Circular dichroism (CD) study of peridinin[ndash ]chlorophyll a protein (PCP) complexes from marine dinoflagellate algae The tetramer approach

Pilch, Mariusz; Pawlikowski, M.

doi:10.1039/a705173e

Cited by 15 publications

(12 citation statements)

References 20 publications

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“…LH1 and LH2 complexes), there is a conspicuous non-coincidence of absorption and CD bands (35), the reason for which remains unclear. Excitonic interactions among Crts could produce such shifts, but the occurrence of direct Crt-Crt interactions has hitherto been demonstrated conclusively only in a single case, the peridinin-chlorophyll protein from dinoflagellates (40,41). No such shifts have been observed with iB873: its CD spectrum shows reasonably well defined maxima in the Crt region between 400 and 570 nm, whose positions coincide with band progression in the absorption.…”

Section: Discussionmentioning

confidence: 93%

Trapping of an Assembly Intermediate of Photosynthetic LH1 Antenna beyond B820 Subunit

Fiedor

Scheer²

2005

Journal of Biological Chemistry

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Most photosynthetic LH1 antennae undergo dissociation into B820 subunits, suggesting their universal character as structural modules. However, dissociation into subunits seems to occur reversibly only in the absence of carotenoids and the subunits were never found to bind carotenoids. The interactions of carotenoids with B820 have been studied in a newly developed reconstitution assay of the LH1 antenna from Rhodospirillum rubrum (Fiedor, L., Akahane, J., and Koyama, Y. (2004) Biochemistry 43, 16487-16496). These model studies show that B820 subunits strongly interact with carotenoids and spontaneously form stable LH1-like complexes with substoichiometric carotenoid content. This is the first experimental evidence that B820 may occur as a short-lived intermediate in the assembly of LH1 in vivo. The resulting complex of B820 subunits with carotenoid, termed iB873, is homogeneous, according to ion exchange chromatography and reproducible pigment composition. The iB873-bound carotenoid is as efficient in energy transfer to bacteriochlorophyll as the one in native antenna. To our knowledge, iB873 is the first complex binding functional carotenoid, with the spectral and biochemical properties intermediate between that of B820 and the fully assembled LH1.The progress in biochemical (1-3), spectroscopic (4 -8), and structural characterization (9 -16) of purple bacterial lightharvesting complexes has greatly advanced our understanding of photosynthesis. These intramembranous antennae are oligomers of small, heterodimeric proteins carrying BChls 1 and Crts. In peripheral light-harvesting complexes, LH2, LH3, or LH4, 8 or 9 such units assemble to a near perfect circular structure (9 -11). The core light-harvesting complex, LH1, is an oligomer of similar units, but here the size and the shape seem to be more flexible (9 -11,17).To understand the assembly of the pigment-protein complexes, a detailed knowledge is necessary about the role of each particular component in the assembly, and of their interactions in the oligomeric state. The oligomeric character and modularity of antenna structures became already apparent before the high resolution structural data were obtained, mainly because of the isolation of a B820 subunit form of LH1 (2,18,19). Virtually all LH1 complexes were found to undergo dissociation into such subunits, suggesting their function as a universal structural motif (2). They are thought to consist of a dimeric form of BChl, non-covalently attached to two short hydrophobic polypeptides ␣ and ␤, organized into a basic unit ␣␤⅐(BChla) 2 or its dimer (20 -22). B820, however, has mostly been obtained from Crt-less LH1, and only here is the process fully reversible: depending on the detergent concentration, B820 can be reversibly oligomerized in vitro to Crt-less LH1 (low detergent concentration) or dissociated into smaller subunits that still contain monomeric BChl (high detergent concentration) (18,20,21,23). If B820 is prepared by dissociation of Crt-containing LH1, the Crts are lost in the process. In this c...

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Section: Discussionmentioning

confidence: 93%

Trapping of an Assembly Intermediate of Photosynthetic LH1 Antenna beyond B820 Subunit

Fiedor

Scheer²

2005

Journal of Biological Chemistry

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“…The S 2 states of peridinins are believed to couple excitonically, as suggested by circular dichroism (CD) spectra (Song et al, 1976). The interpretations of the CD spectra differ, however, favoring either a dimer (Song et al, 1976) or a tetramer (Pilch and Pawlikowski, 1998) exciton model. Excitonic states in other photosynthetic life forms, e.g., purple bacteria, are shown to play an important role in excitation transfer (Hu et al, 1997(Hu et al, , 1998Ritz et al, 1998;Damjanović et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

Excitation Transfer in the Peridinin-Chlorophyll-Protein of Amphidinium carterae

Damjanović

Ritz

Schulten

2000

Biophysical Journal

125

179

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Peridinin-chlorophyll-protein (PCP) is a unique light-harvesting protein that uses carotenoids as its primary light-absorbers. This paper theoretically investigates excitation transfer between carotenoids and chlorophylls in PCP of the dinoflagellate Amphidinium carterae. Calculations based on a description of the electronic states of the participating chromophores and on the atomic level structure of PCP seek to identify the mechanism and pathways of singlet excitation flow. After light absorption the optically allowed states of peridinins share their electronic excitation in excitonic fashion, but are not coupled strongly to chlorophyll residues in PCP. Instead, a gateway to chlorophyll Q(y) excitations is furnished through a low-lying optically forbidden excited state, populated through internal conversion. Carbonyl group and non-hydrogen side groups of peridinin are instrumental in achieving the respective coupling to chlorophyll. Triplet excitation transfer to peridinins, mediated by electron exchange, is found to efficiently protect chlorophylls against photo-oxidation.

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“…Most importantly, the QM/MM calculation, incorporating all of the tuning mechanisms, captures 90% of the experimental S 0 → S 2 spectral range and reproduces each of the Per absorption signatures within 11 nm of the wavelengths from spectral reconstruction (Figure 2a). 3 Our quantitative model of electronically coupled chromophores in PCP permits the first characterization of the excitons long-suspected from circular dichroism spectra to be present in the antenna complex 15,16 but only recently inferred by twodimensional electronic spectroscopy. 13 Figure 3 depicts the nature of the 1 1 Bu + excitons from a natural transition orbital (NTO) perspective.…”

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confidence: 99%

Light Harvesting by Equally Contributing Mechanisms in a Photosynthetic Antenna Protein

Guberman‐Pfeffer

Greco

Birge

et al. 2018

J. Phys. Chem. Lett.

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We report supramolecular quantum mechanics/molecular mechanics simulations on the peridinin-chlorophyll a protein (PCP) complex from the causative algal species of red tides. These calculations reproduce for the first time quantitatively the distinct peridinin absorptions, identify multichromophoric molecular excitations, and elucidate the mechanisms regulating the strongly allowed S (1A) → S (1B) absorptions of the bound peridinins that span a 58 nm spectral range in the region of maximal solar irradiance. We discovered that protein binding site-imposed conformations, local electrostatics, and electronic coupling contribute equally to the spectral inhomogeneity. Electronic coupling causes coherent excitations among the densely packed pigments. Complementary pairing of tuning mechanisms is the result of a competition between pigment-pigment and pigment-environment interactions. We found that the aqueous solvent works in concert with the charge distribution of PCP to produce a strong correlation between peridinin spectral bathochromism and the local dielectric environment.

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Circular dichroism (CD) study of peridinin[ndash ]chlorophyll a protein (PCP) complexes from marine dinoflagellate algae The tetramer approach

Cited by 15 publications

References 20 publications

Trapping of an Assembly Intermediate of Photosynthetic LH1 Antenna beyond B820 Subunit

Trapping of an Assembly Intermediate of Photosynthetic LH1 Antenna beyond B820 Subunit

Excitation Transfer in the Peridinin-Chlorophyll-Protein of Amphidinium carterae

Light Harvesting by Equally Contributing Mechanisms in a Photosynthetic Antenna Protein

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