelle concentration, low pH promoted the formation of large protein oligomers of sizes up to micrometers, and therefore is apparently incompatible with thylakoid membranes. In contrast, LHCII clusters formed at high pH were smaller and homogenous, and yet still capable of efficient quenching. The results altogether set the physiological validity limits of in vitro quenching experiments. Our data also support the idea that the small, moderately quenching LHCII oligomers found at high pH could be relevant with respect to non-photochemical quenching in vivo.


Assuntos
Proteína do Homeodomínio de Antennapedia/genética , Complexos de Proteínas Captadores de Luz/genética , Processos Fototróficos/genética , Agregados Proteicos/genética , Proteína do Homeodomínio de Antennapedia/química , Clorofila/química , Clorofila/genética , Clorofila/efeitos da radiação , Análise por Conglomerados , Fluorescência , Concentração de Íons de Hidrogênio , Luz/efeitos adversos , Complexos de Proteínas Captadores de Luz/química , Fotossíntese/genética , Complexo de Proteína do Fotossistema II/genética , Complexo de Proteína do Fotossistema II/efeitos da radiação , Espectrometria de Fluorescência , Tilacoides/química , Tilacoides/genética , Tilacoides/efeitos da radiação , Zeaxantinas/genética
2.
Nat Commun ; 12(1): 1104, 2021 02 17.
Artigo em Inglês | MEDLINE | ID: mdl-33597527

RESUMO

Photosynthetic electron transfers occur through multiple components ranging from small soluble proteins to large integral membrane protein complexes. Co-crystallization of a bacterial photosynthetic electron transfer complex that employs weak hydrophobic interactions was achieved by using high-molar-ratio mixtures of a soluble donor protein (high-potential iron-sulfur protein, HiPIP) with a membrane-embedded acceptor protein (reaction center, RC) at acidic pH. The structure of the co-complex offers a snapshot of a transient bioenergetic event and revealed a molecular basis for thermodynamically unfavorable interprotein electron tunneling. HiPIP binds to the surface of the tetraheme cytochrome subunit in the light-harvesting (LH1) complex-associated RC in close proximity to the low-potential heme-1 group. The binding interface between the two proteins is primarily formed by uncharged residues and is characterized by hydrophobic features. This co-crystal structure provides a model for the detailed study of long-range trans-protein electron tunneling pathways in biological systems.


Assuntos
Proteínas de Bactérias/química , Chromatiaceae/metabolismo , Proteínas com Ferro-Enxofre/química , Complexos de Proteínas Captadores de Luz/química , Fotossíntese , Complexo de Proteínas do Centro de Reação Fotossintética/química , Proteínas de Bactérias/metabolismo , Sítios de Ligação , Cristalização , Citocromos/química , Citocromos/metabolismo , Transporte de Elétrons , Heme/análogos & derivados , Heme/química , Heme/metabolismo , Proteínas com Ferro-Enxofre/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Modelos Moleculares , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , Conformação Proteica , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz
3.
Nat Commun ; 12(1): 1100, 2021 02 17.
Artigo em Inglês | MEDLINE | ID: mdl-33597543

RESUMO

Photosystem I (PSI) and II (PSII) balance their light energy distribution absorbed by their light-harvesting complexes (LHCs) through state transition to maintain the maximum photosynthetic performance and to avoid photodamage. In state 2, a part of LHCII moves to PSI, forming a PSI-LHCI-LHCII supercomplex. The green alga Chlamydomonas reinhardtii exhibits state transition to a far larger extent than higher plants. Here we report the cryo-electron microscopy structure of a PSI-LHCI-LHCII supercomplex in state 2 from C. reinhardtii at 3.42 Å resolution. The result reveals that the PSI-LHCI-LHCII of C. reinhardtii binds two LHCII trimers in addition to ten LHCI subunits. The PSI core subunits PsaO and PsaH, which were missed or not well-resolved in previous Cr-PSI-LHCI structures, are observed. The present results reveal the organization and assembly of PSI core subunits, LHCI and LHCII, pigment arrangement, and possible pathways of energy transfer from peripheral antennae to the PSI core.


Assuntos
Proteínas de Algas/metabolismo , Chlamydomonas reinhardtii/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Proteínas de Algas/química , Proteínas de Algas/ultraestrutura , Clorofila/metabolismo , Microscopia Crioeletrônica , Transferência de Energia , Complexos de Proteínas Captadores de Luz/química , Complexos de Proteínas Captadores de Luz/ultraestrutura , Modelos Moleculares , Fotossíntese , Complexo de Proteína do Fotossistema I/química , Complexo de Proteína do Fotossistema I/ultraestrutura , Complexo de Proteína do Fotossistema II/química , Complexo de Proteína do Fotossistema II/metabolismo , Complexo de Proteína do Fotossistema II/ultraestrutura , Ligação Proteica , Conformação Proteica , Multimerização Proteica , Tilacoides/metabolismo , Tilacoides/ultraestrutura
4.
Phys Chem Chem Phys ; 23(2): 806-821, 2021 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-33427836

RESUMO

Diatoms are a major group of algae, responsible for a quarter of the global primary production on our planet. Their adaptation to marine environments is ensured by their light-harvesting antenna - the fucoxanthin-chlorophyll protein (FCP) complex, which absorbs strongly in the blue-green spectral region. Although these essential proteins have been the subject of many studies, for a long time their comprehensive description was not possible in the absence of structural data. Last year, the 3D structures of several FCP complexes were revealed. The structure of an FCP dimer was resolved by crystallography for the pennate diatom Phaeodactylum tricornutum [W. Wang et al., Science, 2019, 363, 6427] and the structure of the PSII supercomplex from the centric diatom Chaetoceros gracilis, containing several FCPs, was obtained by electron microscopy [X. Pi et al., Science, 2019, 365, 6452; R. Nagao et al., Nat. Plants, 2019, 5, 890]. In this Perspective article, we evaluate how precisely these structures may account for previously published ultrafast spectroscopy results, describing the excitation energy transfer in the FCP from another centric diatom Cyclotella meneghiniana. Surprisingly, we find that the published FCP structures cannot explain several observations obtained from ultrafast spectroscopy. Using the available structures, and results from electron microscopy, we construct a trimer-based FCP model for Cyclotella meneghiniana, consistent with ultrafast experimental data. As a whole, our observations suggest that the structures from the proteins belonging to the FCP family display larger variations than the equivalent LHC proteins in plants, which may reflect species-specific adaptations or original strategies for adapting to rapidly changing marine environments.


Assuntos
Clorofila A/química , Complexos de Proteínas Captadores de Luz/química , Xantofilas/química , Sequência de Aminoácidos , Clorofila/química , Diatomáceas/química , Transferência de Energia , Conformação Proteica , Espectrometria de Fluorescência
5.
Biochim Biophys Acta Bioenerg ; 1862(1): 148307, 2021 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-32926863

RESUMO

Redox-active quinones play essential roles in efficient light energy conversion in type-II reaction centers of purple phototrophic bacteria. In the light-harvesting 1 reaction center (LH1-RC) complex of purple bacteria, QB is converted to QBH2 upon light-induced reduction and QBH2 is transported to the quinone pool in the membrane through the LH1 ring. In the purple bacterium Rhodobacter sphaeroides, the C-shaped LH1 ring contains a gap for quinone transport. In contrast, the thermophilic purple bacterium Thermochromatium (Tch.) tepidum has a closed O-shaped LH1 ring that lacks a gap, and hence the mechanism of photosynthetic quinone transport is unclear. Here we detected light-induced Fourier transform infrared (FTIR) signals responsible for changes of QB and its binding site that accompany photosynthetic quinone reduction in Tch. tepidum and characterized QB and QBH2 marker bands based on their 15N- and 13C-isotopic shifts. Quinone exchanges were monitored using reconstituted photosynthetic membranes comprised of solubilized photosynthetic proteins, membrane lipids, and exogenous ubiquinone (UQ) molecules. In combination with 13C-labeling of the LH1-RC and replacement of native UQ8 by ubiquinones of different tail lengths, we demonstrated that quinone exchanges occur efficiently within the hydrophobic environment of the lipid membrane and depend on the side chain length of UQ. These results strongly indicate that unlike the process in Rba. sphaeroides, quinone transport in Tch. tepidum occurs through the size-restricted hydrophobic channels in the closed LH1 ring and are consistent with structural studies that have revealed narrow hydrophobic channels in the Tch. tepidum LH1 transmembrane region.


Assuntos
Proteínas de Bactérias/química , Chromatiaceae/enzimologia , Complexos de Proteínas Captadores de Luz/química , Ubiquinona/química , Proteínas de Bactérias/metabolismo , Sítios de Ligação , Transporte Biológico Ativo , Complexos de Proteínas Captadores de Luz/metabolismo , Oxirredução , Ubiquinona/metabolismo
6.
Nat Commun ; 11(1): 4955, 2020 10 02.
Artigo em Inglês | MEDLINE | ID: mdl-33009385

RESUMO

The light-harvesting-reaction center complex (LH1-RC) from the purple phototrophic bacterium Thiorhodovibrio strain 970 exhibits an LH1 absorption maximum at 960 nm, the most red-shifted absorption for any bacteriochlorophyll (BChl) a-containing species. Here we present a cryo-EM structure of the strain 970 LH1-RC complex at 2.82 Å resolution. The LH1 forms a closed ring structure composed of sixteen pairs of the αß-polypeptides. Sixteen Ca ions are present in the LH1 C-terminal domain and are coordinated by residues from the αß-polypeptides that are hydrogen-bonded to BChl a. The Ca2+-facilitated hydrogen-bonding network forms the structural basis of the unusual LH1 redshift. The structure also revealed the arrangement of multiple forms of α- and ß-polypeptides in an individual LH1 ring. Such organization indicates a mechanism of interplay between the expression and assembly of the LH1 complex that is regulated through interactions with the RC subunits inside.


Assuntos
Cálcio/metabolismo , Microscopia Crioeletrônica , Complexos de Proteínas Captadores de Luz/ultraestrutura , Peptídeos/metabolismo , Fotossíntese , Sequência de Aminoácidos , Bacterioclorofila A/metabolismo , Sítios de Ligação , Chromatiaceae/metabolismo , Detergentes/química , Dimerização , Complexos de Proteínas Captadores de Luz/química , Complexos de Proteínas Captadores de Luz/metabolismo , Lipídeos/química , Peptídeos/química , Quinonas/química
7.
Nat Commun ; 11(1): 5081, 2020 10 08.
Artigo em Inglês | MEDLINE | ID: mdl-33033236

RESUMO

Diatom is an important group of marine algae and contributes to around 20% of the global photosynthetic carbon fixation. Photosystem I (PSI) of diatoms is associated with a large number of fucoxanthin-chlorophyll a/c proteins (FCPIs). We report the structure of PSI-FCPI from a diatom Chaetoceros gracilis at 2.38 Å resolution by single-particle cryo-electron microscopy. PSI-FCPI is a monomeric supercomplex consisting of 12 core and 24 antenna subunits (FCPIs), and 326 chlorophylls a, 34 chlorophylls c, 102 fucoxanthins, 35 diadinoxanthins, 18 ß-carotenes and some electron transfer cofactors. Two subunits designated PsaR and PsaS were found in the core, whereas several subunits were lost. The large number of pigments constitute a unique and huge network ensuring efficient energy harvesting, transfer and dissipation. These results provide a firm structural basis for unraveling the mechanisms of light-energy harvesting, transfer and quenching in the diatom PSI-FCPI, and also important clues to evolutionary changes of PSI-LHCI.


Assuntos
Proteínas de Ligação à Clorofila/química , Diatomáceas/metabolismo , Transferência de Energia , Complexo de Proteína do Fotossistema I/química , Complexos de Proteínas Captadores de Luz/química , Complexos de Proteínas Captadores de Luz/metabolismo , Pigmentos Biológicos/química , Pigmentos Biológicos/metabolismo , Subunidades Proteicas/química
8.
Nat Commun ; 11(1): 2481, 2020 05 18.
Artigo em Inglês | MEDLINE | ID: mdl-32424145

RESUMO

Photosynthetic light-harvesting complexes (LHCs) play a pivotal role in collecting solar energy for photochemical reactions in photosynthesis. One of the major LHCs are fucoxanthin chlorophyll a/c-binding proteins (FCPs) present in diatoms, a group of organisms having important contribution to the global carbon cycle. Here, we report a 2.40-Å resolution structure of the diatom photosystem I (PSI)-FCPI supercomplex by cryo-electron microscopy. The supercomplex is composed of 16 different FCPI subunits surrounding a monomeric PSI core. Each FCPI subunit showed different protein structures with different pigment contents and binding sites, and they form a complicated pigment-protein network together with the PSI core to harvest and transfer the light energy efficiently. In addition, two unique, previously unidentified subunits were found in the PSI core. The structure provides numerous insights into not only the light-harvesting strategy in diatom PSI-FCPI but also evolutionary dynamics of light harvesters among oxyphototrophs.


Assuntos
Diatomáceas/metabolismo , Complexos de Proteínas Captadores de Luz/química , Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteína do Fotossistema I/química , Complexo de Proteína do Fotossistema I/metabolismo , Clorofila/metabolismo , Proteínas de Ligação à Clorofila/química , Proteínas de Ligação à Clorofila/ultraestrutura , Transferência de Energia , Complexos de Proteínas Captadores de Luz/ultraestrutura , Modelos Moleculares , Complexo de Proteína do Fotossistema I/ultraestrutura , Ligação Proteica , Subunidades Proteicas/metabolismo , Relação Estrutura-Atividade
9.
Biochim Biophys Acta Bioenerg ; 1861(8): 148205, 2020 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-32305413

RESUMO

An increased robustness against high temperature and the much red-shifted near-infrared absorption spectrum of excitons in the LH1-RC core pigment-protein complex from the thermophilic photosynthetic purple sulfur bacterium Thermochromatium tepidum has recently attracted much interest. In the present work, thermal and hydrostatic pressure stability of the peripheral LH2 and core LH1-RC complexes from this bacterium were in parallel investigated by various optical spectroscopy techniques applied over a wide spectral range from far-ultraviolet to near-infrared. In contrast to expectations, very distinct robustness of the complexes was established, while the sturdiness of LH2 surpassed that of LH1-RC both with respect to temperatures between 288 and 360 K, and pressures between 1 bar and 14 kbar. Subtle structural variances related to the hydrogen bond network are likely responsible for the extra stability of LH2.


Assuntos
Chromatiaceae/enzimologia , Complexos de Proteínas Captadores de Luz/metabolismo , Pressão , Temperatura , Elétrons , Complexos de Proteínas Captadores de Luz/química , Prótons
10.
Nat Commun ; 11(1): 1295, 2020 03 10.
Artigo em Inglês | MEDLINE | ID: mdl-32157079

RESUMO

Plants prevent photodamage under high light by dissipating excess energy as heat. Conformational changes of the photosynthetic antenna complexes activate dissipation by leveraging the sensitivity of the photophysics to the protein structure. The mechanisms of dissipation remain debated, largely due to two challenges. First, because of the ultrafast timescales and large energy gaps involved, measurements lacked the temporal or spectral requirements. Second, experiments have been performed in detergent, which can induce non-native conformations, or in vivo, where contributions from homologous antenna complexes cannot be disentangled. Here, we overcome both challenges by applying ultrabroadband two-dimensional electronic spectroscopy to the principal antenna complex, LHCII, in a near-native membrane. Our data provide evidence that the membrane enhances two dissipative pathways, one of which is a previously uncharacterized chlorophyll-to-carotenoid energy transfer. Our results highlight the sensitivity of the photophysics to local environment, which may control the balance between light harvesting and dissipation in vivo.


Assuntos
Carotenoides/metabolismo , Membrana Celular/metabolismo , Clorofila/metabolismo , Transferência de Energia , Complexos de Proteínas Captadores de Luz/metabolismo , Nanoestruturas/química , Complexos de Proteínas Captadores de Luz/química , Conformação Proteica
11.
Proc Natl Acad Sci U S A ; 117(12): 6502-6508, 2020 03 24.
Artigo em Inglês | MEDLINE | ID: mdl-32139606

RESUMO

Carotenoids play a number of important roles in photosynthesis, primarily providing light-harvesting and photoprotective energy dissipation functions within pigment-protein complexes. The carbon-carbon double bond (C=C) conjugation length of carotenoids (N), generally between 9 and 15, determines the carotenoid-to-(bacterio)chlorophyll [(B)Chl] energy transfer efficiency. Here we purified and spectroscopically characterized light-harvesting complex 2 (LH2) from Rhodobacter sphaeroides containing the N = 7 carotenoid zeta (ζ)-carotene, not previously incorporated within a natural antenna complex. Transient absorption and time-resolved fluorescence show that, relative to the lifetime of the S1 state of ζ-carotene in solvent, the lifetime decreases ∼250-fold when ζ-carotene is incorporated within LH2, due to transfer of excitation energy to the B800 and B850 BChls a These measurements show that energy transfer proceeds with an efficiency of ∼100%, primarily via the S1 → Qx route because the S1 → S0 fluorescence emission of ζ-carotene overlaps almost perfectly with the Qx absorption band of the BChls. However, transient absorption measurements performed on microsecond timescales reveal that, unlike the native N ≥ 9 carotenoids normally utilized in light-harvesting complexes, ζ-carotene does not quench excited triplet states of BChl a, likely due to elevation of the ζ-carotene triplet energy state above that of BChl a These findings provide insights into the coevolution of photosynthetic pigments and pigment-protein complexes. We propose that the N ≥ 9 carotenoids found in light-harvesting antenna complexes represent a vital compromise that retains an acceptable level of energy transfer from carotenoids to (B)Chls while allowing acquisition of a new, essential function, namely, photoprotective quenching of harmful (B)Chl triplets.


Assuntos
Proteínas de Bactérias/metabolismo , Bacterioclorofilas/metabolismo , Carotenoides/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Proteínas de Bactérias/química , Carotenoides/química , Transferência de Energia , Cinética , Complexos de Proteínas Captadores de Luz/química , Fotossíntese , Rhodobacter sphaeroides/química , Rhodobacter sphaeroides/metabolismo
12.
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
13.
Nat Commun ; 11(1): 1542, 2020 03 24.
Artigo em Inglês | MEDLINE | ID: mdl-32210238

RESUMO

Natural photosynthesis can be divided between the chlorophyll-containing plants, algae and cyanobacteria that make up the oxygenic phototrophs and a diversity of bacteriochlorophyll-containing bacteria that make up the anoxygenic phototrophs. Photosynthetic light harvesting and reaction centre proteins from both kingdoms have been exploited for solar energy conversion, solar fuel synthesis and sensing technologies, but the energy harvesting abilities of these devices are limited by each protein's individual palette of pigments. In this work we demonstrate a range of genetically-encoded, self-assembling photosystems in which recombinant plant light harvesting complexes are covalently locked with reaction centres from a purple photosynthetic bacterium, producing macromolecular chimeras that display mechanisms of polychromatic solar energy harvesting and conversion. Our findings illustrate the power of a synthetic biology approach in which bottom-up construction of photosystems using naturally diverse but mechanistically complementary components can be achieved in a predictable fashion through the encoding of adaptable, plug-and-play covalent interfaces.


Assuntos
Proteínas de Arabidopsis/química , Proteínas de Bactérias/química , Bacterioclorofilas/química , Complexos de Proteínas Captadores de Luz/química , Energia Solar , Biologia Sintética/métodos , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/efeitos da radiação , Proteínas de Bactérias/genética , Proteínas de Bactérias/efeitos da radiação , Bacterioclorofilas/genética , Bacterioclorofilas/efeitos da radiação , Carotenoides/química , Carotenoides/efeitos da radiação , Complexos de Proteínas Captadores de Luz/genética , Complexos de Proteínas Captadores de Luz/efeitos da radiação , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/efeitos da radiação , Rhodobacter sphaeroides/química , Rhodobacter sphaeroides/genética , Rhodobacter sphaeroides/efeitos da radiação , Luz Solar
14.
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
15.
Nat Commun ; 11(1): 662, 2020 01 31.
Artigo em Inglês | MEDLINE | ID: mdl-32005811

RESUMO

The photosynthetic apparatus of higher plants can dissipate excess excitation energy during high light exposure, by deactivating excited chlorophylls through a mechanism called nonphotochemical quenching (NPQ). However, the precise molecular details of quenching and the mechanism regulating the quenching level are still not completely understood. Focusing on the major light-harvesting complex LHCII of Photosystem II, we show that a charge transfer state involving Lutein can efficiently quench chlorophyll excitation, and reduce the excitation lifetime of LHCII to the levels measured in the deeply quenched LHCII aggregates. Through a combination of molecular dynamics simulations, multiscale quantum chemical calculations, and kinetic modeling, we demonstrate that the quenching level can be finely tuned by the protein, by regulating the energy of the charge transfer state. Our results suggest that a limited conformational rearrangement of the protein scaffold could act as a molecular switch to activate or deactivate the quenching mechanism.


Assuntos
Carotenoides/metabolismo , Clorofila/metabolismo , Plantas/metabolismo , Carotenoides/química , Clorofila/química , Transporte de Elétrons , Cinética , Luz , Complexos de Proteínas Captadores de Luz/química , Complexos de Proteínas Captadores de Luz/metabolismo , Fotossíntese , Complexo de Proteína do Fotossistema II/química , Complexo de Proteína do Fotossistema II/metabolismo , Plantas/química , Plantas/efeitos da radiação
16.
J Phys Chem Lett ; 11(5): 1636-1643, 2020 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-32013435

RESUMO

High efficiency of light harvesting in photosynthetic pigment-protein complexes is governed by evolutionary-perfected protein-assisted tuning of individual pigment properties and interpigment interactions. Due to the large number of spectrally overlapping pigments in a typical photosynthetic complex, experimental methods often fail to unambiguously identify individual chromophore properties. Here, we report a first-principles-based modeling protocol capable of predicting properties of pigments in protein environment to a high precision. The technique was applied to successfully uncover electronic properties of the Fenna-Matthews-Olson (FMO) pigment-protein complex. Each of the three subunits of the FMO complex contains eight strongly coupled bacteriochlorophyll a (BChl a) pigments. The excitonic structure of FMO can be described by an electronic Hamiltonian containing excitation (site) energies of BChl a pigments and electronic couplings between them. Several such Hamiltonians have been developed in the past based on the information from various spectroscopic measurements of FMO; however, fine details of the excitonic structure and energy transfer in FMO, especially assignments of short-lived high-energy sites, remain elusive. Utilizing polarizable embedding quantum mechanics/molecular mechanics with the effective fragment potentials, we computed the electronic Hamiltonian of FMO that is in general agreement with previously reported empirical Hamiltonians and quantitatively reproduces experimental absorption and circular dichroism spectra of the FMO protein. The developed computational protocol is sufficiently simple and can be utilized for predictive modeling of other wild-type and mutated photosynthetic pigment-protein complexes.


Assuntos
Proteínas de Bactérias/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Simulação de Dinâmica Molecular , Teoria Quântica , Proteínas de Bactérias/química , Bacterioclorofila A/química , Bacterioclorofila A/metabolismo , Chlorobi/metabolismo , Dicroísmo Circular , Transferência de Energia , Gases/química , Complexos de Proteínas Captadores de Luz/química , Fotossíntese
17.
J Phys Chem Lett ; 11(3): 1059-1067, 2020 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-31952446

RESUMO

The interplay between active molecules and the protein environment in light-harvesting complexes tunes the photophysics and the dynamical properties of pigment-protein complexes in a subtle way, which is not fully understood. Here we characterized the photophysics and the ultrafast dynamics of four variants of the water-soluble chlorophyll protein (WSCP) as an ideal model system to study the behavior of strongly interacting chlorophylls. We found that when coordinated by the WSCP protein, the presence of the formyl group in chlorophyll b replacing the methyl group in chlorophyll a strongly affects the exciton energy and the dynamics of the system, opening up the possibility of tuning the photophysics and the transport properties of multichromophores by engineering specific interactions with the surroundings.


Assuntos
Clorofila A/química , Clorofila/química , Complexos de Proteínas Captadores de Luz/química , Modelos Moleculares , Temperatura , Termodinâmica , Água/química
18.
Phys Chem Chem Phys ; 22(19): 10500-10518, 2020 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-31950960

RESUMO

The chromophores of rhodopsins (Rh) and light-harvesting (LH) complexes still represent a major challenge for a quantum chemical description due to their size and complex electronic structure. Since gradient corrected and hybrid density functional approaches have been shown to fail for these systems, only range-separated functionals seem to be a promising alternative to the more time consuming post-Hartree-Fock approaches. For extended sampling of optical properties, however, even more approximate approaches are required. Recently, a long-range corrected (LC) functional has been implemented into the efficient density functional tight binding (DFTB) method, allowing to sample the excited states properties of chromophores embedded into proteins using quantum mechanical/molecular mechanical (QM/MM) with the time-dependent (TD) DFTB approach. In the present study, we assess the accuracy of LC-TD-DFT and LC-TD-DFTB for rhodopsins (bacteriorhodopsin (bR) and pharaonis phoborhodopsin (ppR)) and LH complexes (light-harvesting complex II (LH2) and Fenna-Matthews-Olson (FMO) complex). This benchmark study shows the improved description of the color tuning parameters compared to standard DFT functionals. In general, LC-TD-DFTB can exhibit a similar performance as the corresponding LC functionals, allowing a reliable description of excited states properties at significantly reduced cost. The two chromophores investigated here pose complementary challenges: while huge sensitivity to external field perturbation (color tuning) and charge transfer excitations are characteristic for the retinal chromophore, the multi-chromophoric character of the LH complexes emphasizes a correct description of inter-chromophore couplings, giving less importance to color tuning. None of the investigated functionals masters both systems simultaneously with satisfactory accuracy. LC-TD-DFTB, at the current stage, although showing a systematic improvement compared to TD-DFTB cannot be recommended for studying color tuning in retinal proteins, similar to some of the LC-DFT functionals, because the response to external fields is still too weak. For sampling of LH-spectra, however, LC-TD-DFTB is a viable tool, allowing to efficiently sample absorption energies, as shown for three different LH complexes. As the calculations indicate, geometry optimization may overestimate the importance of local minima, which may be averaged over when using trajectories. Fast quantum chemical approaches therefore may allow for a direct sampling of spectra in the near future.


Assuntos
Bacteriorodopsinas/química , Complexos de Proteínas Captadores de Luz/química , Bacterioclorofila A/química , Beijerinckiaceae/química , Chlorobi/química , Teoria da Densidade Funcional , Modelos Químicos , Retinaldeído/química , Rhodospirillaceae/química
19.
J Biol Chem ; 295(7): 1857-1866, 2020 02 14.
Artigo em Inglês | MEDLINE | ID: mdl-31929108

RESUMO

Integral membrane proteins are exposed to a complex and dynamic lipid environment modulated by nonbilayer lipids that can influence protein functions by lipid-protein interactions. The nonbilayer lipid monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in plant photosynthetic thylakoid membranes, but its impact on the functionality of energy-converting membrane protein complexes is unknown. Here, we optimized a detergent-based reconstitution protocol to develop a proteoliposome technique that incorporates the major light-harvesting complex II (LHCII) into compositionally well-defined large unilamellar lipid bilayer vesicles to study the impact of MGDG on light harvesting by LHCII. Using steady-state fluorescence spectroscopy, CD spectroscopy, and time-correlated single-photon counting, we found that both chlorophyll fluorescence quantum yields and fluorescence lifetimes clearly indicate that the presence of MGDG in lipid bilayers switches LHCII from a light-harvesting to a more energy-quenching mode that dissipates harvested light into heat. It is hypothesized that in the in vitro system developed here, MGDG controls light harvesting of LHCII by modulating the hydrostatic lateral membrane pressure profile in the lipid bilayer sensed by LHCII-bound peripheral pigments.


Assuntos
Galactolipídeos/química , Complexos de Proteínas Captadores de Luz/química , Fotossíntese/genética , Proteolipídeos/genética , Galactolipídeos/metabolismo , Complexos de Proteínas Captadores de Luz/genética , Metabolismo dos Lipídeos/genética , Proteínas Ligadas a Lipídeos/química , Proteínas Ligadas a Lipídeos/genética , Lipídeos/química , Lipídeos/genética , Proteínas de Membrana/química , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Proteínas Quinases/química , Proteínas Quinases/genética , Proteolipídeos/química , Proteolipídeos/metabolismo , Espectrometria de Fluorescência , Tilacoides/metabolismo
20.
Photosynth Res ; 143(3): 263-273, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31894498

RESUMO

Reactive oxygen species (ROS) production is an unavoidable byproduct of electron transport under aerobic conditions. Photosystem II (PS II), the cytochrome  b6/f complex and Photosystem I (PS I) are all demonstrated sources of ROS. It has been proposed that PS I produces substantial levels of a variety of ROS including O2.-, 1O2, H2O2 and, possibly, •OH; however, the site(s) of ROS production within PS I has been the subject of significant debate. We hypothesize that amino acid residues close to the sites of ROS generation will be more susceptible to oxidative modification than distant residues. In this study, we have identified oxidized amino acid residues in spinach PS I which was isolated from field-grown spinach. The modified residues were identified by high-resolution tandem mass spectrometry. As expected, many of the modified residues lie on the surface of the complex. However, a well-defined group of oxidized residues, both buried and surface-exposed, lead from the chl a' of P700 to the surface of PS I. These residues (PsaB: 609F, 611E, 617M, 619W, 620L, and PsaF: 139L, 142A,143D) may identify a preferred route for ROS, probably 1O2, to egress the complex from the vicinity of P700. Additionally, two buried residues located in close proximity to A1B (PsaB:712H and 714S) were modified, which appears consistent with A1B being a source of O2.-. Surprisingly, no oxidatively modified residues were identified in close proximity to the 4Fe-FS clusters FX, FA or FB. These cofactors had been identified as principal targets for ROS damage in the photosystem. Finally, a large number of residues located in the hydrophobic cores of Lhca1-Lhca4 are oxidatively modified. These appear to be the result of 1O2 production by the distal antennae for the photosystem.


Assuntos
Aminoácidos/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Spinacia oleracea/metabolismo , Sequência de Aminoácidos , Complexos de Proteínas Captadores de Luz/química , Modelos Moleculares , Oxirredução , Complexo de Proteína do Fotossistema I/química
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