ISOLATION AND CHARACTERIZATION OF A STRUCTURAL SUBUNIT FROM THE CORE LIGHT‐HARVESTING COMPLEX OF Rhodobacter sphaeroides 2.4.1 AND puc705‐BA

Chang, Mu‐Chieh; Meyer, Leslye; Loach, Paul A.

doi:10.1111/j.1751-1097.1990.tb08696.x

Cited by 49 publications

(50 citation statements)

References 40 publications

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“…Riophys. Acta 807, [10][11][12][13][14][15][16][17][18][19][20][21]. These results indicate that one of these H bonds Is to drrp43, placing this residue in close proximity to the bacteriochlorophyll a macrocycle with which It interacts.…”

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confidence: 67%

“…The LH1 forms a B820 species, which can be reassociated to form a B873 complex. This work has primarily studied LH1 from Rhodospirillum rubrum, but Chang et al (18) have also isolated a B820 species from Rb. sphaeroides and similar B820 complexes have been obtained for Rhodobacter capsulatus (19), Rhodopseudomonas marina (20), and Rhodocyclus gelatinosus (21), leading to the speculation that this bchl dimer is the building block of the LH1 complex.…”

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confidence: 99%

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Modification of a hydrogen bond to a bacteriochlorophyll a molecule in the light-harvesting 1 antenna of Rhodobacter sphaeroides.

Olsen

Sockalingum

Robert

et al. 1994

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

119

141

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Site-directed mutagenesis has been used to examine the function of a highly conserved aromatic residue, darp43, in the light-harvesting 1 antenna ofthe photosynthetic bacterium Rhodobacter sphaeroides. In this antenna dfrp43 is thought to be located near the putative binding site for bacteriochlorophyll; in this work it was changed to both Tyr and The photosynthetic apparatus of the purple bacterium Rhodobacter sphaeroides consists of a membrane protein complex, the reaction center (RC), surrounded by a core light-harvesting complex, LH1, also referred to as B875, in a fixed stoichiometry of -12 LH1 a(3 dimers per RC. An additional peripheral light-harvesting complex, LH2, also referred to as B800-850, occurs in variable amounts in response to environmental levels of light and oxygen (1, 2). The structure of the RC of Rb. sphaeroides is known to atomic resolution (3, 4); however, the structures of the LH1 and LH2 complexes are not known, although diffracting crystals ofvarious LH complexes have been reported (5-10). As yet, these structures have not been solved, so it is necessary to employ other methods such as mutagenesis and spectroscopy to obtain relevant data. As a result of these approaches, more information is becoming available on the interaction of the chromophores of LH1 and LH2 with nearby residues of the antenna polypeptides (11,12). These data can be used to test existing model structures derived from spectroscopic and electrophoretic mobility studies of wild-type (WT) complexes. The models that have been proposed for bacterial LH complexes all follow a similar pattern in that the af8 heterodimer, which in the case of LH1 would bind 2 bacteriochlorophyll (bchl) molecules, is considered to be the minimum possible building block. The topology and conformation of these subunits are thought to be similar, each with a cytoplasmically exposed N terminus, a single transmembrane helix, and a periplasmic C terminus. There are indications of turns at or near the membrane interfaces (13 (20), and Rhodocyclus gelatinosus (21), leading to the speculation that this bchl dimer is the building block of the LH1 complex. Characterization of the B820 form (22) supports the idea that it is an excitonically coupled bchl a dimer. Moreover, resonance Raman measurements of the B820 showed that it differed from the B873 form in the interactions of the C2 acetyl carbonyl; the loss of a H bond was one possible explanation of the Raman data. A more detailed Raman study of the LH1 ofRs. rubrum G9 has shown that upon formation of the B820, the strength of one H bond was increased (23 FT, Fourier transform; WT, wild type; P-OG, n-octyl P-Dglucopyranoside; ODPS, n-octyldipropyl sulfoxide. 7124The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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confidence: 67%

mentioning

confidence: 99%

Modification of a hydrogen bond to a bacteriochlorophyll a molecule in the light-harvesting 1 antenna of Rhodobacter sphaeroides.

Olsen

Sockalingum

Robert

et al. 1994

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

119

141

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“…1 in supplemental material). The conditions that are known to dissociate LH1 of R. sphaeroides into B820 subunits necessitate the use of either a carotenoidless mutant LH1 or the extraction of lyophilized chromatophores with petroleum ether to obtain efficient dissociation of the complex (39). We suggest that the presence of native carotenoids in our complexes protects them against the concentration of ␤-OG used; indeed Scheuring et al (15) used 3% ␤-OG to isolate and purify dimeric core complexes of R. sphaeroides, indicating that delicate higher orders of organization are preserved, even at this high concentration of ␤-OG.…”

Section: Structural Basis For Variations In Size and Shape Of The Lh1mentioning

confidence: 99%

Flexibility and Size Heterogeneity of the LH1 Light Harvesting Complex Revealed by Atomic Force Microscopy

Bahatyrova

Frese

Werf

et al. 2004

Journal of Biological Chemistry

118

100

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Previous electron microscopic studies of bacterial RC-LH1 complexes demonstrated both circular and elliptical conformations of the LH1 ring, and this implied flexibility has been suggested to allow passage of quinol from the Q B site of the RC to the quinone pool prior to reduction of the cytochrome bc 1 complex. We have used atomic force microscopy to demonstrate that these are just two of many conformations for the LH1 ring, which displays large molecule-to-molecule variations, in terms of both shape and size. This atomic force microscope study has used a mutant lacking the reaction center complex, which normally sits within the LH1 ring providing a barrier to substantial changes in shape. This approach has revealed the inherent flexibility and lack of structural coherence of this complex in a reconstituted lipid bilayer at room temperature. Circular, elliptical, and even polygonal ring shapes as well as arcs and open rings have been observed for LH1; in contrast, no such variations in structure were observed for the LH2 complex under the same conditions. The basis for these differences between LH1 and LH2 is suggested to be the H-bonding patterns that stabilize binding of the bacteriochlorophylls to the LH polypeptides. The existence of open rings and arcs provides a direct visualization of the consequences of the relatively weak associations that govern the aggregation of the protomers (␣ 1 ␤ 1 Bchl 2 ) comprising the LH1 complex. The demonstration that the linkage between adjacent protomer units is flexible and can even be uncoupled at room temperature in a detergent-free membrane bilayer provides a rationale for the dynamic separation of individual protomers, and we may now envisage experiments that seek to prove this active opening process.Photosynthetic organisms harvest light energy and convert it to a chemically useful form, using light harvesting (LH) 1 and reaction center (RC) complexes. In the purple photosynthetic bacteria, the reaction center, which is the site of photochemistry, receives excitation energy from the light harvesting LH1 complex, which receives energy in turn from the LH2 complex (reviewed in Ref. 1). The atomic structure of the Rhodopseudomonas acidophila LH2 complex (2) and the cryo-electron microscopy (EM) structure of the Rhodobacter sphaeroides complex (3) both revealed a circular arrangement of nine protomers, each consisting of an ␣ and a ␤ polypeptide. The LH2␣ polypeptides formed an inner ring, with the ␤ ring outermost; in all, 27 bacteriochlorophyll (Bchl) molecules are bound to this structure (2). More recent work has established that LH1 surrounds the RC using an arrangement of 16 ␣␤ protomers and 32 Bchls (4) when there is no prulifloxacin PufX protein. In other bacteria, an LH1 ring of 15 ␣␤ protomers, together with either PufX or a putative PufX homologue (W), form a continuous ring of protein around the RC (5, 6). The demonstration of both circular and elliptical forms of this LH1 complex provided evidence for its flexibility (4). This property of the LH1 complex wa...

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“…In particular here, ␤-octyl glucoside (␤OG) would be the ideal detergent because it has been shown to be capable of reversibly dissociating the native complex. 13 However, perdeuterated ␤OG is not readily available. We have therefore investigated LH1␤ both in organic solvents and bound to perdeuterated sodium dodecyl sulfate (SDS) micelles, and we conclude that in this case organic solvents are preferable for conformational studies of this integral membrane polypeptide.…”

Section: Introductionmentioning

confidence: 99%

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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ISOLATION AND CHARACTERIZATION OF A STRUCTURAL SUBUNIT FROM THE CORE LIGHT‐HARVESTING COMPLEX OF Rhodobacter sphaeroides 2.4.1 AND puc705‐BA

Cited by 49 publications

References 40 publications

Modification of a hydrogen bond to a bacteriochlorophyll a molecule in the light-harvesting 1 antenna of Rhodobacter sphaeroides.

Modification of a hydrogen bond to a bacteriochlorophyll a molecule in the light-harvesting 1 antenna of Rhodobacter sphaeroides.

Flexibility and Size Heterogeneity of the LH1 Light Harvesting Complex Revealed by Atomic Force Microscopy

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

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