Association of Psb28 and Psb27 proteins with PSII-PSI supercomplexes upon exposure of Synechocystis sp. PCC 6803 to high light

Formation of the multi-subunit oxygen-evolving Photosystem II (PSII) complex involves a number of auxiliary protein factors. In this study we compared the location and possible function of two homologous PSII assembly factors, Psb28-1 and Psb28-2, from the cyanobacterium Synechocystis sp. PCC 6803. We show that FLAG-tagged Psb28-2 is present in both the monomeric PSII core complex and a PSII core complex lacking the inner antenna CP43 (RC47) whereas Psb28-1 preferentially binds to RC47. When cells are exposed to increased irradiance, both tagged Psb28 proteins now associate with oligomeric forms of PSII and with PSII-PSI supercomplexes composed of trimeric Photosystem I (PSI) and two PSII monomers as deduced from negative stain electron microscopy. The presence of the Psb27 accessory protein in these complexes suggests the involvement of PSI in PSII biogenesis, possibly by photoprotecting PSII through energy spillover. Under standard cultivation conditions the distribution of PSII complexes is similar in WT and each of the single psb28 null mutants except for loss of RC47 in the absence of Psb28-1. In comparison with WT, growth of mutants lacking Psb28-1 and Psb27, but not Psb28-2, was retarded under high-light and, especially, intermittent highlight-dark conditions, emphasizing the physiological importance of PSII assembly factors for light acclimation

Chlorophyll f synthesis by a super-rogue photosystem II complex

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

Assembly of D1/D2 complexes of photosystem II: binding of pigments and a network of auxiliary proteins

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

Doses from Cs-137 and Sr-90 to Czech population due to milk consumption

Activity concentrations of 137Cs and 90Sr in milk have been monitored in the Czech Republic on a long-term basis. The annual geometric means of 137Cs activity concentrations in milk range from 12 Bq.L−1 in 1986 to 0.02 Bq.L−1 in 2014. The annual geometric means of 90Sr activity concentrations range from 0.69 Bq.L−1 in 1965 to 0.02 Bq.L−1 in 2014. The values of effective and environmental half-lives in milk were calculated for both radionuclides from the annual geometric means and their temporal trends. Doses from both radionuclides due to milk ingestion were estimated

Pod Stalinem:field notes from another modernity

David Frisby’s work was a career-long engagement with modernity, informed by a tradition of classical social theory whose neglect in Anglo-American sociology David did much to remedy through his translations as well as his writings: the ‘sociological impressionism’ that seeks to grasp totalities through ‘snapshots’ and ‘fragments’ whose representatives included Georg Simmel, Siegfried Kracauer, and Walter Benjamin. Conceived as a homage to David’s legacy (and his personal influence on my own intellectual development) rather than a commentary on his work, this essay is a Benjaminian dérive through twentieth-century Prague, which complements and counterpoints David’s beloved Vienna and Berlin. Prague’s modern history, I argue, gives Baudelaire’s celebrated definition of modernity as ‘le transitoire, le fugitif, le contingent’ surreally new dimensions. Indeed, the city might well be regarded as a ‘capital of the twentieth century’ in whose ‘ruins’ we can begin to excavate the ‘prehistory of postmodernity.

Airborne concentrations and chemical considerations of radioactive ruthenium from an undeclared major nuclear release in 2017.

In October 2017, most European countries reported unique atmospheric detections of aerosol-bound radioruthenium (Ru-106). The range of concentrations varied from some tenths of mu Bq.m(-3) to more than 150 mBq.m(-3). The widespread detection at such considerable (yet innocuous) levels suggested a considerable release. To compare activity reports of airborne Ru-106 with different sampling periods, concentrations were reconstructed based on the most probable plume presence duration at each location. Based on airborne concentration spreading and chemical considerations, it is possible to assume that the release occurred in the Southern Urals region (Russian Federation). The Ru-106 age was estimated to be about 2 years. It exhibited highly soluble and less soluble fractions in aqueous media, high radiopurity (lack of concomitant radionuclides), and volatility between 700 and 1,000 degrees C, thus suggesting a release at an advanced stage in the reprocessing of nuclear fuel. The amount and isotopic characteristics of the radioruthenium release may indicate a context with the production of a large Ce-144 source for a neutrino experiment