Distortions of the Xanthophylls Caused by Interactions with Neighboring Pigments and the LHCII Protein Are Crucial for Studying Energy Transfer Pathways within the Complex

Fox, Kieran F.; Bricker, William P.; Lo, Cynthia S.; Duffy, Christopher D. P.

doi:10.1021/acs.jpcb.5b08941

Cited by 5 publications

(4 citation statements)

References 89 publications

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“…This state must be lower in energy than the Chls and/or possess a higher coupling with them. This last condition might derive from an increased dipole character of the S q ←S 0 transition due to a higher degree of twisting of the Car 40 . The heterogeneity in the population rates of S q from the Chls (Fig.…”

Section: Resultsmentioning

confidence: 99%

Different carotenoid conformations have distinct functions in light-harvesting regulation in plants

et al. 2017

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To avoid photodamage plants regulate the amount of excitation energy in the membrane at the level of the light-harvesting complexes (LHCs). It has been proposed that the energy absorbed in excess is dissipated via protein conformational changes of individual LHCs. However, the exact quenching mechanism remains unclear. Here we study the mechanism of quenching in LHCs that bind a single carotenoid species and are constitutively in a dissipative conformation. Via femtosecond spectroscopy we resolve a number of carotenoid dark states, demonstrating that the carotenoid is bound to the complex in different conformations. Some of those states act as excitation energy donors for the chlorophylls, whereas others act as quenchers. Via in silico analysis we show that structural changes of carotenoids are expected in the LHC protein domains exposed to the chloroplast lumen, where acidification triggers photoprotection in vivo. We propose that structural changes of LHCs control the conformation of the carotenoids, thus permitting access to different dark states responsible for either light harvesting or photoprotection.

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Section: Resultsmentioning

confidence: 99%

Different carotenoid conformations have distinct functions in light-harvesting regulation in plants

et al. 2017

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“…Since the Chl c pigments in FCP have a ∼35-nm blue-shifted Q y transition compared with Chl a (17) and transfer excitation energy to Chl a on an ultrafast timescale (37), they do not contribute directly to the lowest-energy excitons in FCP. In LHCII, the lowest-energy excitons are localized on Chls a610, a611, a612, a602, and a603 7, and the close vicinity of xanthophylls to these sites (23) results in strong interactions between these xanthophylls and Chls a610, a611, a612, and a603 (38), while Chl a602 is also affected through its strong coupling with a603. However, since transient absorption spectra of FCP do not show evidence of energy transfer from Fx to Chl c (16,17), we can rule out Chl c's participation in FCP's lowest-energy exciton states.…”

Section: Discussionmentioning

confidence: 99%

How reduced excitonic coupling enhances light harvesting in the main photosynthetic antennae of diatoms

Krüger

Malý

Alexandre

et al. 2017

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

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Strong excitonic interactions are a key design strategy in photosynthetic light harvesting, expanding the spectral cross-section for light absorption and creating considerably faster and more robust excitation energy transfer. These molecular excitons are a direct result of exceptionally densely packed pigments in photosynthetic proteins. The main light-harvesting complexes of diatoms, known as fucoxanthin-chlorophyll proteins (FCPs), are an exception, displaying surprisingly weak excitonic coupling between their chlorophyll (Chl) 's, despite a high pigment density. Here, we show, using single-molecule spectroscopy, that the FCP complexes of switch frequently into stable, strongly emissive states shifted 4-10 nm toward the red. A few percent of isolated FCPa complexes and ∼20% of isolated FCPb complexes, on average, were observed to populate these previously unobserved states, percentages that agree with the steady-state fluorescence spectra of FCP ensembles. Thus, the complexes use their enhanced sensitivity to static disorder to increase their light-harvesting capability in a number of ways. A disordered exciton model based on the structure of the main plant light-harvesting complex explains the red-shifted emission by strong localization of the excitation energy on a single Chl pigment in the terminal emitter domain due to very specific pigment orientations. We suggest that the specific construction of FCP gives the complex a unique strategy to ensure that its light-harvesting function remains robust in the fluctuating protein environment despite limited excitonic interactions.

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“…Xanthophylls have been the continued focus of the search for the ‘true quencher’ of excess energy in the photosynthetic membrane. The role of lutein has been the focus of recent research, most recently with Duffy and co-workers ( Fox et al, 2015 ) have shown through modeling that the degrees of distortions of lutein are more important than the pigments location for quenching in the membrane. Here we addressed and quantified the photoprotective capacities of xanthophylls in vivo for the first time.…”

Section: Discussionmentioning

confidence: 99%

An In Vivo Quantitative Comparison of Photoprotection in Arabidopsis Xanthophyll Mutants

2016

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Contribution of different LHCII antenna carotenoids to protective NPQ (pNPQ) were tested using a range of xanthophyll biosynthesis mutants of Arabidopsis: plants were either devoid of lutein (lut2), violaxanthin (npq2), or synthesized a single xanthophyll species, namely violaxanthin (aba4npq1lut2), zeaxanthin (npq2lut2), or lutein (chy1chy2lut5). A novel pulse amplitude modulated (PAM) fluorescence analysis procedure, that used a gradually increasing actinic light intensity, allowed the efficiency of pNPQ to be tested using the photochemical quenching (qP) parameter measured in the dark (qPd). Furthermore, the yield of photosystem II (ΦPSII) was calculated, and the light intensity which induces photoinhibition in 50% of leaves for each mutant was ascertained. Photoprotective capacities of each xanthophyll were quantified, taking into account chlorophyll a/b ratios and excitation pressure. Here, light tolerance, pNPQ capacity, and ΦPSII were highest in wild type plants. Of the carotenoid mutants, lut2 (lutein-deficient) plants had the highest light tolerance, and the joint the highest ΦPSII with violaxanthin only plants. We conclude that all studied mutants possess pNPQ and a more complete composition of xanthophylls in their natural binding sites is the most important factor governing photoprotection, rather than any one specific xanthophyll suggesting a strong structural effect of the molecules upon the LHCII antenna organization and discuss the results significance for future crop development.

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Distortions of the Xanthophylls Caused by Interactions with Neighboring Pigments and the LHCII Protein Are Crucial for Studying Energy Transfer Pathways within the Complex

Cited by 5 publications

References 89 publications

Different carotenoid conformations have distinct functions in light-harvesting regulation in plants

Different carotenoid conformations have distinct functions in light-harvesting regulation in plants

How reduced excitonic coupling enhances light harvesting in the main photosynthetic antennae of diatoms

An In Vivo Quantitative Comparison of Photoprotection in Arabidopsis Xanthophyll Mutants

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