MINIREVIEW Control of Photosystem Formation in Rhodobacter sphaeroides (original) (raw)
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Biochemistry, 2011
b S Supporting Information B ecause of the unparalleled combination of accessible molecular genetics with an intracytoplasmic membrane (ICM) system that is amenable to a considerable variety of biochemical, spectroscopic, and ultrastructural probes, the photosystem a of the purple bacterium Rhodobacter sphaeroides has served as an important model system for studies of the structural and functional aspects of the light reactions of photosynthesis, as well as related energy transduction processes and the regulatory mechanism controlling the levels of participating protein components. 1 In contrast, much less is known about mechanisms that drive the assembly of the light-harvesting (LH) and reaction center (RC) complexes, how their patterns of localization are established within the cell, and how numerous assembly factors cooperate with the nascent apoproteins and pigments to form functional photosynthetic units within the growing ICM.
FEBS Letters, 1994
The effects of deletion of the gene encoding the PufX protein from Rhodobacter sphaeroides have been examined using bacterial strains with simplified photosystems. We find that the PufX protein is required for photosynthetic growth in strains which have the LHI antenna complex, but is not required in a reaction centre-only strain, suggesting that the PufX protein does not directly facilitate cyclic electron transfer between the reaction centre and the cytochrome bc, complex. The influence of PufX and carotenoid type on the size of the reaction center/LHl core complex has also been examined in these strains.
Model for the Light-Harvesting Complex I (B875) of Rhodobacter sphaeroides
Biophysical Journal, 1998
The light-harvesting complex I (LH-I) of Rhodobacter sphaeroides has been modeled computationally as a hexadecamer of ␣-heterodimers, based on a close homology of the heterodimer to that of light-harvesting complex II (LH-II) of Rhodospirillum molischianum. The resulting LH-I structure yields an electron density projection map that is in agreement with an 8.5-Å resolution electron microscopic projection map for the highly homologous LH-I of Rs. rubrum. A complex of the modeled LH-I with the photosynthetic reaction center of the same species has been obtained by a constrained conformational search. This complex and the available structures of LH-II from Rs. molischianum and Rhodopseudomonas acidophila furnish a complete model of the pigment organization in the photosynthetic membrane of purple bacteria.
2001
Inhibition of electron transport and damage to the protein subunits by visible light has been studied in isolated reaction centers of the non-sulfur purple bacterium Rhodobacter sphaeroides. Illumination by 1100 µEm −2 s −1 light induced only a slight effect in wild type, carotenoid containing 2.4.1. reaction centers. In contrast, illumination of reaction centers isolated from the carotenoidless R26 strain resulted in the inhibition of charge separation as detected by the loss of the initial amplitude of absorbance change at 430 nm arising from the P + Q B − → PQ B recombination. In addition to this effect, the L, M and H protein subunits of the R26 reaction center were damaged as shown by their loss on Coomassie stained gels, which was however not accompanied by specific degradation products. Both the loss of photochemical activity and of protein subunits were suppressed in the absence of oxygen. By applying EPR spin trapping with 2,2,6,6-tetramethylpiperidine we could detect light-induced generation of singlet oxygen in the R26, but not in the 2.4.1. reaction centers. Moreover, artificial generation of singlet oxygen, also led to the loss of the L, M and H subunits. Our results provide evidence for the common hypothesis that strong illumination by visible light damages the carotenoidless reaction center via formation of singlet oxygen. This mechanism most likely proceeds through the interaction of the triplet state of reaction center chlorophyll with the ground state triplet oxygen in a similar way as occurs in Photosystem II.
FEMS Microbiology Letters, 1995
The photosynthetic bacterium Rhodobacter sulfidophilus is able to grow chemotrophically and phototrophically at a broad range of light intensities. In contrast to other facultative phototrophs, R. sulfidophilus synthesizes reaction center and light-harvesting (LH) complexes, B870 (LHI) and B800-850 (LHII) even under full aerobic conditions in the dark. The content of bacteriochlorophyll (BChll varied from 3.8 pg Bchl per mg cell protein when grown at high light intensity (20 000 1~x1 to 60 pg Bchl per mg cell protein when grown at low light intensities (6 lux). After a shit? from high light to low light conditions, the size of the photosynthetic unit increased by a factor of 4. Chromatographic analysis of the LHII complex, isolated and purified from cells grown phototrophically (at high and low light intensities) and chemotrophically, could resolve only one type of a and one type of /3 polypeptide in the purified complex, of which the N-terminal sequences have been determined.
Physical Chemistry Chemical Physics, 2014
Time-resolved fluorescence spectroscopy was used to explore the pathway and kinetics of energy transfer in photosynthetic membrane vesicles (chromatophores) isolated from Rhodobacter (Rba.) sphaeroides cells harvested 2, 4, 6 or 24 hours after a transition from growth in high to low level illumination. As previously observed, this light intensity transition initiates the remodeling of the photosynthetic apparatus and an increase in the number of light harvesting 2 (LH2) complexes relative to light harvesting 1 (LH1) and reaction center (RC) complexes. It has generally been thought that the increase in LH2 complexes served the purpose of increasing the overall energy transmission to the RC. However, fluorescence lifetime measurements and analysis in terms of energy transfer within LH2 and between LH2 and LH1 indicate that, during the remodeling time period measured, only a portion of the additional LH2 generated are well connected to LH1 and the reaction center. The majority of the additional LH2 fluorescence decays with a lifetime comparable to that of free, unconnected LH2 complexes. The presence of large LH2-only domains has been observed by atomic force microscopy in Rba. sphaeroides chromatophores (Bahatyrova et al., Nature, 2004, 430, 1058), providing structural support for the existence of pools of partially connected LH2 complexes. These LH2-only domains represent the light-responsive antenna complement formed after a switch in growth conditions from high to low illumination, while the remaining LH2 complexes occupy membrane regions containing mixtures of LH2 and LH1-RC core complexes. The current study utilized a multi-parameter approach to explore the fluorescence spectroscopic properties related to the remodeling process, shedding light on the structure-function relationship of the photosynthetic assembles. Possible reasons for the accumulation of these largely disconnected LH2-only pools are discussed.