Characterization of the Major Light-Harvesting Complexes (LHCBM) of the Green Alga Chlamydomonas reinhardtii

Natali, Alberto; Croce, Roberta

doi:10.1371/journal.pone.0119211

Cited by 57 publications

(81 citation statements)

References 52 publications

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“…We have recently shown that this is not the case for isolated LHCII in the absence of aggregation from both plants and C. reinhardtii (18,26). Our results here show that LHCII in the membrane is not quenched in response to pH changes, and that the quenching can also not be induced by the interaction of zeaxanthin with LHCBM1.…”

Section: Discussionmentioning

confidence: 40%

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LHCSR1 induces a fast and reversible pH-dependent fluorescence quenching in LHCII in Chlamydomonas reinhardtii cells

Dinc¹,

Tian²,

Roy³

et al. 2016

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

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To avoid photodamage, photosynthetic organisms are able to thermally dissipate the energy absorbed in excess in a process known as nonphotochemical quenching (NPQ). Although NPQ has been studied extensively, the major players and the mechanism of quenching remain debated. This is a result of the difficulty in extracting molecular information from in vivo experiments and the absence of a validation system for in vitro experiments. Here, we have created a minimal cell of the green alga Chlamydomonas reinhardtii that is able to undergo NPQ. We show that LHCII, the main light harvesting complex of algae, cannot switch to a quenched conformation in response to pH changes by itself. Instead, a small amount of the protein LHCSR1 (light-harvesting complex stress related 1) is able to induce a large, fast, and reversible pH-dependent quenching in an LHCII-containing membrane. These results strongly suggest that LHCSR1 acts as pH sensor and that it modulates the excited state lifetimes of a large array of LHCII, also explaining the NPQ observed in the LHCSR3-less mutant. The possible quenching mechanisms are discussed.photosynthesis | light-harvesting | nonphotochemical quenching | green algae | thylakoid membranes P hotosynthetic organisms get their energy from light and have developed a series of mechanisms to respond to the changes in light intensity that occur in their natural environment (1, 2). This is particularly important in high-light conditions, as the energy absorbed in excess can induce photodamage, eventually leading to the death of the organism. Photosynthetic organisms are equipped with many pigment-protein complexes, most of which in plants and green algae are members of the light-harvesting complex (Lhc) multigenic family (3). These complexes maximize light absorption in low light, but can easily become overexcited in high light (4), when a large part of the absorbed light cannot be used for charge separation in the reaction centers of the photosystems. Especially when the changes in light intensity are very fast, and thus protein degradation is not an option, photoprotective mechanisms need to be switched on to avoid the formation of singlet oxygen. The most rapid response to high light intensity is the dissipation of a large part of the absorbed energy as heat in a series of processes known as nonphotochemical quenching (NPQ) (1,5,6).The general idea is that the LHCs can switch between a lightharvesting conformation, characterized by a long excited-state lifetime, and a quenched (Q) conformation that shows a shorter lifetime because of the presence of competing de-excitation processes (7). How this switch is induced and the nature of these de-excitation processes is a matter of debate. It is known that NPQ is triggered by low luminal pH, which is a signal for the overexcitation of the membrane; this activates the quenching processes (5, 8), which involves the proteins PsbS (in plants and mosses) (9, 10) and/or lightharvesting complex stress related (LHCSR) (in green algae, mosses, and diatoms) (10-12)....

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Section: Discussionmentioning

confidence: 40%

“…The PCR product and expression vector petMHis were digested with BamHI and XhoI, ligated, and transformed into BL21 Escherichia coli for expression (42). LhcbM1 was cloned and expressed as described (26). The apoproteins were quantified using a bicinchoninic acid assay (Sigma).…”

Section: Methodsmentioning

confidence: 99%

LHCSR1 induces a fast and reversible pH-dependent fluorescence quenching in LHCII in Chlamydomonas reinhardtii cells

Dinc¹,

Tian²,

Roy³

et al. 2016

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

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“…Ϫ1 as found for isolated LHCII trimers of C. reinhardtii (41). The complete kinetic scheme (Scheme SI2-1) also contains precursors populating the other compartments on the ps time scale, with relative amounts varying depending on excitation wavelength (Table SI1-2), and a disconnected compartment corresponding to species with ns lifetimes.…”

Section: Methodsmentioning

confidence: 95%

The High Efficiency of Photosystem I in the Green Alga Chlamydomonas reinhardtii Is Maintained after the Antenna Size Is Substantially Increased by the Association of Light-harvesting Complexes II

Quiniou¹,

Oort²,

Drop³

et al. 2015

Journal of Biological Chemistry

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Background: Photosystems acclimate to different light conditions modulating their antenna size. Results: In PSI-LHCI-LHCII, energy transfer from LHCII to Photosystem I is relatively slow but still very efficient. Conclusion: The association of LHCII to PSI increases its absorption cross section by ϳ50%, maintaining ϳ96% quantum efficiency. Significance: The antenna size of PSI can be increased considerably without sacrificing its efficiency.

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“…At the same time, the fluorescence lifetime decreased down to a minimum of 0.97 ns (Table 1). On the other hand, the lifetime of the sample in liposomes with a high lipid/protein molar ratio of ϳ7000:1 (0.1 g of Chl a) had a similar value compared with isolated monomeric LHCII in detergent (Table 1) (30,31). A further decrease in the amount of protein per liposome (0.05 g of Chl a equal to a lipid/protein molar ratio of ϳ14,000:1) induced the appearance of free Chls in the sample.…”

Section: Incorporation Of Chlamydomonas Reinhardtii Lhcii Intomentioning

confidence: 92%

Light-harvesting Complexes (LHCs) Cluster Spontaneously in Membrane Environment Leading to Shortening of Their Excited State Lifetimes

Natali

Gruber

Dietzel

et al. 2016

Journal of Biological Chemistry

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The light reactions of photosynthesis, which include lightharvesting and charge separation, take place in the amphiphilic environment of the thylakoid membrane. The light-harvesting complex II (LHCII) is the main responsible for light absorption in plants and green algae and is involved in photoprotective mechanisms that regulate the amount of excited states in the membrane. The dual function of LHCII has been extensively studied in detergent micelles, but recent results have indicated that the properties of this complex differ in a lipid environment. In this work we checked these suggestions by studying LHCII in liposomes. By combining bulk and single molecule measurements, we monitored the fluorescence characteristics of liposomes containing single complexes up to densely packed proteoliposomes. We show that the natural lipid environment per se does not alter the properties of LHCII, which for single complexes remain very similar to that in detergent. However, we show that LHCII has the strong tendency to cluster in the membrane and that protein interactions and the extent of crowding modulate the lifetimes of the excited state in the membrane. Finally, the presence of LHCII monomers at low concentrations of complexes per liposome is discussed.Photosynthetic organisms evolved the capacity to harvest the energy of solar radiation and store it into chemical compounds. In vascular plants and green algae, sunlight is absorbed by a series of membrane proteins called light-harvesting complexes (LHC).3 The most abundant of these pigment-protein complexes is LHCII. The LHCs have a dual function; in low light conditions they absorb solar energy and efficiently transfer the excitation energy to the reaction center, and in high light they additionally play a role in photoprotection by dissipating the energy absorbed in excess as heat (1, 2). This last process called non-photochemical quenching (NPQ) leads to a decrease of the excited state lifetime of chlorophyll a (Chl a), limiting the possibility of Chl triplet formation and thus the production of singlet oxygen (3). The fast, on the timescale of seconds, and fully reversible part of NPQ is called qE. This mechanism is triggered by the acidification of the lumenal space of the thylakoids, which activates PsbS (4) and LhcSR (5), the proteins responsible for NPQ in plants and green algae, respectively, and the violaxanthin de-epoxidase, which converts violaxanthin into zeaxanthin (for reviews, see Refs. 6 and 7). Although the precise molecular mechanism of quenching has not been fully elucidated yet, a prominent idea discussed in literature is that NPQ is regulated via conformational changes of LHCII. Those changes could be correlated to, or even caused by, LHCII aggregation (8, 9). It was observed that low pH and zeaxanthin, both occurring in high light, enhance LHCII aggregation (10). Aggregation of LHCII in vitro is accompanied by a decrease of the Chl a fluorescence yield, indicating an increased rate of energy dissipation (9, 11). The generation of new quenching sit...

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Characterization of the Major Light-Harvesting Complexes (LHCBM) of the Green Alga Chlamydomonas reinhardtii

Cited by 57 publications

References 52 publications

LHCSR1 induces a fast and reversible pH-dependent fluorescence quenching in LHCII in Chlamydomonas reinhardtii cells

LHCSR1 induces a fast and reversible pH-dependent fluorescence quenching in LHCII in Chlamydomonas reinhardtii cells

The High Efficiency of Photosystem I in the Green Alga Chlamydomonas reinhardtii Is Maintained after the Antenna Size Is Substantially Increased by the Association of Light-harvesting Complexes II

Light-harvesting Complexes (LHCs) Cluster Spontaneously in Membrane Environment Leading to Shortening of Their Excited State Lifetimes

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