Modelling excitation energy transfer and trapping in the filamentous cyanobacterium Anabaena variabilis PCC 7120

Abstract

The phycobilisome (PBS) serves as the major light-harvesting system, funnelling excitation energy to both photosystems (PS) in cyanobacteria and red algae. The picosecond kinetics involving the excitation energy transfer has been studied within the isolated systems and intact filaments of the cyanobacterium Anabaena variabilis PCC 7120. A target model is proposed which resolves the dynamics of the different chromophore groups. The energy transfer rate of 8.5 ± 1.0/ns from the rod to the core is the rate-limiting step, both in vivo and in vitro. The PBS-PSI-PSII supercomplex reveals efficient excitation energy migration from the low-energy allophycocyanin, which is the terminal emitter, in the PBS core to the chlorophyll a in the photosystems. The terminal emitter of the phycobilisome transfers energy to both PSI and PSII with a rate of 50 ± 10/ns, equally distributing the solar energy to both photosystems. Finally, the excitation energy is trapped by charge separation in the photosystems with trapping rates estimated to be 56 ± 6/ns in PSI and 14 ± 2/ns in PSII.

A kaleidoscope of photosynthetic antenna proteins and their emerging roles

“…Compartmental modeling analysis of picosecond time-resolved fluorescence studies revealed that, in intact cyanobacterial cells, the excitation energy from PBS can be rapidly distributed to the PSs ( Tian et al, 2011 ; Acuña et al, 2018 ). The varying architecture and the composition of PBSs among cyanobacterial species seem to hardly affect the energy funneling from the PBSs to the PSs ( Tian et al, 2011 ; Acuña et al, 2018 ; Akhtar et al, 2020 ; Biswas et al, 2020 ).…”

Energy transfer from phycobilisomes to photosystem I at room temperature

“…Picosecond time-resolved measurements were carried out using a synchroscan streak-camera setup described elsewhere ( van Stokkum et al., 2008 ; Acuña et al., 2018 ; Biswas et al., 2020 ). Briefly, the femtosecond laser source, Coherent Vitesse Duo, pumped the regenerative Coherent RegA 900, and the output from the RegA further fed into the optical parametric amplifier Coherent OPA 9400, which had an output wavelength range from 470 to 770 nm.…”

“…Mullineaux ( Mullineaux, 1994 ) reported that, at 77K, PSII-deficient Synechocystis cells exhibit a quantum efficiency of around 80% for PBS-to-PSI EET, contrasting with the 40% observed in wild-type (WT) cells. Conversely, room temperature picosecond studies, combined with functional kinetic modeling of experimental data, estimated a 50% EET to PSI within a PB-PSII-PSI megacomplex ( Tian et al., 2011 ; Biswas et al., 2020 ). In Synechococcus elongatus sp.…”

Efficient Broadband Light Absorption in a Bioinspired Silicon Photonic Structure

“…27,28 PBS is found on the thylakoid membrane in red algae cyanobacteria. 29,30 The unique properties of PBS have some advantages in light harvesting, e.g., broadband absorption, fast and efficient energy transfer, angular robustness, and amplification of light concentration. 31 The structural organization of PBS can be classified into several categories such as hemidiscoidal, hemiellipsoidal, bundle-shaped, and block-shaped.…”

“…One of the natural organisms that utilize the antenna system as a light concentrator is cyanobacteria, and they have perfected their absorption mechanism through an evolution of ∼3.5 billion years. Cyanobacteria contain light-harvesting antennae known as phycobilisomes (PBS) that consist of ∼1500 protein pigments. , PBS is found on the thylakoid membrane in red algae cyanobacteria. , The unique properties of PBS have some advantages in light harvesting, e.g., broadband absorption, fast and efficient energy transfer, angular robustness, and amplification of light concentration . The structural organization of PBS can be classified into several categories such as hemidiscoidal, hemiellipsoidal, bundle-shaped, and block-shaped. , One of the species of cyanobacteria Synechocystis sp.…”