Inter-subunit energy transfer processes in a minimal plant photosystem II supercomplex

Abstract

Photosystem II (PSII) is an integral part of the photosynthesis machinery, in which several light-harvesting complexes rely on inter-complex excitonic energy transfer (EET) processes to channel energy to the reaction center. In this paper, we report on a direct observation of the inter-complex EET in a minimal PSII supercomplex from plants, containing the trimeric light-harvesting complex II (LHCII), the monomeric light-harvesting complex CP26, and the monomeric PSII core complex. Using two-dimensional (2D) electronic spectroscopy, we measure an inter-complex EET timescale of 50 picoseconds for excitations from the LHCII-CP26 peripheral antenna to the PSII core. The 2D electronic spectra also reveal that the transfer timescale is nearly constant over the pump spectrum of 600 to 700 nanometers. Structure-based calculations reveal the contribution of each antenna complex to the measured inter-complex EET time. These results provide a step in elucidating the full inter-complex energy transfer network of the PSII machinery.

Ultrafast Energy Transfer in a Diatom Photosystem II Supercomplex

“…Note that similar calculations of the C 1 S 1 complex of A. thaliana resulted in a 67 ps rise lifetime of the core antenna after preferential LHCII excitation, which qualitatively concur with the ∼50 ps time scale measured. Therefore, the Redfield–generalized Förster calculations are useful in obtaining qualitative results indicative of the actual measurements.…”

“…The results strongly suggest that EET in the PSII–FCPII antenna is unusually fast, at least compared to plant PSII–LHCII, which has a slower trapping rate, limited by the exciton migration in the antenna. ,,, Just equilibration within the trimeric plant LHCII can take more than 10–20 ps at low temperatures , and longer in the multisubunit LHCII antenna . The EET transfer time between LHCII and the PSII core in a minimal PSII–LHCII supercomplex was found to be around 50 ps at 77 K . In contrast, the present results suggest that at least in part energy is transferred from FCPII to the core complex in 3 ps or less in PSII–FCPII of T.…”

“…For a better understanding of the molecular basis of the observed rapid EET, we performed structure-based calculations of the electronic couplings, exciton states, spectral lineshapes, and dynamics using a dynamic theory of optical spectra (see the Supporting Information). ,, The rates of EET and the exciton population kinetics were computed applying a combined Redfield–generalized Förster theory. ,, The model parameters are similar to the recent calculation of the C 1 S 1 supercomplex from Arabidopsis thaliana …”

“…Picosecond time-resolved fluorescence measurements were performed with a time-correlated single-photon counting instrument . Fourier transform femtosecond 2DES was performed using a partially collinear “pump-probe” geometry setup described elsewhere . Briefly, the excitation pulse spectrum was centered at approximately 670 nm and is depicted in Figure .…”

Insights into Energy Transfer in Light-Harvesting Complex II Through Machine-Learning Assisted Simulations

“…Energy transfer processes that occur within the Chls of LHCII have been extensively studied, but an unambiguous characterization of the most important pathways has still to be reached. Time-resolved spectroscopy experiments, especially transient absorption (TA) and two-dimensional electronic spectroscopy (2DES), − have been widely employed to investigate the fast and ultrafast dynamics in LHCII, − but the complexity of the system requires theoretical models to disentangle spectral features and map them back to the dynamics . In particular, the exciton Hamiltonian and its parameters, namely the site energies of the pigments and the electronic couplings between them, cannot be extracted exclusively from the experiments.…”