The secondary electron acceptor of photosystem I in Gloeobacter violaceus PCC 7421 is menaquinone-4 that is synthesized by a unique but unknown pathway (original) (raw)
Related papers
Biochemistry, 1998
Photosynthetically active reaction center complexes were prepared from the green sulfur bacterium Chlorobium Vibrioforme NCIMB 8327, and the content of quinones was determined by extraction and high-performance liquid chromatography. The analysis showed a stoichiometry of 1.7 molecules of menaquinone-7/reaction center. No other quinones were detected in the isolated reaction centers, whereas membrane preparations also contained chlorobiumquinone. The possible involvement of quinones in electron transport was investigated by electron paramagnetic resonance (EPR) spectroscopy. A highly anisotropic radical was detected by Q-band EPR spectroscopy in both membranes and isolated reaction centers following dark reduction with sodium dithionite and photoaccumulation at 205 K. At 34 GHz, the EPR spectrum is characterized by a g tensor with g xx ) 2.0063, g yy ) 2.0052, g zz ) 2.0020 and ∆B of 0.7 mT, consistent with its identification as a quinone. This spectrum is highly similar in terms of g values and line widths to photoaccumulated A 1in photosystem I of Synechococcus sp. PCC 7002. The results indicate that menaquinone-7 in the green sulfur bacterial reaction center is analogous to phylloquinone in photosystem I.
Cyanobacterial Photosystem II at 3.2 Å resolution – the plastoquinone binding pockets
Photosynthesis Research, 2005
Photosystem II from thylakoid membranes of the thermophilic cyanobacterium Thermosynechococcus elongatus was solubilized with n-b-dodecylmaltoside and purified using anion exchange chromatography. Molecular weight, pigment stoichiometry and subunit composition were assayed using various techniques. The holocomplex is dimeric with a molecular mass of 756 ± 18 kDa and functionally fully active. Crystals obtained from these samples showed significantly improved quality leading to a 3D structure at 3.2 Å resolution. Several loop regions of the principal protein subunits are now defined that were not interpretable at lower (3.8 Å ) resolution, thus resulting in a more complete model. The head groups of the cofactors of the electron transfer chain and of the antennae have been modeled, coordinating and hydrogen bonding amino acids identified and the nature of the binding pockets derived. The orientations of these cofactors resemble those of the reaction centre from anoxygenic purple bacteria. For the two plastoquinones, electron density was only found for the head group of Q A and none for Q B indicating low or even no occupancy of this site in the crystal structure. Both binding pockets and problems related to the Q B site are discussed here and compared to the situation in the purple bacterial reaction centre. Abbreviations: AAS -atom absorption spectroscopy; b-DMn-b-D D -dodecylmaltoside; Carb-carotene; Chl a -Chlorophyll a; cyt -cytochrome; DLS -dynamic light scattering; GPC -gel permeation chromatography; MALDI-TOF MS -matrix assisted laser desorption ionisation time of flight mass spetrometry; PbRC -purple bacterial reaction centre; Pheoa -Pheophytin a; PQ9 -plastoquinone 9; PSphotosystem; Q A -primary quinone; Q B -secondary quinone; RPC -reverse phase chromatography; TLC -thin layer chromatography; UC -ultracentrifugation Photosynthesis Research (2005) 84: 153-159 Ó Springer 2005
Photosystem I from the unusual cyanobacterium Gloeobacter violaceus
Photosynthesis research, 2002
Photosystem I (PS I) from the primitive cyanobacterium Gloeobacter violaceus has been purified and characterised. Despite the fact that the isolated complexes have the same subunit composition as complexes from other cyanobacteria, the amplitude of flash-induced absorption difference spectra indicates a much bigger antenna size with about 150 chlorophylls per P700 as opposed to the usual 90. Image analysis of the PS I preparation from Gloeobacter reveals that the PS I particles exist both in a trimeric and in a monomeric form and that their size and shape closely resembles other cyanobacterial PS I particles. However, the complexes exhibit a higher molecular weight as could be shown by gel filtration. The preparation contains novel polypeptides not related to known Photosystem I subunits. The N-terminal sequence of one of those polypeptides has been determined and reveals no homology to known or hypothetical proteins. Immunoblotting shows a cross-reaction of three of the polypeptide...
Photosystem I (PS I) from the primitive cyanobacterium Gloeobacter violaceus has been purified and characterised. Despite the fact that the isolated complexes have the same subunit composition as complexes from other cyanobacteria, the amplitude of flash-induced absorption difference spectra indicates a much bigger antenna size with about 150 chlorophylls per P700 as opposed to the usual 90. Image analysis of the PS I preparation from Gloeobacter reveals that the PS I particles exist both in a trimeric and in a monomeric form and that their size and shape closely resembles other cyanobacterial PS I particles. However, the complexes exhibit a higher molecular weight as could be shown by gel filtration. The preparation contains novel polypeptides not related to known Photosystem I subunits. The N-terminal sequence of one of those polypeptides has been determined and reveals no homology to known or hypothetical proteins. Immunoblotting shows a cross-reaction of three of the polypeptide bands with an antibody raised against the major LHC from the diatom Cyclotella cryptica. Electron microscopy reveals a novel T-shaped complex which has never been observed in any other cyanobacterial PS I preparation. 77 K spectra of purified PS I show an extreme blue-shift of the fluorescence emission, indicating an unusual organisation of the PS I antenna system in Gloeobacter.
Menaquinone as pool quinone in a purple bacterium
Proceedings of the National Academy of Sciences, 2009
Purple bacteria have thus far been considered to operate lightdriven cyclic electron transfer chains containing ubiquinone (UQ) as liposoluble electron and proton carrier. We show that in the purple ␥-proteobacterium Halorhodospira halophila, menaquinone-8 (MK-8) is the dominant quinone component and that it operates in the QB-site of the photosynthetic reaction center (RC). The redox potentials of the photooxidized pigment in the RC and of the Rieske center of the bc1 complex are significantly lower (Em ؍ ؉270 mV and ؉110 mV, respectively) than those determined in other purple bacteria but resemble those determined for species containing MK as pool quinone. These results demonstrate that the photosynthetic cycle in H. halophila is based on MK and not on UQ. This finding together with the unusual organization of genes coding for the bc1 complex in H. halophila suggests a specific scenario for the evolutionary transition of bioenergetic chains from the low-potential menaquinones to higher-potential UQ in the proteobacterial phylum, most probably induced by rising levels of dioxygen 2.5 billion years ago. This transition appears to necessarily proceed through bioenergetic ambivalence of the respective organisms, that is, to work both on MK-and on UQ-pools. The establishment of the corresponding low-and high-potential chains was accompanied by duplication and redox optimization of the bc1 complex or at least of its crucial subunit oxidizing quinols from the pool, the Rieske protein. Evolutionary driving forces rationalizing the empirically observed redox tuning of the chain to the quinone pool are discussed. electron transport ͉ evolution ͉ photosynthesis
Recruitment of a Foreign Quinone into the A1 Site of Photosystem I
2000
Genes encoding enzymes of the biosynthetic pathway leading to phylloquinone, the secondary electron acceptor of photosystem (PS) I, were identified in Synechocystis sp. PCC 6803 by comparison with genes encoding enzymes of the menaquinone biosynthetic pathway in Escherichia coli. Targeted inactivation of the menA and menB genes, which code for phytyl transferase and 1,4-dihydroxy-2-naphthoate synthase, respectively, prevented the synthesis of phylloquinone, thereby confirming the participation of these two gene products in the biosynthetic pathway. The menA and menB mutants grow photoautotrophically under low light conditions (20 microE m(-2) s(-1)), with doubling times twice that of the wild type, but they are unable to grow under high light conditions (120 microE m(-2) s(-1)). The menA and menB mutants grow photoheterotrophically on media supplemented with glucose under low light conditions, with doubling times similar to that of the wild type, but they are unable to grow under high light conditions unless atrazine is present to inhibit PS II activity. The level of active PS II per cell in the menA and menB mutant strains is identical to that of the wild type, but the level of active PS I is about 50-60% that of the wild type as assayed by low temperature fluorescence, P700 photoactivity, and electron transfer rates. PS I complexes isolated from the menA and menB mutant strains contain the full complement of polypeptides, show photoreduction of F(A) and F(B) at 15 K, and support 82-84% of the wild type rate of electron transfer from cytochrome c(6) to flavodoxin. HPLC analyses show high levels of plastoquinone-9 in PS I complexes from the menA and menB mutants but not from the wild type. We propose that in the absence of phylloquinone, PS I recruits plastoquinone-9 into the A(1) site, where it functions as an efficient cofactor in electron transfer from A(0) to the iron-sulfur clusters.
Electron transfer in menaquinone-depleted membranes of Heliobacterium chlorum
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1993
Treatment of membranes of Heliobacterium chlorum with diethyl ether at various levels of water saturation resulted in extraction of bacteriochlorophyll (BChl) g and menaquinones. Only a minor enrichment of P-798 with respect to antenna BChl g could be achieved, whereas menaquinone (vitamin K-2), the only quinone found in this species (Hiraishi, A. (1989) Arch. Microbiol. 151, 378-379), was essentially completely removed. Extraction of menaquinone, however, did not result in significant changes in electron transport. Electron transport to secondary electron acceptors was not impaired by wet ether extraction, either at room temperature or at low temperature. As in intact membranes, radical pair recombination and subsequent triplet formation were only observed under strongly reducing conditions. These results suggest that menaquinone is not an essential participant in the electron acceptor chain of heliobacteria.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2003
The genome of the cyanobacterium Synechocystis sp. PCC 6803 contains genes identified as menD and menE, homologs of Escherichia coli genes that code for 2-succinyl-6-hydroxyl-2,4-cyclohexadiene-1-carboxylate (SHCHC) synthase and O-succinylbenzoic acid -CoA ligase in the menaquinone biosynthetic pathway. In cyanobacteria, the product of this pathway is 2-methyl-3-phytyl-1,4-naphthoquinone (phylloquinone), a molecule used exclusively as an electron transfer cofactor in Photosystem (PS) I. The menD À and menE À strains were generated, and both were found to lack phylloquinone. Hence, no alternative pathways exist in cyanobacteria to produce O-succinylbenzoyl -CoA. Q-band EPR studies of photoaccumulated quinone anion radical and optical kinetic studies of the P700 + [F A /F B ] À backreaction indicate that in the mutant strains, plastoquinone-9 functions as the electron transfer cofactor in the A 1 site of PS I. At a light intensity of 40 AE m À2 s À1 , the menD À and menE À mutant strains grew photoautotrophically and photoheterotrophically, but with doubling times slower than the wild type. Both of which are sensitive to high light intensities. Low-temperature fluorescence studies show that in the menD À and menE À mutants, the ratio of PS I to PS II is reduced relative to the wild type. Whole-chain electron transfer rates in the menD À and menE À mutant cells are correspondingly higher on a chlorophyll basis. The slower growth rate and high-light sensitivity of the menD À and menE À mutants are therefore attributed to a lower content of PS I per cell. D
Turnover of ubiquinone-0 at the acceptor side of photosynthetic reaction center
European Biophysics Journal, 2008
The steady-state operation of photosynthetic reaction center from Rhodobacter sphaeroides was investigated by measuring the rate of cytochrome photooxidation under intensive continuous illumination (808 nm, 5 W cm-2). The native quinone UQ 10 in Q B binding site of the reaction center was substituted by tailless UQ 0 and the binding parameters and the turnover rate of the UQ 0 was studied to test the recently discovered lightintensity dependent acceptor side effect (Gerencsér and Maróti 2006). The binding parameters of UQ 0 (k on = 2.1 9 10 5 M-1 s-1 and k off = 100 s-1) were characteristic to the RC exposed to high light-intensity. The dissociation constant (K D = 480 lM) determined under high light intensity is 2-3 times larger than that determined from flash-experiments. The light-intensity dependent acceleration of cytochrome turnover measured on reaction center of inhibited proton binding was independent of the type of the quinone and was sensitive only to the size (''pressure'') of the quinone pool. The dissociation constants of different types of semiquinones show similarly high (several orders of magnitude) increase in the modified conformation of the Q B binding pocket due to high intensity of illumination. This result indicates the exclusive role of the quinone headgroup in the binding of semiquinone to different conformations of the protein. Keywords Bacterial photosynthesis Á Reaction center protein Á Cytochrome turnover Á Quinone binding Á Redox potentiometry Abbreviations DEAE Diethylaminoethyl DMBQ 2,5-Dimethyl-1,4-benzoquinone EDTA Ethylenediaminetetraacetic acid LDAO N,N 0-Dimethyl dodecylamine N-oxide NHE Normal hydrogen electrode P (P +) Reduced (oxidized) bacteriochlorophyll dimer Q A and Q B Primary and secondary quinone, respectively RC Reaction center protein SOD Superoxide dismutase TMPD N,N,N 0 ,N 0-Tetramethyl-1,4phenylenediamine Triton X-100 Polyoxyethylene(10) isooctylphenyl ether UQ n 2,3-Dimethoxy-5-methyl-1,4benzoquinone with n isoprenoid units in the tail