Publications
173 results found
Yu J, Knoppova J, Michoux F, et al., 2018, Ycf48 involved in the biogenesis of the oxygen-evolving photosystem II complex is a seven-bladed beta-propeller protein, Proceedings of the National Academy of Sciences, Vol: 115, Pages: E7824-E7833, ISSN: 0027-8424
Robust photosynthesis in chloroplasts and cyanobacteria requires the participation of accessory proteins to facilitate the assembly and maintenance of the photosynthetic apparatus located within the thylakoid membranes. The highly conserved Ycf48 protein acts early in the biogenesis of the oxygen-evolving photosystem II (PSII) complex by binding to newly synthesized precursor D1 subunit and by promoting efficient association with the D2 protein to form a PSII reaction center (PSII RC) assembly intermediate. Ycf48 is also required for efficient replacement of damaged D1 during the repair of PSII. However, the structural features underpinning Ycf48 function remain unclear. Here we show that Ycf48 proteins encoded by the thermophilic cyanobacterium Thermosynechococcus elongatus and the red alga Cyanidioschyzon merolae form seven-bladed beta-propellers with the 19-aa insertion characteristic of eukaryotic Ycf48 located at the junction of blades 3 and 4. Knowledge of these structures has allowed us to identify a conserved “Arg patch” on the surface of Ycf48 that is important for binding of Ycf48 to PSII RCs but also to larger complexes, including trimeric photosystem I (PSI). Reduced accumulation of chlorophyll in the absence of Ycf48 and the association of Ycf48 with PSI provide evidence of a more wide-ranging role for Ycf48 in the biogenesis of the photosynthetic apparatus than previously thought. Copurification of Ycf48 with the cyanobacterial YidC protein insertase supports the involvement of Ycf48 during the cotranslational insertion of chlorophyll-binding apopolypeptides into the membrane.
Sawa M, Fantuzzi A, Nixon P, et al., 2018, Development of printed solar biobattery for use in bioelectronics, Arm Summit 2018, Publisher: Arm
There is an urgent need to develop a sustainable battery technology that is cheap, environmentally friendly, easy to fabricate and to dispose of, especially to tackle the world-wide increase in illegally dumped electronic wastes. Microbial biophotovoltaic (BPV) technology is a renewable bioenergy system currently being developed at the laboratory scale. It generates electricity from the photosynthetic metabolism of cyanobacteria and microalgae and exploits their ability to convert light energy into electrical current using water as the source of electrons. Innovative approaches are needed to solve scale-up issues such as cost, ease of fabrication (particularly the fabrication of the inorganic and biological (microbes) parts).In this talk, I will report the feasibility of using a simple commercial thermal-inkjet printer to fabricate a thin-film paper-based BPV cell consisting of a layer of cyanobacterial cells on top of a carbon nanotube conducting surface on plain copy paper. The digitally printed thin-film BPV system produced electricity both in the light and dark, with a maximum electrical power output of 0.38 mW m-2 in one system and the sustained electrical current production over 100 hours in another more fully printed system. I will address limitations and challenges as well possible applications in the area of printed bioelectronics.
Cardona T, Shao S, Nixon PJ, 2018, Enhancing photosynthesis in plants: the light reactions, Essays in Biochemistry, Vol: 62, Pages: 85-94, ISSN: 0071-1365
In this review, we highlight recent research and current ideas on how to improve the efficiency of the light reactions of photosynthesis in crops. We note that the efficiency of photosynthesis is a balance between how much energy is used for growth and the energy wasted or spent protecting the photosynthetic machinery from photodamage. There are reasons to be optimistic about enhancing photosynthetic efficiency, but many appealing ideas are still on the drawing board. It is envisioned that the crops of the future will be extensively genetically modified to tailor them to specific natural or artificial environmental conditions.
Shao S, Cardona T, Nixon PJ, 2018, Early emergence of the FtsH proteases involved in Photosystem II repair, Photosynthetica, Vol: 56, Pages: 163-177, ISSN: 0300-3604
Efficient degradation of damaged D1 during the repair of PSII is carried out by a set of dedicated FtsH proteases in the thylakoid membrane. Here we investigated whether the evolution of FtsH could hold clues to the origin of oxygenic photosynthesis. A phylogenetic analysis of over 6000 FtsH protease sequences revealed that there are three major groups of FtsH proteases originating from gene duplication events in the last common ancestor of bacteria, and that the FtsH proteases involved in PSII repair make a distinct clade branching out before the divergence of FtsH proteases found in all groups of anoxygenic phototrophic bacteria. Furthermore, we showed that the phylogenetic tree of FtsH proteases in phototrophic bacteria is similar to that for Type I and Type II reaction centre proteins. We conclude that the phylogeny of FtsH proteases is consistent with an early origin of water oxidation chemistry.
Sawa M, Fantuzzi A, Bombelli P, et al., 2017, Electricity generation from digitally printed cyanobacteria, Nature Communications, Vol: 8, Pages: 1-10, ISSN: 2041-1723
Microbial biophotovoltaic cells exploit the ability of cyanobacteria and microalgae to convert light energy into electrical current using water as the source of electrons. Such bioelectrochemical systems have a clear advantage over more conventional microbial fuel cells which require the input of organic carbon for microbial growth. However, innovative approaches are needed to address scale-up issues associated with the fabrication of the inorganic (electrodes) and biological (microbe) parts of the biophotovoltaic device. Here we demonstrate the feasibility of using a simple commercial inkjet printer to fabricate a thin-film paper-based biophotovoltaic cell consisting of a layer of cyanobacterial cells on top of a carbon nanotube conducting surface. We show that these printed cyanobacteria are capable of generating a sustained electrical current both in the dark (as a ‘solar bio-battery’) and in response to light (as a ‘bio-solar-panel’) with potential applications in low-power devices.
Beckova M, Yu J, Krynicka V, et al., 2017, Structure of Psb29/Thf1 and its association with the FtsH protease complex involved in photosystem II repair in cyanobacteria, Philosophical Transactions of the Royal Society B: Biological Sciences, Vol: 372, ISSN: 1471-2970
One strategy for enhancing photosynthesis in crop plants is to improve the ability to repair photosystem II (PSII) in response to irreversible damage by light. Despite the pivotal role of thylakoid embedded FtsH protease complexes in the selective degradation of PSII subunits during repair, little is known about the factors involved in regulating FtsH expression. Here we show using the cyanobacterium Synechocystis sp. PCC 6803 that the Psb29 subunit, originally identified as a minor component of His tagged PSII preparations, physically interacts with FtsH complexes in vivo and is required for normal accumulation of the FtsH2/FtsH3 hetero oligomeric complex involved in PSII repair. We show using X ray crystallography that Psb29 from Thermosynechococcus elongatushas a unique fold consisting of a helical bundle and an extended C terminal helix and contains a highly conserved region that might be involved in binding to FtsH. A similar interaction is likely to occur in Arabidopsis chloroplasts between the Psb29 homologue, termed THF1, and the FTSH2/FTSH5 complex. The direct involvement of Psb29/THF1 in FtsH accumulation helps explain why THF1 is a target during the hypersensitive response in plants induced by pathogen infection. Downregulating FtsH function and the PSII repair cycle via THF1 would contribute to the production
Foyer CH, Ruban AV, Nixon PJ, 2017, Photosynthesis solutions to enhance productivity, Philosophical Transactions of the Royal Society of London: Biological Sciences, Vol: 372, ISSN: 0962-8436
The concept that photosynthesis is a highly inefficient process in terms ofconversion of light energy into biomass is embedded in the literature. It isonly in the past decade that the processes limiting photosynthetic efficiencyhave been understood to an extent that allows a step change in our ability tomanipulate light energy assimilation into carbon gain. We can thereforeenvisage that future increases in the grain yield potential of our majorcrops may depend largely on increasing the efficiency of photosynthesis.The papers in this issue provide new insights into the nature of current limitationson photosynthesis and identify new targets that can be used for cropimprovement, together with information on the impacts of a changingenvironment on the productivity of photosynthesis on land and in ouroceans.This article is part of the themed issue ‘Enhancing photosynthesis in cropplants: targets for improvement’.
Barretto S, Michoux F, Hellgardt K, et al., 2016, Pneumatic hydrodynamics influence transplastomic protein yields and biological responses during in vitro shoot regeneration of Nicotiana tabacum callus: Implications for bioprocess routes to plant-made biopharmaceuticals, Biochemical Engineering Journal, Vol: 11, Pages: 73-81, ISSN: 1369-703X
Transplastomic plants are capable of high-yield production of recombinant biopharmaceutical proteins. Planttissue culture combines advantages of agricultural cultivation with the bioprocess consistency associated withsuspension culture. Overexpression of recombinant proteins through regeneration of transplastomic Nicotianatabacum shoots from callus tissue in RITA® temporary immersion bioreactors has been previously demonstrated.In this study we investigated the hydrodynamics of periodic pneumatic suspension of liquid medium duringtemporary immersion culture (4 minutes aeration every 8 hours), and the impact on biological responses andtransplastomic expression of fragment C of tetanus toxin (TetC). Biomass was grown under a range of aerationrates for 3, 20 and 40-day durations. Growth, mitochondrial activity (a viability indicator) and TetC protein yieldswere correlated against the hydrodynamic parameters, shear rate and energy dissipation rate (per kg of medium).A critical aeration rate of 440 ml min-1 was identified, corresponding to a shear rate of 96.7 s-1, pneumatic powerinput of 8.8 mW kg-1and initial 20-day pneumatic energy dissipation of 127 J kg-1, at which significant reductionsin biomass accumulation and mitochondrial activity were observed. There was an exponential decline in TetCyields with increasing aeration rates at 40 days, across the entire range of conditions tested. These observationshave important implications for the optimisation and scale-up of transplastomic plant tissue culture bioprocessesfor biopharmaceutical production.
Ahmad N, Michoux F, Lossl AG, et al., 2016, Challenges and perspectives in commercializing plastid transformation technology, Journal of Experimental Botany, Vol: 67, Pages: 5945-5960, ISSN: 1460-2431
Plastid transformation has emerged as an alternative platform to generate transgenic plants. Attractive features of this technology include specific integration of transgenes—either individually or as operons—into the plastid genome through homologous recombination, the potential for high-level protein expression, and transgene containment because of the maternal inheritance of plastids. Several issues associated with nuclear transformation such as gene silencing, variable gene expression due to the Mendelian laws of inheritance, and epigenetic regulation have not been observed in the plastid genome. Plastid transformation has been successfully used for the production of therapeutics, vaccines, antigens, and commercial enzymes, and for engineering various agronomic traits including resistance to biotic and abiotic stresses. However, these demonstrations have usually focused on model systems such as tobacco, and the technology per se has not yet reached the market. Technical factors limiting this technology include the lack of efficient protocols for the transformation of cereals, poor transgene expression in non-green plastids, a limited number of selection markers, and the lengthy procedures required to recover fully segregated plants. This article discusses the technology of transforming the plastid genome, the positive and negative features compared with nuclear transformation, and the current challenges that need to be addressed for successful commercialization.
Bečková M, Gardian Z, Yu J, et al., 2016, Association of Psb28 and Psb27 proteins with PSII-PSI supercomplexes upon exposure of Synechocystis sp. PCC 6803 to high light, Molecular Plant, Vol: 10, Pages: 62-72, ISSN: 1752-9867
Formation of the multi-subunit oxygen-evolving Photosystem II (PSII) complex involvesa number of auxiliary protein factors. In this study we compared the location and possiblefunction of two homologous PSII assembly factors, Psb28-1 and Psb28-2, from thecyanobacterium Synechocystis sp. PCC 6803. We show that FLAG-tagged Psb28-2 ispresent in both the monomeric PSII core complex and a PSII core complex lacking theinner antenna CP43 (RC47) whereas Psb28-1 preferentially binds to RC47. When cellsare exposed to increased irradiance, both tagged Psb28 proteins now associate witholigomeric forms of PSII and with PSII-PSI supercomplexes composed of trimericPhotosystem I (PSI) and two PSII monomers as deduced from negative stain electronmicroscopy. The presence of the Psb27 accessory protein in these complexes suggests theinvolvement of PSI in PSII biogenesis, possibly by photoprotecting PSII through energyspillover. Under standard cultivation conditions the distribution of PSII complexes issimilar in WT and each of the single psb28 null mutants except for loss of RC47 in theabsence of Psb28-1. In comparison with WT, growth of mutants lacking Psb28-1 andPsb27, but not Psb28-2, was retarded under high-light and, especially, intermittent highlight-darkconditions, emphasizing the physiological importance of PSII assembly factorsfor light acclimation.
Knoppova J, Yu J, Konik P, et al., 2016, CyanoP Is involved in the early steps of Photosystem two assembly in thecyanobacterium synechocystis sp. PCC 6803, Plant and Cell Physiology, Vol: 57, Pages: 1921-1931, ISSN: 1471-9053
Although the Photosystem II (PSII) complex is highly conserved in cyanobacteria and chloroplasts, the PsbU and PsbV subunits stabilizing the oxygen-evolving Mn4 CaO5 cluster in cyanobacteria are absent in chloroplasts and have been replaced by the PsbP and PsbQ subunits. There is, however, a distant cyanobacterial homologue of PsbP, termed CyanoP, of unknown function. Here we show that CyanoP plays a role in the early stages of PSII biogenesis in Synechocystis sp. PCC 6803. CyanoP is present in the PSII reaction centre assembly complex (RCII) lacking both the CP47 and CP43 modules and binds to the smaller D2 module. A small amount of larger PSII core complexes co-purifying with FLAG-tagged CyanoP indicates that CyanoP can accompany PSII on most of its assembly pathway. A role in biogenesis is supported by the accumulation of unassembled D1 precursor and impaired formation of RCII in a mutant lacking CyanoP. Interestingly, the pull-down preparations of CyanoP-FLAG from a strain lacking CP47 also contained PsbO indicating engagement of this protein with PSII at a much earlier stage in assembly than previously assumed.
Michoux F, Ahmad N, Wei Z-Y, et al., 2016, Testing the role of the N-terminal tail of D1 in the maintenance of photosystem II in tobacco chloroplasts, Frontiers in Plant Science, Vol: 7, ISSN: 1664-462X
A key step in the repair of photoinactivated oxygen-evolving photosystem II (PSII) complexes is the selective recognition and degradation of the damaged PSII subunit, usually the D1 reaction centre subunit. FtsH proteases play a major role in D1 degradation in both cyanobacteria and chloroplasts. In the case of the cyanobacterium Synechocystis sp. PCC 6803, analysis of an N-terminal truncation mutant of D1 lacking 20 amino-acid residues has provided evidence that FtsH complexes can remove damaged D1 in a processive reaction initiated at the exposed N-terminal tail. To test the importance of the N-terminal D1 tail in higher plants, we have constructed the equivalent truncation mutant in tobacco using chloroplast transformation techniques. The resulting mutant grew poorly and only accumulated about 25 % of wild-type levels of PSII in young leaves which declined as the leaves grew so that there was little PSII activity in mature leaves. Truncating D1 led to the loss of PSII supercomplexes and dimeric complexes in the membrane. Extensive and rapid non-photochemical quenching (NPQ) was still induced in the mutant, supporting the conclusion that PSII complexes are not required for NPQ. Analysis of leaves exposed to high light indicated that PSII repair in the truncation mutant was impaired at the level of synthesis and/or assembly of PSII but that D1 could still be degraded. These data support the idea that tobacco plants possess a number of back-up and compensatory pathways for removal of damaged D1 upon severe light stress.
Barretto S, Michoux F, Nixon PJ, 2016, Temporary Immersion Bioreactors for the Contained Production of Recombinant Proteins in Transplastomic Plants., Recombinant Proteins from Plants: Methods and Protocols, Publisher: Springer, Pages: 149-160, ISBN: 978-1-4939-3288-7
Despite the largely maternal inheritance of plastid genomes, the risk of transgene dissemination from transplastomic plants can limit the scope for field cultivation. There is a need for a cost-effective, scalable process to grow large quantities of transplastomic plant biomass for biosynthesis of biopharmaceuticals and other high-value heterologous proteins. Temporary immersion culture is a means of achieving this under fully contained conditions. This method describes the organogenesis of transplastomic Nicotiana tabacum callus in RITA(®) temporary immersion bioreactors to produce rootless leafy biomass, and subsequent total soluble protein extraction, SDS-PAGE, and Western immunoblot analysis of heterologous protein expression. This method can be used for propagation of plastid or nuclear transformants, though is especially suitable for transplastomic biomass, as organogenesis leads to greater expression and accumulation of transplastomic proteins due to increases in chloroplast number and size.
Burgess SJ, Hussein T, Yeoman JA, et al., 2015, Identification of the elusive pyruvate reductase of Chlamydomonas reinhardtii chloroplasts, Plant and Cell Physiology, Vol: 57, Pages: 82-94, ISSN: 1471-9053
Under anoxic conditions the green alga Chlamydomonas reinhardtii activates various 67 fermentation pathways leading to the creation of formate, acetate, ethanol and small 68 amounts of other metabolites including D-lactate and hydrogen. Progress has been 69 made in identifying the enzymes involved in these pathways and their sub-cellular 70 locations; however, the identity of the enzyme involved in reducing pyruvate to D-71 lactate has remained unclear. Based on sequence comparisons, enzyme activity 72 measurements, X-ray crystallography, biochemical fractionation and analysis of 73 knock-down mutants we conclude that pyruvate reduction in the chloroplast is 74 catalysed by a tetrameric NAD⁺-dependent D-lactate dehydrogenase encoded by 75 Cre07.g324550. Its expression during aerobic growth supports a possible function as a 76 ‘lactate valve’ for the export of lactate to the mitochondrion for oxidation by 77 cytochrome-dependent D-lactate dehydrogenases and by glycolate dehydrogenase. 78 We also present a revised spatial model of fermentation based on our 79 immunochemical detection of the likely pyruvate decarboxylase, PDC3, in the 80 cytoplasm.
Krynická V, Shao S, Nixon PJ, et al., 2015, Accessibility controls selective degradation ofphotosystem II subunits by FtsH protease, Nature Plants, Vol: 1, ISSN: 2055-0278
The oxygen-evolving photosystem II (PSII) complex located inchloroplasts and cyanobacteria is sensitive to light-induceddamage1 that unless repaired causes reduction in photosyntheticcapacity and growth. Although a potential target forcrop improvement, the mechanism of PSII repair remainsunclear. The D1 reaction center protein is the main target forphotodamage2, with repair involving the selective degradationof the damaged protein by FtsH protease3. How a singledamaged PSII subunit is recognized for replacement isunknown. Here, we have tested the dark stability of PSII subunitsin strains of the cyanobacterium Synechocystis PCC6803 blocked at specific stages of assembly. We have foundthat when D1, which is normally shielded by the CP43subunit, becomes exposed in a photochemically active PSIIcomplex lacking CP43, it is selectively degraded by FtsH evenin the dark. Removal of the CP47 subunit, which increasesaccessibility of FtsH to the D2 subunit, induced dark degradationof D2 at a faster rate than that of D1. In contrast,CP47 and CP43 are resistant to degradation in the dark. Ourresults indicate that protease accessibility induced by PSII disassemblyis an important determinant in the selection of the D1and D2 subunits to be degraded by FtsH.
Sacharz J, Bryan SJ, Yu J, et al., 2015, Sub-cellular location of FtsH proteases in the cyanobacterium Synechocystis sp PCC 6803 suggests localised PSII repair zones in the thylakoid membranes, Molecular Microbiology, Vol: 96, Pages: 448-462, ISSN: 1365-2958
In cyanobacteria and chloroplasts, exposure to HL damages the photosynthetic apparatus, especially the D1 subunit of Photosystem II. To avoid chronic photoinhibition, a PSII repair cycle operates to replace damaged PSII subunits with newly synthesised versions. To determine the sub-cellular location of this process, we examined the localisation of FtsH metalloproteases, some of which are directly involved in degrading damaged D1. We generated transformants of the cyanobacterium Synechocystis sp. PCC6803 expressing GFP-tagged versions of its four FtsH proteases. The ftsH2–gfp strain was functional for PSII repair under our conditions. Confocal microscopy shows that FtsH1 is mainly in the cytoplasmic membrane, while the remaining FtsH proteins are in patches either in the thylakoid or at the interface between the thylakoid and cytoplasmic membranes. HL exposure which increases the activity of the Photosystem II repair cycle led to no detectable changes in FtsH distribution, with the FtsH2 protease involved in D1 degradation retaining its patchy distribution in the thylakoid membrane. We discuss the possibility that the FtsH2–GFP patches represent Photosystem II ‘repair zones’ within the thylakoid membranes, and the possible advantages of such functionally specialised membrane zones. Anti-GFP affinity pull-downs provide the first indication of the composition of the putative repair zones.
Krynicka V, Tichy M, Krafl J, et al., 2014, Two essential FtsH proteases control the level of the Fur repressor during iron deficiency in the cyanobacterium <i>Synechocystis</i> sp PCC 6803, MOLECULAR MICROBIOLOGY, Vol: 94, Pages: 609-624, ISSN: 0950-382X
- Author Web Link
- Cite
- Citations: 34
Bryan SJ, Burroughs NJ, Shevela D, et al., 2014, Localisation and interactions of the Vipp1 protein in cyanobacteria, Molecular Microbiology, Vol: 94, Pages: 1179-1195, ISSN: 1365-2958
The Vipp1 protein is essential in cyanobacteria andchloroplasts for the maintenance of photosyntheticfunction and thylakoid membrane architecture. Toinvestigate its mode of action we generated strainsof the cyanobacteria Synechocystis sp. PCC6803and Synechococcus sp. PCC7942 in which Vipp1was tagged with green fluorescent protein at theC-terminus and expressed from the native chromosomallocus. There was little perturbation of function. Live-cell fluorescence imaging shows dramatic relocalisationof Vipp1 under high light. Under low light,Vipp1 is predominantly dispersed in the cytoplasmwith occasional concentrations at the outer peripheryof the thylakoid membranes. High light induces Vipp1coalescence into localised puncta within minutes, withnet relocation of Vipp1 to the vicinity of the cytoplasmicmembrane and the thylakoid membranes. Pulldownsand mass spectrometry identify an extensivecollection of proteins that are directly or indirectlyassociated with Vipp1 only after high-light exposure.These include not only photosynthetic and stressrelatedproteins but also RNA-processing, translationand protein assembly factors. This suggests that theVipp1 puncta could be involved in protein assembly.One possibility is that Vipp1 is involved in the formationof stress-induced localised protein assemblycentres, enabling enhanced protein synthesis anddelivery to membranes under stress conditions.
Burroughs NJ, Boehm M, Eckert C, et al., 2014, Solar powered biohydrogen production requires specific localization of the hydrogenase., Energy Environ Sci, Vol: 7, Pages: 3791-3800, ISSN: 1754-5692
Cyanobacteria contain a bidirectional [NiFe] hydrogenase which transiently produces hydrogen upon exposure of anoxic cells to light, potentially acting as a "valve" releasing excess electrons from the electron transport chain. However, its interaction with the photosynthetic electron transport chain remains unclear. By GFP-tagging the HoxF diaphorase subunit we show that the hydrogenase is thylakoid associated, comprising a population dispersed uniformly through the thylakoids and a subpopulation localized to discrete puncta in the distal thylakoid. Thylakoid localisation of both the HoxH and HoxY hydrogenase subunits is confirmed by immunogold electron microscopy. The diaphorase HoxE subunit is essential for recruitment to the dispersed thylakoid population, potentially anchoring the hydrogenase to the membrane, but aggregation to puncta occurs through a distinct HoxE-independent mechanism. Membrane association does not require NDH-1. Localization is dynamic on a scale of minutes, with anoxia and high light inducing a significant redistribution between these populations in favour of puncta. Since HoxE is essential for access to its electron donor, electron supply to the hydrogenase depends on a physiologically controlled localization, potentially offering a new avenue to enhance photosynthetic hydrogen production by exploiting localization/aggregation signals.
Michoux F, Boehm M, Bialek W, et al., 2014, Crystal structure of CyanoQ from the thermophilic cyanobacterium <i>Thermosynechococcus elongatus</i> and detection in isolated photosystem II complexes, PHOTOSYNTHESIS RESEARCH, Vol: 122, Pages: 57-67, ISSN: 0166-8595
- Author Web Link
- Open Access Link
- Cite
- Citations: 20
Shinopoulos KE, Yu J, Nixon PJ, et al., 2014, Using site-directed mutagenesis to probe the role of the D2 carotenoid in the secondary electron-transfer pathway of photosystem II, Photosynthesis Research, Vol: 120, Pages: 141-152, ISSN: 1573-5079
Secondary electron transfer in photosystem II(PSII), which occurs when water oxidation is inhibited,involves redox-active carotenoids (Car), as well as chlorophylls(Chl), and cytochrome b559 (Cyt b559), and is believedto play a role in photoprotection. CarD2 may be the initialpoint of secondary electron transfer because it is the closestcofactor to both P680, the initial oxidant, and to Cyt b559, theterminal secondary electron donor within PSII. In order tocharacterize the role of CarD2 and to determine the effects ofperturbing CarD2 on both the electron-transfer events and onthe identity of the redox-active cofactors, it is necessary tovary the properties of CarD2 selectively without affecting theten other Car per PSII. To this end, site-directed mutationsaround the binding pocket of CarD2 (D2-G47W, D2-G47F,and D2-T50F) have been generated in Synechocystissp. PCC6803. Characterization by near-IR and EPR spectroscopyprovides the first experimental evidence that CarD2 is one ofthe redox-active carotenoids in PSII. There is a specificperturbation of the Car•? near-IR spectrum in all threemutated PSII samples, allowing the assignment of thespectral signature of CarD2•?; CarD2•? exhibits a near-IR peak at 980 nm and is the predominant secondary donor oxidized ina charge separation at low temperature in ferricyanide-treatedwild-type PSII. The yield of secondary donor radicals issubstantially decreased in PSII complexes isolated from eachmutant. In addition, the kinetics of radical formation arealtered in the mutated PSII samples. These results are consistentwith oxidation of CarD2 being the initial step in secondaryelectron transfer. Furthermore, normal light levelsduring mutant cell growth perturb the shape of the Chl•?near-IR absorption peak and generate a dark-stable radicalobservable in the EPR spectra, indicating a higher susceptibilityto photodamage further linking the secondary electron-transferpathway to photoprotection.
Knoppova J, Sobotka R, Tichy M, et al., 2014, Discovery of a chlorophyll binding protein complex involved in the early steps of photosystem II assembly in synechocystis, The Plant Cell, Vol: 26, Pages: 1200-1212, ISSN: 1040-4651
Efficient assembly and repair of the oxygen-evolving photosystem II (PSII) complex is vital for maintaining photosynthetic activity in plants, algae, and cyanobacteria. How chlorophyll is delivered to PSII during assembly and how vulnerable assembly complexes are protected from photodamage are unknown. Here, we identify a chlorophyll and β-carotene binding protein complex in the cyanobacterium Synechocystis PCC 6803 important for formation of the D1/D2 reaction center assembly complex. It is composed of putative short-chain dehydrogenase/reductase Ycf39, encoded by the slr0399 gene, and two members of the high-light-inducible protein (Hlip) family, HliC and HliD, which are small membrane proteins related to the light-harvesting chlorophyll binding complexes found in plants. Perturbed chlorophyll recycling in a Ycf39-null mutant and copurification of chlorophyll synthase and unassembled D1 with the Ycf39-Hlip complex indicate a role in the delivery of chlorophyll to newly synthesized D1. Sequence similarities suggest the presence of a related complex in chloroplasts.
Hamilton ML, Franco E, Deák Z, et al., 2014, Investigating the photoprotective role of cytochrome b-559 in photosystem II in a mutant with altered ligation of the haem, Plant and Cell Physiology, Vol: 55, Pages: 1276-1285, ISSN: 0032-0781
Despite many years of study, the physiological role of cytochrome b-559 (Cyt b-559) within the photosystem II (PSII) complex still remains unclear. Here we describe the analysis of a mutant of the green alga Chlamydomonas reinhardtii in which the His ligand to the haem, provided by the alpha subunit, has been replaced by a Cys residue. The mutant is unable to grow photoautotrophically but can assemble oxygen-evolving PSII supercomplexes to 15-20% of the levels found in the wild-type control. Haem is still detected in the isolated PSII supercomplexes but at sub-stoichiometric levels consistent with weaker binding to the mutated cytochrome. Analysis of PSII activity in cells indicates slowed electron transfer in the mutant between plastoquinones QA and QB. We show that PSII activity in the mutant is more sensitive to chronic photoinhibition than the WT control because of two effects: a faster rate of damage and an impaired PSII repair cycle at the level of synthesis and/or incorporation of D1 into PSII. We also demonstrate that Cyt b-559 plays a role during the critical stage of assembling the Mn 4CaO5 cluster. Overall we conclude that Cyt b-559 optimises electron transfer on the acceptor side of PSII and plays physiologically important roles in the assembly, repair and maintenance of the complex. © 2014 The Author 2014.
Bialek W, Wen S, Michoux F, et al., 2013, Crystal structure of the Psb28 accessory factor of <i>Thermosynechococcus elongatus</i> photosystem II at 2.3 Å, PHOTOSYNTHESIS RESEARCH, Vol: 117, Pages: 375-383, ISSN: 0166-8595
- Author Web Link
- Cite
- Citations: 8
Krupnik T, Kotabova E, van Bezouwen LS, et al., 2013, A Reaction Center-dependent Photoprotection Mechanism in a Highly Robust Photosystem II from an Extremophilic Red Alga, <i>Cyanidioschyzon merolae</i>, JOURNAL OF BIOLOGICAL CHEMISTRY, Vol: 288, Pages: 23529-23542, ISSN: 0021-9258
- Author Web Link
- Cite
- Citations: 47
Wobbe L, Nixon PJ, 2013, The mTERF protein MOC1 terminates mitochondrial DNA transcription in the unicellular green alga Chlamydomonas reinhardtii, Nucleic Acids Research, Vol: 41, Pages: 6553-6567, ISSN: 1362-4962
The molecular function of mTERFs (mitochondrialtranscription termination factors) has so far onlybeen described for metazoan members of theprotein family and in animals they control mitochondrialreplication, transcription and translation. Cells ofphotosynthetic eukaryotes harbour chloroplasts andmitochondria, which are in an intense cross-talk thatis vital for photosynthesis. Chlamydomonasreinhardtii is a unicellular green alga widely used asa model organism for photosynthesis research andgreen biotechnology. Among the six nuclear C.reinhardtii mTERF genes is mTERF-like gene ofChlamydomonas (MOC1), whose inactivation altersmitorespiration and interestingly also light-acclimationprocesses in the chloroplast that favour theenhanced production of biohydrogen. We show herefrom in vitro studies that MOC1 binds specifically to asequence within the mitochondrial rRNA-codingmodule S3, and that a knockout of MOC1 in themutant stm6 increases read-through transcription atthis site, indicating that MOC1 acts as a transcriptionterminator in vivo. Whereas the level of certainantisense RNA species is higher in stm6, the amountof unprocessed mitochondrial sense transcripts isstrongly reduced, demonstrating that a loss of MOC1causes perturbed mitochondrial DNA (mtDNA) expression.Overall, we provide evidence for the existenceof mitochondrial antisense RNAs in C. reinhardtiiand show that mTERF-mediated transcription terminationis an evolutionary-conserved mechanismoccurring in phototrophic protists and metazoans.
Suzuki H, Yu J, Kobayashi T, et al., 2013, Functional Roles of D2-Lys317 and the Interacting Chloride Ion in the Water Oxidation Reaction of Photosystem II As Revealed by Fourier Transform Infrared Analysis, BIOCHEMISTRY, Vol: 52, Pages: 4748-4757, ISSN: 0006-2960
Photosynthetic water oxidation in plants andcyanobacteria is catalyzed by a Mn4CaO5 cluster within thephotosystem II (PSII) protein complex. Two Cl− ions boundnear the Mn4CaO5 cluster act as indispensable cofactors, buttheir functional roles remain to be clarified. We haveinvestigated the role of the Cl− ion interacting with D2-K317 (designated Cl-1) by Fourier transform infraredspectroscopy (FTIR) analysis of the D2-K317R mutant ofSynechocystis sp. PCC 6803 in combination with Cl−/NO3−replacement. The D2-K317R mutation perturbed the bands inthe regions of the COO− stretching and backbone amidevibrations in the FTIR difference spectrum upon the S1 → S2 transition. In addition, this mutation altered the 15N isotope-editedNO3− bands in the spectrum of NO3−-treated PSII. These results provide the first experimental evidence that the Cl-1 site iscoupled with the Mn4CaO5 cluster and its interaction is affected by the S1 → S2 transition. It was also shown that a negative bandat 1748 cm−1 arising from COOH group(s) was altered to a positive intensity by the D2-K317R mutation as well as by NO3−treatment, suggesting that the Cl-1 site affects the pKa of COOH/COO− group(s) near the Mn4CaO5 cluster in a commonhydrogen bond network. Together with the observation that the efficiency of the S3 → S0 transition significantly decreased in thecore complexes of D2-K317R upon moderate dehydration, it is suggested that D2-K317 and Cl-1 are involved in a protontransfer pathway from the Mn4CaO5 cluster to the lumen, which functions in the S3 → S0 transition.
Michoux F, Ahmad N, Hennig A, et al., 2013, Production of leafy biomass using temporary immersion bioreactors: an alternative platform to express proteins in transplastomic plants with drastic phenotypes, PLANTA, Vol: 237, Pages: 903-908, ISSN: 0032-0935
- Author Web Link
- Cite
- Citations: 26
Kargul J, Boehm M, Morgner N, et al., 2013, Compositional and structural analyses of the photosystem II isolated from the red alga cyanidioschyzon merolae, Advanced Topics in Science and Technology in China, Pages: 59-63
Members of the rhodophytan order Cyanidiales are unique among phototrophs in their ability to live in extremely low pH levels and moderately high temperatures. The photosynthetic apparatus of the red alga Cyanidioschyzon merolae represents an intermediate type between cyanobacteria and higher plants, suggesting that this alga may provide the evolutionary link between prokaryotic and eukaryotic phototrophs. While red algal PSI resembles that of the higher plants, the PSII complex is more reminiscent of the cyanobacterial ancestor in that it contains phycobilisomes as the light-harvesting system instead of Chla/b binding proteins of green algae and higher plants, as well as the PsbU and PsbV subunits stabilising the oxygen evolving complex (OEC). The most remarkable feature of the red algal PSII is the presence of the fourth extrinsic protein of 20 kDa (PsbQ’) which is not found in the cyanobacterial OEC and which is distantly related with the green algal PsbQ. This feature together with some differences in the structural cooperation between the OEC subunits suggests that the lumenal side of red algal PSII may vary from the prokaryotic ancestor. In order to elucidate the structural differences between cyanobacterial and eukaryotic PSII, we have isolated highly active and stable dimeric complexes of the C. merolae PSII and subjected them to high throughput crystallization and mass spectrometry analyses. Here we report the full subunit composition and preliminary results of 3D crystallization of the dimeric C. merolae PSII.
Eckert C, Boehm M, Carrieri D, et al., 2012, Genetic Analysis of the Hox Hydrogenase in the Cyanobacterium <i>Synechocystis</i> sp PCC 6803 Reveals Subunit Roles in Association, Assembly, Maturation, and Function, JOURNAL OF BIOLOGICAL CHEMISTRY, Vol: 287, Pages: 43502-43515
- Author Web Link
- Cite
- Citations: 30
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.