Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
BBA - Bioenergetics (v.1787, #1)
Mechanism and regulation of the violaxanthin cycle: The role of antenna proteins and membrane lipids by Peter Jahns; Dariusz Latowski; Kazimierz Strzalka (pp. 3-14).
The violaxanthin cycle describes the reversible conversion of violaxanthin to zeaxanthin via the intermediate antheraxanthin. This light-dependent xanthophyll conversion is essential for the adaptation of plants and algae to different light conditions and allows a reversible switch of photosynthetic light-harvesting complexes between a light-harvesting state under low light and a dissipative state under high light. The photoprotective functions of zeaxanthin have been intensively studied during the last decade, but much less attention has been directed to the mechanism and regulation of xanthophyll conversion. In this review, an overview is given on recent progress in the understanding of the role of (i) xanthophyll binding by antenna proteins and of (ii) the lipid properties of the thylakoid membrane in the regulation of xanthophyll conversion. The consequences of these findings for the mechanism and regulation of xanthophyll conversion in the thylakoid membrane will be discussed.
Keywords: Abbreviations; ASC; ascorbate; ASCH; acid form of ascorbate; Ax; antheraxanthin; Chl; chlorophyll; Ddx; diadinoxanthin; DHA; dehydroascorbate; DGDG; digalactosyldiacylglycerol; Dtx; diatoxanthin; LHCII; light-harvesting complex of photosystem II; MGDG; monogalactosyldiacylglycerol; NPQ; non-photochemical quenching; PC; phosphatidylcholine; PE; phosphatidylethanolamine; PSII; photosystem II; VAZ; sum of violaxanthin, antheraxanthin and zeaxanthin; Vx; violaxanthin; VDE; violaxanthin de-epoxidase; Zx; zeaxanthin; ZE; zeaxanthin epoxidaseLipids; H; II; phase; Non-photochemical quenching; Photo-oxidative stress; Violaxanthin; Xanthophyll cycle; Zeaxanthin
Mitochondrial inhibitors activate influx of external Ca2+ in sea urchin sperm by F. Ardón; E. Rodríguez-Miranda; C. Beltrán; A. Hernández-Cruz; A. Darszon (pp. 15-24).
Sea urchin sperm have a single mitochondrion which, aside from its main ATP generating function, may regulate motility, intracellular Ca2+ concentration ([Ca2+]i) and possibly the acrosome reaction (AR). We have found that acute application of agents that inhibit mitochondrial function via differing mechanisms (CCCP, a proton gradient uncoupler, antimycin, a respiratory chain inhibitor, oligomycin, a mitochondrial ATPase inhibitor and CGP37157, a Na+/Ca2+ exchange inhibitor) increases [Ca2+]i with at least two differing profiles. These increases depend on the presence of extracellular Ca2+, which indicates they involve Ca2+ uptake and not only mitochondrial Ca2+ release. The plasma membrane permeation pathways activated by the mitochondrial inhibitors are permeable to Mn2+. Store-operated Ca2+ channel (SOC) blockers (Ni2+, SKF96365 and Gd2+) and internal-store ATPase inhibitors (thapsigargin and bisphenol) antagonize Ca2+ influx induced by the mitochondrial inhibitors. The results indicate that the functional status of the sea urchin sperm mitochondrion regulates Ca2+ entry through SOCs. As neither CCCP nor dicycloexyl carbodiimide (DCCD), another mitochondrial ATPase inhibitor, eliminate the oligomycin induced increase in [Ca2+]i, apparently oligomycin also has an extra mitochondrial target.
Keywords: Abbreviations; ASW; artificial sea water; BF; bisphenol; [Ca; 2+; ]cyt; cytosolic Ca; 2+; concentration; [Ca; 2+; ]mt; mitochondrial Ca; 2+; concentration; [Ca; 2+; ]; i; intracellular Ca; 2+; concentration; CCCP; carbonyl cyanide m-chlorophenylhydrazone; CGP37157; 7-chloro-5-(2-chlorophenyl)-1,5-dihydro-4,1-benzothiazepin-2(3H)-one; DCCD; dicycloexyl carbodiimide; DMSO; dimethylsulfoxide; ER; endoplasmic reticulum; PM; plasma membrane; SKF96365; (1-[b-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole hydrochloride); SOCC; store operated calcium channels; TG; thapsigarginMitochondria; Calcium influx; Sea urchin sperm
Fragmentation and separation analysis of the photosynthetic membrane from spinach by Ravi Danielsson; Per-Åke Albertsson (pp. 25-36).
Membrane vesicles, originating from grana, grana core (appressed grana regions), grana margins and stroma lamellae/end membranes, were analysed by counter current distribution (CCD) using aqueous dextran-polyethylene glycol two-phase systems. Each vesicle population gave rise to distinct peaks in the CCD diagram representing different vesicle subpopulations. The grana vesicles and grana core vesicles each separated into 3 different subpopulations having different chlorophyll a/b ratios and PSI/PSII ratios. Two of the grana core subpopulations had a chlorophyll a/b ratio of 2.0 and PSI/PSII ratio of 0.10 and are among the most PSII enriched thylakoid vesicle preparation obtained so far by a non detergent method. The margin vesicles separated into 3 different populations, with about the same chlorophyll a/b ratios, but different fluorescence emission spectra. The stroma lamellae/end membrane vesicles separated into 4 subpopulations. Plastoglobules, connected to membrane vesicles, were highly enriched in 2 of these subpopulations and it is proposed that these 2 subpopulations originate from stroma lamellae while the 2 others originate from end membranes. Fragmentation and separation analysis shows that the margins of grana constitute a distinct domain of the thylakoid and also allows the estimation of the chlorophyll antenna sizes of PSI and PSII in different thylakoid domains.
Keywords: Abbreviations; CCD; counter current distribution; Chl; chlorophyll; (a; +; b); LHCII; light harvesting complex; PEG; polyethylene glycol; PpBQ; phenyl-p-benzoquinone; PSI; photo system I; PSII; photo system IIPhoto system I; Photo system II; Thylakoid; Plastoglobule; Phase partition; Counter-current distribution; Antenna size
The cytochrome ba complex from the thermoacidophilic crenarchaeote Acidianus ambivalens is an analog of bc1 complexes by Tiago M. Bandeiras; Patricia N. Refojo; Smilja Todorovic; Daniel H. Murgida; Peter Hildebrandt; Christian Bauer; Manuela M. Pereira; Arnulf Kletzin; Miguel Teixeira (pp. 37-45).
A novel cytochrome ba complex was isolated from aerobically grown cells of the thermoacidophilic archaeon Acidianus ambivalens. The complex was purified with two subunits, which are encoded by the cbsA and soxN genes. These genes are part of the pentacistronic cbsAB–soxLN–odsN locus. The spectroscopic characterization revealed the presence of three low-spin hemes, two of the b and one of the as-type with reduction potentials of +200, +400 and +160 mV, respectively. The SoxN protein is proposed to harbor the heme b of lower reduction potential and the heme as, and CbsA the other heme b. The soxL gene encodes a Rieske protein, which was expressed in E. coli; its reduction potential was determined to be +320 mV. Topology predictions showed that SoxN, CbsB and CbsA should contain 12, 9 and one transmembrane α-helices, respectively, with SoxN having a predicted fold very similar to those of the cytochromes b in bc1 complexes. The presence of two quinol binding motifs was also predicted in SoxN. Based on these findings, we propose that the A. ambivalens cytochrome ba complex is analogous to the bc1 complexes of bacteria and mitochondria, however with distinct subunits and heme types.
Keywords: Abbreviations; DDM; n-Dodecyl β-; d; -maltoside; IPTG; isopropyl β-; d; -1-thiogalacto-pyranosideArchaea; bc; 1; complex; Rieske; Cytochrome; b; b; 6; f; complex; Sulfolobales
Genetic analysis of the Photosystem I subunits from the red alga, Galdieria sulphuraria by Christopher Vanselow; Andreas P.M. Weber; Kirsten Krause; Petra Fromme (pp. 46-59).
Currently, there are very little data available regarding the photosynthetic apparatus of red algae. We have analyzed the genes for Photosystem I in the recently sequenced genome of the red alga Galdieria sulphuraria. All subunits that are conserved between plants and cyanobacteria were unambiguously identified in the Galdieria genome: PsaA, PsaB, PsaC, PsaD, PsaE, PsaF, PsaI, PsaJ, PsaK and PsaL. From the plant specific subunits, PsaN and PsaO were identified but the sequence homology was much lower than for the subunits that are present in plants and cyanobacteria. The subunit PsaX, which is specific for thermophilic cyanobacteria, is not present in the Galdieria genome, whereas PsaM is a plastid-encoded protein as in other red algae. The sequences of the core subunits of PSI were further analyzed by mapping of the conserved areas in the crystal structures of cyanobacterial and plant PSI. The structural comparison shows that PSI from the red alga Galdieria may represent a common ancestral structure at the interface between cyanobacterial and plant PSI. Some subunits have a “zwitter” structure that contains structural elements that show similarities with either plant or cyanobacterial PSI. The structure of PsaL, which is responsible for the trimerization of PSI in cyanobacteria, lacks a short helix and the Ca2+ binding site, which are essential for trimer formation indicating that the Galdieria PSI is a monomer. However the sequence homology to plant PsaL is low and lacks strong conservation of the interaction sites with PsaH. Furthermore, the sites for interaction of plant PSI with the LHCI complex are not well conserved between plants and Galdieria, which may indicate that Galdieria may contain a PSI that is evolutionarily much more ancient than PSI from green algae, plants and the current cyanobacteria.
Keywords: Photosynthesis; Red algae; Photosystem I; Evolution; Gene identification; Light harvesting; Electron transfer
Megacomplex organization of the oxidative phosphorylation system by structural analysis of respiratory supercomplexes from potato by Jelle B. Bultema; Hans-Peter Braun; Egbert J. Boekema ⁎; Roman Kouřil ⁎ (pp. 60-67).
The individual protein complexes of the oxidative phosphorylation system (OXPHOS complexes I to V) specifically interact and form defined supramolecular structures, the so-called “respiratory supercomplexes”. Some supercomplexes appear to associate into larger structures, or megacomplexes, such as a string of dimeric ATP synthase (complex V2). A row-like organization of OXPHOS complexes I, III and IV into respiratory strings has also been proposed. These transient strings cannot be purified after detergent solubilization. Hence the shape and composition of the respiratory string was approached by an extensive structural characterization of all its possible building blocks, which are the supercomplexes. About 400,000 molecular projections of supercomplexes from potato mitochondria were processed by single particle electron microscopy. We obtained two-dimensional projection maps of at least five different supercomplexes, including the supercomplex I+III2, III2+IV1, V2, I+III2+IV1 and I2+III2 in different types of position. From these maps the relative position of the individual complexes in the largest unit, the I2+III2+IV2 supercomplex, could be determined in a coherent way. The maps also show that the I+III2+IV1 supercomplex, or respirasome, differs from its counterpart in bovine mitochondria. The new structural features allow us to propose a consistent model of the respiratory string, composed of repeating I2+III2+IV2 units, which is in agreement with dimensions observed in former freeze-fracture electron microscopy data.
Keywords: Respiratory supercomplex; Respiratory string; Electron microscopy; Single particle analysis
The role of the invariant glutamate 95 in the catalytic site of Complex I from Escherichia coli by Liliya Euro ⁎; Galina Belevich; Dmitry A. Bloch; Michael I. Verkhovsky; Mårten Wikström; Marina Verkhovskaya ⁎ (pp. 68-73).
Replacement of glutamate 95 for glutamine in the NADH- and FMN-binding NuoF subunit of E. coli Complex I decreased NADH oxidation activity 2.5–4.8 times depending on the used electron acceptor. The apparent K m for NADH was 5.2 and 10.4 μM for the mutant and wild type, respectively. Analysis of the inhibitory effect of NAD+ on activity showed that the E95Q mutation caused a 2.4-fold decrease of K iNAD+ in comparison to the wild type enzyme. ADP-ribose, which differs from NAD+ by the absence of the positively charged nicotinamide moiety, is also a competitive inhibitor of NADH binding. The mutation caused a 7.5-fold decrease of K iADP-ribose relative to wild type enzyme. Based on these findings we propose that the negative charge of Glu95 accelerates turnover of Complex I by electrostatic interaction with the negatively charged phosphate groups of the substrate nucleotide during operation, which facilitates release of the product NAD+. The E95Q mutation was also found to cause a positive shift of the midpoint redox potential of the FMN, from −350 mV to −310 mV, which suggests that the negative charge of Glu95 is also involved in decreasing the midpoint potential of the primary electron acceptor of Complex I.
Keywords: Abbreviations; DDM; n-dodecyl β-; d; -maltopyranoside; HAR; hexaammineruthenium (III) chloride; DQ; decylubiquinone; dNADH; nicotinamide hypoxanthine dinucleotide reduced sodium salt; ADP-ribose; adenosine 5′-diphosphoribose sodium salt; PMSF; phenylmethanesulfonyl fluoride; FeCy; ferricyanideComplex I; NuoF subunit; NADH-binding site