The Single Chlorophyll a Molecule in the Cytochrome b6f Complex: Unusual Optical Properties Protect the Complex against Singlet Oxygen

Dashdorj, Naranbaatar; Zhang, Huamin; Kim, Hanyoup; Yan, Jiusheng; Cramer, William A.; Savikhin, Sergei

doi:10.1529/biophysj.104.058693

Cited by 66 publications

(111 citation statements)

References 55 publications

(88 reference statements)

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“…One, rather extreme example was observed in a study of the Cytb 6 f complex, which binds one isolated chlorophyll molecule, in which the pigment-protein coupling reduced the excited-state lifetime of the chlorophyll to 215 ps, 40 probably because of electron transfer to a nearby aromatic amino acid. 41 Most likely, all of the above-mentioned effects influence the lifetimes of the studied Lhca proteins. The red pigments of LHCI have been shown to carry a large Huang-Rhys factor (on the order of 3), which leads to strong (in)homogeneous broadening and large Stokes' shift.…”

Section: Discussionmentioning

confidence: 98%

Excitation Decay Pathways of Lhca Proteins: A Time-Resolved Fluorescence Study

et al. 2005

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Light-harvesting complex I (LHCI), which serves as a peripheral antenna for photosystem I (PSI) in green plants, consists mainly of four polypeptides, Lhca1-4. We report room temperature emission properties of individual reconstituted monomeric Lhca proteins (Lhca1, -2, -3, and -4) and dimeric Lhca1/4, performed by steady-state and time-resolved fluorescence techniques. The emission quantum yields of the samples are approximately 0.12, 0.085, 0.081, 0.041, and 0.063 for Lhca1, -2, -3, -4, and the -1/4 dimer, respectively, which is considerably lower than the value of 0.22 found for light-harvesting complex II (LHCII), the main peripheral antenna complex of photosystem II in green plants. The decay components of LHCI proteins can be divided in two categories: Lhca1 and Lhca3 have decay times of 1.1-1.6 ns and 3.3-3.6 ns, and Lhca2 and Lhca4 have decay times of 0.7-0.9 ns and 3.1-3.2 ns. These categories seem to correlate with the pigment composition of the samples. All decay times are faster than that observed previously for LHCII. When the absolute emission yields and the lifetimes of the Lhca samples are combined, the overall emission properties of the individual Lhca proteins are expressed in terms of their emitting dipole moment strength. In the samples without extreme red states, that is, Lhca1 and Lhca2, the emitting dipole moment has a value close to unity (relative to monomeric chlorophyll in acetone), which is similar to that for LHCII, whereas, in the samples with the red-most state (F-730), that is, Lhca3, -4, and the -1/4 dimer, the emitting dipole moment has a value less than unity (0.6-0.8), which can be explained by mixing the red-most (exciton) state with a dark charge-transfer state, as suggested in previous PSI red pigment studies. In addition, we find a lifetime component of ∼50-150 ps in all red-pigment-containing samples, which cannot be due to "slow" energy transfer, but is instead assigned to an unrelaxed state of the pigment-protein, which, on this time-scale, is converted into the final emitting state.

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Section: Discussionmentioning

confidence: 98%

Excitation Decay Pathways of Lhca Proteins: A Time-Resolved Fluorescence Study

et al. 2005

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“…Thus, Cyt f is a potential client of ALB4. It was shown previously that the cytochrome b 6 f complex contains one molecule of chlorophyll a per molecule of Cyt f (Dashdorj et al, 2005;Baniulis et al, 2011), and so this complex may be (partly) responsible for the residual pigment-binding activity Figure 2. Phenotypic analysis of alb3 alb4 double-mutant plants.…”

Section: Double-mutant Alb3 Alb4 Plants Are Visibly Paler Than the Almentioning

confidence: 98%

Genetic and Physical Interaction Studies Reveal Functional Similarities between ALBINO3 and ALBINO4 in Arabidopsis

et al. 2015

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ALBINO3 (ALB3) is a well-known component of a thylakoid protein-targeting complex that interacts with the chloroplast signal recognition particle (cpSRP) and the cpSRP receptor, chloroplast filamentous temperature-sensitive Y (cpFtsY). Its proteininserting function has been established mainly for light-harvesting complex proteins, which first interact with the unique chloroplast cpSRP43 component and then are delivered to the ALB3 integrase by a GTP-dependent cpSRP-cpFtsY interaction. In Arabidopsis (Arabidopsis thaliana), a subsequently discovered ALB3 homolog, ALB4, has been proposed to be involved not in light-harvesting complex protein targeting, but instead in the stabilization of the ATP synthase complex. Here, however, we show that ALB3 and ALB4 share significant functional overlap, and that both proteins are required for the efficient insertion of cytochrome f and potentially other subunits of pigment-bearing protein complexes. Genetic and physical interactions between ALB4 and ALB3, and physical interactions between ALB4 and cpSRP, suggest that the two ALB proteins may engage similar sets of interactors for their specific functions. We propose that ALB4 optimizes the insertion of thylakoid proteins by participating in the ALB3-cpSRP pathway for certain substrates (e.g. cytochrome f and the Rieske protein). Although ALB4 has clearly diverged from ALB3 in relation to the partner-recruiting C-terminal domain, our analysis suggests that one putative cpSRP-binding motif has not been entirely lost.

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“…2 and 3b). They are within the range of van der Waals interactions, and consequently they may produce fluorescence quenching of excited Chl by means of electron exchange (29).…”

Section: Tetrameric Assembly Of the Wscp-chl Complex And Formation Ofmentioning

confidence: 99%

“…Such a quenching mechanism of a light-excited chromophore has been well demonstrated in riboflavin-binding proteins, in which electron exchange efficiently occurs with two nearby aromatic residues (Tyr-75 and Trp-156) that sandwich riboflavin in a hydrophobic cleft (36). The possible involvement of aromatic residues in fluorescence quenching of bacteriochlorophyll and Chl molecules is also discussed in (29,37,38).…”

mentioning

confidence: 90%

Structural Mechanism and Photoprotective Function of Water-soluble Chlorophyll-binding Protein

Horigome

Satoh²,

Itoh

et al. 2007

Journal of Biological Chemistry

105

216

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A water-soluble chlorophyll-binding protein (WSCP) is the single known instance of a putative chlorophyll (Chl) carrier in green plants. Recently the photoprotective function of WSCP has been demonstrated by EPR measurements; the light-induced singlet-oxygen formation of Chl in the WSCP tetramer is about four times lower than that of unbound Chl. This paper describes the crystal structure of the WSCP-Chl complex purified from leaves of Lepidium virginicum (Virginia pepperweed) to clarify the mechanism of its photoprotective function. The WSCP-Chl complex is a homotetramer comprising four protein chains of 180 amino acids and four Chl molecules. At the center of the complex one hydrophobic cavity is formed in which all of the four Chl molecules are tightly packed and isolated from bulk solvent. With reference to the novel Chl-binding mode, we propose that the photoprotection mechanism may be based on the inhibition of physical contact between the Chl molecules and molecular oxygen.Water-soluble chlorophyll-binding proteins (WSCPs), 4 which form a complex with chlorophyll (Chl), have been isolated from Amaranthaceae, Chenopodiaceae, and Polygonaceae (class-I) and from Brassicaceae (class-II). The two WSCP classes differ in that the protein-Chl complexes of the former change their absorption spectra upon illumination, whereas those of the latter show no photoconversion of their absorption behavior (2). The amino acid sequence of class-I WSCP shows no similarity to that of class-II WSCP.The class-II WSCPs (hereafter referred to as "WSCPs") are water-soluble proteins of ϳ20 kDa, which form a tetrameric assembly upon binding Chl molecules with a Chl-to-protein ratio of one or less, and exhibit high thermal and photostability (1, 3). The physiological function of WSCPs is still not known. Although WSCPs have a sequence similarity of ϳ30% with Künitz-type proteinase inhibitors, no significant protease inhibitor activity of WSCPs has yet been identified (4 -6). The low Chl content per protein makes it unlikely that WSCPs are involved in the light reaction of photosynthesis. Meanwhile, it has been speculated (7, 8) that WSCP acts as a scavenger of free Chl, by transporting it from the thylakoid membrane to the chloroplast envelope, where Chlase, the enzyme that initiates the Chl catabolism, is thought to reside (9).An in vitro binding assay with the recombinant apo-WSCP cloned from cauliflower (Brassica oleralcea var. Botrys) and Chl or its derivatives showed that the central Mg 2ϩ ion and the phytyl tail of Chl were essential for protein-pigment binding and tetrameric assembly, respectively (1). Furthermore, the recombinant apo-WSCP was able to remove Chl from the thylakoid membrane in vitro and organize the tetrameric WSCPChl complex (3). The absorption spectrum of the reconstituted complex is very similar to that of the native WSCP-Chl complex purified from fresh leaves (1, 3).The WSCP-Chl complex retains its fresh green color under dim light for months, enough for a long term crystallization experiment. Free Chl, on t...

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The Single Chlorophyll a Molecule in the Cytochrome b6f Complex: Unusual Optical Properties Protect the Complex against Singlet Oxygen

Cited by 66 publications

References 55 publications

Excitation Decay Pathways of Lhca Proteins: A Time-Resolved Fluorescence Study

Excitation Decay Pathways of Lhca Proteins: A Time-Resolved Fluorescence Study

Genetic and Physical Interaction Studies Reveal Functional Similarities between ALBINO3 and ALBINO4 in Arabidopsis

Structural Mechanism and Photoprotective Function of Water-soluble Chlorophyll-binding Protein

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