Imperial College London

ProfessorPeterNixon

Faculty of Natural SciencesDepartment of Life Sciences

Professor of Biochemistry
 
 
 
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Contact

 

+44 (0)20 7594 5269p.nixon

 
 
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Location

 

705Sir Ernst Chain BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

172 results found

Zhao Z, Vercellino I, Knoppová J, Sobotka R, Murray JW, Nixon PJ, Sazanov LA, Komenda Jet al., 2023, The Ycf48 accessory factor occupies the site of the oxygen-evolving manganese cluster during photosystem II biogenesis, Nature Communications, Vol: 14, Pages: 1-11, ISSN: 2041-1723

Robust oxygenic photosynthesis requires a suite of accessory factors to ensure efficient assembly and repair of the oxygen-evolving photosystem two (PSII) complex. The highly conserved Ycf48 assembly factor binds to the newly synthesized D1 reaction center polypeptide and promotes the initial steps of PSII assembly, but its binding site is unclear. Here we have used cryo-electron microscopy to determine the structure of a cyanobacterial PSII D1/D2 reaction center assembly complex with Ycf48 attached. Ycf48, a 7-bladed beta propeller, binds to the amino-acid residues of D1 that ultimately ligate the water-oxidising Mn4CaO5 cluster, thereby preventing the premature binding of Mn2+ and Ca2+ ions and protecting the site from damage. Interactions with D2 help explain how Ycf48 promotes assembly of the D1/D2 complex. Overall, our work provides valuable insights into the early stages of PSII assembly and the structural changes that create the binding site for the Mn4CaO5 cluster.

Journal article

Chen T, Hojka M, Davey P, Sun Y, Dykes GF, Zhou F, Lawson T, Nixon PJ, Lin Y, Liu L-Net al., 2023, Engineering α-carboxysomes into chloroplasts to support autotrophic photosynthesis, Nature Communications, ISSN: 2041-1723

Journal article

Masuda T, Beckova M, Turóczy Z, Pilný J, Sobotka R, Trinugroho JP, Nixon PJ, Prasil O, Komenda Jet al., 2023, Accumulation of cyanobacterial photosystem II containing the “rogue” D1 subunit is controlled by FtsH protease and synthesis of the standard D1 protein, Plant and Cell Physiology, ISSN: 0032-0781

Journal article

Qi M, Zhao Z, Nixon PJ, 2023, The photosynthetic electron transport chain of oxygenic photosynthesis, Bioelectricity, Vol: 5, Pages: 31-38, ISSN: 2576-3105

Oxygenic photosynthesis, performed by plants, algae, and cyanobacteria, is the major route by which solar energy is converted into chemical energy on earth. This process provides the essentials (e.g., food and fuels) for humans to survive and is responsible for oxygenating the earth's atmosphere, which allowed the evolution of multicellular life. Photon energy is harvested during the so-called “light reactions” and used to extract electrons from water, which are then transported through an electron transport chain—in a type of bioelectric current—that is coupled to the movement of protons across the thylakoid membrane, storing energy in the form of a proton electrochemical gradient. The net result of the light reactions is the synthesis of adenosine triphosphate and reduced nicotinamide adenine dinucleotide phosphate, which are used by the “dark” or “light-independent” reactions to convert carbon dioxide into carbohydrates in the Calvin–Benson cycle. In this study, we summarize the structure and function of the main redox-active proteins involved in electron transfer and highlight some recent developments aiming to enhance the efficiency and robustness of the light reactions.

Journal article

Chen T, Riaz S, Davey P, Zhao Z, Sun Y, Dykes GF, Zhou F, Hartwell J, Lawson T, Nixon PJ, Lin Y, Liu L-Net al., 2023, Producing fast and active Rubisco in tobacco to enhance photosynthesis., Plant Cell, Vol: 35, Pages: 795-807

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) performs most of the carbon fixation on Earth. However, plant Rubisco is an intrinsically inefficient enzyme given its low carboxylation rate, representing a major limitation to photosynthesis. Replacing endogenous plant Rubisco with a faster Rubisco is anticipated to enhance crop photosynthesis and productivity. However, the requirement of chaperones for Rubisco expression and assembly has obstructed the efficient production of functional foreign Rubisco in chloroplasts. Here, we report the engineering of a Form 1A Rubisco from the proteobacterium Halothiobacillus neapolitanus in Escherichia coli and tobacco (Nicotiana tabacum) chloroplasts without any cognate chaperones. The native tobacco gene encoding Rubisco large subunit was genetically replaced with H. neapolitanus Rubisco (HnRubisco) large and small subunit genes. We show that HnRubisco subunits can form functional L8S8 hexadecamers in tobacco chloroplasts at high efficiency, accounting for ∼40% of the wild-type tobacco Rubisco content. The chloroplast-expressed HnRubisco displayed a ∼2-fold greater carboxylation rate and supported a similar autotrophic growth rate of transgenic plants to that of wild-type in air supplemented with 1% CO2. This study represents a step toward the engineering of a fast and highly active Rubisco in chloroplasts to improve crop photosynthesis and growth.

Journal article

Yamamoto H, Cheuk A, Shearman J, Nixon PJ, Meier T, Shikanai Tet al., 2023, Impact of engineering the ATP synthase rotor ring on photosynthesis in tobacco chloroplasts, Plant Physiology, ISSN: 0032-0889

Journal article

Krynická V, Skotnicová P, Jackson PJ, Barnett S, Yu J, Wysocka A, Kaňa R, Dickman MJ, Nixon PJ, Hunter CN, Komenda Jet al., 2023, FtsH4 protease controls biogenesis of the PSII complex by dual regulation of high light-inducible proteins., Plant Commun, Vol: 4

FtsH proteases are membrane-embedded proteolytic complexes important for protein quality control and regulation of various physiological processes in bacteria, mitochondria, and chloroplasts. Like most cyanobacteria, the model species Synechocystis sp. PCC 6803 contains four FtsH homologs, FtsH1-FtsH4. FtsH1-FtsH3 form two hetero-oligomeric complexes, FtsH1/3 and FtsH2/3, which play a pivotal role in acclimation to nutrient deficiency and photosystem II quality control, respectively. FtsH4 differs from the other three homologs by the formation of a homo-oligomeric complex, and together with Arabidopsis thaliana AtFtsH7/9 orthologs, it has been assigned to another phylogenetic group of unknown function. Our results exclude the possibility that Synechocystis FtsH4 structurally or functionally substitutes for the missing or non-functional FtsH2 subunit in the FtsH2/3 complex. Instead, we demonstrate that FtsH4 is involved in the biogenesis of photosystem II by dual regulation of high light-inducible proteins (Hlips). FtsH4 positively regulates expression of Hlips shortly after high light exposure but is also responsible for Hlip removal under conditions when their elevated levels are no longer needed. We provide experimental support for Hlips as proteolytic substrates of FtsH4. Fluorescent labeling of FtsH4 enabled us to assess its localization using advanced microscopic techniques. Results show that FtsH4 complexes are concentrated in well-defined membrane regions at the inner and outer periphery of the thylakoid system. Based on the identification of proteins that co-purified with the tagged FtsH4, we speculate that FtsH4 concentrates in special compartments in which the biogenesis of photosynthetic complexes takes place.

Journal article

Nixon P, Telfer A, 2022, Remembering James Barber (1940-2020), Photosynthesis Research, Vol: 153, Pages: 1-20, ISSN: 0166-8595

James Barber, known to colleagues and friends as Jim, passed away in January 2020 after a long battle against cancer. During his long and distinguished career in photosynthesis research, Jim made many outstanding contributions with the pinnacle achieving his dream of determining the first detailed structure of the Mn cluster involved in photosynthetic water oxidation. Here, colleagues and friends remember Jim and reflect upon his scientific career and the impact he had on their lives and the scientific community.

Journal article

Knoppová J, Sobotka R, Yu J, Bečková M, Pilný J, Trinugroho JP, Csefalvay L, Bína D, Nixon PJ, Komenda Jet al., 2022, Assembly of D1/D2 complexes of photosystem II: binding of pigments and a network of auxiliary proteins, Plant Physiology, Vol: 189, Pages: 790-804, ISSN: 0032-0889

Photosystem II (PSII) is the multi-subunit light-driven oxidoreductase that drives photosynthetic electron transport using electrons extracted from water. To investigate the initial steps of PSII assembly, we used strains of the cyanobacterium Synechocystis sp. PCC 6803 arrested at early stages of PSII biogenesis and expressing affinity-tagged PSII subunits to isolate PSII reaction center assembly (RCII) complexes and their precursor D1 and D2 modules (D1mod and D2mod). RCII preparations isolated using either a His-tagged D2 or a FLAG-tagged PsbI subunit contained the previously described RCIIa and RCII* complexes that differ with respect to the presence of the Ycf39 assembly factor and high-light-inducible proteins (Hlips) and a larger complex consisting of RCIIa bound to monomeric PSI. All RCII complexes contained the PSII subunits D1, D2, PsbI, PsbE, and PsbF and the assembly factors rubredoxin A (RubA) and Ycf48, but we also detected PsbN, Slr1470, and the Slr0575 proteins, which all have plant homologs. The RCII preparations also contained prohibitins/stomatins (Phbs) of unknown function and FtsH protease subunits. RCII complexes were active in light-induced primary charge separation and bound chlorophylls, pheophytins, beta-carotenes, and heme. The isolated D1mod consisted of D1/PsbI/Ycf48 with some Ycf39 and Phb3, while D2mod contained D2/cytochrome b559 with co-purifying PsbY, Phb1, Phb3, FtsH2/FtsH3, CyanoP, and Slr1470. As stably bound chlorophyll was detected in D1mod but not D2mod, formation of RCII appears to be important for stable binding of most of the chlorophylls and both pheophytins. We suggest that chlorophyll can be delivered to RCII from either monomeric PSI or Ycf39/Hlip complexes.

Journal article

Yi L, Liu B, Nixon PJ, Yu J, Chen Fet al., 2022, Recent advances in understanding the structural and functional evolution of FtsH proteases, Frontiers in Plant Science, Vol: 13, Pages: 1-16, ISSN: 1664-462X

The FtsH family of proteases are membrane-anchored, ATP-dependent, zinc metalloproteases. They are universally present in prokaryotes and the mitochondria and chloroplasts of eukaryotic cells. Most bacteria bear a single ftsH gene that produces hexameric homocomplexes with diverse house-keeping roles. However, in mitochondria, chloroplasts and cyanobacteria, multiple FtsH homologues form homo and heterocomplexes with specialised functions in maintaining photosynthesis and respiration. The diversification of FtsH homologues combined with selective pairing of FtsH isomers is a versatile strategy to enable functional adaptation. In this article we summarise recent progress in understanding the evolution, structure and function of FtsH proteases with a focus on the role of FtsH in photosynthesis and respiration.

Journal article

Huokko T, Ni T, Dykes GF, Simpson DM, Brownridge P, Conradi FD, Beynon RJ, Nixon PJ, Mullineaux CW, Zhang P, Liu L-Net al., 2021, Probing the biogenesis pathway and dynamics of thylakoid membranes, Nature Communications, ISSN: 2041-1723

Journal article

Knoppová J, Yu J, Janouškovec J, Halada P, Nixon PJ, Whitelegge JP, Komenda Jet al., 2021, The Photosystem II assembly factor Ycf48 from the cyanobacterium Synechocystis sp. PCC 6803 is lipidated using an atypical lipobox sequence, International Journal of Molecular Sciences, ISSN: 1422-0067

Journal article

Murray JW, Rutherford AW, Nixon PJ, 2020, Photosystem II in a state of disassembly, Joule, Vol: 4, Pages: 2082-2084, ISSN: 2542-4351

The light-driven oxidation of water to oxygen characteristic of oxygenic photosynthesis is catalyzed by a redox-active manganese/calcium cluster embedded in the Photosystem II (PSII) complex. How the cluster is assembled during the biogenesis and repair of PSII is unclear. Cryo-electron microscopy data have now provided new insights into the structure of a PSII complex lacking the cluster and have identified features that might be important for delivery and stabilization of Mn during assembly.

Journal article

Feng Y, Morgan M, Fraser PD, Hellgardt K, Nixon PJet al., 2020, Crystal structure of geranylgeranyl pyrophosphate synthase (CrtE) involved in cyanobacterial terpenoid biosynthesis, Frontiers in Plant Science, Vol: 11, ISSN: 1664-462X

Cyanobacteria are photosynthetic prokaryotes that perform oxygenic photosynthesis. Due to their ability to use the photon energy of sunlight to fix carbon dioxide into biomass, cyanobacteria are promising hosts for the sustainable production of terpenoids, also known as isoprenoids, a diverse class of natural products with potential as advanced biofuels and high-value chemicals. However, the cyanobacterial enzymes involved in the biosynthesis of the terpene precursors needed to make more complicated terpenoids are poorly characterized. Here we show that the predicted type II prenyltransferase CrtE encoded by the model cyanobacterium Synechococcus sp. PCC 7002 is homodimeric and able to synthesize C20-geranylgeranyl pyrophosphate (GGPP) from C5-isopentenyl pyrophosphate (IPP) and C5-dimethylallyl pyrophosphate (DMAPP). The crystal structure of CrtE solved to a resolution of 2.7 Å revealed a strong structural similarity to the large subunit of the heterodimeric geranylgeranyl pyrophosphate synthase 1 from Arabidopsis thaliana with each subunit containing 14 helices. Using mutagenesis, we confirmed that the fourth and fifth amino acids (Met-87 and Ser-88) before the first conserved aspartate-rich motif (FARM) play important roles in controlling chain elongation. While the WT enzyme specifically produced GGPP, variants M87F and S88Y could only generate C15-farnesyl pyrophosphate (FPP), indicating that residues with large side chains obstruct product elongation. In contrast, replacement of M87 with the smaller Ala residue allowed the formation of the longer C25-geranylfarnesyl pyrophosphate (GFPP) product. Overall, our results provide new structural and functional information on the cyanobacterial CrtE enzyme that could lead to the development of improved cyanobacterial platforms for terpenoid production.

Journal article

Włodarczyk A, Selão TT, Norling B, Nixon PJet al., 2020, Newly discovered Synechococcus sp. PCC 11901 is a robust cyanobacterial strain for high biomass production, Communications Biology, Vol: 3, ISSN: 2399-3642

Cyanobacteria, which use solar energy to convert carbon dioxide into biomass, are potential solar biorefineries for the sustainable production of chemicals and biofuels. However, yields obtained with current strains are still uncompetitive compared to existing heterotrophic production systems. Here we report the discovery and characterization of a new cyanobacterial strain, Synechococcus sp. PCC 11901, with promising features for green biotechnology. It is naturally transformable, has a short doubling time of ≈2 hours, grows at high light intensities and in a wide range of salinities and accumulates up to ≈33 g dry cell weight per litre when cultured in a shake-flask system using a modified growth medium − 1.7 to 3 times more than other strains tested under similar conditions. As a proof of principle, PCC 11901 engineered to produce free fatty acids yielded over 6 mM (1.5 g L−1), an amount comparable to that achieved by similarly engineered heterotrophic organisms.

Journal article

Ahmad N, Khan MO, Islam E, Wei Z-Y, McAusland L, Lawson T, Johnson GN, Nixon PJet al., 2020, Contrasting responses to stress displayed by tobacco overexpressing an algal plastid terminal oxidase in the chloroplast, Frontiers in Plant Science, Vol: 11, ISSN: 1664-462X

The plastid terminal oxidase (PTOX) – an interfacial diiron carboxylate protein found in the thylakoid membranes of chloroplasts – oxidizes plastoquinol and reduces molecular oxygen to water. It is believed to play a physiologically important role in the response of some plant species to light and salt (NaCl) stress by diverting excess electrons to oxygen thereby protecting photosystem II (PSII) from photodamage. PTOX is therefore a candidate for engineering stress tolerance in crop plants. Previously, we used chloroplast transformation technology to over express PTOX1 from the green alga Chlamydomonas reinhardtii in tobacco (generating line Nt-PTOX-OE). Contrary to expectation, growth of Nt-PTOX-OE plants was more sensitive to light stress. Here we have examined in detail the effects of PTOX1 on photosynthesis in Nt-PTOX-OE tobacco plants grown at two different light intensities. Under ‘low light’ (50 μmol photons m–2 s–1) conditions, Nt-PTOX-OE and WT plants showed similar photosynthetic activities. In contrast, under ‘high light’ (125 μmol photons m–2 s–1) conditions, Nt-PTOX-OE showed less PSII activity than WT while photosystem I (PSI) activity was unaffected. Nt-PTOX-OE grown under high light also failed to increase the chlorophyll a/b ratio and the maximum rate of CO2 assimilation compared to low-light grown plants, suggesting a defect in acclimation. In contrast, Nt-PTOX-OE plants showed much better germination, root length, and shoot biomass accumulation than WT when exposed to high levels of NaCl and showed better recovery and less chlorophyll bleaching after NaCl stress when grown hydroponically. Overall, our results strengthen the link between PTOX and the resistance of plants to salt stress.

Journal article

Pope M, Hodge J, Nixon PJ, 2020, An improved natural transformation protocol for the cyanobacterium Synechocystis sp. PCC 6803, Frontiers in Plant Science, Vol: 11, ISSN: 1664-462X

The naturally transformable cyanobacterium Synechocystis sp. PCC 6803 is a widely used chassis strain for the photosynthetic production of chemicals. However, Synechocystis possesses multiple genome copies per cell which means that segregating mutations across all genome copies can be time-consuming. Here we use flow cytometry in combination with DNA staining to investigate the effect of phosphate deprivation on the genome copy number of the glucose-tolerant GT-P sub-strain of Synechocystis 6803. Like the PCC 6803 wild type strain, the ploidy of GT-P cells grown in BG-11 medium is growth phase dependent with an average genome copy number of 6.05 ± 0.27 in early growth (OD740 = 0.1) decreasing to 2.49 ± 0.11 in late stationary phase (OD740 = 7). We show that a 10-fold reduction in the initial phosphate concentration of the BG-11 growth medium reduces the average genome copy number of GT-P cells from 4.51 ± 0.20 to 2.94 ± 0.13 and increases the proportion of monoploid cells from 0 to 6% after 7 days of growth. In addition, we also show that the DnaA protein, which unusually for bacteria is not required for DNA replication in Synechocystis, plays a role in restoring polyploidy upon subsequent phosphate supplementation. Based on these observations, we have developed an alternative natural transformation protocol involving phosphate depletion that decreases the time required to obtain fully segregated mutants.

Journal article

Trinugroho J, Bečková M, Shao S, Yu J, Zhao Z, Murray JW, Sobotka R, Komenda J, Nixon PJet al., 2020, Chlorophyll f synthesis by a super-rogue photosystem II complex, Nature Plants, Vol: 6, Pages: 238-244, ISSN: 2055-0278

Certain cyanobacteria synthesize chlorophyll molecules (Chl d and Chl f) that absorb in the far-red region of the solar spectrum, thereby extending the spectral range of photosynthetically active radiation1,2. The synthesis and introduction of these far-red chlorophylls into the photosynthetic apparatus of plants might improve the efficiency of oxygenic photosynthesis, especially in far-red enriched environments, such as in the lower regions of the canopy3. Production of Chl f requires the ChlF subunit, also known as PsbA4 (ref. 4) or super-rogue D1 (ref. 5), a paralogue of the D1 subunit of photosystem II (PSII) which, together with D2, bind cofactors involved in the light-driven oxidation of water. Current ideas suggest that ChlF oxidizes Chl a to Chl f in a homodimeric ChlF reaction centre (RC) complex and represents a missing link in the evolution of the heterodimeric D1/D2 RC of PSII (refs. 4,6). However, unambiguous biochemical support for this proposal is lacking. Here, we show that ChlF can substitute for D1 to form modified PSII complexes capable of producing Chl f. Remarkably, mutation of just two residues in D1 converts oxygen-evolving PSII into a Chl f synthase. Overall, we have identified a new class of PSII complex, which we term ‘super-rogue’ PSII, with an unexpected role in pigment biosynthesis rather than water oxidation.

Journal article

Selão TT, Jebarani J, Ismail NA, Norling B, Nixon PJet al., 2020, Enhanced production of D-lactate in cyanobacteria by re-routing photosynthetic cyclic and pseudo-cyclic electron flow, Frontiers in Plant Science, Vol: 10, ISSN: 1664-462X

Cyanobacteria are promising chassis strains for the photosynthetic production of platform and specialty chemicals from carbon dioxide. Their efficient light harvesting and metabolic flexibility has allowed a wide range of biomolecules, such as the bioplastic polylactate precursor D lactate, to be produced, though usually at relatively low yields. In order to increase photosynthetic electron flow towards the production of D-lactate, we have generated several strains of the marine cyanobacterium Synechococcus sp. PCC 7002 (Syn7002) with deletions in genes involved in cyclic or pseudo-cyclic electron flow around photosystem I. Using a variant of the Chlamydomonas reinhardtii D-lactate dehydrogenase (LDHSRT 25 , engineered to efficiently utilize NADPH in vivo), we show that deletion of either of the two flavodiiron flv homologues (involved in pseudo-cyclic electron transport) or the Syn7002 pgr5 homologue (proposed to be a vital part of the cyclic electron transport pathway) is able to increase D-lactate production in Syn7002 strains expressing LDHSRT 29 and the Escherichia coli LldP (lactate permease), especially at low temperature (25 °C) and 0.04% (v/v) CO2, though at elevated temperatures (38 °C) and/or high (1%) CO2 concentrations the effect was less obvious. The Δpgr5 background seemed to be particularly beneficial at 25 °C and 0.04% (v/v) CO2, with a nearly 7-fold increase in D lactate accumulation in comparison to the wild-type background (≈1000 vs ≈150 mg/L) and decreased side effects in comparison to the flv deletion strains. Overall, our results show that manipulation of photosynthetic electron flow is a viable strategy to increase production of platform chemicals in cyanobacteria under ambient conditions.

Journal article

Zhang L, Selão TT, Nixon PJ, Norling Bet al., 2019, Photosynthetic conversion of CO2 to hyaluronic acid by engineered strains of the cyanobacterium Synechococcus sp. PCC 7002, Algal Research, Vol: 44, ISSN: 2211-9264

Hyaluronic acid (HA), consisting of alternating N-acetylglucosamine and glucuronic acid units, is a natural polymer with diverse cosmetic and medical applications. Currently, HA is produced by overexpressing HA synthases from gram-negative Pasteurella multocida (encoded by pmHAS) or gram-positive Streptococcus equisimilis (encoded by seHasA) in various heterotrophic microbial production platforms. Here we introduced these two different types of HA synthase into the fast-growing cyanobacterium Synechococcus sp. PCC 7002 (Syn7002) to explore the capacity for producing HA in a photosynthetic system. Our results show that both HA synthases enable Syn7002 to produce HA photoautotrophically, but that overexpression of the soluble HA synthase (PmHAS) is less deleterious to cell growth and results in higher production. Genetic disruption of the competing cellulose biosynthetic pathway increased the HA titer by over 5-fold (from 14 mg/L to 80 mg/L) and the relative proportion of HA with molecular mass greater than 2 MDa. Introduction of glmS and glmU, coding for enzymes involved in the biosynthesis of the precursor UDP-N-acetylglucosamine, in combination with partial glycogen depletion, allowed photosynthetic production of 112 mg/L of HA in 5 days, an 8-fold increase in comparison to the initial PmHAS expressing strain. Addition of tuaD and gtaB (coding for genes involved in UDP-glucuronic acid biosynthesis) also improved the HA yield, albeit to a lesser extent. Overall our results have shown that cyanobacteria hold promise for the sustainable production of pharmaceutically important polysaccharides from sunlight and CO2.

Journal article

Viola S, Bailleul B, Yu J, Nixon P, Sellés J, Joliot P, Wollman F-Aet al., 2019, Probing the electric field across thylakoid membranes in cyanobacteria., Proc Natl Acad Sci U S A, Vol: 116, Pages: 21900-21906

In plants, algae, and some photosynthetic bacteria, the ElectroChromic Shift (ECS) of photosynthetic pigments, which senses the electric field across photosynthetic membranes, is widely used to quantify the activity of the photosynthetic chain. In cyanobacteria, ECS signals have never been used for physiological studies, although they can provide a unique tool to study the architecture and function of the respiratory and photosynthetic electron transfer chains, entangled in the thylakoid membranes. Here, we identified bona fide ECS signals, likely corresponding to carotenoid band shifts, in the model cyanobacteria Synechococcus elongatus PCC7942 and Synechocystis sp. PCC6803. These band shifts, most likely originating from pigments located in photosystem I, have highly similar spectra in the 2 species and can be best measured as the difference between the absorption changes at 500 to 505 nm and the ones at 480 to 485 nm. These signals respond linearly to the electric field and display the basic kinetic features of ECS as characterized in other organisms. We demonstrate that these probes are an ideal tool to study photosynthetic physiology in vivo, e.g., the fraction of PSI centers that are prebound by plastocyanin/cytochrome c6 in darkness (about 60% in both cyanobacteria, in our experiments), the conductivity of the thylakoid membrane (largely reflecting the activity of the ATP synthase), or the steady-state rates of the photosynthetic electron transport pathways.

Journal article

Kiss E, Knoppova J, Pascual Aznar G, Pilny J, Yu J, Halada P, Nixon PJ, Sobotka R, Komenda Jet al., 2019, A photosynthesis-specific rubredoxin-like protein is required for efficient association of the D1 and D2 proteins during the initial steps of photosystem II assembly, The Plant Cell, Vol: 31, Pages: 2241-2258, ISSN: 1040-4651

Oxygenic photosynthesis relies on accessory factors to promote the assembly and maintenance ofthe photosynthetic apparatus in the thylakoid membranes. The highly conserved membrane-boundrubredoxin-like protein RubA has previously been implicated in the accumulation of bothphotosystem I (PSI) and photosystem II (PSII) but its mode of action remains unclear. Here weshow that RubA in the cyanobacterium Synechocystis sp. PCC 6803 is required forphotoautotrophic growth in fluctuating light and acts early in PSII biogenesis by promoting theformation of the heterodimeric D1/D2 reaction center complex, the site of primary photochemistry.We find that RubA, like the accessory factor Ycf48, is a component of the initial D1 assemblymodule as well as larger PSII assembly intermediates and that the redox-responsive rubredoxinlike domain is located on the cytoplasmic surface of PSII complexes. Fusion of RubA to Ycf48still permits normal PSII assembly suggesting a spatiotemporal proximity of both proteins duringtheir action. RubA is also important for the accumulation of PSI but this is an indirect effectstemming from the downregulation of light-dependent chlorophyll biosynthesis induced by PSII deficiency. Overall our data support the involvement of RubA in the redox control of PSIIbiogenesis.

Journal article

Selão TT, Włodarczyk A, Nixon PJ, Norling Bet al., 2019, Growth and selection of the cyanobacterium Synechococcus sp. PCC 7002 using alternative nitrogen and phosphorus sources, Metabolic Engineering, Vol: 54, Pages: 255-263, ISSN: 1096-7176

Cyanobacteria, such as Synechococcus sp. PCC 7002 (Syn7002), are promising chassis strains for “green” biotechnological applications as they can be grown in seawater using oxygenic photosynthesis to fix carbon dioxide into biomass. Their other major nutritional requirements for efficient growth are sources of nitrogen (N) and phosphorus (P). As these organisms are more economically cultivated in outdoor open systems, there is a need to develop cost-effective approaches to prevent the growth of contaminating organisms, especially as the use of antibiotic selection markers is neither economically feasible nor ecologically desirable due to the risk of horizontal gene transfer. Here we have introduced a synthetic melamine degradation pathway into Syn7002 and evolved the resulting strain to efficiently use the nitrogen-rich xenobiotic compound melamine as the sole N source. We also show that expression of phosphite dehydrogenase in the absence of its cognate phosphite transporter permits growth of Syn7002 on phosphite and can be used as a selectable marker in Syn7002. We combined these two strategies to generate a strain that can grow on melamine and phosphite as sole N and P sources, respectively. This strain is able to resist deliberate contamination in large excess and should be a useful chassis for metabolic engineering and biotechnological applications using cyanobacteria.

Journal article

Zhang L, Selao T, Norling B, Nixon PJet al., 2019, Photosynthetic hyaluronic acid production by metabolically engineered cyanobacteria

Patent

Barber J, Nixon PJ, Ruban AV, 2019, Preface, ISBN: 9789813276918

Book

Barber J, Ruban AV, Nixon PJ, 2019, Oxygen Production and Reduction in Artificial and Natural Systems, Publisher: World Scientific Publishing

Book

, 2019, Oxygen Production and Reduction in Artificial and Natural Systems, Publisher: World Scientific

Book

Shao S, Yu J, Nixon PJ, 2019, Selective replacement of the damaged D1 reaction center subunit during the repair of the oxygen-evolving photosystem II complex, Oxygen Production and Reduction in Artificial and Natural Systems, Editors: Barber, Ruban, Nixon, Publisher: World Scientific, Pages: 319-338

The multi-subunit photosystem II (PSII) pigment-protein complex found in plants, algae and cyanobacteria is nature’s biological catalyst for producing oxygen from water. PSII needs sunlight to drive water oxidation but too much light can cause irreversible damage to pigments and proteins within PSII and loss of enzyme activity. Damaged PSII complexes can, however, be repaired in a highly selective process involving the replacement of damaged components by newly synthesized copies and the recycling of undamaged protein subunits and co-factors. Although substantial progress has been made to identify the enzymes and accessory factors involved in repair, many fundamental questions remain unanswered. In this chapter we discuss recent ideas on how the damaged D1 reaction center subunit, which is the subunit most prone to damage in PSII, is specifically recognized for replacement. Detachment of CP43 allowing access by FtsH proteases to the N-terminal tail of D1 seems to underpin selective degradation.

Book chapter

Selao TT, Norling B, Nixon PJ, 2018, Genetically engineered cyanobacteria for growth in unsterilized conditions using antibiotic-free selection

Patent

Yu J, Knoppova J, Michoux F, Bialek W, Cota Segura E, Shukla M, Straskova A, Aznar G, Sobotka R, Komenda J, Murray J, Nixon PJet 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.

Journal article

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