Structure of a monomeric photosystem II core complex from a cyanobacterium acclimated to far-red light reveals the functions of chlorophylls d and f

Far-red light (FRL) photoacclimation in cyanobacteria provides a selective growth advantage for some terrestrial cyanobacteria by expanding the range of photosynthetically active radiation to include far-red/near-infrared light (700-800 nm). During this photoacclimation process, photosystem II (PSII), the water:plastoquinone photooxidoreductase involved in oxygenic photosynthesis, is modified. The resulting FRL-PSII is comprised of FRL-specific core subunits and binds chlorophyll (Chl) d and Chl f molecules in place of several of the Chl a molecules found when cells are grown in visible light. These new Chls effectively lower the energy canonically thought to define the red limit for light required to drive photochemical catalysis of water oxidation. Changes to the architecture of FRL-PSII were previously unknown, and the positions of Chl d and Chl f molecules had only been proposed from indirect evidence. Here, we describe the 2.25 angstrom resolution cryo-EM structure of a monomeric FRL-PSII core complex from Synechococcus sp. PCC 7335 cells that were acclimated to FRL. We identify one Chl d molecule in the Chl(D1) position of the electron transfer chain and four Chl f molecules in the core antenna. We also make observations that enhance our understanding of PSII biogenesis, especially on the acceptor side of the complex where a bicarbonate molecule is replaced by a glutamate side chain in the absence of the assembly factor Psb28. In conclusion, these results provide a structural basis for the lower energy limit required to drive water oxidation, which is the gateway for most solar energy utilization on earth

About some problems in physical preparation young experts

This article describes the problems in the physical training of young specialistsВ данной статье раскрываются проблемы в физической подготовке молодых специалисто

Structure of a dimeric photosystem II complex from a cyanobacterium acclimated to far-red light

Photosystem II (PSII) is the water-splitting enzyme central to oxygenic photosynthesis. To drive water oxidation, light is harvested by accessory pigments, mostly chlorophyll (Chl) a molecules, which absorb visible light (400–700 nm). Some cyanobacteria facultatively acclimate to shaded environments by altering their photosynthetic machinery to additionally absorb far-red light (FRL, 700–800 nm), a process termed far-red light photoacclimation or FaRLiP. During far-red light photoacclimation, FRL-PSII is assembled with FRL-specific isoforms of the subunits PsbA, PsbB, PsbC, PsbD, and PsbH, and some Chl-binding sites contain Chls d or f instead of the usual Chl a. The structure of an apo-FRL-PSII monomer lacking the FRL-specific PsbH subunit has previously been determined, but visualization of the dimeric complex has remained elusive. Here, we report the cryo-EM structure of a dimeric FRL–PSII complex. The site assignments for Chls d and f are consistent with those assigned in the previous apo-FRL-PSII monomeric structure. All sites that bind Chl d or Chl f at high occupancy exhibit a FRL-specific interaction of the formyl moiety of the Chl d or Chl f with the protein environment, which in some cases involves a phenylalanine sidechain. The structure retains the FRL-specific PsbH2 subunit, which appears to alter the energetic landscape of FRL-PSII, redirecting energy transfer from the phycobiliprotein complex to a Chl f molecule bound by PsbB2 that acts as a bridge for energy transfer to the electron transfer chain. Collectively, these observations extend our previous understanding of the structure-function relationship that allows PSII to function using lower energy FRL

Characterization of chlorophyll f synthase heterologously produced in Synechococcus sp. PCC 7002.

In diverse terrestrial cyanobacteria, Far-Red Light Photoacclimation (FaRLiP) promotes extensive remodeling of the photosynthetic apparatus, including photosystems (PS)I and PSII and the cores of phycobilisomes, and is accompanied by the concomitant biosynthesis of chlorophyll (Chl) d and Chl f. Chl f synthase, encoded by chlF, is a highly divergent paralog of psbA; heterologous expression of chlF from Chlorogloeopsis fritscii PCC 9212 led to the light-dependent production of Chl f in Synechococcus sp. PCC 7002 (Ho et al., Science 353, aaf9178 (2016)). In the studies reported here, expression of the chlF gene from Fischerella thermalis PCC 7521 in the heterologous system led to enhanced synthesis of Chl f. N-terminally [His]10-tagged ChlF7521 was purified and identified by immunoblotting and tryptic-peptide mass fingerprinting. As predicted from its sequence similarity to PsbA, ChlF bound Chl a and pheophytin a at a ratio of ~ 3-4:1, bound β-carotene and zeaxanthin, and was inhibited in vivo by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Cross-linking studies and the absence of copurifying proteins indicated that ChlF forms homodimers. Flash photolysis of ChlF produced a Chl a triplet that decayed with a lifetime (1/e) of ~ 817 µs and that could be attributed to intersystem crossing by EPR spectroscopy at 90 K. When the chlF7521 gene was expressed in a strain in which the psbD1 and psbD2 genes had been deleted, significantly more Chl f was produced, and Chl f levels could be further enhanced by specific growth-light conditions. Chl f synthesized in Synechococcus sp. PCC 7002 was inserted into trimeric PSI complexes

Structure of a monomeric photosystem II core complex from a cyanobacterium acclimated to far-red light reveals the functions of chlorophylls d and f

Far-red light (FRL) photoacclimation in cyanobacteria provides a selective growth advantage for some terrestrial cyanobacteria by expanding the range of photosynthetically active radiation to include far-red/near-infrared light (700–800 nm). During this photoacclimation process, photosystem II (PSII), the water:plastoquinone photooxidoreductase involved in oxygenic photosynthesis, is modified. The resulting FRL-PSII is comprised of FRL-specific core subunits and binds chlorophyll (Chl) d and Chl f molecules in place of several of the Chl a molecules found when cells are grown in visible light. These new Chls effectively lower the energy canonically thought to define the “red limit” for light required to drive photochemical catalysis of water oxidation. Changes to the architecture of FRL-PSII were previously unknown, and the positions of Chl d and Chl f molecules had only been proposed from indirect evidence. Here, we describe the 2.25 Å resolution cryo-EM structure of a monomeric FRL-PSII core complex from Synechococcus sp. PCC 7335 cells that were acclimated to FRL. We identify one Chl d molecule in the ChlD1 position of the electron transfer chain and four Chl f molecules in the core antenna. We also make observations that enhance our understanding of PSII biogenesis, especially on the acceptor side of the complex where a bicarbonate molecule is replaced by a glutamate side chain in the absence of the assembly factor Psb28. In conclusion, these results provide a structural basis for the lower energy limit required to drive water oxidation, which is the gateway for most solar energy utilization on earth

Использование методологии SAR для идентификации аллелохемиков пресноводных макрофитов с высоким антицианобактериальным эффектом в отношении планктонных цианобактерий

Controlling harmful cyanobacterial “blooms” through developing a new generation of algaecides based on allelochemical substances is a challenge facing modern aquatic ecology and biotechnology. The present article is devoted to the use of the SAR (Structure-Activity-Relationship) information technology to identify allelochemicals from aquatic macrophytes (floating-leaved Nuphar lutea (L.) Sm. and several species of submerged macrophytes: Ceratophyllum demersum L., Myriophyllum spicatum L., Elodea canadensis Michx, and species of the genus Potamogeton) effective against planktonic cyanobacteria. Detection and identification of compounds were performed using gas chromatography-mass spectrometry. The PASS (Prediction of Activity Spectra for Substances) computer program has been applied to predict biological activity spectra of the major components of macrophyte metabolomes and discover their ecological potential against cyanobacteria. A study of the biological activities of major low-molecular-weight organic compounds showed that monocarboxylic acids, gallic acid, cis‑6-octadecenoic acid, cis‑9-octadecenoic acid, palmitoleic acid, linolenic acid, and 9-cis‑12-cis-linoleic acid are the most promising compounds for the experimental verification and creation of nature-like algaecides of a new generation. PASS predictions were successfully compared to the available information on the biological activity of those compounds and confirmed experimentally. The present study shows that some organic acids significantly inhibit the growth of Synechocystis aquatilis Sauvageau and Aphanizomenon flos-aquae Ralfs ex Bornet and Flahault and can be used as algaecides for suppression of cyanobacteria. The inhibitory effect of the combined mixture of these allelochemicals is stronger than the effect of each individual component, suggesting that there are various mechanisms of cyanobacterial growth inhibitionПроблема борьбы с опасными цианобактериальными «цветениями» посредством разработки нового поколения альгицидов, основанных на аллелохемиках растений, актуальна на современной стадии развития водной экологии и биотехнологии. Статья посвящена использованию информационной технологии SAR (cвязь структура – активность) для выявления эффективных аллелохемиков водных макрофитов (с плавающими листьями – Nuphar lutea (L.) Sm., и нескольких видов погруженных макрофитов: Ceratophyllum demersum L., Myriophyllum spicatum L., Elodea canadensis Michx и виды рода Potamogeton) против планктонных цианобактерий. Обнаружение и идентификацию соединений проводили с использованием метода газовой хромато-масс- спектрометрии. Компьютерная программа PASS (прогнозирование спектров активности для веществ) была применена для прогнозирования спектров биологической активности мажорных компонентов метаболома макрофитов, чтобы обнаружить их экологический потенциал против цианобактерий. Изучение биологической активности основных низкомолекулярных органических соединений показало, что монокарбоновые кислоты, галловая кислота, цис‑6-октадеценовая кислота, цис‑9-октадеценовая кислота, пальмитолеиновая кислота, линоленовая кислота и 9-цис‑12- цис-линолевая кислота являются наиболее перспективными соединениями для экспериментальной проверки и создания природоподобных альгицидов нового поколения. Прогнозные оценки PASS были успешно сопоставлены с доступной информацией о биологической активности этих соединений, а также подтверждены экспериментально. Было показано, что некоторые жирные кислоты значительно ингибировали рост Synechocystis aquatilis Sauvageau и Aphanizomenon flos-aque Ralfs ex Bornet and Flahault и могут использоваться в качестве альгицидов для подавления цианобактерий. Поскольку ингибирующий эффект комбинированной смеси аллелохемиков был сильнее, чем у отдельных компонентов, имеются основания предполагать, что существуют различные механизмы ингибирования роста цианобактери

Polyoxa- and Polyazamacrocycles Incorporating 6,7-Diaminoquinoxaline Moiety: Synthesis and Application as Tunable Optical pH-Indicators in Aqueous Solution

Synthetic approach to fluorescent polyaza- and polyoxadiazamacrocycles comprising a structural fragment of 6,7-diamino-2,3-diphenylquinoxaline has been elaborated using Pd-catalyzed amination providing target compounds in yields up to 77%. A series of nine novel N- and N,O-containing macrocyclic ligands differing by the number of donor sites and cavity size has been obtained. These compounds possess well-pronounced fluorescent properties with emission maxima in a blue region in aprotic solvents and high quantum yields of fluorescence, while in proton media, fluorescence shifts towards the green region of the spectrum. Using macrocycles 5c and 5e as examples, we have shown that such compounds can serve as dual-channel (colorimetric and fluorimetric) pH indicators in water media, with pH transition point and response being dependent on the macrocycle structure due to different sequences of protonation steps

Optimal reconstruction of signals from a set of linear measurements

The problem of statistically optimal reconstruction of a signal based on its arbitrary linear projection is considered. The general solution to the problem is obtained in the form of the optimal reverse filter. The equation defining the filter represents an extension of the Wiener-Hopf equation to the case when N observations are a noise-bearing projection of a continuous random signal onto the space RN