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1.
J Phys Chem B ; 128(3): 731-743, 2024 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-38198639

RESUMO

The exciton states on the smallest type-I photosynthetic reaction center complex of a green sulfur bacterium Chlorobaculum tepidum (GsbRC) consisting of 26 bacteriochlorophylls a (BChl a) and four chlorophylls a (Chl a) located on the homodimer of two PscA reaction center polypeptides were investigated. This analysis involved the study of exciton states through a combination of theoretical modeling and the genetic removal of BChl a pigments at eight sites. (1) A theoretical model of the pigment assembly exciton state on GsbRC was constructed using Poisson TrESP (P-TrESP) and charge density coupling (CDC) methods based on structural information. The model reproduced the experimentally obtained absorption spectrum, circular dichroism spectrum, and excitation transfer dynamics, as well as explained the effects of mutation. (2) Eight BChl a molecules at different locations on the GsbRC were selectively removed by genetic exchange of the His residue, which ligates the central Mg atom of BChl a, with the Leu residue on either one or two PscAs in the RC. His locations are conserved among all type-I RC plant polypeptide, cyanobacteria, and bacteria amino acid sequences. (3) Purified mutant-GsbRCs demonstrated distinct absorption and fluorescence spectra at 77 K, which were different from each other, suggesting successful pigment removal. (4) The same mutations were applied to the constructed theoretical model to analyze the outcomes of these mutations. (5) The combination of theoretical predictions and experimental mutations based on structural information is a new tool for studying the function and evolution of photosynthetic reaction centers.


Assuntos
Chlorobi , Cianobactérias , Complexo de Proteínas do Centro de Reação Fotossintética , Complexo de Proteínas do Centro de Reação Fotossintética/química , Chlorobi/química , Mutação , Cianobactérias/metabolismo , Enxofre/metabolismo , Bacterioclorofilas/química , Proteínas de Bactérias/química
2.
Trends Microbiol ; 32(1): 38-52, 2024 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-37380557

RESUMO

Bacterial photosynthesis is essential for sustaining life on Earth as it aids in carbon assimilation, atmospheric composition, and ecosystem maintenance. Many bacteria utilize anoxygenic photosynthesis to convert sunlight into chemical energy while producing organic matter. The core machinery of anoxygenic photosynthesis performed by purple photosynthetic bacteria and Chloroflexales is the reaction center-light-harvesting 1 (RC-LH1) pigment-protein supercomplex. In this review, we discuss recent structural studies of RC-LH1 core complexes based on the advancement in structural biology techniques. These studies have provided fundamental insights into the assembly mechanisms, structural variations, and modularity of RC-LH1 complexes across different bacterial species, highlighting their functional adaptability. Understanding the natural architectures of RC-LH1 complexes will facilitate the design and engineering of artificial photosynthetic systems, which can enhance photosynthetic efficiency and potentially find applications in sustainable energy production and carbon capture.


Assuntos
Complexo de Proteínas do Centro de Reação Fotossintética , Complexo de Proteínas do Centro de Reação Fotossintética/química , Complexos de Proteínas Captadores de Luz/química , Complexos de Proteínas Captadores de Luz/metabolismo , Ecossistema , Fotossíntese , Carbono , Proteínas de Bactérias/metabolismo
3.
Chemphyschem ; 25(2): e202300335, 2024 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-37953408

RESUMO

A new tractable linear electronic transition dipole moment time correlation function (ETDMTCF) that accurately accounts for electronic dephasing, asymmetry, and width of 1-phonon profile, which the zero-phonon line (ZPL) contributes to it, in Rhodopseudomonas viridis bacterial reaction center is derived. This time correlation function proves to be superior to other frequency-domain expressions in case of strong electron-phonon coupling (which is often the case in bacterial RCs and pigment-protein complexes), many vibrational modes involved, and high temperature, whereby more vibronic and electronic (sequence) transitions would arise. The Fourier transform of this ETDMTCF leads to asymmetric multiphonon profiles composed of Lorentzian distribution and Gaussian distribution on the high- and low-energy sides, respectively, whereby the overtone widths fold themselves with that of the one-phonon profile. This ETDMTCF also features expedient computation in large systems using asymmetric phonon profiles to account correctly for dephasing and pigment-protein interaction (electron-phonon coupling). The derived ETDMTCF allows computing all nonlinear optical signals in both time and frequency domains, through the nonlinear dipole moment time correlation functions (as guided by nonlinear optical response theory) in line with the eight Liouville space pathways. The linear transition dipole moment time correlation function is of a central value as the nonlinear transition dipole moment time correlation function is expressed in terms of the linear transition dipole moment time correlation function, derived herein. One of the great advantages of presenting this ETDMTCF is its applicability to nonlinear transition dipole moment time correlation functions in line with the eight Liouville space pathways needed in computing nonlinear signals. As such, there is more to the utility and applicability of the presented ETDMTCF besides computational expediency and efficiency. Results show good agreement with the reported literature. The intimate connection between a one-phonon profile and the corresponding bath spectral density in photosynthetic complexes is discussed.


Assuntos
Bactérias , Complexo de Proteínas do Centro de Reação Fotossintética , Complexo de Proteínas do Centro de Reação Fotossintética/química
4.
Phys Chem Chem Phys ; 25(41): 28437-28451, 2023 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-37843877

RESUMO

A bacteriochlorophyll a (Bchla) dimer is a basic functional unit in the LH1 and LH2 photosynthetic pigment-protein antenna complexes of purple bacteria, where an ordered, close arrangement of Bchla pigments-secured by noncovalent bonding to a protein template-enables exciton delocalization at room temperature. Stable and tunable synthetic analogs of this key photosynthetic subunit could lead to facile engineering of exciton-based systems such as in artificial photosynthesis, organic optoelectronics, and molecular quantum computing. Here, using a combination of synthesis and theory, we demonstrate that exciton delocalization can be achieved in a dimer of a synthetic bacteriochlorin (BC) featuring stability, high structural modularity, and spectral properties advantageous for exciton-based devices. The BC dimer was covalently templated by DNA, a stable and highly programmable scaffold. To achieve exciton delocalization in the absence of pigment-protein interactions critical for the Bchla dimer, we relied on the strong transition dipole moment in BC enabled by two auxochromes along the Qy transition, and omitting the central metal and isocyclic ring. The spectral properties of the synthetic "free" BC closely resembled those of Bchla in an organic solvent. Applying spectroscopic modeling, the exciton delocalization in the DNA-templated BC dimer was evaluated by extracting the excitonic hopping parameter, J to be 214 cm-1 (26.6 meV). For comparison, the same method applied to the natural protein-templated Bchla dimer yielded J of 286 cm-1 (35.5 meV). The smaller value of J in the BC dimer likely arose from the partial bacteriochlorin intercalation and the difference in medium effect between DNA and protein.


Assuntos
Complexos de Proteínas Captadores de Luz , Complexo de Proteínas do Centro de Reação Fotossintética , Complexos de Proteínas Captadores de Luz/química , Metodologias Computacionais , Teoria Quântica , Complexo de Proteínas do Centro de Reação Fotossintética/química , DNA
5.
J Phys Chem B ; 127(33): 7283-7290, 2023 08 24.
Artigo em Inglês | MEDLINE | ID: mdl-37556839

RESUMO

Elucidating the photosynthetic processes that occur within the reaction center-light-harvesting 1 (RC-LH1) supercomplexes from purple bacteria is crucial for uncovering the assembly and functional mechanisms of natural photosynthetic systems and underpinning the development of artificial photosynthesis. Here, we examined excitation energy transfer of various RC-LH1 supercomplexes of Rhodobacter sphaeroides using transient absorption spectroscopy, coupled with lifetime density analysis, and studied the roles of the integral transmembrane polypeptides, PufX and PufY, in energy transfer within the RC-LH1 core complex. Our results show that the absence of PufX increases both the LH1 → RC excitation energy transfer lifetime and distribution due to the role of PufX in defining the interaction and orientation of the RC within the LH1 ring. While the absence of PufY leads to the conformational shift of several LH1 subunits toward the RC, it does not result in a marked change in the excitation energy transfer lifetime.


Assuntos
Complexo de Proteínas do Centro de Reação Fotossintética , Rhodobacter sphaeroides , Complexo de Proteínas do Centro de Reação Fotossintética/química , Complexos de Proteínas Captadores de Luz/química , Rhodobacter sphaeroides/metabolismo , Peptídeos , Fotossíntese , Transferência de Energia , Proteínas de Bactérias/química
6.
J Phys Chem Lett ; 14(31): 7038-7044, 2023 Aug 10.
Artigo em Inglês | MEDLINE | ID: mdl-37524046

RESUMO

Multiscale molecular modeling is utilized to predict optical absorption and circular dichroism spectra of two single-point mutants of the Fenna-Matthews-Olson photosynthetic pigment-protein complex. The modeling approach combines classical molecular dynamics simulations with structural refinement of photosynthetic pigments and calculations of their excited states in a polarizable protein environment. The only experimental input to the modeling protocol is the X-ray structure of the wild-type protein. The first-principles modeling reproduces changes in the experimental optical spectra of the considered mutants, Y16F and Q198V. Interestingly, the Q198V mutation has a negligible effect on the electronic properties of the targeted bacteriochlorophyll a pigment. Instead, the electronic properties of several other pigments respond to this mutation. The molecular modeling demonstrates that a single-point mutation can induce long-range effects on the protein structure, while extensive structural changes near a pigment do not necessarily lead to significant changes in the electronic properties of that pigment.


Assuntos
Complexos de Proteínas Captadores de Luz , Complexo de Proteínas do Centro de Reação Fotossintética , Complexos de Proteínas Captadores de Luz/química , Proteínas de Bactérias/química , Complexo de Proteínas do Centro de Reação Fotossintética/química , Simulação de Dinâmica Molecular , Mutação
7.
Anal Chem ; 95(25): 9555-9563, 2023 06 27.
Artigo em Inglês | MEDLINE | ID: mdl-37322814

RESUMO

Photosynthesis, as the core of solar energy biotransformation, is driven by photosynthetic membrane protein complexes in plants and algae. Current methods for intracellular photosynthetic membrane protein complex analysis mostly require the separation of specific chloroplasts or the change of the intracellular environment, which causes the missing of real-time and on-site information. Thus, we explored a method for in vivo crosslinking and mapping of photosynthetic membrane protein complexes in the chloroplasts of living Chlamydomonas reinhardtii (C. reinhardtii) cells under cultural conditions. Poly(lactic-co-glycolic acid) (PLGA) and poly(lactic-co-glycolic acid)-poly(ethylene glycol) (PLGA-PEG) nanoparticles were fabricated to deliver bis(succinimidyl)propargyl with a nitro compound (BSPNO) into the chloroplasts to crosslink photosynthetic membrane protein complexes. After the in vivo crosslinked protein complexes were extracted and digested, mass spectrometry was employed to detect lysine-specific crosslinked peptides for further elucidating the protein conformations and interactions. With this method, the weak interactions between extrinsic proteins in the luminal side (PsbL and PsbH) and the core subunits (CP47 and CP43) in photosynthetic protein complexes were directly captured in living cells. Additionally, the previously uncharacterized protein (Cre07.g335700) was bound to the light-harvesting proteins, which was related to the biosynthesis of light-harvesting antennae. These results indicated that in vivo analysis of photosynthetic protein complexes based on crosslinker nanocarriers was expected to not only figure out the difficulty in the study of photosynthetic protein complexes in living cells but also provide an approach to explore transient and weak interactions and the function of uncharacterized proteins.


Assuntos
Chlamydomonas reinhardtii , Complexo de Proteínas do Centro de Reação Fotossintética , Complexo de Proteínas do Centro de Reação Fotossintética/química , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , Chlamydomonas reinhardtii/metabolismo , Proteínas de Membrana/metabolismo , Copolímero de Ácido Poliláctico e Ácido Poliglicólico , Complexos de Proteínas Captadores de Luz/metabolismo , Cloroplastos
8.
J Chem Phys ; 158(19)2023 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-37184025

RESUMO

In purple bacteria, the fundamental charge-separation step that drives the conversion of radiation energy into chemical energy proceeds along one branch-the A branch-of a heterodimeric pigment-protein complex, the reaction center. Here, we use first principles time-dependent density functional theory (TDDFT) with an optimally-tuned range-separated hybrid functional to investigate the electronic and excited-state structure of the six primary pigments in the reaction center of Rhodobacter sphaeroides. By explicitly including amino-acid residues surrounding these six pigments in our TDDFT calculations, we systematically study the effect of the protein environment on energy and charge-transfer excitations. Our calculations show that a forward charge transfer into the A branch is significantly lower in energy than the first charge transfer into the B branch, in agreement with the unidirectional charge transfer observed experimentally. We further show that the inclusion of the protein environment redshifts this excitation significantly, allowing for energy transfer from the coupled Qx excitations. Through analysis of transition and difference densities, we demonstrate that most of the Q-band excitations are strongly delocalized over several pigments and that both their spatial delocalization and charge-transfer character determine how strongly affected they are by thermally-activated molecular vibrations. Our results suggest a mechanism for charge-transfer in this bacterial reaction center and pave the way for further first-principles investigations of the interplay between delocalized excited states, vibronic coupling, and the role of the protein environment in this and other complex light-harvesting systems.


Assuntos
Complexo de Proteínas do Centro de Reação Fotossintética , Rhodobacter sphaeroides , Rhodobacter sphaeroides/metabolismo , Complexo de Proteínas do Centro de Reação Fotossintética/química , Eletrônica
9.
Biosystems ; 226: 104873, 2023 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-36906114

RESUMO

Photosynthesis is the predominant biochemical process of carbon dioxide assimilation in the biosphere. To reduce carbon dioxide into organic compounds, photosynthetic organisms have one or two distinct photochemical reaction centre complexes with which they capture solar energy and generate ATP and reducing power. The core polypeptides of the photosynthetic reaction centres show low homologies but share overlapping structural folds, overall architecture, similar functional properties and highly conserved positions in protein sequences suggesting a common ancestry. However, the other biochemical components of photosynthetic apparatus appear to be a mosaic resulting from different evolutionary trajectories. The current proposal focusses on the nature and biosynthetic pathways of some organic redox cofactors that participate in the photosynthetic systems: quinones, chlorophyll and heme rings and their attached isoprenoid side chains, as well as on the coupled proton motive forces and associated carbon fixation pathways. This perspective highlights clues about the involvement of the phosphorus and sulphur chemistries that would have shaped the different types of photosynthetic systems.


Assuntos
Dióxido de Carbono , Complexo de Proteínas do Centro de Reação Fotossintética , Fósforo , Fotossíntese , Clorofila , Complexo de Proteínas do Centro de Reação Fotossintética/química , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo
10.
Bioconjug Chem ; 34(4): 629-637, 2023 04 19.
Artigo em Inglês | MEDLINE | ID: mdl-36896985

RESUMO

A supramolecular construct for solar energy conversion is developed by covalently bridging the reaction center (RC) from the photosynthetic bacterium Rhodobacter sphaeroides and cytochrome c (Cyt c) proteins with a tailored organic light harvesting antenna (hCy2). The RC-hCy2-Cyt c biohybrid mimics the working mechanism of biological assemblies located in the bacterial cell membrane to convert sunlight into metabolic energy. hCy2 collects visible light and transfers energy to the RC, increasing the rate of photocycle between a RC and Cyt c that are linked in such a way that enhances proximity without preventing protein mobility. The biohybrid obtained with average 1 RC/10 hCy2/1.5 Cyt c molar ratio features an almost doubled photoactivity versus the pristine RC upon illumination at 660 nm, and ∼10 times higher photocurrent versus an equimolar mixture of the unbound proteins. Our results represent an interesting insight into photoenzyme chemical manipulation, opening the way to new eco-sustainable systems for biophotovoltaics.


Assuntos
Citocromos c , Complexo de Proteínas do Centro de Reação Fotossintética , Citocromos c/metabolismo , Complexo de Proteínas do Centro de Reação Fotossintética/química , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , Luz , Transporte de Elétrons , Proteínas de Bactérias/metabolismo
11.
Proc Natl Acad Sci U S A ; 120(5): e2216734120, 2023 01 31.
Artigo em Inglês | MEDLINE | ID: mdl-36693097

RESUMO

Light energy absorption and transfer are very important processes in photosynthesis. In green sulfur bacteria light is absorbed primarily by the chlorosomes and its energy is transferred via the Fenna-Matthews-Olson (FMO) proteins to a homodimeric reaction center (RC). Here, we report the cryogenic electron microscopic structure of the intact FMO-RC apparatus from Chlorobaculum tepidum at 2.5 Å resolution. The FMO-RC apparatus presents an asymmetric architecture and contains two FMO trimers that show different interaction patterns with the RC core. Furthermore, the two permanently bound transmembrane subunits PscC, which donate electrons to the special pair, interact only with the two large PscA subunits. This structure fills an important gap in our understanding of the transfer of energy from antenna to the electron transport chain of this RC and the transfer of electrons from reduced sulfur compounds to the special pair.


Assuntos
Chlorobi , Complexo de Proteínas do Centro de Reação Fotossintética , Complexo de Proteínas do Centro de Reação Fotossintética/química , Chlorobi/metabolismo , Microscopia Crioeletrônica , Proteínas de Bactérias/metabolismo , Enxofre/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo
12.
J Integr Plant Biol ; 65(1): 223-234, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-36125941

RESUMO

The photosynthetic reaction center complex (RCC) of green sulfur bacteria (GSB) consists of the membrane-imbedded RC core and the peripheric energy transmitting proteins called Fenna-Matthews-Olson (FMO). Functionally, FMO transfers the absorbed energy from a huge peripheral light-harvesting antenna named chlorosome to the RC core where charge separation occurs. In vivo, one RC was found to bind two FMOs, however, the intact structure of RCC as well as the energy transfer mechanism within RCC remain to be clarified. Here we report a structure of intact RCC which contains a RC core and two FMO trimers from a thermophilic green sulfur bacterium Chlorobaculum tepidum at 2.9 Å resolution by cryo-electron microscopy. The second FMO trimer is attached at the cytoplasmic side asymmetrically relative to the first FMO trimer reported previously. We also observed two new subunits (PscE and PscF) and the N-terminal transmembrane domain of a cytochrome-containing subunit (PscC) in the structure. These two novel subunits possibly function to facilitate the binding of FMOs to RC core and to stabilize the whole complex. A new bacteriochlorophyll (numbered as 816) was identified at the interspace between PscF and PscA-1, causing an asymmetrical energy transfer from the two FMO trimers to RC core. Based on the structure, we propose an energy transfer network within this photosynthetic apparatus.


Assuntos
Carcinoma de Células Renais , Chlorobi , Neoplasias Renais , Complexo de Proteínas do Centro de Reação Fotossintética , Complexo de Proteínas do Centro de Reação Fotossintética/química , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , Chlorobi/química , Chlorobi/metabolismo , Microscopia Crioeletrônica , Proteínas de Bactérias/metabolismo
13.
Photosynth Res ; 156(1): 75-87, 2023 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-35672557

RESUMO

The light-harvesting complex 2 (LH2) of purple bacteria is one of the most studied photosynthetic antenna complexes. Its symmetric structure and ring-like bacteriochlorophyll arrangement make it an ideal system for theoreticians and spectroscopists. LH2 complexes from most bacterial species are thought to have eightfold or ninefold symmetry, but recently a sevenfold symmetric LH2 structure from the bacterium Mch. purpuratum was solved by Cryo-Electron microscopy. This LH2 also possesses unique near-infrared absorption and circular dichroism (CD) spectral properties. Here we use an atomistic strategy to elucidate the spectral properties of Mch. purpuratum LH2 and understand the differences with the most commonly studied LH2 from Rbl. acidophilus. Our strategy exploits a combination of molecular dynamics simulations, multiscale polarizable quantum mechanics/molecular mechanics calculations, and lineshape simulations. Our calculations reveal that the spectral properties of LH2 complexes are tuned by site energies and exciton couplings, which in turn depend on the structural fluctuations of the bacteriochlorophylls. Our strategy proves effective in reproducing the absorption and CD spectra of the two LH2 complexes, and in uncovering the origin of their differences. This work proves that it is possible to obtain insight into the spectral tuning strategies of purple bacteria by quantitatively simulating the spectral properties of their antenna complexes.


Assuntos
Complexos de Proteínas Captadores de Luz , Complexo de Proteínas do Centro de Reação Fotossintética , Complexos de Proteínas Captadores de Luz/metabolismo , Microscopia Crioeletrônica , Complexo de Proteínas do Centro de Reação Fotossintética/química , Bacterioclorofilas/química , Simulação de Dinâmica Molecular , Proteobactérias/metabolismo
14.
J Phys Chem B ; 126(33): 6210-6220, 2022 08 25.
Artigo em Inglês | MEDLINE | ID: mdl-35960270

RESUMO

Reaction centers from Rhodobacter sphaeroides with residue M265 mutated from isoleucine to threonine, serine, and asparagine (M265IT, M265IS, and M265IN, respectively) in the QA-· state are studied by high-resolution electron spin echo envelope modulation (ESEEM) and electron nuclear double resonance spectroscopy methods to investigate the structural characteristics of these mutants influencing the redox properties of the QA site. All three mutants decrease the redox midpoint potential (Em) of QA by ∼0.1 V, yet the mechanism for this drop in Em is unclear. In this work, we examine (i) the hydrogen bonding interactions between QA-· and residues histidine M219 and alanine M260, (ii) the electron spin density distribution of the semiquinone, and (iii) the orientations of the ubiquinone methoxy substituents. 13C measurements show no significant contribution of methoxy dihedral angles to the observed decrease in Em for the QA mutants. Instead, 14N three-pulse ESEEM data suggest that electrostatic or hydrogen bond formation between the mutated M265 side chain and His-M219 Nδ may be involved in the observed lowering of the QA midpoint potential. For mutant M265IN, analysis of the proton hyperfine couplings reveals a weakened hydrogen bond network, resulting in an altered QA-· spin density distribution. The magnetic resonance study presented here is most consistent with an electrostatic or structural perturbation of the His-M219 Nδ hydrogen bond in these mutants as a mechanism for the ∼0.1 V decrease in QA Em.


Assuntos
Complexo de Proteínas do Centro de Reação Fotossintética , Rhodobacter sphaeroides , Espectroscopia de Ressonância de Spin Eletrônica , Eletrônica , Ligação de Hidrogênio , Mutação , Complexo de Proteínas do Centro de Reação Fotossintética/química , Complexo de Proteínas do Centro de Reação Fotossintética/genética , Rhodobacter sphaeroides/química , Rhodobacter sphaeroides/genética
15.
Acta Crystallogr D Struct Biol ; 78(Pt 6): 698-708, 2022 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-35647917

RESUMO

Serial crystallography is a rapidly growing method that can yield structural insights from microcrystals that were previously considered to be too small to be useful in conventional X-ray crystallography. Here, conditions for growing microcrystals of the photosynthetic reaction centre of Blastochloris viridis within a lipidic cubic phase (LCP) crystallization matrix that employ a seeding protocol utilizing detergent-grown crystals with a different crystal packing are described. LCP microcrystals diffracted to 2.25 Šresolution when exposed to XFEL radiation, which is an improvement of 0.15 Šover previous microcrystal forms. Ubiquinone was incorporated into the LCP crystallization media and the resulting electron density within the mobile QB pocket is comparable to that of other cofactors within the structure. As such, LCP microcrystallization conditions will facilitate time-resolved diffraction studies of electron-transfer reactions to the mobile quinone, potentially allowing the observation of structural changes associated with the two electron-transfer reactions leading to complete reduction of the ubiquinone ligand.


Assuntos
Complexo de Proteínas do Centro de Reação Fotossintética , Cristalização , Cristalografia por Raios X , Lipídeos/química , Proteínas de Membrana/química , Complexo de Proteínas do Centro de Reação Fotossintética/química , Ubiquinona
16.
J Am Chem Soc ; 144(20): 8977-8986, 2022 05 25.
Artigo em Inglês | MEDLINE | ID: mdl-35543627

RESUMO

Inspired by light-induced processes in nature to mimic the primary events in the photosynthetic reaction centers, novel functional materials combine electron donors and acceptors, i.e., (metallo)porphyrins (ZnP) and fullerenes (C60), respectively, with emerging materials, i.e., nanographenes. We utilized hexa-peri-hexabenzocoronene (HBC) due to its versatility regarding functionalization and physicochemical properties, to construct three regioisomeric ZnP-HBC-C60 conjugates, which foster geometrical diversity by arranging ZnP and C60 in ortho-, meta-, and para-positions to each other. The corresponding hexaarylbenzene (HAB) motifs, with an interrupted π-system, were also prepared. Transient absorption measurements disclosed the fast population of charge transfer as well as singlet and triplet charge-separated states. With the help of density functional theory (DFT) calculations, we further conceive the communication across the HBCs and HABs. This work reveals the impact of both the geometrical arrangement with respect to through-space versus through-bond interactions and the structural rigidity/flexibility on the charge management across the different π-systems.


Assuntos
Fulerenos , Complexo de Proteínas do Centro de Reação Fotossintética , Porfirinas , Elétrons , Fulerenos/química , Complexo de Proteínas do Centro de Reação Fotossintética/química , Porfirinas/química
17.
Methods Enzymol ; 666: 413-450, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35465926

RESUMO

Light-induced reactions in photosynthetic reaction centers are initiated by the absorption of a photon, which results in the transfer of a single electron and the generation of radical ions in the donor and acceptor molecules involved in the charge-separated state. Electron paramagnetic resonance (EPR) spectroscopy is the ideal method for the study of such reactions. In addition to measuring spectra of the electron transfer cofactors in continuous light, reactions can be initiated by brief flashes of light, thereby allowing the kinetics of forward electron transfer as well as recombination reactions to be obtained. Because the donor and acceptor pairs are so closely spaced and because light induced charge separation is so rapid, the donor and early acceptors are in a quantum mechanically spin entangled state, which confers properties such as increased sensitivity, the ability to measure reactions on the nanosecond timescale, and the determination of bond angles between cofactors. Additionally, distances between pairs of cofactors can be measured by detecting the modulation of a phase shifted "out-of-phase" electron spin echo signal. In this methods article, we will describe how continuous wave EPR, time resolved EPR, and pulsed EPR can be used to measure these properties in Type I photosynthetic reaction centers. Methods of analysis are described for the bound electron transfer cofactors in the heterodimeric Photosystem I reaction center of plants and cyanobacteria and in the homodimeric reaction centers found in phototrophic members of the phyla Bacillota, Chlorobiota, and Acidobacteriota.


Assuntos
Cianobactérias , Complexo de Proteínas do Centro de Reação Fotossintética , Cianobactérias/metabolismo , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Transporte de Elétrons , Elétrons , Complexo de Proteínas do Centro de Reação Fotossintética/química , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo
18.
J Phys Chem B ; 126(13): 2476-2485, 2022 04 07.
Artigo em Inglês | MEDLINE | ID: mdl-35344367

RESUMO

Proteins are polyelectrolytes with acidic and basic amino acids Asp, Glu, Arg, Lys, and His, making up ≈25% of the residues. The protonation state of residues, cofactors, and ligands defines a "protonation microstate". In an ensemble of proteins some residues will be ionized and others neutral, leading to a mixture of protonation microstates rather than in a single one as is often assumed. The microstate distribution changes with pH. The protein environment also modifies residue proton affinity so microstate distributions change in different reaction intermediates or as ligands are bound. Particular protonation microstates may be required for function, while others exist simply because there are many states with similar energy. Here, the protonation microstates generated in Monte Carlo sampling in MCCE are characterized in HEW lysozyme as a function of pH and bacterial photosynthetic reaction centers (RCs) in different reaction intermediates. The lowest energy and highest probability microstates are compared. The ΔG, ΔH, and ΔS between the four protonation states of Glu35 and Asp52 in lysozyme are shown to be calculated with reasonable precision. At pH 7 the lysozyme charge ranges from 6 to 10, with 24 accepted protonation microstates, while RCs have ≈50,000. A weighted Pearson correlation analysis shows coupling between residue protonation states in RCs and how they change when the quinone in the QB site is reduced. Protonation microstates can be used to define input MD parameters and provide insight into the motion of protons coupled to reactions.


Assuntos
Complexo de Proteínas do Centro de Reação Fotossintética , Rhodobacter sphaeroides , Transporte de Elétrons , Concentração de Íons de Hidrogênio , Ligantes , Método de Monte Carlo , Muramidase/metabolismo , Complexo de Proteínas do Centro de Reação Fotossintética/química , Prótons , Rhodobacter sphaeroides/metabolismo
19.
J Chem Phys ; 156(10): 105102, 2022 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-35291800

RESUMO

The photosynthetic reaction center of heliobacteria (hRC) is a homodimeric chromoprotein responsible for light harvesting and photoelectric conversion. The fluorescence of the hRC is radiated from a bacteriochlorophyll (Bchl) g having the lowest energy level, called red-Bchl g. The homodimeric architecture of the hRC indicates that it includes two red-Bchls g arranged symmetrically in pairs. Red-Bchl g is a fluorescent probe useful for monitoring the energy transfer network in the RC. Here, we show the fluorescence polarization dependences of two red-Bchls g, individually measured with selective excitation of chlorophyll a serving as the primary electron acceptor. The two red-Bchls g exhibit almost the same polarization dependences. Based on the polarization dependence and structural data of the hRC, we propose a candidate molecule for red-Bchl g. The fluorescence spectra of single hRCs represent the spectral heterogeneity reflecting the local conformational inhomogeneity. A time series of the fluorescence spectra indicates occasional peak shifts between blue- and red-shifted states without significant changes in the fluorescence intensity. The spectral fluctuation is interpreted to be due to the local conformational dynamics around a Bchl g mediating the energy transfer, switching the terminal energy acceptor between two red-Bchls g. In conclusion, while the energy transfer network in the RC can be perturbed by microscopic dynamics, the total energy transfer efficiency, i.e., the light-harvesting function, is rather robust. The functional robustness may be due to multiple energy transfer pathways composed of many antenna pigments in the RC.


Assuntos
Bacterioclorofilas , Complexo de Proteínas do Centro de Reação Fotossintética , Bacterioclorofilas/química , Clorofila A , Transferência de Energia , Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteínas do Centro de Reação Fotossintética/química , Imagem Individual de Molécula
20.
STAR Protoc ; 3(1): 101044, 2022 03 18.
Artigo em Inglês | MEDLINE | ID: mdl-34977685

RESUMO

The formation of defined surfaces consisting of photosynthetic reaction centers (RCs) in biohybrid solar cells is challenging. Here, we start with the production of engineered RCs for oriented binding. RCs are deposited onto gold electrodes, and 6-mercapto-1-hexanol (MCH) is used to displace multilayers and non-specifically adsorbed RCs. The resulting electrode surfaces are analyzed for photocurrent generation using an intensity-modulated light and lock-in amplifier. Atomic force microscopy (AFM) is used to characterize the surface and the formation of RC structural assemblies. For complete details on the use and execution of this profile, please refer to Jun et al. (2021).


Assuntos
Complexo de Proteínas do Centro de Reação Fotossintética , Rhodobacter sphaeroides , Eletrodos , Ouro/química , Microscopia de Força Atômica/métodos , Complexo de Proteínas do Centro de Reação Fotossintética/química , Rhodobacter sphaeroides/química
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