Light harvesting in cyanobacteria: The phycobilisomes

Bar-Eyal, Leeat; Shperberg-Avni, Anat; Paltiel, Yossi; Keren, Nir; Adir, Noam; Croce, Roberta; Grondelle, Rienk van; Amerongen, Herbert van; Stokkum, Ivo H. M. van

doi:10.1201/9781351242899-5

Cited by 4 publications

(1 citation statement)

References 1 publication

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“…PCC 6803 (hereafter denoted as Synechocystis ) with an overall resolution of 2.1-3.5 Å. The PB are formed by phycobiliproteins, consisting of two polypeptide subunits designated as α and β, often forming a heterodimer (αβ), each covalently binding open chain tetrapyrrole chromophores (phycobilin) and colorless linker proteins ( Ducret et al., 1994 ; MacColl, 1998 ; Adir, 2005 ; Bar-Eyal et al., 2018 ; Adir et al., 2020 ). The αβ heterodimers self-assemble into either disc-like trimers (αβ 3 ) or further aggregate into hexamers [(αβ 3 )] 2 , serving as the basic building blocks of PBs.…”

Section: Introductionmentioning

confidence: 99%

Energy transfer from phycobilisomes to photosystem I at room temperature

Biswas,

Akhtar,

Lambrev

et al. 2024

Front. Plant Sci.

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The phycobilisomes function as the primary light-harvesting antennae in cyanobacteria and red algae, effectively harvesting and transferring excitation energy to both photosystems. Here we investigate the direct energy transfer route from the phycobilisomes to photosystem I at room temperature in a mutant of the cyanobacterium Synechocystis sp. PCC 6803 that lacks photosystem II. The excitation dynamics are studied by picosecond time-resolved fluorescence measurements in combination with global and target analysis. Global analysis revealed several fast equilibration time scales and a decay of the equilibrated system with a time constant of ≈220 ps. From simultaneous target analysis of measurements with two different excitations of 400 nm (chlorophyll a) and 580 nm (phycobilisomes) a transfer rate of 42 ns-1 from the terminal emitter of the phycobilisome to photosystem I was estimated.

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Section: Introductionmentioning

confidence: 99%

Energy transfer from phycobilisomes to photosystem I at room temperature

Biswas,

Akhtar,

Lambrev

et al. 2024

Front. Plant Sci.

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The antenna of far-red absorbing cyanobacteria increases both absorption and quantum efficiency of Photosystem II

et al. 2022

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Cyanobacteria carry out photosynthetic light-energy conversion using phycobiliproteins for light harvesting and the chlorophyll-rich photosystems for photochemistry. While most cyanobacteria only absorb visible photons, some of them can acclimate to harvest far-red light (FRL, 700–800 nm) by integrating chlorophyll f and d in their photosystems and producing red-shifted allophycocyanin. Chlorophyll f insertion enables the photosystems to use FRL but slows down charge separation, reducing photosynthetic efficiency. Here we demonstrate with time-resolved fluorescence spectroscopy that on average charge separation in chlorophyll-f-containing Photosystem II becomes faster in the presence of red-shifted allophycocyanin antennas. This is different from all known photosynthetic systems, where additional light-harvesting complexes increase the overall absorption cross section but slow down charge separation. This remarkable property can be explained with the available structural and spectroscopic information. The unique design is probably important for these cyanobacteria to efficiently switch between visible and far-red light.

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Ultrafast excitation quenching by the oxidized photosystem II reaction center

Akhtar

Sipka

Han

et al. 2022

The Journal of Chemical Physics

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Photosystem II (PSII) is the pigment–protein complex driving the photoinduced oxidation of water and reduction of plastoquinone in all oxygenic photosynthetic organisms. Excitations in the antenna chlorophylls are photochemically trapped in the reaction center (RC) producing the chlorophyll–pheophytin radical ion pair P+ Pheo−. When electron donation from water is inhibited, the oxidized RC chlorophyll P+ acts as an excitation quencher, but knowledge on the kinetics of quenching is limited. Here, we used femtosecond transient absorption spectroscopy to compare the excitation dynamics of PSII with neutral and oxidized RC (P+). We find that equilibration in the core antenna has a major lifetime of about 300 fs, irrespective of the RC redox state. Two-dimensional electronic spectroscopy revealed additional slower energy equilibration occurring on timescales of 3–5 ps, concurrent with excitation trapping. The kinetics of PSII with open RC can be described well with previously proposed models according to which the radical pair P+ Pheo− is populated with a main lifetime of about 40 ps, which is primarily determined by energy transfer between the core antenna and the RC chlorophylls. Yet, in PSII with oxidized RC (P+), fast excitation quenching was observed with decay lifetimes as short as 3 ps and an average decay lifetime of about 90 ps, which is shorter than the excited-state lifetime of PSII with open RC. The underlying mechanism of this extremely fast quenching prompts further investigation.

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Light harvesting in cyanobacteria: The phycobilisomes

Cited by 4 publications

References 1 publication

Energy transfer from phycobilisomes to photosystem I at room temperature

Energy transfer from phycobilisomes to photosystem I at room temperature

The antenna of far-red absorbing cyanobacteria increases both absorption and quantum efficiency of Photosystem II

Ultrafast excitation quenching by the oxidized photosystem II reaction center

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