Structure-Function Relationships in Core Light-Harvesting Complexes (LHI) As Determined by Characterization of the Structural Subunit and by Reconstitution Experiments

Loach, Paul A.; Parkes-Loach, Pamela S.

doi:10.1007/0-306-47954-0_21

Cited by 41 publications

(68 citation statements)

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“…Both the B820 subunit and the LH1 complex have also been reconstituted from the separately isolated components (16)(17)(18). The isolated B820 subunit of this mutant strain is believed to be composed either of one R -polypeptide pair and two BChl molecules (13,19) or of two R polypeptide pairs and four BChl molecules (14,15). However, spectroscopic evidence strongly favors B820 being a dimer of bacteriochlorophylls (20)(21)(22).…”

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Oligomerization of Light-Harvesting I Antenna Peptides of Rhodospirillum rubrum

Pandit

Visschers²,

Stokkum

et al. 2001

Biochemistry

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We investigated the oligomerization of the core light-harvesting complex (LH1) of Rhodospirillum rubrum from the separated R BChl 2 subunits (B820) and the oligomerization of the B820 subunit from its monomeric peptides. The full LH1 complex was reversibly associated from B820 subunits by either varying the temperature in the range 277-300 K or by varying the detergent concentration in the buffer from 0.36 to 0.52% n-octyl--D-glucopyranoside. Temperature-induced transition measurements showed hysteresis: raising the temperature induced dissociation of B873 directly into B820 subunits whereas upon recooling an intermediate spectral form was observed with an absorption maximum located around 850 nm. This intermediate form was also observed in detergent-induced transitions. It is speculated that the B850 form is a small aggregate of B820, for instance a dimer. Additionally, during a temperaturemediated transition at low detergent concentration, a set of spectral forms with maxima slightly blueshifted from 873 nm were observed, possibly due to opened rings with one or only a few R BChl 2 units missing. The temperature-induced transition of LH1 is discussed in terms of a simple assembly model. It is concluded that a moderately cooperative assembly explains the formation of small aggregates of B820 as well as of incomplete rings. Furthermore, the B820 subunits were reversibly dissociated into the monomeric B777 form by increasing either the temperature or the detergent concentration. Estimations of the enthalpy and entropy changes for the dimeric association reaction of B777 into B820 yielded an enthalpy change of -216 kJ mol -1 and an entropy change of -0.59 kJ mol -1 K -1 , at a detergent concentration of 0.8% n-octyl--D-glucopyranoside.The light-harvesting complexes in the membranes of photosynthetic bacteria are responsible for the initial capture of light and transfer of excitation energy to the photosynthetic reaction centers. In purple non-sulfur bacteria, two types of light-harvesting complexes occur: the LH1 1 core antenna surrounding the reaction center and the LH2 peripheral antenna that is connected to the LH1 (1-4). Both types of complexes consist of ringlike oligomers of two types of pigment-protein subunits, the so-called R and polypeptides, that each bind one or two bacteriochlorophyll pigments. For all species, both the R and polypeptide contain one transmembrane R-helical stretch as a highly conserved structural element (1, 5). The structures of LH2 of Rhodopseudomonas. acidophila (6) and LH2 of Rhodospirillum. molischianum (7) have been resolved to high resolution: both complexes were shown to contain an inner ring of R-polypeptides and an outer ring of -polypeptides with a ring of bacteriochlorophylls, absorbing at 850 nm and called B850s, sandwiched between the two rings. Between the -polypeptides, a second ring of bacteriochlorophylls absorbing at 800 nm occurs, and these are called B800s and are positioned parallel to the membrane plane, close to the cytosolic surface. The LH2 ring of ...

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“…sphaeroides, but not for subunit formation of Rs. rubrum (19). Second, ion pairing of amino acid residues contributes to stabilization of both the dimer subunits and the full complex.…”

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confidence: 99%

Oligomerization of Light-Harvesting I Antenna Peptides of Rhodospirillum rubrum

Pandit

Visschers²,

Stokkum

et al. 2001

Biochemistry

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“…In the background, Klaus Schulten was attempting to use computational methods to solve the structure of LH2 from R. molischianum (Hu et al 1995). The race was finally won in Glasgow once Neil Isaacs arrived in 1989 and took up the Chair of Protein Crystallography, after which the structure was finally completed in the winter of 1994 (McDermott et al 1995), following 10 years of work.…”

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“…In the 1980s, Paul Loach's group (Loach and Parkes-Loach 1995) developed an in vitro system to reconstitute the LH1 complex from its constituent components. This proved to be, and still is, a very useful way in which to begin to study the process of assembly of purple bacterial antenna complexes in vitro.…”

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Purple Bacterial Light-harvesting Complexes: From Dreams to Structures

Cogdell

Hashimoto

Gardiner

2004

Photosynthesis Research

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“…In vitro assembly of LH complexes As examined in detail by Paul Loach's group (Loach and Parkes-Loach 1995), treatment of LH1 complexes with β-octyl glucoside gives rise to the B820 subunit form (α 1 β 1 BChl 2 ), which can be reconstituted into the oligomeric LH 1 complex after detergent dilution. Reconstitution has been achieved with several BChl a-type LH 1s and the BChl b-type of B. viridis, and with partially truncated or mutated polypeptides and structural analogs of BChl.…”

Section: The Assembly Of Integral Membrane Complexesmentioning

confidence: 99%

Membrane biogenesis in anoxygenic photosynthetic prokaryotes

Drews

Niederman

Discoveries in Photosynthesis

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Following the discovery of photosynthetic bacteria in the nineteenth century, technical developments of the 1950s led to their use in membrane biogenesis studies. These investigations had their origins in the isolation of subcellular particles designated as 'chromatophores' by Roger Stanier and colleagues, which were shown to be photosynthetically competent by Albert Frenkel, and to originate from the intracytoplasmic membrane (ICM) continuum observed in electron micrographs. These ultrastrucutral studies by the G. Drews group, Germaine Cohen-Bazire and others also suggested that the ICM originates by invagination of the cytoplasmic membrane, as later established in the biochemical and biophysical work of the R. Niederman and Drews groups. Through a combination of genetic approaches, first introduced in the early 1980s by Barry Marrs, and the atomic resolution structures determined for light-harvesting antennae and reaction centers, a detailed understanding is emerging of mechanisms regulating their levels in the membrane and the roles played by specific protein domains and additional factors in their assembly and supramolecular organization. Prospects for additional progress during the twenty-first century include further elucidation of molecular aspects of the assembly process and the application of newer spectroscopic probes to photosynthetic unit formation.

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Structure-Function Relationships in Core Light-Harvesting Complexes (LHI) As Determined by Characterization of the Structural Subunit and by Reconstitution Experiments

Cited by 41 publications

References 124 publications

Oligomerization of Light-Harvesting I Antenna Peptides of Rhodospirillum rubrum

Oligomerization of Light-Harvesting I Antenna Peptides of Rhodospirillum rubrum

Purple Bacterial Light-harvesting Complexes: From Dreams to Structures

Membrane biogenesis in anoxygenic photosynthetic prokaryotes

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