Nejvíce citovaný článek - PubMed ID 19219048
The growth of plants, algae, and cyanobacteria relies on the catalytic activity of the oxygen-evolving PSII complex, which uses solar energy to extract electrons from water to feed into the photosynthetic electron transport chain. PSII is proving to be an excellent system to study how large multi-subunit membrane-protein complexes are assembled in the thylakoid membrane and subsequently repaired in response to photooxidative damage. Here we summarize recent developments in understanding the biogenesis of PSII, with an emphasis on recent insights obtained from biochemical and structural analysis of cyanobacterial PSII assembly/repair intermediates. We also discuss how chlorophyll synthesis is synchronized with protein synthesis and suggest a possible role for PSI in PSII assembly. Special attention is paid to unresolved and controversial issues that could be addressed in future research.
In our earlier works, we have shown that the rate-limiting steps, associated with the dark-to-light transition of Photosystem II (PSII), reflecting the photochemical activity and structural dynamics of the reaction center complex, depend largely on the lipidic environment of the protein matrix. Using chlorophyll-a fluorescence transients (ChlF) elicited by single-turnover saturating flashes, it was shown that the half-waiting time (Δτ 1/2) between consecutive excitations, at which 50% of the fluorescence increment was reached, was considerably larger in isolated PSII complexes of Thermostichus (T.) vulcanus than in the native thylakoid membrane (TM). Further, it was shown that the addition of a TM lipid extract shortened Δτ 1/2 of isolated PSII, indicating that at least a fraction of the 'missing' lipid molecules, replaced by detergent molecules, caused the elongation of Δτ 1/2. Here, we performed systematic experiments to obtain information on the nature of TM lipids that are capable of decreasing Δτ 1/2. Our data show that while all lipid species shorten Δτ 1/2, the negatively charged lipid phosphatidylglycerol appears to be the most efficient species - suggesting its prominent role in determining the structural dynamics of PSII reaction center.
- Klíčová slova
- chlorophyll-a fluorescence, core complex of photosystem II, rate-limiting step, structural dynamics, thylakoid lipids, waiting time,
- Publikační typ
- časopisecké články MeSH
Photosystem II (PSII) represents the most vulnerable component of the photosynthetic machinery and its response in plants subjected to abiotic stress has been widely studied over many years. PSII is a thylakoid membrane-located multiprotein pigment complex that catalyses the light-induced electron transfer from water to plastoquinone with the concomitant production of oxygen. PSII is rich in intrinsic (PsbA and PsbD, namely D1 and D2, CP47 or PsbB and CP43 or PsbC) but also extrinsic proteins. The first ones are more largely conserved from cyanobacteria to higher plants while the extrinsic proteins are different among species. It has been found that extrinsic proteins involved in oxygen evolution change dramatically the PSII efficiency and PSII repair systems. However, little information is available on the effects of abiotic stress on their function and structure.
- Klíčová slova
- abiotic stress, extrinsic protein, intrinsic protein, photosynthesis, photosystem II,
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
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 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 (Chls), 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, Chl was detected in D1mod but not D2mod, formation of RCII appears to be important for stable binding of most of the Chls and both pheophytins. We suggest that Chl can be delivered to RCII from either monomeric Photosystem I or Ycf39/Hlips complexes.
- MeSH
- chlorofyl metabolismus MeSH
- feofytiny metabolismus MeSH
- fotosystém I - proteinový komplex metabolismus MeSH
- fotosystém II - proteinový komplex * metabolismus MeSH
- Synechocystis * metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- chlorofyl MeSH
- feofytiny MeSH
- fotosystém I - proteinový komplex MeSH
- fotosystém II - proteinový komplex * MeSH
Reactive oxygen species (ROS) are formed in photosystem II (PSII) under various types of abiotic and biotic stresses. It is considered that ROS play a role in chloroplast-to-nucleus retrograde signaling, which changes the nuclear gene expression. However, as ROS lifetime and diffusion are restricted due to the high reactivity towards biomolecules (lipids, pigments, and proteins) and the spatial specificity of signal transduction is low, it is not entirely clear how ROS might transduce signal from the chloroplasts to the nucleus. Biomolecule oxidation was formerly connected solely with damage; nevertheless, the evidence appears that oxidatively modified lipids and pigments are be involved in chloroplast-to-nucleus retrograde signaling due to their long diffusion distance. Moreover, oxidatively modified proteins show high spatial specificity; however, their role in signal transduction from chloroplasts to the nucleus has not been proven yet. The review attempts to summarize and evaluate the evidence for the involvement of ROS in oxidative signaling in PSII.
- Klíčová slova
- Chloroplast-to-nucleus retrograde signaling, Lipid peroxidation, Protein oxidation, Reactive oxygen species,
- MeSH
- chloroplasty * metabolismus MeSH
- fotosystém II - proteinový komplex * metabolismus MeSH
- lipidy MeSH
- oxidační stres MeSH
- reaktivní formy kyslíku metabolismus MeSH
- signální transdukce fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
- Názvy látek
- fotosystém II - proteinový komplex * MeSH
- lipidy MeSH
- reaktivní formy kyslíku MeSH
Photosystem II (PSII) is a multi-subunit pigment-protein complex and is one of several protein assemblies that function cooperatively in photosynthesis in plants and cyanobacteria. As more structural data on PSII become available, new questions arise concerning the nature of the charge separation in PSII reaction center (RC). The crystal structure of PSII RC from cyanobacteria Thermosynechococcus vulcanus was selected for the computational study of conformational changes in photosystem II associated to the charge separation process. The parameterization of cofactors and lipids for classical MD simulation with Amber force field was performed. The parametrized complex of PSII was embedded in the lipid membrane for MD simulation with Amber in Gromacs. The conformational behavior of protein and the cofactors directly involved in the charge separation were studied by MD simulations and QM/MM calculations. This study identified the most likely mechanism of the proton-coupled reduction of plastoquinone QB. After the charge separation and the first electron transfer to QB, the system undergoes conformational change allowing the first proton transfer to QB- mediated via Ser264. After the second electron transfer to QBH, the system again adopts conformation allowing the second proton transfer to QBH-. The reduced QBH2 would then leave the binding pocket.
- Klíčová slova
- MD simulations, Photosystem II reaction center, Plastoquinone, Proton-coupled reduction,
- MeSH
- bakteriální proteiny chemie MeSH
- fotosystém II - proteinový komplex chemie MeSH
- lipidové dvojvrstvy chemie MeSH
- simulace molekulární dynamiky * MeSH
- sinice enzymologie MeSH
- Thermosynechococcus MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- bakteriální proteiny MeSH
- fotosystém II - proteinový komplex MeSH
- lipidové dvojvrstvy MeSH
Biological membranes are tricky to investigate. They are complex in terms of molecular composition and structure, functional over a wide range of time scales, and characterized by nonequilibrium conditions. Because of all of these features, simulations are a great technique to study biomembrane behavior. A significant part of the functional processes in biological membranes takes place at the molecular level; thus computer simulations are the method of choice to explore how their properties emerge from specific molecular features and how the interplay among the numerous molecules gives rise to function over spatial and time scales larger than the molecular ones. In this review, we focus on this broad theme. We discuss the current state-of-the-art of biomembrane simulations that, until now, have largely focused on a rather narrow picture of the complexity of the membranes. Given this, we also discuss the challenges that we should unravel in the foreseeable future. Numerous features such as the actin-cytoskeleton network, the glycocalyx network, and nonequilibrium transport under ATP-driven conditions have so far received very little attention; however, the potential of simulations to solve them would be exceptionally high. A major milestone for this research would be that one day we could say that computer simulations genuinely research biological membranes, not just lipid bilayers.
- MeSH
- biologické modely * MeSH
- fosfolipidy chemie metabolismus MeSH
- kyseliny karboxylové chemie metabolismus MeSH
- lidé MeSH
- lipidomika metody MeSH
- membránové lipidy chemie metabolismus MeSH
- membrány chemie metabolismus fyziologie MeSH
- počítačová simulace MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- fosfolipidy MeSH
- kyseliny karboxylové MeSH
- membránové lipidy MeSH
The extrinsic PsbU and PsbV proteins are known to play a critical role in stabilizing the Mn4CaO5 cluster of the PSII oxygen-evolving complex (OEC). However, most isolates of the marine cyanobacterium Prochlorococcus naturally miss these proteins, even though they have kept the main OEC protein, PsbO. A structural homology model of the PSII of such a natural deletion mutant strain (P. marinus MED4) did not reveal any obvious compensation mechanism for this lack. To assess the physiological consequences of this unusual OEC, we compared oxygen evolution between Prochlorococcus strains missing psbU and psbV (PCC 9511 and SS120) and two marine strains possessing these genes (Prochlorococcus sp. MIT9313 and Synechococcus sp. WH7803). While the low light-adapted strain SS120 exhibited the lowest maximal O2 evolution rates (Pmax per divinyl-chlorophyll a, per cell or per photosystem II) of all four strains, the high light-adapted strain PCC 9511 displayed even higher PChlmax and PPSIImax at high irradiance than Synechococcus sp. WH7803. Furthermore, thermoluminescence glow curves did not show any alteration in the B-band shape or peak position that could be related to the lack of these extrinsic proteins. This suggests an efficient functional adaptation of the OEC in these natural deletion mutants, in which PsbO alone is seemingly sufficient to ensure proper oxygen evolution. Our study also showed that Prochlorococcus strains exhibit negative net O2 evolution rates at the low irradiances encountered in minimum oxygen zones, possibly explaining the very low O2 concentrations measured in these environments, where Prochlorococcus is the dominant oxyphototroph.
- Klíčová slova
- Marine cyanobacteria, Oxygen minimum zones, Oxygen-evolving complex, Photoacclimation, Photosystem II, Prochlorococcus, Synechococcus,
- MeSH
- bakteriální proteiny chemie genetika fyziologie MeSH
- chlorofyl metabolismus MeSH
- fotosyntéza fyziologie MeSH
- fotosystém II - proteinový komplex chemie genetika fyziologie MeSH
- genom bakteriální MeSH
- kyslík metabolismus MeSH
- molekulární modely MeSH
- průtoková cytometrie MeSH
- sinice genetika metabolismus MeSH
- světlo MeSH
- Publikační typ
- časopisecké články MeSH
- srovnávací studie MeSH
- Názvy látek
- bakteriální proteiny MeSH
- chlorofyl MeSH
- fotosystém II - proteinový komplex MeSH
- kyslík MeSH
Photosystem II (PSII) catalyses the photoinduced oxygen evolution and, by producing reducing equivalents drives, in concert with PSI, the conversion of carbon dioxide to sugars. Our knowledge about the architecture of the reaction centre (RC) complex and the mechanisms of charge separation and stabilisation is well advanced. However, our understanding of the processes associated with the functioning of RC is incomplete: the photochemical activity of PSII is routinely monitored by chlorophyll-a fluorescence induction but the presently available data are not free of controversy. In this work, we examined the nature of gradual fluorescence rise of PSII elicited by trains of single-turnover saturating flashes (STSFs) in the presence of a PSII inhibitor, permitting only one stable charge separation. We show that a substantial part of the fluorescence rise originates from light-induced processes that occur after the stabilisation of charge separation, induced by the first STSF; the temperature-dependent relaxation characteristics suggest the involvement of conformational changes in the additional rise. In experiments using double flashes with variable waiting times (∆τ) between them, we found that no rise could be induced with zero or short ∆τ, the value of which depended on the temperature - revealing a previously unknown rate-limiting step in PSII.
- MeSH
- chlorofyl a metabolismus MeSH
- fluorescence * MeSH
- fotosyntéza MeSH
- fotosystém II - proteinový komplex antagonisté a inhibitory metabolismus MeSH
- Spinacia oleracea metabolismus MeSH
- Synechococcus metabolismus MeSH
- Synechocystis metabolismus MeSH
- teplota MeSH
- tylakoidy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- chlorofyl a MeSH
- fotosystém II - proteinový komplex MeSH
The monomeric photosystem I-light-harvesting antenna complex I (PSI-LHCI) supercomplex from the extremophilic red alga Cyanidioschyzon merolae represents an intermediate evolutionary link between the cyanobacterial PSI reaction center and its green algal/higher plant counterpart. We show that the C. merolae PSI-LHCI supercomplex is characterized by robustness in various extreme conditions. By a combination of biochemical, spectroscopic, mass spectrometry, and electron microscopy/single particle analyses, we dissected three molecular mechanisms underlying the inherent robustness of the C. merolae PSI-LHCI supercomplex: (1) the accumulation of photoprotective zeaxanthin in the LHCI antenna and the PSI reaction center; (2) structural remodeling of the LHCI antenna and adjustment of the effective absorption cross section; and (3) dynamic readjustment of the stoichiometry of the two PSI-LHCI isomers and changes in the oligomeric state of the PSI-LHCI supercomplex, accompanied by dissociation of the PsaK core subunit. We show that the largest low light-treated C. merolae PSI-LHCI supercomplex can bind up to eight Lhcr antenna subunits, which are organized as two rows on the PsaF/PsaJ side of the core complex. Under our experimental conditions, we found no evidence of functional coupling of the phycobilisomes with the PSI-LHCI supercomplex purified from various light conditions, suggesting that the putative association of this antenna with the PSI supercomplex is absent or may be lost during the purification procedure.
- MeSH
- biologická adaptace MeSH
- chlorofyl metabolismus MeSH
- cirkulární dichroismus MeSH
- fluorescenční spektrometrie MeSH
- fotosystém I - proteinový komplex chemie metabolismus MeSH
- koncentrace vodíkových iontů MeSH
- molekulární evoluce MeSH
- Rhodophyta chemie fyziologie MeSH
- sinice chemie fyziologie MeSH
- světlo MeSH
- světlosběrné proteinové komplexy chemie metabolismus MeSH
- teplota MeSH
- zeaxanthiny metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- chlorofyl MeSH
- fotosystém I - proteinový komplex MeSH
- světlosběrné proteinové komplexy MeSH
- zeaxanthiny MeSH
