Oxygenic photosynthesis evolved more than 3 billion years ago in cyanobacteria. The increased complexity of photosystem I (PSI) became apparent from the high-resolution structures that were obtained ...for the complexes that were isolated from various organisms, ranging from cyanobacteria to plants. These complexes are all evolutionarily linked. In this paper, the researchers have uncovered the increased complexity of PSI in a single organism demonstrated by the coexistance of two distinct PSI compositions. The Large Dunaliella PSI contains eight additional subunits, six in PSI core and two light harvesting complexes. Two additional chlorophyll a molecules pertinent for efficient excitation energy transfer in state II transition were identified in PsaL and PsaO. Short distances between these newly identified chlorophylls correspond with fast excitation transfer rates previously reported during state II transition. The apparent PSI conformations could be a coping mechanism for the high salinity.
Photosystem II (PSII) generates an oxidant whose redox potential is high enough to enable water oxidation , a substrate so abundant that it assures a practically unlimited electron source for life on ...earth . Our knowledge on the mechanism of water photooxidation was greatly advanced by high-resolution structures of prokaryotic PSII . Here, we show high-resolution cryogenic electron microscopy (cryo-EM) structures of eukaryotic PSII from the green alga
at two distinct conformations. The conformers are also present in stacked PSII, exhibiting flexibility that may be relevant to the grana formation in chloroplasts of the green lineage. CP29, one of PSII associated light-harvesting antennae, plays a major role in distinguishing the two conformations of the supercomplex. We also show that the stacked PSII dimer, a form suggested to support the organisation of thylakoid membranes , can appear in many different orientations providing a flexible stacking mechanism for the arrangement of grana stacks in thylakoids. Our findings provide a structural basis for the heterogenous nature of the eukaryotic PSII on multiple levels.
Green alga
is known for its ability to carry out photosynthesis under harsh conditions. Using cryogenic electron microscopy (cryoEM), we obtained a high-resolution structure of PSII at 2.72 Å. This ...structure revealed 64 subunits, which encompassed 386 chlorophylls, 86 carotenoids, four plastoquinones, and several structural lipids. At the luminal side of PSII, a unique subunit arrangement was observed to protect the oxygen-evolving complex. This arrangement involved PsbO (OEE1), PsbP (OEE2), PsbB, and PsbU (a homolog of plant OEE3). PsbU interacted with PsbO, PsbC, and PsbP, thereby stabilizing the shield of the oxygen-evolving complex. Significant changes were also observed at the stromal electron acceptor side. PsbY, identified as a transmembrane helix, was situated alongside PsbF and PsbE, which enclosed cytochrome
. Supported by the adjacent C-terminal helix of Psb10, these four transmembrane helices formed a bundle that shielded cytochrome
from the surrounding solvent. Moreover, the bulk of Psb10 formed a protective cap, which safeguarded the quinone site and likely contributed to the stacking of PSII complexes. Based on our findings, we propose a protective mechanism that prevents Q
(plastoquinone B) from becoming fully reduced. This mechanism offers insights into the regulation of electron transfer within PSII.
Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) contains two flavin residues as redox-active prosthetic groups attached by a phosphoester bond to threonine residues in subunits NqrB and NqrC. ...We demonstrate here that flavinylation of truncated Vibrio harveyi NqrC at Thr-229 in Escherichia coli cells requires the presence of a co-expressed Vibrio apbE gene. The apbE genes cluster with genes for Na+-NQR and other FMN-binding flavoproteins in bacterial genomes and encode proteins with previously unknown function. Experiments with isolated NqrC and ApbE proteins confirmed that ApbE is the only protein factor required for NqrC flavinylation and also indicated that the reaction is Mg2+-dependent and proceeds with FAD but not FMN. Inactivation of the apbE gene in Klebsiella pneumoniae, wherein the nqr operon and apbE are well separated in the chromosome, resulted in a complete loss of the quinone reductase activity of Na+-NQR, consistent with its dependence on covalently bound flavin. Our data thus identify ApbE as a novel modifying enzyme, flavin transferase.
Background: The ApbE protein with unknown function is widespread in bacteria.
Results: ApbE catalyzes Mg2+-dependent FMN transfer from FAD to Thr residues of flavoproteins in vitro and in vivo.
Conclusion: ApbE is a novel modifying enzyme involved in the maturation of flavoproteins.
Significance: Broad distribution of ApbE suggests a wide utilization of flavoproteins containing FMN attached via a phospho- ester bond.
Photosynthetic hydrogen production from microalgae is considered to have potential as a renewable energy source. Yet, the process has two main limitations holding it back from scaling up; (i) ...electron loss to competing processes, mainly carbon fixation and (ii) sensitivity to O
which diminishes the expression and the activity of the hydrogenase enzyme catalyzing H
production. Here we report a third, hitherto unknown challenge: We found that under anoxia, a slow-down switch is activated in photosystem II (PSII), diminishing the maximal photosynthetic productivity by three-fold. Using purified PSII and applying in vivo spectroscopic and mass spectrometric techniques on Chlamydomonas reinhardtii cultures, we show that this switch is activated under anoxia, within 10 s of illumination. Furthermore, we show that the recovery to the initial rate takes place following 15 min of dark anoxia, and propose a mechanism in which, modulation in electron transfer at the acceptor site of PSII diminishes its output. Such insights into the mechanism broaden our understanding of anoxic photosynthesis and its regulation in green algae and inspire new strategies to improve bio-energy yields.
Redox properties of all EPR-detectable prosthetic groups of Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) from Vibrio harveyi were studied at pH 7.5 using cryo-EPR spectroelectrochemistry. ...Titration shows five redox transitions. One with E m = −275 mV belongs to the reduction of the 2Fe-2S cluster, and the four others reflect redox transitions of flavin cofactors. Two transitions (E m 1 = −190 mV and E m 2 = −275 mV) originate from the formation of FMN anion radical, covalently bound to the NqrC subunit, and its subsequent reduction. The remaining two transitions arise from the two other flavin cofactors. A high potential (E m = −10 mV) transition corresponds to the reduction of riboflavin neutral radical, which is stable at rather high redox potentials. An E m = −130 mV transition reflects the formation of FMN anion radical from a flavin covalently bound to the NqrB subunit, which stays as a radical down to very low potentials. Taking into account the EPR-silent, two-electron transition of noncovalently bound FAD located in the NqrF subunit, there are four flavins in Na+-NQR all together. Defined by dipole−dipole magnetic interaction measurements, the interspin distance between the 2Fe-2S+ cluster and the NqrB subunit-bound FMN anion radical is found to be 22.5 ± 1.5 Å, which means that for the functional electron transfer between these two centers another cofactor, most likely FMN bound to the NqrC subunit, should be located.
Chemical industry today needs new high-tech and cheap sealed containers for devices. The material on the usage of 3D technology in production of device's drum is presented in this article. Samples of ...device's containers for chemical industry were fabricated by means of 3D printer with different parameters of the 3D printing (thickness of the drum and layer's height). The leak tightness of device's containers was tested under the air pressure. The optimum regimes for 3D printing of sealed containers for devices correspond to minimum possible thickness of sealed containers. The obtained results can be used in low cost production of chemical devices with complex body shape.
The catalytic properties of sodium-translocating NADH:quinone oxidoreductases (Na⁺-NQRs) from the marine bacterium Vibrio harveyi, the enterobacterium Klebsiella pneumoniae, and the soil ...microorganism Azotobacter vinelandii have been comparatively analyzed. It is shown that these enzymes drastically differ in their affinity to sodium ions. The enzymes also possess different sensitivity to inhibitors. Na⁺-NQR from A. vinelandii is not sensitive to low 2-n-heptyl-4-hydroxyquinoline N-oxide (HQNO) concentrations, while Na⁺-NQR from K. pneumoniae is fully resistant to either Ag⁺ or N-ethylmaleimide. All the Na⁺-NQR-type enzymes are sensitive to diphenyliodonium, which is shown to modify the noncovalently bound FAD of the enzyme.
Green alga Chlorella ohadii is known for its ability to carry out photosynthesis under harsh conditions. Using cryogenic electron microscopy (cryoEM), we obtained a high-resolution structure of PSII ...at 2.72 Å. This structure revealed 64 subunits, which encompassed 386 chlorophylls, 86 carotenoids, four plastoquinones, and several structural lipids. At the luminal side of PSII, a unique subunit arrangement was observed to protect the oxygen-evolving complex. This arrangement involved PsbO (OEE1), PsbP (OEE2), PsbB, and PsbU (a homolog of plant OEE3). PsbU interacted with PsbO, PsbC, and PsbP, thereby stabilizing the shield of the oxygen-evolving complex. Significant changes were also observed at the stromal electron acceptor side. PsbY, identified as a transmembrane helix, was situated alongside PsbF and PsbE, which enclosed cytochrome b559. Supported by the adjacent C-terminal helix of Psb10, these four transmembrane helices formed a bundle that shielded cytochrome b559 from the surrounding solvent. Moreover, the bulk of Psb10 formed a protective cap, which safeguarded the quinone site and likely contributed to the stacking of PSII complexes. Based on our findings, we propose a protective mechanism that prevents Qsub.B (plastoquinone B) from becoming fully reduced. This mechanism offers insights into the regulation of electron transfer within PSII.
The expression of genes encoding sodium-translocating NADH:quinone oxidoreductase (Na⁺-NQR) was studied in the marine bacterium Vibrio harveyi and in the enterobacterium Klebsiella pneumoniae. It has ...been shown that such parameters as NaCl concentration, pH value, and presence of an uncoupler in the growth media do not influence significantly the level of nqr expression. However, nqr expression depends on the growth substrates used by these bacteria. Na⁺-NQR is highly repressed in V. harveyi during anaerobic growth, and nqr expression is modulated by electron acceptors and values of their redox potentials. The latter effect was shown to be independent of the ArcAB regulatory system.
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