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Biochimica Et Biophysica Acta 2013The direct conversion of sunlight into biofuels is an intriguing alternative to a continued reliance on fossil fuels. Natural photosynthesis has long been investigated... (Review)
Review
The direct conversion of sunlight into biofuels is an intriguing alternative to a continued reliance on fossil fuels. Natural photosynthesis has long been investigated both as a potential solution, and as a model for utilizing solar energy to drive a water-to-fuel cycle. The molecules and organizational structure provide a template to inspire the design of efficient molecular systems for photocatalysis. A clear design strategy is the coordination of molecular interactions that match kinetic rates and energetic levels to control the direction and flow of energy from light harvesting to catalysis. Energy transduction and electron-transfer reactions occur through interfaces formed between complexes of donor-acceptor molecules. Although the structures of several of the key biological complexes have been solved, detailed descriptions of many electron-transfer complexes are lacking, which presents a challenge to designing and engineering biomolecular systems for solar conversion. Alternatively, it is possible to couple the catalytic power of biological enzymes to light harvesting by semiconductor nanomaterials. In these molecules, surface chemistry and structure can be designed using ligands. The passivation effect of the ligand can also dramatically affect the photophysical properties of the semiconductor, and energetics of external charge-transfer. The length, degree of bond saturation (aromaticity), and solvent exposed functional groups of ligands can be manipulated to further tune the interface to control molecular assembly, and complex stability in photocatalytic hybrids. The results of this research show how ligand selection is critical to designing molecular interfaces that promote efficient self-assembly, charge-transfer and photocatalysis. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems.
Topics: Electron Transport; Models, Molecular; Nanostructures; Static Electricity; Sunlight
PubMed: 23541891
DOI: 10.1016/j.bbabio.2013.03.006 -
Chemical Reviews Feb 2021This review focuses on key components of respiratory and photosynthetic energy-transduction systems: the cytochrome and (Cyt/) membranous multisubunit homodimeric... (Review)
Review
This review focuses on key components of respiratory and photosynthetic energy-transduction systems: the cytochrome and (Cyt/) membranous multisubunit homodimeric complexes. These remarkable molecular machines catalyze electron transfer from membranous quinones to water-soluble electron carriers (such as cytochromes or plastocyanin), coupling electron flow to proton translocation across the energy-transducing membrane and contributing to the generation of a transmembrane electrochemical potential gradient, which powers cellular metabolism in the majority of living organisms. Cyts/ share many similarities but also have significant differences. While decades of research have provided extensive knowledge on these enzymes, several important aspects of their molecular mechanisms remain to be elucidated. We summarize a broad range of structural, mechanistic, and physiological aspects required for function of Cyt/, combining textbook fundamentals with new intriguing concepts that have emerged from more recent studies. The discussion covers but is not limited to (i) mechanisms of energy-conserving bifurcation of electron pathway and energy-wasting superoxide generation at the quinol oxidation site, (ii) the mechanism by which semiquinone is stabilized at the quinone reduction site, (iii) interactions with substrates and specific inhibitors, (iv) intermonomer electron transfer and the role of a dimeric complex, and (v) higher levels of organization and regulation that involve Cyts/. In addressing these topics, we point out existing uncertainties and controversies, which, as suggested, will drive further research in this field.
Topics: Animals; Catalysis; Cytochrome b6f Complex; Electron Transport Complex III; Humans; Membranes; Molecular Dynamics Simulation; Photosynthesis; Protein Conformation; Respiration; Rhodobacter capsulatus; Thermodynamics
PubMed: 33464892
DOI: 10.1021/acs.chemrev.0c00712 -
The Journal of Biological Chemistry Sep 2016Copper is an essential transition metal for living organisms. In the plant model Arabidopsis thaliana, half of the copper content is localized in the chloroplast, and as...
Copper is an essential transition metal for living organisms. In the plant model Arabidopsis thaliana, half of the copper content is localized in the chloroplast, and as a cofactor of plastocyanin, copper is essential for photosynthesis. Within the chloroplast, copper delivery to plastocyanin involves two transporters of the PIB-1-ATPases subfamily: HMA6 at the chloroplast envelope and HMA8 in the thylakoid membranes. Both proteins are high affinity copper transporters but share distinct enzymatic properties. In the present work, the comparison of 140 sequences of PIB-1-ATPases revealed a conserved region unusually rich in histidine and cysteine residues in the TMA-L1 region of eukaryotic chloroplast copper ATPases. To evaluate the role of these residues, we mutated them in HMA6 and HMA8. Mutants of interest were selected from phenotypic tests in yeast and produced in Lactococcus lactis for further biochemical characterizations using phosphorylation assays from ATP and Pi Combining functional and structural data, we highlight the importance of the cysteine and the first histidine of the CX3HX2H motif in the process of copper release from HMA6 and HMA8 and propose a copper pathway through the membrane domain of these transporters. Finally, our work suggests a more general role of the histidine residue in the transport of copper by PIB-1-ATPases.
Topics: Adenosine Triphosphatases; Amino Acid Motifs; Arabidopsis; Arabidopsis Proteins; Copper; Histidine; Lactococcus lactis; Recombinant Proteins; Saccharomyces cerevisiae; Thylakoid Membrane Proteins; Thylakoids
PubMed: 27493208
DOI: 10.1074/jbc.M115.706978 -
Antioxidants & Redox Signaling Sep 2013Photosynthesis, the process that drives life on earth, relies on transition metal (e.g., Fe and Cu) containing proteins that participate in electron transfer in the... (Review)
Review
SIGNIFICANCE
Photosynthesis, the process that drives life on earth, relies on transition metal (e.g., Fe and Cu) containing proteins that participate in electron transfer in the chloroplast. However, the light reactions also generate high levels of reactive oxygen species (ROS), which makes metal use in plants a challenge.
RECENT ADVANCES
Sophisticated regulatory networks govern Fe and Cu homeostasis in response to metal ion availability according to cellular needs and priorities. Molecular remodeling in response to Fe or Cu limitation leads to its economy to benefit photosynthesis. Fe toxicity is prevented by ferritin, a chloroplastic Fe-storage protein in plants. Recent studies on ferritin function and regulation revealed the interplay between iron homeostasis and the redox balance in the chloroplast.
CRITICAL ISSUES
Although the connections between metal excess and ROS in the chloroplast are established at the molecular level, the mechanistic details and physiological significance remain to be defined. The causality/effect relationship between transition metals, redox signals, and responses is difficult to establish.
FUTURE DIRECTIONS
Integrated approaches have led to a comprehensive understanding of Cu homeostasis in plants. However, the biological functions of several major families of Cu proteins remain unclear. The cellular priorities for Fe use under deficiency remain largely to be determined. A number of transcription factors that function to regulate Cu and Fe homeostasis under deficiency have been characterized, but we have not identified regulators that mediate responses to excess. Importantly, details of metal sensing mechanisms and cross talk to ROS-sensing mechanisms are so far poorly documented in plants.
Topics: Chloroplasts; Copper; Homeostasis; Iron; Metals; Oxidation-Reduction; Oxidative Stress; Plants; Plastocyanin; Reactive Oxygen Species; Superoxide Dismutase
PubMed: 23199018
DOI: 10.1089/ars.2012.5084 -
Photosynthesis Research Dec 2017Properties and performance of the recently introduced Dual/KLAS-NIR spectrophotometer for simultaneous measurements of ferredoxin (Fd), P700, and plastocyanin (PC) redox...
Properties and performance of the recently introduced Dual/KLAS-NIR spectrophotometer for simultaneous measurements of ferredoxin (Fd), P700, and plastocyanin (PC) redox changes, together with whole leaf chlorophyll a (Chl) fluorescence (emission >760, 540 nm excitation) are outlined. Spectral information on in vivo Fd, P700, and PC in the near-infrared region (NIR, 780-1000 nm) is presented, on which the new approach is based. Examples of application focus on dark-light and light-dark transitions, where maximal redox changes of Fd occur. After dark-adaptation, Fd reduction induced by moderate light parallels the Kautsky effect of Chl fluorescence induction. Both signals are affected analogously by removal of O. A rapid type of Fd reoxidation, observed after a short pulse of light before light activation of linear electron transport (LET), is more pronounced in C4 compared to C3 leaves and interpreted to reflect cyclic PS I (CET). Light activation of LET, as assessed via the rate of Fd reoxidation after short light pulses, occurs at very low intensities and is slowly reversed (half-time ca. 20 min). Illumination with strong far-red light (FR, 740 nm) reveals two fractions of PS I, PS I (LET), and PS I (CET), differing in the rates of Fd reoxidation upon FR-off and the apparent equilibrium constants between P700 and PC. Parallel information on oxidation of Fd and reduction of P700 plus PC proves essential for identification of CET. Comparison of maize (C4) with sunflower and ivy (C3) responses leads to the conclusion that segregation of two types of PS I may not only exist in C4 (mesophyll and bundle sheath cells), but also in C3 photosynthesis (grana margins plus end membranes and stroma lamellae).
Topics: Electrons; Ferredoxins; Fluorescence; Kinetics; Light; Oxidation-Reduction; Photosystem I Protein Complex; Plant Leaves; Plants; Plastocyanin; Time Factors
PubMed: 28497192
DOI: 10.1007/s11120-017-0394-7 -
Biochimica Et Biophysica Acta 2006This paper summarized our present view on the mechanism of cyclic electron flow in C3 plants. We propose that cyclic and linear pathways are in competition for the... (Review)
Review
This paper summarized our present view on the mechanism of cyclic electron flow in C3 plants. We propose that cyclic and linear pathways are in competition for the reoxidation of the soluble primary PSI acceptor, Ferredoxin (Fd), that freely diffuses in the stromal compartment. In the linear mode, Fd binds ferredoxin-NADP-reductase and electrons are transferred to NADP+ and then to the Benson and Calvin cycle. In the cyclic mode, Fd binds a site localized on the stromal side of the cytochrome b6f complex and electrons are transferred to P700 via a mechanism derived from the Q-cycle. In dark-adapted leaves, the cyclic flow operates at maximum rate, owing to the partial inactivation of the Benson and Calvin cycle. For increasing time of illumination, the activation of the Benson and Calvin cycle, and thus, that of the linear flow, is associated with a subsequent decrease in the rate of the cyclic flow. Under steady-state conditions of illumination, the contribution of cyclic flow to PSI turnover increases as a function of the light intensity (from 0 to approximately 50% for weak to saturating light, respectively). Lack of CO2 is associated with an increase in the efficiency of the cyclic flow. ATP concentration could be one of the parameters that control the transition between linear and cyclic modes.
Topics: Chlorophyll; Chloroplasts; Cytochrome b6f Complex; Darkness; Electron Transport; Ferredoxin-NADP Reductase; Ferredoxins; Infrared Rays; Kinetics; NADP; Oxidation-Reduction; Photosynthesis; Plant Leaves; Plastocyanin; Spinacia oleracea
PubMed: 16762315
DOI: 10.1016/j.bbabio.2006.02.018 -
Biochimica Et Biophysica Acta Oct 2001Cyanobacterial photosystem (PS) I is remarkably similar to its counterpart in the chloroplast of plants and algae. Therefore, it has served as a prototype for the type I... (Review)
Review
Cyanobacterial photosystem (PS) I is remarkably similar to its counterpart in the chloroplast of plants and algae. Therefore, it has served as a prototype for the type I reaction centers of photosynthesis. Cyanobacterial PS I contains 11-12 proteins. Some of the cyanobacterial proteins are modified post-translationally. Reverse genetics has been used to generate subunit-deficient cyanobacterial mutants, phenotypes of which have revealed the functions of the missing proteins. The cyanobacterial PS I proteins bind cofactors, provide docking sites for electron transfer proteins, participate in tertiary and quaternary organization of the complex and protect the electron transfer centers. Many of these mutants are now being used in sophisticated structure-function analyses. Yet, the roles of some proteins of the cyanobacterial PS I are unknown. It is necessary to examine functions of these proteins on a global scale of cell physiology, biogenesis and evolution.
Topics: Cyanobacteria; Electron Transport; Electrophoresis, Gel, Two-Dimensional; Ferredoxins; Photosynthetic Reaction Center Complex Proteins; Photosystem I Protein Complex; Plant Proteins; Plastocyanin; Protein Processing, Post-Translational; Proteins
PubMed: 11687206
DOI: 10.1016/s0005-2728(01)00208-0 -
FEBS Letters Mar 2012Transient complexes, with a lifetime ranging between microseconds and seconds, are essential for biochemical reactions requiring a fast turnover. That is the case of the... (Review)
Review
Transient complexes, with a lifetime ranging between microseconds and seconds, are essential for biochemical reactions requiring a fast turnover. That is the case of the interactions between proteins engaged in electron transfer reactions, which are involved in relevant physiological processes such as respiration and photosynthesis. In the latter, the copper protein plastocyanin acts as a soluble carrier transferring electrons between the two membrane-embedded complexes cytochrome b(6)f and photosystem I. Here we review the combination of experimental efforts in the literature to unveil the functional and structural features of the complex between cytochrome f and plastocyanin, which have widely been used as a suitable model for analyzing transient redox interactions.
Topics: Bacterial Proteins; Cytochromes f; Electron Transport; Kinetics; Models, Molecular; Multiprotein Complexes; Plastocyanin; Protein Binding; Protein Conformation; Protein Structure, Tertiary
PubMed: 21889503
DOI: 10.1016/j.febslet.2011.08.035 -
International Journal of Molecular... May 2024Photosynthesis, as the primary source of energy for all life forms, plays a crucial role in maintaining the global balance of energy, entropy, and enthalpy in living... (Review)
Review
Photosynthesis, as the primary source of energy for all life forms, plays a crucial role in maintaining the global balance of energy, entropy, and enthalpy in living organisms. Among its various building blocks, photosystem I (PSI) is responsible for light-driven electron transfer, crucial for generating cellular reducing power. PSI acts as a light-driven plastocyanin-ferredoxin oxidoreductase and is situated in the thylakoid membranes of cyanobacteria and the chloroplasts of eukaryotic photosynthetic organisms. Comprehending the structure and function of the photosynthetic machinery is essential for understanding its mode of action. New insights are offered into the structure and function of PSI and its associated light-harvesting proteins, with a specific focus on the remarkable structural conservation of the core complex and high plasticity of the peripheral light-harvesting complexes.
Topics: Photosystem I Protein Complex; Photosynthesis; Light-Harvesting Protein Complexes; Cyanobacteria; Models, Molecular; Electron Transport
PubMed: 38791114
DOI: 10.3390/ijms25105073 -
The Plant Cell Jan 2009Expression of miR398 is induced in response to copper deficiency and is involved in the degradation of mRNAs encoding copper/zinc superoxide dismutase in Arabidopsis...
Expression of miR398 is induced in response to copper deficiency and is involved in the degradation of mRNAs encoding copper/zinc superoxide dismutase in Arabidopsis thaliana. We found that SPL7 (for SQUAMOSA promoter binding protein-like7) is essential for this response of miR398. SPL7 is homologous to Copper response regulator1, the transcription factor that is required for switching between plastocyanin and cytochrome c(6) in response to copper deficiency in Chlamydomonas reinhardtii. SPL7 bound directly to GTAC motifs in the miR398 promoter in vitro, and these motifs were essential and sufficient for the response to copper deficiency in vivo. SPL7 is also required for the expression of multiple microRNAs, miR397, miR408, and miR857, involved in copper homeostasis and of genes encoding several copper transporters and a copper chaperone, indicating its central role in response to copper deficiency. Consistent with this idea, the growth of spl7 plants was severely impaired under low-copper conditions.
Topics: Arabidopsis; Arabidopsis Proteins; Copper; Gene Expression Regulation, Plant; MicroRNAs; Oligonucleotide Array Sequence Analysis; Plants, Genetically Modified; Promoter Regions, Genetic; Protein Binding; RNA, Messenger; RNA, Plant; Transcription Factors; Transcription, Genetic
PubMed: 19122104
DOI: 10.1105/tpc.108.060137