Red Antenna States of Photosystem I from Cyanobacteria Synechocystis PCC 6803 and Thermosynechococcus elongatus:  Single-Complex Spectroscopy and Spectral Hole-Burning Study

Abstract

Hole-burning and single photosynthetic complex spectroscopy were used to study the excitonic structure and excitation energy-transfer processes of cyanobacterial trimeric Photosystem I (PS I) complexes from Synechocystis PCC 6803 and Thermosynechococcus elongatus at low temperatures. It was shown that individual PS I complexes of Synechocystis PCC 6803 (which have two red antenna states, i.e., C706 and C714) reveal only a broad structureless fluorescence band with a maximum near 720 nm, indicating strong electron-phonon coupling for the lowest energy C714 red state. The absence of zero-phonon lines (ZPLs) belonging to the C706 red state in the emission spectra of individual PS I complexes from Synechocystis PCC 6803 suggests that the C706 and C714 red antenna states of Synechocystis PCC 6803 are connected by efficient energy transfer with a characteristic transfer time of approximately 5 ps. This finding is in agreement with spectral hole-burning data obtained for bulk samples of Synechocystis PCC 6803. The importance of comparing the results of ensemble (spectral hole burning) and single-complex measurements was demonstrated. The presence of narrow ZPLs near 710 nm in addition to the broad fluorescence band at approximately 730 nm in Thermosynechococcus elongatus (Jelezko et al. J. Phys. Chem. B 2000, 104, 8093-8096) has been confirmed. We also demonstrate that high-quality samples obtained by dissolving crystals of PS I of Thermosynechococcus elongatus exhibit stronger absorption in the red antenna region than any samples studied so far by us and other groups.

The structure of a red-shifted photosystem I reveals a red site in the core antenna

“…Therefore, we suggest that the oscillator strength of the low-energy states has increased due to intensity stealing. Since the B31-B32 dimer in Synechocystis was previously assigned to the C706 state 31 , we confirm that this state is indeed one of the low-energy states in WT PSI. Due to addition of B33 Chl to the B31-B32 dimer, and increased interaction between the three Chls, the maximum of this state shifts to 710.4 nm.…”

Evidence for direct binding of glycerol to photosystem I

“…Their maxima and respective widths (full width at half maximum – fwhm) were found at 726.5 ± 0.5 nm/31.8 ± 0.5 nm (buffer), 731.0 ± 0.5 nm/31.5 ± 0.5 nm (66% glycerol/buffer mixture), and 731.0 ± 0.5 nm/27.0 ± 0.5 nm (re‐diluted buffer). The emission maxima reported for low temperature measurements at the ensemble level (with ⩾50% glycerol concentration) vary between 730 and 732 nm [15–17]. The ensemble values agree well with the fluorescence maximum determined for the average spectra in 66% glycerol/buffer mixture and in re‐diluted buffer, whereas for buffer solution a blue‐shift of several nanometers is observed, discussed in detail in Ref.…”

Exciton Delocalization and Transport in Photosystem I of Cyanobacteria Synechococcus elongates: Simulation Study of Coherent Two-Dimensional Optical Signals

“…Trimerization slightly increases the relative red absorption strength 1. Low temperature hole-burning spectra indicate that three red states are responsible for peaks at 710, 714, and 719 nm 7,8. Bands 714 and 719 are similar for two species ( Synechocystis PCC 6803 and Thermosynechococcus ) 8.…”

“…Low temperature hole-burning spectra indicate that three red states are responsible for peaks at 710, 714, and 719 nm 7,8. Bands 714 and 719 are similar for two species ( Synechocystis PCC 6803 and Thermosynechococcus ) 8. Hole-burning studies of the red states7 further revealed large permanent dipole moment and large linear pressure shift indicating strong electron–phonon coupling.…”