Enhanced photosynthetic electron transfer in microalgae–conjugated microporous polymer biohybrid: Unraveling mechanisms for high-efficiency water decontamination

Fullerenes as Novel Acceptors in Photosynthetic Electron Transfer

We propose a novel strategy using fullerenes for the construction of solar energy conversion systems that mimic the primary electron transfer events in photosynthesis. Redox-active fullerenes such as C60 and C70 were covalently bound to a porphyrin and the photophysical properties of the resulting compounds were investigated. Regardless of solvent and linkage, the charge-separated state is produced efficiently in zincporphyrin–fullerene dyads, showing that fullerenes are good electron acceptors. The most intriguing characteristic of fullerenes in electron transfer is that they accelerate photoinduced charge separation as well as charge shift and slow down charge recombination, properties that are in sharp contrast with those of conventional two-dimensional aromatic acceptors such as quinones and imides. The peculiar electron transfer properties of fullerenes can be explained by the small reorganization energies, which make it possible to optimize artificial photosynthetic multistep charge separation. A combination of the two strategies, multistep electron transfer and small reorganization energy of fullerenes, has been applied to light energy conversion systems as well as the more complex molecular systems such as triads. Highly efficient photosynthetic multistep electron transfer has been realized at gold electrodes modified with self-assembled monolayers of fullerene-containing molecules. These results will provide new principles and concepts to develop artificial photosynthetic materials as well as molecular devices.

Fullerenes as Novel Acceptors in Photosynthetic Electron Transfer

PGRL1 RNA and protein levels are increased in iron-deficient Chlamydomonas reinhardtii cells. In an RNAi strain, which accumulates lower PGRL1 levels in both iron-replete and -starved conditions, the photosynthetic electron transfer rate is decreased, respiratory capacity in iron-sufficient conditions is increased, and the efficiency of cyclic electron transfer under iron-deprivation is diminished. Pgrl1-kd cells exhibit iron deficiency symptoms at higher iron concentrations than wild-type cells, although the cells are not more depleted in cellular iron relative to wild-type cells as measured by mass spectrometry. Thiol-trapping experiments indicate iron-dependent and redox-induced conformational changes in PGRL1 that may provide a link between iron metabolism and the partitioning of photosynthetic electron transfer between linear and cyclic flow. We propose, therefore, that PGRL1 in C. reinhardtii may possess a dual function in the chloroplast; that is, iron sensing and modulation of electron transfer.

The paper presents the review of works on modeling the interaction of photosynthetic proteins using the multiparticle Brownian dynamics method developed at the Department of Biophysics, Biological Faculty, Lomonosov Moscow State University. The method describes the displacement of individual macromolecules – mobile electron carriers, and their electrostatic interactions between each other and with pigment-protein complexes embedded in photosynthetic membrane. Three-dimensional models of the protein molecules were constructed on the basis of the data from the Protein Data Bank. We applied the Brownian methods coupled to molecular dynamic simulations to reveal the role of electrostatic interactions and conformational motions in the transfer of an electron from the cytochrome complex Cyt b6f) membrane we developed the model which combines events of proteins Pc diffusion along the thylakoid membrane, electrostatic interactions of Pc with the membrane charges, formation of Pc super-complexes with multienzyme complexes of Photosystem I and to the molecule of the mobile carrier plastocyanin (Pc) in plants, green algae and cyanic bacteria. Taking into account the interior of photosynthetic membrane we developed the model which combines events of proteins Pc diffusion along the thylakoid membrane, electrostatic interactions of Pc with the membrane charges, formation of Pc super-complexes with multienzyme complexes of Photosystem I and Cyt b6f, embedded in photosynthetic membrane, electron transfer and complex dissociation. Multiparticle Brownian simulation method can be used to consider the processes of protein interactions in subcellular systems in order to clarify the role of individual stages and the biophysical mechanisms of these processes.

A novel simulation calculation model based on photosynthetic electron transfer for microalgal growth prediction in any photobioreactor

In this review, we address bioenergetic pathways in the chloroplast of Chlamydomonas reinhardtii, with a focus on photosynthetic electron transfer. The conversion of solar energy into chemical energy by oxygenic photosynthesis, as performed by plants, green algae and cyanobacteria, supports the life on this planet. The production of oxygen (O2) and the assimilation of carbon dioxide (CO2) into organic matter determine, to a large extent, the composition of our atmosphere. Plant photosynthesis is conducted by a series of reactions that occur mainly in the chloroplast, resulting in light-dependent H2O oxidation, NADP+ reduction and ATP formation. NADPH and ATP, produced by linear electron flow (LEF), are required for carbon fixation via the Calvin-Benson-Bassham (CBB) cycle. Besides, photosynthetic electron transfer may operate in a cyclic electron flow (CEF) mode to satisfy the cellular ATP demand. Electrons derived from LEF may also be diverted to various other metabolic pathways, e.g. via ferredoxin (FDX). In addition, photosynthesis evolved to maximize its outcome while minimizing photooxidative stress. In this regard, mechanisms such as non-photochemical quenching (NPQ) and state transitions regulate energy influx at different light availabilities, which feedback to the proton-motive force (pmf) and the redox state of the plastoquinone/plastoquinol (PQ) pool, thereby also regulating LEF and CEF. To overcome possible limitations in electron transfer at the acceptor side of photosystem (PSI), alternative electron transfer pathways evolved, including flavodiiron proteins (FDPs), allowing safe utilization of O2 as alternative electron acceptor, as well as the hydrogenase, which utilizes two electrons and two protons to produce H2. Nevertheless, reactive oxygen species (ROS) may be formed, e.g. via the Mehler reaction at the acceptor side of PSI, which is why photosynthetic electrons are also utilized in detoxification mechanisms to prevent excessive damage. In conclusion, photosynthetic electron transfer is interwoven in a regulatory network that is aimed at adjusting ATP and NADPH production in a way that electron transfer is not harmful to the cell.

Electron transfer (ET) reactions in systems involving proteins require an oriented interaction between electron donor and acceptor in order to accommodate their respective redox centres in optimal orientation for efficient ET. Such type of reactions are critical for the maintenance of the physiological functions of living organisms, since they are implicated in vital actions, as is, for example, in the photosynthetic ET chain that leads to NADPH reduction. In this particular case, a small redox protein ET chain is responsible for ET from Photosystem I (PS I) to NADP(+). In this system the enzyme responsible for NADP(+) reduction is ferredoxin-NADP(+) reductase (FNR), a FAD-containing NADP(+) dependent reductase. In order to produce such reduction, this enzyme receives electrons from a [2Fe-2S] plant-type ferredoxin (Fd), which is previously reduced by PS I. Moreover, in the case of some algae and cyanobacteria, an FMN-dependent protein, flavodoxin (Fld), has been shown to replace Fd in this function. The processes of interaction and ET between FNR and all of its substrates involved in the photosynthetic ET chain, namely Fd, Fld and NADP(+)/H have been extensively investigated in recent years using a large number of techniques, including the introduction of site-specific mutations in combination with kinetic and structural studies of the produced mutants. The present manuscript summarises the information so far reported for an efficient interaction between FNR and its substrates, compares such information with that revealed by other systems for which the FNR structure is a prototype and, finally, discusses the implications of the processes of association in ET between FNR and its substrates.

This research project involves the design, synthesis and study of the molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. Specifically, the molecules are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they model carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

This research project involves the design, synthesis and study of molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. The knowledge gained from the study of synthetic model systems which abstract features of the natural photosynthetic apparatus can be used to design artificial photosynthetic systems which employ the basic physics and chemistry of photosynthesis to help meet mankind's energy needs. More specifically, the proposed models are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties.

This research project involves the design, synthesis and study of molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. The knowledge gained from the study of synthetic model systems which abstract features of the natural photosynthetic apparatus can be used to design artificial photosynthetic systems which employ the basic physics and chemistry of photosynthesis to help meet mankind`s energy needs. More specifically, the proposed models are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties.

This research project involves the design, synthesis and study of molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. Specifically, the molecules are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they model carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

This project involves the design, synthesis and study of molecules which mimic some of the important aspects of photosynthetic electron and energy transfer. This research project is leading to a better understanding of the energy conserving steps of photosynthesis via the study of synthetic model systems which abstract features of the natural photosynthetic apparatus. The knowledge gained from these studies will aid in the design of artificial photosynthetic reaction centers which employ the basic chemistry and physics of photosynthesis to help meet mankind`s energy needs. The approach to artificial photosynthesis employed in this project is to use synthetic pigments, electron donors, and electron acceptors similar to those found in biological reaction centers, but to replace the protein component with covalent bonds. These chemical linkages determine the electronic coupling between the various moieties by controlling separation, relative orientation, and overlap of electronic orbitals. The model systems are designed to mimic the following aspects of natural photosynthetic electron transfer: electron donation from a tetrapyrrole excited single state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they mimic carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

The reduction of the photo-oxidized special chlorophyll pair P700 of photosystem I (PSI) in the photosynthetic electron transport chain of eukaryotic organisms is facilitated by the soluble copper-containing protein plastocyanin (pc). In the absence of copper, pc is functionally replaced by the heme-containing protein cytochrome c6 (cyt c6) in the green alga Chlamydomonas reinhardtii. Binding and electron transfer between both donors and PSI follows a two-step mechanism that depends on electrostatic and hydrophobic recognition between the partners. Although the electrostatic and hydrophobic recognition sites on pc and PSI are well known, the precise electrostatic recognition site on cyt c6 is unknown. To specify the interaction sites on a molecular level, we cross-linked cyt c6 and PSI using a zero-length cross-linker and obtained a cross-linked complex competent in fast and efficient electron transfer. As shown previously, cyt c6 cross-links specifically with the PsaF subunit of PSI. Mass spectrometric analysis of tryptic peptides from the cross-linked product revealed specific interaction sites between residues Lys27 of PsaF and Glu69 of cyt c6 and between Lys23 of PsaF and Glu69/Glu70 of cyt c6. Using these new data, we present a molecular model of the intermolecular electron transfer complex between eukaryotic cyt c6 and PSI.

Possible role of protein in photosynthetic electron transfer