Absorption and CD Spectroscopy and Modeling of Various LH2 Complexes from Purple Bacteria

Georgakopoulou, Sofia; Frese, Raoul N.; Johnson, E. T.; Koolhaas, Corline; Cogdell, Richard J.; Grondelle, Rienk van; Zwan, Gert van der

doi:10.1016/s0006-3495(02)75565-3

Cited by 133 publications

(205 citation statements)

References 53 publications

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“…In the LH2 complexes studied in the past, 41,40 we do not observe such a strong loss of the conservative nature of the Q Y CD signal for various carotenoid-containing complexes. The NIR CD signal of those LH2 complexes is much more intense than the one of the LH1s studied here, and this can render the carotenoid effect unnoticeable.…”

Section: Discussioncontrasting

confidence: 54%

“…By using absorption and CD spectroscopy and modeling, we have been able to contemplate a more detailed organization of LH complexes. [39][40][41] On the basis of the known structures, we have explained several aspects of their absorption and CD spectra, like the origin of the red-shift of the zero crossing in the CD signal with respect to the absorption maximum. 42 Moreover, we have been able to estimate the interaction energy between nearest neighbors in the B850 ring by identifying the high exciton component, 43 the position of which has been debated for many years.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of the Effects of Different Carotenoids on the Absorption and CD Signals of Light Harvesting 1 Complexes

et al. 2006

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Absorption and circular dichroism (CD) spectra of light-harvesting (LH)1 complexes from the purple bacteria Rhodobacter (Rba.) sphaeroides and Rhodospirillum (Rsp.) rubrum are presented. The complexes exhibit very low intensity, highly nonconservative, near-infrared (NIR) CD spectra. Absorption and CD spectra from several mutant and reconstituted LH1 complexes, with the carotenoid neurosporene and the precursor phytoene replacing the wild-type (WT) carotenoids, are also examined. The experiments show that the position of the carotenoid bands as well as the bacteriochlorophyll (BChl)/carotenoid ratio affect the NIR CD spectra: bluer bands and larger ratios make the NIR CD signal more conservative. Modeling results that support this finding are presented. This study, combined with the theoretical approach of the companion paper, where modeling of such complexes is presented and discussed in detail, provide a complete explanation of the origin of the nonconservative NIR CD spectra of LH1 and B820.

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Section: Discussioncontrasting

confidence: 54%

Section: Introductionmentioning

confidence: 99%

Investigation of the Effects of Different Carotenoids on the Absorption and CD Signals of Light Harvesting 1 Complexes

et al. 2006

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“…An abundance of LH2 complexes in more curved regions explains a decrease in LD relative to LH1: the curvature will lead to an extra anisotropy for LH2 relative to LH1. The transition dipole moments of the B850 BChls are not oriented exactly perpendicular to the orientation axis (25), which causes a reduction of the averaged LD signal.…”

Section: Resultsmentioning

confidence: 99%

The long-range organization of a native photosynthetic membrane

Frese

Siebert

Niederman

et al. 2004

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

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Photosynthesis relies on the delicate interplay between a specific set of membrane-bound pigment-protein complexes that harvest and transport solar energy, execute charge separation, and conserve the energy. We have investigated the organization of the light-harvesting (LH) and reaction-center (RC) complexes in native bacterial photosynthetic membranes of the purple bacterium Rhodobacter sphaeroides by using polarized light spectroscopy, linear dichroism (LD) on oriented membranes. These LD measurements show that in native membranes, which contain LH2 as the major energy absorber, the RC-LH1-PufX complexes are highly organized in a way similar to that which we found previously for a mutant lacking LH2. The relative contribution of LH1 and LH2 light-harvesting complexes to the LD spectrum shows that LH2 preferentially resides in highly curved parts of the membrane. Combining the spectroscopic data with our recent atomic force microscopy (AFM) results, we propose an organization for this photosynthetic membrane that features domains containing linear arrays of RC-LH1-PufX complexes interspersed with LH2 complexes and some LH2 found in separate domains. The study described here allows the simultaneous assessment of both global and local structural information on the organization of intact, untreated membranes. membrane organization ͉ photosynthesis ͉ polarized spectroscopy P hotosynthetic purple bacteria are among the oldest species known (1, 2). Within the class of photosynthetic organisms, they have specialized in growing on low-energy photons under dim light conditions (3). The main characteristic of the photosystems of these bacteria is their ''less is more'' design: They are constructed by the repetitive use of identical protein units as building blocks, resulting in highly symmetric pigment-protein complexes (''rings'') with carefully tuned light-absorption properties. Protein-bound chromophores, carotenoids and bacteriochlorophylls (BChls), are the light-interacting functional groups that carry out the photosynthetic process: the conversion of light energy into a stable charge separation. The incoming light is collected by specialized lightharvesting (LH) complexes, and, by means of intra-and intercomplex energy transfer, the excitation energy is transported to a reaction center (RC). Here charge separation takes place, which fuels subsequent electron-and proton-transfer reactions that build up the transmembrane electrochemical gradient that is eventually used for the formation of ATP.Photosynthetic purple bacteria may contain two different types of pigment-protein complexes involved in energy-and electrontransfer reactions: the RC-LH1 core complexes and the peripheral light-harvesting complex 2 (LH2). Both LH complexes are composed of two concentric rings of roughly circularly arranged ␣-helices that bind the carotenoid and BChl pigments. The peripheral LH2 feeds its excitations into LH1, which surrounds the RC, enabling efficient energy transfer from the LH1 BChls to the primary RC energy acceptor͞electron...

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“…Different ring systems have characteristic UV-visible absorbance, circular dichroism (CD), and fluorescent spectral properties, which can be used for identification and to characterize the metal binding properties of the molecule (131, 133-136, 138, 148, 151-153). Excitation energy transfer occurs between the two rings in mb (136,154), as observed for the chromophores of light-harvesting complexes (155)(156)(157), resulting in the fluorescent properties of mbs. For example, the emission intensity of mbs increases with selective hydrolysis of the one of the rings, and emission intensity often increases following metal addition (132, 136-138, 141, 148, 154).…”

Section: Methanobactins As Chalkophoresmentioning

confidence: 91%

Methanobactin and the Link between Copper and Bacterial Methane Oxidation

DiSpirito

Semrau

Murrell

et al. 2016

Microbiol Mol Biol Rev

125

157

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SUMMARYMethanobactins (mbs) are low-molecular-mass (<1,200 Da) copper-binding peptides, or chalkophores, produced by many methane-oxidizing bacteria (methanotrophs). These molecules exhibit similarities to certain iron-binding siderophores but are expressed and secreted in response to copper limitation. Structurally, mbs are characterized by a pair of heterocyclic rings with associated thioamide groups that form the copper coordination site. One of the rings is always an oxazolone and the second ring an oxazolone, an imidazolone, or a pyrazinedione moiety. The mb molecule originates from a peptide precursor that undergoes a series of posttranslational modifications, including (i) ring formation, (ii) cleavage of a leader peptide sequence, and (iii) in some cases, addition of a sulfate group. Functionally, mbs represent the extracellular component of a copper acquisition system. Consistent with this role in copper acquisition, mbs have a high affinity for copper ions. Following binding, mbs rapidly reduce Cu2+to Cu1+. In addition to binding copper, mbs will bind most transition metals and near-transition metals and protect the host methanotroph as well as other bacteria from toxic metals. Several other physiological functions have been assigned to mbs, based primarily on their redox and metal-binding properties. In this review, we examine the current state of knowledge of this novel type of metal-binding peptide. We also explore its potential applications, how mbs may alter the bioavailability of multiple metals, and the many roles mbs may play in the physiology of methanotrophs.

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Absorption and CD Spectroscopy and Modeling of Various LH2 Complexes from Purple Bacteria

Cited by 133 publications

References 53 publications

Investigation of the Effects of Different Carotenoids on the Absorption and CD Signals of Light Harvesting 1 Complexes

Investigation of the Effects of Different Carotenoids on the Absorption and CD Signals of Light Harvesting 1 Complexes

The long-range organization of a native photosynthetic membrane

Methanobactin and the Link between Copper and Bacterial Methane Oxidation

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