Structure of a dimeric photosystem II complex from a cyanobacterium acclimated to far-red light

Christopher J. Gisriel*, Gaozhong Shen, David A. Flesher, Vasily Kurashov, John H. Golbeck, Gary W. Brudvig, Muhamed Amin, Donald A. Bryant

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Photosystem II (PSII) is the water-splitting enzyme central to oxygenic photosynthesis. To drive water oxidation, light is harvested by accessory pigments, mostly chlorophyll (Chl) a molecules, which absorb visible light (400–700 nm). Some cyanobacteria facultatively acclimate to shaded environments by altering their photosynthetic machinery to additionally absorb far-red light (FRL, 700–800 nm), a process termed far-red light photoacclimation or FaRLiP. During far-red light photoacclimation, FRL-PSII is assembled with FRL-specific isoforms of the subunits PsbA, PsbB, PsbC, PsbD, and PsbH, and some Chl-binding sites contain Chls d or f instead of the usual Chl a. The structure of an apo-FRL-PSII monomer lacking the FRL-specific PsbH subunit has previously been determined, but visualization of the dimeric complex has remained elusive. Here, we report the cryo-EM structure of a dimeric FRL–PSII complex. The site assignments for Chls d and f are consistent with those assigned in the previous apo-FRL-PSII monomeric structure. All sites that bind Chl d or Chl f at high occupancy exhibit a FRL-specific interaction of the formyl moiety of the Chl d or Chl f with the protein environment, which in some cases involves a phenylalanine sidechain. The structure retains the FRL-specific PsbH2 subunit, which appears to alter the energetic landscape of FRL-PSII, redirecting energy transfer from the phycobiliprotein complex to a Chl f molecule bound by PsbB2 that acts as a bridge for energy transfer to the electron transfer chain. Collectively, these observations extend our previous understanding of the structure-function relationship that allows PSII to function using lower energy FRL.

Original languageEnglish
Article number102815
Number of pages12
JournalJournal of Biological Chemistry
Issue number1
Publication statusPublished - Jan-2023


  • chlorophyll
  • cofactor assignment
  • cryo-EM
  • cyanobacteria
  • electron transfer
  • energy transfer
  • far-red light photoacclimation
  • photosynthesis
  • photosystem II
  • PsbH

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