On the Red Antenna States of Photosystem i Mutants from Cyanobacteria Synechocystis PCC 6803

Anton Khmelnitskiy, Hila Toporik, Yuval Mazor, Ryszard Jankowiak*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


To identify the molecular composition of the low-energy states in cyanobacterial Photosystem I (PSI) of Synechocystis PCC6803, we focus on high-resolution (low-temperature) absorption, emission, resonant, and nonresonant hole-burned spectra obtained for wild-type (WT) PSI and three PSI mutants. In the Red_a mutant, the B33 chlorophyll (Chl) is added to the B31-B32 dimer; in Red_b, histidine 95 (His95) on PsaB (which coordinates Mg in the B7 Chl within the His95-B7-A31-A32-cluster) is replaced with glutamine (Gln), while in the Red_ab mutant, both mutations are made. We show that the C706 state (B31-B32) changes to the C710 state (B31-B32-B33) in both Red_a and Red_ab mutants, while the C707 state in WT Synechocystis (localized on the His95-B7-A31-A32 cluster) is modified to C716 in both Red_b and Red_ab. Excitation energy transfer from C706 to the C714 trap in the WT PSI and Red_b mutant is hampered as reflected by a weak emission at 712 nm. Large electron-phonon coupling strength (exposed via resonant hole-burned spectra) is consistent with a strong mixing of excited states with intermolecular charge transfer states leading to significantly red-shifted emission spectra. We conclude that excitation energy transfer in PSI is controlled by fine-tuning the electronic states of a small number of highly conserved red states. Finally, we show that mutations modify the protein potential energy landscape as revealed by different shapes and shifts of the blue- and red-shifted antiholes.

Original languageAmerican English
Pages (from-to)8504-8515
Number of pages12
JournalJournal of Physical Chemistry B
Issue number39
StatePublished - 1 Oct 2020
Externally publishedYes

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Copyright © 2020 American Chemical Society.


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