In situ formation of photoactive B-ring reduced chlorophyll isomer in photosynthetic protein LH2

Saga, Yoshitaka; Otsuka, Yuji; Funakoshi, Daichi; Masaoka, Yuto; Kihara, Yu; Hidaka, Tsubasa; Hatano, Hiroka; Asakawa, Hitoshi; Nagasawa, Yutaka; Tamiaki, Hitoshi

doi:10.1038/s41598-020-76540-1

Cited by 8 publications

(9 citation statements)

References 31 publications

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“…Near the time of submission of this manuscript, chemical oxidation of the exposed ring D of the B 800 BChl a molecules of isolated light-harvesting complexes (LH2) from Phaeospirillium molischianum was reported. 61 The spectrum of the LH2 BChl a oxidation product in methanol shows a 7 nm bathochromic shift of the Q y band relative to that for 3-AcChl a and is identical to the spectrum obtained here for Chl X in methanol (Figure 6 and Figure S1-7D).…”

supporting

confidence: 76%

“…Absorption spectra of samples in methanol from this study (gold and green) and from ref (black dashed) for (A) 3-AcChl a and (B) Chl X from this study and oxidized LH2 B800 BChl a (e.g., 17,18-didehydro BChl a ) from ref . Also shown are structures of 3-AcChl a (i.e., 7,8-didehydro BChl a ) (top right) in which ring B of BChl a is oxidized and of 17,18-didehydro BChl a (bottom right) in which ring D of BChl a is oxidized.…”

Section: Results and Discussionmentioning

confidence: 91%

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In Situ, Protein-Mediated Generation of a Photochemically Active Chlorophyll Analogue in a Mutant Bacterial Photosynthetic Reaction Center

et al. 2021

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All possible natural amino acids have been substituted for the native LeuL185 positioned near the B-side bacteriopheophytin (H B ) in the bacterial reaction center (RC) from Rhodobacter sphaeroides. Additional mutations that enhance electron transfer to the normally inactive B-side cofactors are present. Approximately half of the isolated RCs with Glu at L185 contain a magnesium chlorin (C B ) in place of H B . The chlorin is not the common BChl a oxidation product 3-desvinyl-3-acetyl chlorophyll a with a C−C bond in ring D and a CC bond in ring B but has properties consistent with reversal of these bond orders, giving 17,18-didehydro BChl a. In such RCs, charge-separated state P + C B − forms in ∼5% yield. The other half of the GluL185-containing RCs have a bacteriochlorophyll a (BChl a) denoted β B in place of H B .Residues His, Asp, Asn, and Gln at L185 yield RCs with ≥85% β B in the H B site, while most other amino acids result in RCs that retain H B (≥95%). To the best of our knowledge, neither bacterial RCs that harbor five BChl a molecules and one chlorophyll analogue nor those with six BChl a molecules have been reported previously. The finding that altering the local environment within a cofactor binding site of a transmembrane complex leads to in situ generation of a photoactive chlorin with an unusual ring oxidation pattern suggests new strategies for amino acid control over pigment type at specific sites in photosynthetic proteins.

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confidence: 76%

Section: Results and Discussionmentioning

confidence: 91%

In Situ, Protein-Mediated Generation of a Photochemically Active Chlorophyll Analogue in a Mutant Bacterial Photosynthetic Reaction Center

et al. 2021

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“…molischianum and Mch. purpuratum , this absorption band is blue shifted to 846 nm ( 14 ) and 828 nm, respectively (fig. S7).…”

Section: Discussionmentioning

confidence: 96%

The 2.4 Å cryo-EM structure of a heptameric light-harvesting 2 complex reveals two carotenoid energy transfer pathways

et al. 2021

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We report the 2.4 Ångström resolution structure of the light-harvesting 2 (LH2) complex from Marichromatium (Mch.) purpuratum determined by cryogenic electron microscopy. The structure contains a heptameric ring that is unique among all known LH2 structures, explaining the unusual spectroscopic properties of this bacterial antenna complex. We identify two sets of distinct carotenoids in the structure and describe a network of energy transfer pathways from the carotenoids to bacteriochlorophyll a molecules. The geometry imposed by the heptameric ring controls the resonant coupling of the long-wavelength energy absorption band. Together, these details reveal key aspects of the assembly and oligomeric form of purple bacterial LH2 complexes that were previously inaccessible by any technique.

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“…One strategy for this is the attachment of energy-donating dyes to the polypeptides of target complexes. − Recent reports on chemical modifications of LH2 with artificial dyes indicated that the modified LH2 had two kinds of energy donors to B850 and unique EET dynamics among the two donors and the acceptor (B850). , Such LH2 variants would be good candidates for recently developing spectroscopies such as two-dimensional electronic spectroscopy. The substitution of native BChl a with other pigments in LH2 proteins is another promising strategy for changing the energy donor in LH2 proteins, − and time-resolved spectroscopy of B800-substituted LH2 variants was performed. ,,, In situ oxidation of B800 BChl a is also useful for engineering LH2 proteins. , The direct conversion of B800 BChl a into Chl pigments is advantageous for facile preparation of LH2 variants containing two types of energy-donating (B)Chls in the B800 sites and provides new insights into the excited-state dynamics of chromophores in the B800 sites.…”

Section: Introductionmentioning

confidence: 99%

Energy Transfer Dynamics in Light-Harvesting Complex 2 Variants Containing Oxidized B800 Bacteriochlorophyll a

et al. 2021

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Excitation energy transfer (EET) in light-harvesting proteins is vital for photosynthetic activities. The pigment compositions and their organizations in these proteins are responsible for the EET functions. Thus, changing the pigment compositions in light-harvesting proteins contributes to a better understanding of EET mechanisms. In this study, we investigated the EET dynamics of two light-harvesting complex 2 (LH2) variants, in which nine B800 bacteriochlorophyll (BChl) a pigments were entirely or half converted to 3-acetyl chlorophyll (AcChl) a. The AcChl a pigments showed a Qy band, which was blue-shifted by 107 nm from B800 BChl a in the two variants. EET from AcChl a to B850 BChl a was observed in both fully oxidized and half-oxidized LH2 variants, but the EET rates were lower than that from B800 to B850 BChl a. EET from AcChl a to the co-present B800 was barely detected in the half-oxidized LH2. The preferential EET from AcChl a to B850 instead of B800 was rationalized by little spectral overlap of AcChl a with B800 BChl a and the pigment geometry in the protein. The EET rate from B800 to B850 BChl a in the half-oxidized LH2 was analogous to that in native LH2, indicating that partial oxidation of B800 did not disturb the EET channel from the residual B800 to B850.

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In situ formation of photoactive B-ring reduced chlorophyll isomer in photosynthetic protein LH2

Cited by 8 publications

References 31 publications

In Situ, Protein-Mediated Generation of a Photochemically Active Chlorophyll Analogue in a Mutant Bacterial Photosynthetic Reaction Center

In Situ, Protein-Mediated Generation of a Photochemically Active Chlorophyll Analogue in a Mutant Bacterial Photosynthetic Reaction Center

The 2.4 Å cryo-EM structure of a heptameric light-harvesting 2 complex reveals two carotenoid energy transfer pathways

Energy Transfer Dynamics in Light-Harvesting Complex 2 Variants Containing Oxidized B800 Bacteriochlorophyll a

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