Are the light-harvesting I complexes from Rhodospirillum rubrum arranged around the reaction centre in a square geometry? 1 1Edited by R. Huber

Stahlberg, Henning; Dubochet, Jacques; Vogel, Horst; Ghosh, Robin

doi:10.1006/jmbi.1998.1975

Cited by 51 publications

(44 citation statements)

References 38 publications

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“…In all of the structural and biophysical studies performed with purified LH1 or RC-LH1 complexes in our laboratory so far (26,59,61), we have observed without exception that the absorption maximum at either 880 nm (for the wild-type strain R. rubrum S1) or 873 nm (for the carotenoid-less strain R. rubrum G9) is always correlated with a perfectly assembled closed ring of ␣␤(BChl) 2 dimers. It has also been demonstrated that this is true for LH1 reconstituted with phospholipids (59), and we believe that it is true for the in vivo situation.…”

Section: Discussionmentioning

confidence: 72%

“…Recent structural studies (6,20,22,25,31,36,37,43,(59)(60)(61) have indicated that the component ␣␤ dimers of LH1, each of which binds two bacteriochlorophyll (BChl) molecules and at least one molecule of carotenoid, form a ring around the RC. For Rhodospirillum rubrum (33,37,59,61) and Blastochloris viridis (previously called Rhodopseudomonas viridis) (60), both of which contain only a single light-harvesting complex, LH1 appears to completely surround the RC. In Rhodobacter sphaeroides, however, recent electron micrographic evidence (36) has suggested that the LH1 in this organism may not be completely closed, although the low resolution of the data in this study may not have been sufficient to allow a definite conclusion to be drawn.…”

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confidence: 99%

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The Reaction Center H Subunit Is Not Required for High Levels of Light-Harvesting Complex 1 in Rhodospirillum rubrum Mutants

Lupo

Ghosh

2004

J Bacteriol

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The gene (puhA) encoding the H subunit of the reaction center (RC) was deleted by site-directed interposon mutagenesis by using a kanamycin resistance cassette lacking transcriptional terminators to eliminate polar effects in both the wild-type strain Rhodospirillum rubrum S1 and the carotenoid-less strain R. rubrum G9. The puhA interposon mutants were incapable of photoheterotrophic growth but grew normally under aerobic chemoheterotrophic conditions. Absorption spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the RCs were absent. In minimal medium and also in modified medium containing succinate and fructose, the light-harvesting 1 complex (LH1) levels of the S1-derived mutants were about 70 to 100% of the wild-type levels in the same media. The correct assembly of LH1 in the membrane and the pigment-pigment interaction were confirmed by near-infrared circular dichroism spectroscopy. LH1 formation was almost absent when the carotenoid-less G9-derived puhA mutants were grown in standard minimal medium, suggesting that carotenoids may stabilize LH1. In the fructose-containing medium, however, the LH1 levels of the G9 mutants were 70 to 100% of the parental strain levels. Electron micrographs of thin sections of R. rubrum revealed photosynthetic membranes in all mutants grown in succinate-fructose medium. These studies indicate that the H subunit of the RC is necessary neither for maximal formation of LH1 nor for photosynthetic membrane formation but is essential for functional RC assembly.It is well established that in phototrophic purple bacteria the photosynthetic unit is expressed in a specialized intracytoplasmic membrane (ICM) (16,18) and is composed of a reaction center (RC) surrounded by a light-harvesting complex (1,17,44). Although most phototrophic bacteria contain two kinds of light-harvesting complexes, light-harvesting complex 1 (LH1) and light-harvesting complex 2 (LH2), only one of these, LH1, is in intimate contact with the RC. Recent structural studies (6,20,22,25,31,36,37,43,(59)(60)(61) have indicated that the component ␣␤ dimers of LH1, each of which binds two bacteriochlorophyll (BChl) molecules and at least one molecule of carotenoid, form a ring around the RC. For Rhodospirillum rubrum (33,37,59,61) and Blastochloris viridis (previously called Rhodopseudomonas viridis) (60), both of which contain only a single light-harvesting complex, LH1 appears to completely surround the RC. In Rhodobacter sphaeroides, however, recent electron micrographic evidence (36) has suggested that the LH1 in this organism may not be completely closed, although the low resolution of the data in this study may not have been sufficient to allow a definite conclusion to be drawn. In all cases, however, it appears that the assembly of RCs and LH1 in vivo is always perfectly coordinated, and neither biochemical nor spectroscopic evidence has indicated the presence of empty LH1 rings or incorrectly assembled RCs. A continuing puzzle, therefore, concerns the mechanism of assembly of...

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Section: Discussionmentioning

confidence: 72%

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confidence: 99%

The Reaction Center H Subunit Is Not Required for High Levels of Light-Harvesting Complex 1 in Rhodospirillum rubrum Mutants

Lupo

Ghosh

2004

J Bacteriol

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“…Because of the lack of a high-resolution x-ray structure, most proposed geometries are based on low-resolution electron microscopy/atomic force microscopy data (24)(25)(26)(27)(28). A detailed discussion on this issue can be found in ref.…”

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Refinement of the x-ray structure of the RC–LH1 core complex from Rhodopseudomonas palustris by single-molecule spectroscopy

Richter

Baier

Southall

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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A unique combination of single-molecule spectroscopy with numerical simulations has allowed us to achieve a refined structural model for the bacteriochlorophyll a (BChl a) pigment arrangement in reaction center-light-harvesting 1 core complexes of Rhodopseudomonas palustris. Details in the optical spectra, such as spectral separation and mutual polarizations of spectral bands, are compared with results from numerical simulations for various models of the BChl a arrangement that were all well within the 4.8-Å limit of the accuracy of the available x-ray structure. The experimental data are consistent with a geometry where 15 BChl a dimers, each taken homologous to those from light-harvesting 2 complex from Rhodopseudomonas acidophila, are arranged in an overall elliptical structure featuring a gap on the long side of the ellipse.bacterial photosynthesis ͉ light harvesting ͉ supramolecular arrangement I n photosynthesis solar radiation is absorbed by the lightharvesting (LH) apparatus, and the excitation energy is then transferred efficiently to a reaction center (RC), where it is used to create a charge-separated state that ultimately drives all of the subsequent metabolic reactions. Most purple photosynthetic bacteria contain two types of antenna complexes, LH1 complex and LH2 complex (1, 2). The RC is closely associated with LH1, whereas LH2s are arranged around the perimeter of RC-LH1 in a 2D array, the structure of which depends on how the bacteria are grown (3-5). The progress made in high-resolution structural studies of the LH2s (6-9) has strongly stimulated research to understand the detailed mechanisms of the efficient energy transfer processes that take place in these antenna systems. The basic building block of LH2 is a protein heterodimer (␣␤), which accommodates three bacteriochlorophyll a (BChl a) pigments and one carotenoid molecule (8). Depending on the bacterial species LH2 consists either of eight or nine copies of these heterodimers, which are arranged in a ring-like structure. It has now been well established that the spatial arrangement of the pigments determines, to a large extent, the spectroscopic features of the complexes and that in these systems collective effects have to be considered to appropriately describe their electronically excited states (10-16). These effects lead to so-called Frenkel excitons, which arise from the interactions of the transition-dipole moments of the individual pigments and correspond to delocalized electronically excited states (17). Because the interaction strength between the individual pigments can be calculated on the basis of the available structural data, information about the pigment arrangement within the LH complexes becomes accessible via optical spectroscopy. From this perspective LH2 has served as a cornerstone for the development of a detailed understanding of structure-function relationships in such antenna systems (18).In contrast to LH2, where highly resolved x-ray structures are available, the discussion in the literature about the structural...

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“…Sherman et al, 1998, applied multivariate statistical analysis to 2D crystal images. Stahlberg et al, 1998, used single particle methods to detect and correct for the non-crystallographic orientation of the photosynthetic reaction center within well-ordered 2D crystal images of the surrounding light-harvesting-complex I. Tahara et al, 2000, could significantly improve the resolution of a Na+/K+-ATPase projection map by applying single particle processing methods to 2D crystal images and allowing for sample heterogeneity.…”

Section: Introductionmentioning

confidence: 99%

A maximum likelihood approach to two-dimensional crystals

Zeng

Stahlberg

Grigorieff

2007

Journal of Structural Biology

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Maximum Likelihood (ML) processing of transmission electron microscopy images of protein particles can produce reconstructions of superior resolution due to a reduced reference bias. We have investigated a ML processing approach to images centered on the unit cells of two-dimensional (2D) crystal images. The implemented software makes use of the predictive lattice node tracking in the MRC software, which is used to window particle stacks. These are then noise-whitened and subjected to ML processing. Resulting ML maps are translated into amplitudes and phases for further processing within the 2dx software package. Compared with ML processing for randomly oriented single particles, the required computational costs are greatly reduced as the 2D crystals restrict the parameter search space. The software was applied to images of negatively stained or frozen hydrated 2D crystals of different crystal order. We find that the ML algorithm is not free from reference bias, even though its sensitivity to noise correlation is lower than for pure cross-correlation alignment. Compared with crystallographic processing, the newly developed software yields better resolution for 2D crystal images of lower crystal quality, and it performs equally well for well-ordered crystal images.

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Are the light-harvesting I complexes from Rhodospirillum rubrum arranged around the reaction centre in a square geometry? 1 1Edited by R. Huber

Cited by 51 publications

References 38 publications

The Reaction Center H Subunit Is Not Required for High Levels of Light-Harvesting Complex 1 in Rhodospirillum rubrum Mutants

The Reaction Center H Subunit Is Not Required for High Levels of Light-Harvesting Complex 1 in Rhodospirillum rubrum Mutants

Refinement of the x-ray structure of the RC–LH1 core complex from Rhodopseudomonas palustris by single-molecule spectroscopy

A maximum likelihood approach to two-dimensional crystals

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