Structural characterization of the B800–850 and B875 light-harvesting antenna complexes from Rhodobacter sphaeroides by electron microscopy

Boonstra, Arjen F.; Visschers, Ronald W.; Calkoen, Florentine; Grondelle, Rienk van; Bruggen, E.F.J. Van; Boekema, Egbert J.

doi:10.1016/0005-2728(93)90100-t

Cited by 49 publications

(47 citation statements)

References 19 publications

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“…However electron microscopy measurements on an identically prepared sample have shown that the sample mainly consists of small isolated rings. 22 As was stated above, to calculate the absolute amount of superradiance (or emitting dipole strength) from the radiative rate, both the refractive index of the medium and the relative dielectric constant of the protein need to be known. The experimentally obtained higher value of the emitting dipole strength at room temperature for LH-1 could indicate that the dielectric constant in this complex is somewhat lower.…”

Section: Discussionmentioning

confidence: 99%

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

et al. 1997

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We present temperature-dependent fluorescence quantum yield and lifetime measurements on the LH-1 and LH-2 complexes of Rhodobacter sphaeroides and on the isolated B820 subunit of Rhodospirillum rubrum. From these measurements the superradiance is calculated, which is related to the delocalization of excitations in these complexes. In the B820 preparation we find a radiative rate that is 30% higher than that of monomeric bacteriochlorophyll, in agreement with a dimer model of this subunit. At room temperature both LH-1 and LH-2 are superradiant relative to monomeric Bchl-a with enhancement factors of 3.8 and 2.8, respectively. In LH-2 the radiative rate does not change significantly upon lowering the temperature to 4 K. LH-1 however exhibits a strong temperature dependence, giving rise to a 2.4 times higher radiative rate at 4 K relative to room temperature. From modeling of the superradiance using a Hamiltonian based on the LH-2 structure and including site inhomogeneity, we conclude that the ratio of inhomogeneity over the coupling between the pigments is around 1 for LH-1 and 2-3 for LH-2. From the Monte Carlo simulations we estimate the delocalization length in LH-1 and LH-2 to be on the order of 3-4 pigments at room temperature.

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Section: Discussionmentioning

confidence: 99%

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

et al. 1997

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“…LH2 of Rb. sphaeroides was estimated to be (R ) 6 , 15 while the others were crystallized as (R ) 9 4,5 or (R ) 8 . 6,33 Furthermore, LH1, with a Tr(∆r) of 1300-1800 Å 3 /f 2 , has an estimated ring size of (R ) 16 .…”

Section: Discussionmentioning

confidence: 99%

“…sphaeroides LH2 complexes suggests a hexameric structure indicating a (R ) 6 organization. 15 Rsp. molischianum LH2 is built up of eight R -subunits and has a similar overall arrangement of the pigments as in Rps.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the Light-Harvesting Antennas of Photosynthetic Purple Bacteria by Stark Spectroscopy. 2. LH2 Complexes: Influence of the Protein Environment

et al. 1997

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We have performed low-temperature Stark spectroscopy on a variety of different LH2 complexes from four photosynthetic bacteria, with the aim of characterizing the electric field response of the B800 and B850 absorption properties as a function of the protein environment. The following LH2 complexes were investigated: B800-850 and B800-820 of Rhodopseudomonas (Rps) acidophila; B800-850, B800-840 (RTyr +13 fPhe), and B800-826 (RTyr +13 fPhe, RTyr +14 fLeu) of Rhodobacter (Rb.) sphaeroides; B800-850 and B800-830 (obtained at high LDAO) of Ectothiorhodospira sp.; and B800-850 of Rhodospirillum (Rsp.) molischianum. For all these cases the spectral blue shift of B850 has been assigned to the loss hydrogenbonding interaction with the acetyl carbonyl of bacteriochlorophyll a. |∆µ| values for the 850 nm bands as well as for the blue-shifted bands are all on the order of 3-4.5 D/f. The loss of hydrogen-bonding interactions has only small effects on |∆µ| in these complexes. The values of the difference polarizability, Tr(∆r), are large (600-1400 Å 3 /f 2 ). The results are discussed in terms of crystal-structure-based models for LH2, in which pigment-pigment and pigment-protein interactions are considered; strong pigment-pigment interactions were found to be especially important. The values of |∆µ| for the 800 nm band are small, 1.0-1.5 D/f for LH2 complexes from Rb. sphaeroides and Rps. acidophila. However, in Rsp. molischianum and Ectothiorhodospira sp. |∆µ| values are much larger, of the order of 3 D/f. The difference in the B800 band is assigned to the difference in orientation of the B800 pigments in Rsp. molischianum and Ectothiorhodospira sp., as compared to the Rps. acidophila and Rb. sphaeroides. Due to the difference in orientation, the interactions of the Bchl a with the surrounding protein and neighboring carotenoid pigments are also not identical.

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“…These heterodimers aggregate to a large complex, functioning as light-harvesting antennae. The size of the aggregate depends on the type of light-harvesting complex and varies from species to species, ranging from a putative hexamer for LH-11 of Rhodobacfer sphaeroides (Boonstra et al, 1993) to a hexadecamer for LH-1 of Rhodospirillum rubrum (Karrasch et al, 1995). Various models have been proposed for the light-harvesting complex of purple bacteria (Zuber, 1986;Zuber & Brunisholz, 1991;Olsen & Hunter, 1994).…”

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Predicting the structure of the light-harvesting complex II ofrhodospirillum molischianum

Hamer

et al. 1995

Protein Sci.

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We attempted to predict through computer modeling the structure of the light-harvesting complex II (LH-Ii) of Rhodospirillum molischianum, before the impending publication of the structure of a homologous protein solved by means of X-ray diffraction. The protein studied is an integral membrane protein of 16 independent polypeptides, 8 a-apoproteins and 8 @-apoproteins, which aggregate and bind to 24 bacteriochlorophyll-a's and 12 lycopenes. Available diffraction data of a crystal of the protein, which could not be phased due to a lack of heavy metal derivatives, served to test the predicted structure, guiding the search. In order to determine the secondary structure, hydropathy analysis was performed to identify the putative transmembrane segments and multiple sequence alignment propensity analyses were used to pinpoint the exact sites of the 20-residue-long transmembrane segment and the 4-residue-long terminal sequence at both ends, which were independently verified and improved by homology modeling. A consensus assignment for the secondary structure was derived from a combination of all the prediction methods used. Three-dimensional structures for the cy-and the @-apoprotein were built by comparative modeling. The resulting tertiary structures are combined, using X-PLOR, into an a@ dimer pair with bacteriochlorophyll-a's attached under constraints provided by site-directed mutagenesis and spectral data. The a@ dimer pairs were then aggregated into a quaternary structure through further molecular dynamics simulations and energy minimization. The structure of LH-I1 so determined is an octamer of a@ heterodimers forming a ring with a diameter of 70 A.

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Structural characterization of the B800–850 and B875 light-harvesting antenna complexes from Rhodobacter sphaeroides by electron microscopy

Cited by 49 publications

References 19 publications

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

Characterization of the Light-Harvesting Antennas of Photosynthetic Purple Bacteria by Stark Spectroscopy. 2. LH2 Complexes: Influence of the Protein Environment

Predicting the structure of the light-harvesting complex II ofrhodospirillum molischianum

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