-
Genome Biology and Evolution Aug 2021During photosynthesis, electrons are transferred between the cytochrome b6f complex and photosystem I. This is carried out by the protein plastocyanin in plant...
During photosynthesis, electrons are transferred between the cytochrome b6f complex and photosystem I. This is carried out by the protein plastocyanin in plant chloroplasts, or by either plastocyanin or cytochrome c6 in many cyanobacteria and eukaryotic algal species. There are three further cytochrome c6 homologs: cytochrome c6A in plants and green algae, and cytochromes c6B and c6C in cyanobacteria. The function of these proteins is unknown. Here, we present a comprehensive analysis of the evolutionary relationship between the members of the cytochrome c6 family in photosynthetic organisms. Our phylogenetic analyses show that cytochromes c6B and c6C are likely to be orthologs that arose from a duplication of cytochrome c6, but that there is no evidence for separate origins for cytochromes c6B and c6C. We therefore propose renaming cytochrome c6C as cytochrome c6B. We show that cytochrome c6A is likely to have arisen from cytochrome c6B rather than by an independent duplication of cytochrome c6, and present evidence for an independent origin of a protein with some of the features of cytochrome c6A in peridinin dinoflagellates. We conclude with a new comprehensive model of the evolution of the cytochrome c6 family which is an integral part of understanding the function of the enigmatic cytochrome c6 homologs.
Topics: Cytochromes; Cytochromes c6; Electron Transport; Electrons; Photosynthesis; Phylogeny
PubMed: 34165554
DOI: 10.1093/gbe/evab146 -
The Biochemical Journal Jun 2021Photosystem I is defined as plastocyanin-ferredoxin oxidoreductase. Taking advantage of genetic engineering, kinetic analyses and cryo-EM, our data provide novel...
Photosystem I is defined as plastocyanin-ferredoxin oxidoreductase. Taking advantage of genetic engineering, kinetic analyses and cryo-EM, our data provide novel mechanistic insights into binding and electron transfer between PSI and Pc. Structural data at 2.74 Å resolution reveals strong hydrophobic interactions in the plant PSI-Pc ternary complex, leading to exclusion of water molecules from PsaA-PsaB/Pc interface once the PSI-Pc complex forms. Upon oxidation of Pc, a slight tilt of bound oxidized Pc allows water molecules to accommodate the space between Pc and PSI to drive Pc dissociation. Such a scenario is consistent with the six times larger dissociation constant of oxidized as compared with reduced Pc and mechanistically explains how this molecular machine optimized electron transfer for fast turnover.
Topics: Binding Sites; Chlamydomonas reinhardtii; Electron Transport; Hydrophobic and Hydrophilic Interactions; Kinetics; Models, Molecular; Oxidation-Reduction; Photosystem I Protein Complex; Plastocyanin; Protein Binding; Protein Conformation
PubMed: 34085703
DOI: 10.1042/BCJ20210267 -
Biochimica Et Biophysica Acta.... Sep 2021Many cyanobacteria species can use both plastocyanin and cytochrome c as lumenal electron carriers to shuttle electrons from the cytochrome bf to either photosystem I or...
Many cyanobacteria species can use both plastocyanin and cytochrome c as lumenal electron carriers to shuttle electrons from the cytochrome bf to either photosystem I or the respiratory cytochrome c oxidase. In Synechocystis sp. PCC6803 placed in darkness, about 60% of the active PSI centres are bound to a reduced electron donor which is responsible for the fast re-reduction of Pin vivo after a single charge separation. Here, we show that both cytochrome c and plastocyanin can bind to PSI in the dark and participate to the fast phase of P reduction, but the fraction of pre-bound PSI is smaller in the case of cytochrome c than with plastocyanin. Because of the inter-connection of respiration and photosynthesis in cyanobacteria, the inhibition of the cytochrome c oxidase results in the over-reduction of the photosynthetic electron transfer chain in the dark that translates into a lag in the kinetics of P oxidation at the onset of light. We show that this is true both with plastocyanin and cytochrome c, indicating that the partitioning of electron transport between respiration and photosynthesis is regulated in the same way independently of which of the two lumenal electron carriers is present, although the mechanisms of such regulation are yet to be understood.
Topics: Chlorophyll; Cyanobacteria; Cytochromes c6; Electron Transport; Electron Transport Complex IV; Kinetics; Oxidation-Reduction; Photosynthesis; Photosystem I Protein Complex; Plastocyanin; Synechocystis; Thylakoids
PubMed: 34004195
DOI: 10.1016/j.bbabio.2021.148449 -
Frontiers in Microbiology 2021biopriming enhances rice growth in drought-stressed soils by triggering various plant metabolic pathways related to antioxidative defense, secondary metabolites, and...
biopriming enhances rice growth in drought-stressed soils by triggering various plant metabolic pathways related to antioxidative defense, secondary metabolites, and hormonal upregulation. In the present study, transcriptomic analysis of rice cultivar IR64 bioprimed with under drought stress was carried out in comparison with drought-stressed samples using next-generation sequencing techniques. Out of the 2,506 significant ( < 0.05) differentially expressed genes (DEGs), 337 (15%) were exclusively expressed in drought-stressed plants, 382 (15%) were expressed in -treated drought-stressed plants, and 1,787 (70%) were commonly expressed. Furthermore, comparative analysis of upregulated and downregulated genes under stressed conditions showed that 1,053 genes (42%) were upregulated and 733 genes (29%) were downregulated in -treated drought-stressed rice plants. The genes exclusively expressed in treated drought-stressed plants were mostly photosynthetic and antioxidative such as plastocyanin, small chain of Rubisco, PSI subunit Q, PSII subunit PSBY, osmoproteins, proline-rich protein, aquaporins, stress-enhanced proteins, and chaperonins. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis states that the most enriched pathways were metabolic (38%) followed by pathways involved in the synthesis of secondary metabolites (25%), carbon metabolism (6%), phenyl propanoid (7%), and glutathione metabolism (3%). Some of the genes were selected for validation using real-time PCR which showed consistent expression as RNA-Seq data. Furthermore, to establish host- interaction, transcriptome analysis of was also carried out. The Gene Ontology (GO) analysis of transcriptome suggested that the annotated genes are functionally related to carbohydrate binding module, glycoside hydrolase, GMC oxidoreductase, and trehalase and were mainly upregulated, playing an important role in establishing the mycelia colonization of rice roots and its growth. Overall, it can be concluded that biopriming delays drought stress in rice cultivars by a multitude of molecular programming.
PubMed: 33927706
DOI: 10.3389/fmicb.2021.655165 -
Plant & Cell Physiology Oct 2021In cyanobacteria and most green algae of the eukaryotic green lineage, the copper-protein plastocyanin (Pc) alternatively replaces the heme-protein cytochrome c6 (Cc6)... (Review)
Review
In cyanobacteria and most green algae of the eukaryotic green lineage, the copper-protein plastocyanin (Pc) alternatively replaces the heme-protein cytochrome c6 (Cc6) as the soluble electron carrier from cytochrome f (Cf) to photosystem I (PSI). The functional and structural equivalence of 'green' Pc and Cc6 has been well established, representing an example of convergent evolution of two unrelated proteins. However, plants only produce Pc, despite having evolved from green algae. On the other hand, Cc6 is the only soluble donor available in most species of the red lineage of photosynthetic organisms, which includes, among others, red algae and diatoms. Interestingly, Pc genes have been identified in oceanic diatoms, probably acquired by horizontal gene transfer from green algae. However, the mechanisms that regulate the expression of a functional Pc in diatoms are still unclear. In the green eukaryotic lineage, the transfer of electrons from Cf to PSI has been characterized in depth. The conclusion is that in the green lineage, this process involves strong electrostatic interactions between partners, which ensure a high affinity and an efficient electron transfer (ET) at the cost of limiting the turnover of the process. In the red lineage, recent kinetic and structural modeling data suggest a different strategy, based on weaker electrostatic interactions between partners, with lower affinity and less efficient ET, but favoring instead the protein exchange and the turnover of the process. Finally, in diatoms the interaction of the acquired green-type Pc with both Cf and PSI may not yet be optimized.
Topics: Chlorophyta; Cyanobacteria; Cytochromes f; Electron Transport; Evolution, Molecular; Kinetics; Molecular Docking Simulation; Photosystem I Protein Complex; Protein Structure, Tertiary
PubMed: 33772595
DOI: 10.1093/pcp/pcab044 -
Proceedings of the National Academy of... Feb 2021After the Great Oxidation Event (GOE), iron availability was greatly decreased, and photosynthetic organisms evolved several alternative proteins and mechanisms. One of...
After the Great Oxidation Event (GOE), iron availability was greatly decreased, and photosynthetic organisms evolved several alternative proteins and mechanisms. One of these proteins, plastocyanin, is a type I blue-copper protein that can replace cytochrome as a soluble electron carrier between cytochrome and photosystem I. In most cyanobacteria, expression of these two alternative proteins is regulated by copper availability, but the regulatory system remains unknown. Herein, we provide evidence that the regulatory system is composed of a BlaI/CopY-family transcription factor (PetR) and a BlaR-membrane protease (PetP). PetR represses (plastocyanin) expression and activates (cytochrome ), while PetP controls PetR levels in vivo. Using whole-cell extracts, we demonstrated that PetR degradation requires both PetP and copper. Transcriptomic analysis revealed that the PetRP system regulates only four genes (, , , and ), highlighting its specificity. Furthermore, the presence of and in early branching cyanobacteria indicates that acquisition of these genes could represent an early adaptation to decreased iron bioavailability following the GOE.
Topics: Bacterial Proteins; Base Sequence; Copper; Cytochromes c; Epistasis, Genetic; Models, Biological; Mutation; Peptide Hydrolases; Plastocyanin; Promoter Regions, Genetic; Protein Binding; Proteolysis; Regulon; Synechocystis
PubMed: 33495331
DOI: 10.1073/pnas.2017898118 -
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 -
Biochimica Et Biophysica Acta.... May 2021Cytochrome bf (cytbf) lies at the heart of the light-dependent reactions of oxygenic photosynthesis, where it serves as a link between photosystem II (PSII) and... (Review)
Review
Cytochrome bf (cytbf) lies at the heart of the light-dependent reactions of oxygenic photosynthesis, where it serves as a link between photosystem II (PSII) and photosystem I (PSI) through the oxidation and reduction of the electron carriers plastoquinol (PQH) and plastocyanin (Pc). A mechanism of electron bifurcation, known as the Q-cycle, couples electron transfer to the generation of a transmembrane proton gradient for ATP synthesis. Cytbf catalyses the rate-limiting step in linear electron transfer (LET), is pivotal for cyclic electron transfer (CET) and plays a key role as a redox-sensing hub involved in the regulation of light-harvesting, electron transfer and photosynthetic gene expression. Together, these characteristics make cytbf a judicious target for genetic manipulation to enhance photosynthetic yield, a strategy which already shows promise. In this review we will outline the structure and function of cytbf with a particular focus on new insights provided by the recent high-resolution map of the complex from Spinach.
Topics: Cell Respiration; Cytochrome b6f Complex; Electron Transport; Electrons; Photosynthesis
PubMed: 33460588
DOI: 10.1016/j.bbabio.2021.148380 -
Biochimica Et Biophysica Acta.... Mar 2021Photosynthetic electron flow, driven by photosystem I and II, provides chemical energy for carbon fixation. In addition to a linear mode a second cyclic route exists,...
Photosynthetic electron flow, driven by photosystem I and II, provides chemical energy for carbon fixation. In addition to a linear mode a second cyclic route exists, which only involves photosystem I. The exact contributions of linear and cyclic transport are still a matter of debate. Here, we describe the development of a method that allows quantification of electron flow in absolute terms through photosystem I in a photosynthetic organism for the first time. Specific in-vivo protocols allowed to discern the redox states of plastocyanin, P700 and the FeS-clusters including ferredoxin at the acceptor site of PSI in the cyanobacterium Synechocystis sp. PCC 6803 with the near-infrared spectrometer Dual-KLAS/NIR. P700 absorbance changes determined with the Dual-KLAS/NIR correlated linearly with direct determinations of PSI concentrations using EPR. Dark-interval relaxation kinetics measurements (DIRK) were applied to determine electron flow through PSI. Counting electrons from hydrogen oxidation as electron donor to photosystem I in parallel to DIRK measurements confirmed the validity of the method. Electron flow determination by classical PSI yield measurements overestimates electron flow at low light intensities and saturates earlier compared to DIRK. Combination of DIRK with oxygen evolution measurements yielded a proportion of 35% of surplus electrons passing PSI compared to PSII. We attribute these electrons to cyclic electron transport, which is twice as high as assumed for plants. Counting electrons flowing through the photosystems allowed determination of the number of quanta required for photosynthesis to 11 per oxygen produced, which is close to published values.
Topics: Bacterial Proteins; Electron Transport; Oxidation-Reduction; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Synechocystis
PubMed: 33346012
DOI: 10.1016/j.bbabio.2020.148353 -
Physiologia Plantarum Feb 2021We have investigated if the heterologous expression of a functional green alga plastocyanin in the diatom Phaeodactylum tricornutum can improve photosynthetic activity...
We have investigated if the heterologous expression of a functional green alga plastocyanin in the diatom Phaeodactylum tricornutum can improve photosynthetic activity and cell growth. Previous in vitro assays showed that a single-mutant of the plastocyanin from the green algae Chlamydomonas reinhardtii is effective in reducing P. tricornutum photosystem I. In this study, in vivo assays with P. tricornutum strains expressing this plastocyanin indicate that even the relatively low intracellular concentrations of holo-plastocyanin detected (≈4 μM) are enough to promote an increased growth (up to 60%) under iron-deficient conditions as compared with the WT strain, measured as higher cell densities, content in pigments and active photosystem I, global photosynthetic rates per cell, and even cell volume. In addition, the presence of plastocyanin as an additional photosynthetic electron carrier seems to decrease the over-reduction of the plastoquinone pool. Consequently, it promotes an improvement in the maximum quantum yield of both photosystem II and I, together with a decrease in the acceptor side photoinhibition of photosystem II-also associated to a reduced oxidative stress-a decrease in the peroxidation of membrane lipids in the choroplast, and a lower degree of limitation on the donor side of photosystem I. Thus the heterologous plastocyanin appears to act as a functional electron carrier, alternative to the native cytochrome c , under iron-limiting conditions.
Topics: Diatoms; Electron Transport; Iron; Photosynthesis; Photosystem I Protein Complex; Plastocyanin
PubMed: 33247466
DOI: 10.1111/ppl.13290