The 8.5 A projection map of the light-harvesting complex I from Rhodospirillum rubrum reveals a ring composed of 16 subunits.

Karrasch, Simone; Bullough, P.A.; Ghosh, Robin

doi:10.1002/j.1460-2075.1995.tb07041.x

Cited by 610 publications

(590 citation statements)

References 28 publications

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“…In this regard, the recent publications of the 2.5-Å (1 Å ϭ 0.1 nm) resolution crystal structure of the B800-850 complex from Rhodopseudomonas acidophila (21) and the 8.5-Å resolution electron density map of the B870 complex of Rhodospirillum rubrum (17) are of great value. Since the amino acid sequences of light-harvesting antenna complex proteins are so similar (35), we use these structural data to help extrapolate to a general model.…”

Section: Fig 7 (A)mentioning

confidence: 99%

“…The B870 antenna complex is thought to surround the reaction center, with a stoichiometry of 16 ␣␤ dimers per reaction center (17). The antenna structures appear to be closed rings (17,21) in that there is no obvious pathway for quinones, which are membrane soluble, and cytochrome c y , which is membrane bound, to move through these complexes.…”

Section: Fig 7 (A)mentioning

confidence: 99%

“…The antenna structures appear to be closed rings (17,21) in that there is no obvious pathway for quinones, which are membrane soluble, and cytochrome c y , which is membrane bound, to move through these complexes. Data from Karrasch et al and McDermott et al indicate that the transmembrane ␣ helices in the ␣␤ dimers are not in contact with each other, but that there are interactions between the extramembrane segments of ␣ and ␤ proteins (17,21). The two types of antenna apoproteins seem to form the inner (␣) and outer (␤) walls of transmembrane cylinders, with the Bchl and carotenoid pigments located between these two walls (17,21).…”

Section: Fig 7 (A)mentioning

confidence: 99%

“…Data from Karrasch et al and McDermott et al indicate that the transmembrane ␣ helices in the ␣␤ dimers are not in contact with each other, but that there are interactions between the extramembrane segments of ␣ and ␤ proteins (17,21). The two types of antenna apoproteins seem to form the inner (␣) and outer (␤) walls of transmembrane cylinders, with the Bchl and carotenoid pigments located between these two walls (17,21). Therefore, the overall structures would form a barrier to the lateral diffusion of quinols within the membrane, since noncovalently bound carotenoid and Bchl molecules tightly fill the space between the ␣ and ␤ proteins (shown most clearly in the B800-850 structure).…”

Section: Fig 7 (A)mentioning

confidence: 99%

“…We use the information summarized above and the results of a number of independent studies (2,7,17,18,19,21,22) to propose a speculative model in which the PufX protein creates a void in the structure of the B870 antenna complex, where a local absence of pigments allows passage of quinones between the reaction center and the b-c 1 complex.…”

Section: Fig 7 (A)mentioning

confidence: 99%

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Mutation of the Ser2 codon of the light-harvesting B870 alpha polypeptide of Rhodobacter capsulatus partially suppresses the pufX phenotype

1995

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The exact function of the pufX gene product of Rhodobacter capsulatus is uncertain, but deletion of the pufX gene renders cells incapable of phototrophic growth on a minimal medium, and photosynthetic electron transfer is impaired in vitro. However, suppressor mutants that are able to grow phototropically are readily isolated. Two such suppressor mutants were characterized as to their phototrophic growth properties, their fluorescence at different incident light intensities, the integrity of their chromatophores, and their abilities to generate a transmembrane potential. We found that the photosynthetic apparatus in the suppressor mutants was less stable than that of the pseudo-wild-type and primary mutant strains and that the suppressor mutants used light energy less efficiently than the pseudo-wild-type strain. Therefore, the suppressor strains are more precisely designated partial suppressor mutants. The locations and sequences of the suppressor mutations were determined, and both were found to change the second codon of the pufA gene. It is hypothesized that the serine residue specified by this codon is important in interactions between the B870 ␣ protein and other membrane-bound polypeptides and that suppressor mutations at this position partially compensate for loss of the PufX protein. A model is proposed for the function of the PufX protein.The purple nonsulfur bacterium Rhodobacter capsulatus is capable of both respiratory and phototrophic growth under appropriate conditions. Since the photosynthetic apparatus can be gratuitously induced during aerobic dark growth simply by lowering the oxygen concentration, R. capsulatus is a good model organism for mutational studies of the assembly and function of photosynthetic membrane-bound electron transport complexes.Energy capture during phototrophic growth is accomplished by what is herein designated the photosynthetic unit. The photosynthetic unit of R. capsulatus is composed of three types of integral membrane polypeptide complexes: the light-harvesting antennae (although several designations have been given for light-harvesting complexes in different species of purple bacteria, in this report we use B800-850 for LH2 and B870 for LH1 complexes); the reaction center, which mediates the formation of a transmembrane potential by using the energy captured by the antenna complexes; and the ubiquinol:cytochrome b-c 1 complex (b-c 1 complex), which converts the transmembrane potential to a proton gradient. A variety of experimental and theoretical data are consistent with the view that in wildtype cells of purple nonsulfur bacteria, these three types of complexes are organized in the membrane in such a way as to enhance functional interactions with each other (16,34). A structural interaction between the R. capsulatus reaction center and B870 antenna complex was indicated by the finding that a single amino acid change of the B870 ␣ polypeptide caused the loss of the B870 complex and resulted in a change in the position of the reaction center. Consequently, the reac...

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Section: Fig 7 (A)mentioning

confidence: 99%

Section: Fig 7 (A)mentioning

confidence: 99%

Section: Fig 7 (A)mentioning

confidence: 99%

Section: Fig 7 (A)mentioning

confidence: 99%

Section: Fig 7 (A)mentioning

confidence: 99%

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Mutation of the Ser2 codon of the light-harvesting B870 alpha polypeptide of Rhodobacter capsulatus partially suppresses the pufX phenotype

1995

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A light-harvesting antenna protein retains its folded conformation in the absence of protein-lipid and protein-pigment interactions

et al. 1999

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The first study by nmr of the integral membrane protein, the bacterial light‐harvesting (LH) antenna protein LH1β, is reported. The photosynthetic apparatus of purple bacteria contains two different kinds of antenna complexes (LH1 and LH2), which consist of two small integral membrane proteins α and β, each of approximately 6 kDa, and bacteriochlorophyll and carotenoid pigments. We have purified the antenna polypeptide LH1β from Rhodobacter sphaeroides, and have recorded CD spectra and a series of two‐dimensional nmr spectra. A comparison of CD spectra of LH1β observed in organic solvents and detergent micelles shows that the helical character of the peptide does not change appreciably between the two milieus. A significantly high‐field shifted methyl signal was observed both in organic solvents and in detergent micelles, implying that a similar three‐dimensional structure is present in each case. However, the 1H‐nmr signals observed in organic solvents had a narrower line width and better resolution, and it is shown that in this case organic solvents provide a better medium for nmr studies than detergent micelles. A sequential assignment has been carried out on the C‐terminal transmembrane region, which is the region in which the pigment is bound. The region is shown to have a helical structure by the chemical shift values of the α‐CH protons and the presence of nuclear Overhauser effects characteristic of helices. An analysis of the amide proton chemical shifts of the residues surrounding the histidine chlorophyll ligand suggests that the local structure is well ordered even in the absence of protein–lipid and protein–pigment interactions. Its structure was determined from 348 nmr‐derived constraints by using distance geometry calculations. The polypeptide contains an α‐helix extending from Leu19 (position of cytoplasmic surface) to Trp44 (position of periplasmic surface). The helix is bent, as expected from the amide proton chemical shifts, and it is similar to the polypeptide fold of the previously determined crystal structure of Rhodopseudomonas acidophila Ac10050 LH2β (S. M. Prince et al., Journal of Molecular Biology, 1997, Vol. 268, pp. 412–423). It is concluded that the polypeptide conformation of this region may facilitate assembly of the LH complex. © 1999 John Wiley & Sons, Inc. Biopoly 49: 361–372, 1999

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Excitation energy trapping by the reaction center ofRhodobacter Sphaeroides

Damjanovi

Ritz

Schulten

2000

Int. J. Quant. Chem.

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The excitation energy transfer between light-harvesting complex I (LH-I)and the photosynthetic reaction center (RC) of the purple bacterium Rhodobacter (Rb.) sphaeroides is investigated on the basis of the atomic level structures of the two proteins, assuming a ring-shaped model for LH-I. Rates of excitation energy transfer are calculated, based on Förster theory. The LH-I and RC electronic excitations are described through effective Hamiltonians established previously, with parameters derived from quantum chemistry calculations by Cory and co-workers. We also present an effective Hamiltonian description with parameters based on spectroscopic properties. We study two extreme models of LH-I excitations: electronic excitations delocalized over the entire LH-I ring and excitations localized on single bacteriochlorophylls. The role of accessory bacteriochlorophylls in bridging the excitation energy transfer is investigated. The rates of back-transfer, i.e., RC → LH-I excitation energy transfer, are determined, too.

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The 8.5 A projection map of the light-harvesting complex I from Rhodospirillum rubrum reveals a ring composed of 16 subunits.

Cited by 610 publications

References 28 publications

Mutation of the Ser2 codon of the light-harvesting B870 alpha polypeptide of Rhodobacter capsulatus partially suppresses the pufX phenotype

Mutation of the Ser2 codon of the light-harvesting B870 alpha polypeptide of Rhodobacter capsulatus partially suppresses the pufX phenotype

A light-harvesting antenna protein retains its folded conformation in the absence of protein-lipid and protein-pigment interactions

Excitation energy trapping by the reaction center ofRhodobacter Sphaeroides

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