Altering the exciton landscape by removal of specific chlorophylls in monomeric LHCII provides information on the sites of triplet formation and quenching by means of ODMR and EPR spectroscopies

Agostini, Alessandro; Nicol, Lauren; Roit, Nicola Da; Bortolus, Marco; Croce, Roberta; Carbonera, Donatella

doi:10.1016/j.bbabio.2021.148481

Cited by 14 publications

(13 citation statements)

References 45 publications

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“…The 3 Chl a * production yielded via ISC from 1 Chl a * is mostly quenched by Lut620 and Lut621; however, a minor portion of 3 Chl a * is known to be left unquenched, − which will impose the danger of oxidative deterioration on the pigment–protein complexes by sensitizing the formation of 1 O 2 . Under aerobic conditions, the unquenched 3 Chl a * exceeding 90 μs cannot be detected by ns-TA owing to the rapid quenching of 3 Chl a * by O 2 (vide supra).…”

Section: Resultsmentioning

confidence: 99%

“…For the LHCII micelle, the potency of the lutein pair, i.e., their TEET efficiency, in quenching 3 Chl a * were previously shown to be largely dependent on the overall pigment arrangement. For instance, a depression of a 612 ends up with an enhanced 3 Lut621* production . In addition, a point mutation of the luminal loop of LHCII trimer results in a deviation of 9′- cis neoxanthin-Chl b coupling from the wild-type LHCII, which, in turn, alters the distribution of triplet over 3 Lut620* and 3 Lut621* .…”

Section: Discussionmentioning

confidence: 99%

“…According to time-resolved electron paramagnetic resonance (TR-EPR) and optically detected magnetic resonance (ODMR) studies, among the Chls a belonging to both branches, a612 and a603 are the most probable quenching sites of 3 Chl a*; 10,11 however, a small fraction of 3 Chl a* remains unquenched as also found in the present work. In this regard, a602 and a610 are likely the unprotected Chls, 10,11 which would lead to the formation of unwanted 1 O 2 or other ROS species.…”

Section: Discussionmentioning

confidence: 99%

“…For instance, a depression of a612 ends up with an enhanced 3 Lut621* production. 10 In addition, a point mutation of the luminal loop of LHCII trimer results in a deviation of 9′-cis neoxanthin-Chl b coupling from the wildtype LHCII, which, in turn, alters the distribution of triplet over 3 Lut620* and 3 Lut621*. 33 Further, the incomplete occupancy or the vacancy of the neoxanthin site leads to the drop of 3 Chl a* quenching efficiency from 95 to 70%, 9 and the monomerization or the detergent treatment result in a substantial decrease in the Chl-to-Car TTET efficiency.…”

Section: Discussionmentioning

confidence: 99%

“…In photosynthetic membranes, carotenoids (Cars) are responsible for quenching 3 Chl a * via triplet excitation energy transfer (TEET) and for directly scavenging 1 O 2 in an emergency. , In the major light-harvesting complex of photosystem II (LHCII) binding most chlorophylls of thylakoid membranes, the 3 Chl a * deactivation is executed by a pair of lutein molecules, Lut620 and Lut621, bound in the central domain of each subunit of a trimeric LHCII. − Since the TEET governed by Dexter’s electron exchange mechanism requires an orbital overlap between the donor and the acceptor, the quenching efficiency relies highly on the spatial relationship between the Chl and the Car cofactors, which are regulated by the LHCII conformation. The triplet quenching efficiency is ∼95% for a trimeric LHCII, whereas it drops to ∼80% for a monomeric LHCII separated from the trimer. , In the case of minor LHCs that are natively in monomeric form, e.g., CP24 and CP26 homologous to an LHCII monomer, the 3 Chl a * quenching efficiency are 70 and 88%, respectively. , As shown for the LHCIIs reconstituted with different Car compositions, the peripheral 9′- cis neoxanthin molecule, in addition to lutein, may be indirectly involved in quenching 3 Chl a * by promoting the conformation to be prone to the TEET from Chl a to lutein.…”

Section: Introductionmentioning

confidence: 99%

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Lipid-Enhanced Photoprotection of LHCII in Membrane Nanodisc by Reducing Chlorophyll Triplet Production

et al. 2022

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Carotenoid (Car) quenching chlorophyll triplet state (3Chl a*), an unwanted photosensitizer yielding harmful reactive oxygen species, is crucial for the survival of oxygenic photosynthetic organisms. For the major light-harvesting complex of photosystem II (LHCII) in isolated form, 3Chl a* is deactivated via sub-nanosecond Chl-to-Car triplet excitation energy transfer by lutein in the central domain of LHCII; however, the mechanistic difference from LHCII in vivo remains to be explored. To investigate the intrinsic Car-photoprotection properties of LHCII in a bio-mimicking circumstance, we reconstituted trimeric spinach LHCII into the discoidal membrane of nanosize made from l-α-phosphatidylcholine and examined the triplet excited dynamics. Time-resolved optical absorption combined with circular dichroism spectroscopies revealed that, with reference to LHCII in buffer, LHCII in the membrane nanodisc shows appreciable conformational variation in the neoxanthin and the Lut621 domains and in the Chl a-terminal cluster owing to the lipid–protein interactions, which, in turn, alters the triplet population of Lut620 and Lut621 and their partition. Importantly, the unquenched 3Chl a* population in the complex was reduced by 60%, indicating that LHCII in the membrane adopts a conformation that is optimized for the alleviation of photoinhibition.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%