Mutational analysis of a higher plant antenna protein provides identification of chromophores bound into multiple sites

Bassi, Roberto; Croce, Roberta; Cugini, Daniela; Sandonà, Dorianna

doi:10.1073/pnas.96.18.10056

Cited by 226 publications

(385 citation statements)

References 37 publications

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“…Considering that the 675-nm band is the only negative contribution observed in the spectra, it can be concluded that the monomers are isoenergetics. Similar values for the absorption of monomeric Chl A5 were found in LHCII and CP29 (21,22), thus supporting the present conclusion. We have to highlight the fact that the bandwidth of the red-most transition is very large, as is expected in the case of a Chl dimer because of strong electronphonon coupling, whereas the absorption at 675 nm has the FWHM typical of a Chl monomer.…”

Section: Is the Presence Of Asn As Ligand For Chl A5 Sufficient To Lesupporting

confidence: 80%

“…It has to be considered that the His versus Asn substitution appears to be a usual tool for modulation of Chl-Chl interactions in Lhc proteins; Chl A2, when coordinated by Asn in Lhcb1, establishes excitonic interactions with neighbor pigments, namely Chl B2 and Chl A4. This interaction is absent in Lhcb4 (CP29) in which His is the ligand for Chl A2 (21,22) and again present in the Asn-bearing Lhcb5 (CP26), whose overall biochemical and spectral characteristics are very close to those of CP29 (19).…”

Section: Is Asn As Ligand For Chl A5 Necessary To Yield To the Low mentioning

confidence: 96%

“…In reaction centers, the presence of dimers of the Chl molecule confers the "special" nature of a primary donor. In antenna proteins, energy levels of each individual chlorophyll chromophore are modulated by interactions with amino acid groups and carotenoid molecules to optimize both energy transfer and photoprotection (21)(22)(23). In Photosystem II, the protein environment also provides modulation of chlorophyll fluorescence lifetime and, thus, of the efficiency of energy transfer to P680 by undergoing conformational changes induced by the binding of violaxanthin versus zeaxanthin to an allosteric site called L2 (24).…”

Section: Discussionmentioning

confidence: 99%

“…WT and mutant apoproteins were isolated from the SG13009 strain of Escherichia coli transformed with constructs following a protocol described previously (17,(21)(22)(23). Reconstitution and purification of protein-pigment complexes were performed as described (11,12).…”

Section: Dna Constructions and Isolation Of Overexpressed Lhcamentioning

confidence: 99%

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The Nature of a Chlorophyll Ligand in Lhca Proteins Determines the Far Red Fluorescence Emission Typical of Photosystem I

Morosinotto

Breton

Bassi

et al. 2003

Journal of Biological Chemistry

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Photosystem I of higher plants is characterized by a typically long wavelength fluorescence emission associated to its light-harvesting complex I moiety. The origin of these low energy chlorophyll spectral forms was investigated by using site-directed mutagenesis of Lhca1-4 genes and in vitro reconstitution into recombinant pigment-protein complexes. We showed that the red-shifted absorption originates from chlorophyll-chlorophyll (Chl) excitonic interactions involving Chl A5 in each of the four Lhca antenna complexes. An essential requirement for the presence of the red-shifted absorption/fluorescence spectral forms was the presence of asparagine as a ligand for the Chl a chromophore in the binding site A5 of Lhca complexes. In Lhca3 and Lhca4, which exhibit the most red-shifted red forms, its substitution by histidine maintains the pigment binding and, yet, the red spectral forms are abolished. Conversely, in Lhca1, having very low amplitude of red forms, the substitution of Asn for His produces a red shift of the fluorescence emission, thus confirming that the nature of the Chl A5 ligand determines the correct organization of chromophores leading to the excitonic interaction responsible for the red-most forms. The red-shifted fluorescence emission at 730 nm is here proposed to originate from an absorption band at ϳ700 nm, which represents the low energy contribution of an excitonic interaction having the high energy band at 683 nm. Because the mutation does not affect Chl A5 orientation, we suggest that coordination by Asn of Chl A5 holds it at the correct distance with Chl B5.Photosystem I is a multisubunit pigment-protein complex of the chloroplast membrane acting as a plastocyanin/ferredoxin oxido-reductase in oxygenic photosynthesis. One important spectroscopic feature of PSI 1 is the presence of Chls absorbing at energy lower than the PSI primary electron donor, P700.Although these spectral forms account for only a small percentage of the total absorption, their effect in the energy transfer and trapping of PSI is very prominent (1), with at least 80% of excitation in the complex transiting through them on their way to P700 (2). It has been widely proposed that these forms represent the low energy contributions of excitonic interactions, which involve two or more Chl molecules (3-5); however, the identity of the chromophores involved and the details of the interaction are still unknown.Although the presence of low energy-absorbing Chls is ubiquitous in the PSI of different organisms, their amounts and energies appear to be highly species-dependent (1). In the PSI of higher plants, the red forms are associated with the outer antenna, LHCI (6, 7). LHCI is composed by four pigmentbinding proteins, namely Lhca1-4 (6, 8). These complexes, localized on one side of the core complex (9, 10), are organized in dimers with 10 Chl molecules per subunit (11).As for their properties, Lhca2 and Lhca4 differ from Lhca1 and Lhca3 in many respects. The first two have higher Chl b content with respect to Lhca1 and Lhca3 an...

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Section: Is the Presence Of Asn As Ligand For Chl A5 Sufficient To Lesupporting

confidence: 80%

Section: Is Asn As Ligand For Chl A5 Necessary To Yield To the Low mentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

Section: Dna Constructions and Isolation Of Overexpressed Lhcamentioning

confidence: 99%

See 2 more Smart Citations

The Nature of a Chlorophyll Ligand in Lhca Proteins Determines the Far Red Fluorescence Emission Typical of Photosystem I

Morosinotto

Breton

Bassi

et al. 2003

Journal of Biological Chemistry

Self Cite

180

220

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show abstract

“…2A). Reconstitution and mutagenesis experiments on Chl a͞b proteins suggest that at least some of the eight Chl-binding sites common to all Chl a͞b proteins (10, 11) can ligate either Chl a or b (11)(12)(13). One of these proteins can even be reconstituted almost exclusively with Chl b, although with somewhat altered energy transfer characteristics (13).…”

mentioning

confidence: 99%

Was “molecular opportunism” a factor in the evolution of different photosynthetic light-harvesting pigment systems?

Green

2001

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

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The potential for the improvement of carotenoid levels in foods and the likely systemic effects

Berg

Faulks

Granado

et al. 2000

J. Sci. Food Agric.

425

226

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Carotenoids form one of the most important classes of plant pigments and play a crucial role in defining the quality parameters of fruit and vegetables. Their role in the plant is to act as accessory pigments for light harvesting and in the prevention of photo‐oxidative damage, as well as acting as attractants for pollinators. Their function as antioxidants in the plant shows interesting parallels with their potential role as antioxidants in foods and humans. Carotenoids are products of the isoprenoid biosynthetic pathway. The enzymes leading to carotenoid biosynthesis have all been characterised, and more recently the genes encoding these enzymes have been cloned from bacteria, fungi and plants. New information on enzyme activities and the factors leading to the regulation of the pathway is reviewed. Vitamin A deficiency is a widespread problem in the developing world, causing blindness, particularly in the young. This has driven research into finding ways of introducing provitamin A carotenoids into staple crops, and this has recently been achieved in rice and canola through genetic manipulation. The fact that carotenoids show protective activity in vitro and in vivo against a variety of degenerative disease end points has also give impetus to studying whether increasing intakes of the commonly consumed carotenoids would have public health benefits in the developed world. Human intervention studies have been undertaken using supplements of β‐carotene rather than utilising foods with enhanced carotenoid levels, but no potential benefit has been shown. Indeed, there is evidence of an increased health risk from the consumption of β‐carotene supplements. These observations suggest that the threshold between the beneficial and adverse effects of some carotenoids is low and provides a strong stimulus to further understanding the functional effects of specific carotenoids. Specific needs for future research are identified in the review. © 2000 Society of Chemical Industry

show abstract

Mutational analysis of a higher plant antenna protein provides identification of chromophores bound into multiple sites

Cited by 226 publications

References 37 publications

The Nature of a Chlorophyll Ligand in Lhca Proteins Determines the Far Red Fluorescence Emission Typical of Photosystem I

The Nature of a Chlorophyll Ligand in Lhca Proteins Determines the Far Red Fluorescence Emission Typical of Photosystem I

Was “molecular opportunism” a factor in the evolution of different photosynthetic light-harvesting pigment systems?

The potential for the improvement of carotenoid levels in foods and the likely systemic effects

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