Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 298, Issue 1, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.jbc.2021.101408
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Funding
- National Science Foundation [MCB-1613022]
- Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences [DE-FG02-05ER15646]
- National Institute of General Medical Sciences of the National Institutes of Health [K99GM140174]
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Some cyanobacteria can use far-red light for photosynthesis. The study identified the specific binding sites of chlorophyll f in photosystem I and revealed structural differences in far-red light-acclimated cyanobacteria.
Far-red light photoacclimation exhibited by some cyanobacteria allows these organisms to use the far-red region of the solar spectrum (700-800 nm) for photosynthesis. Part of this process includes the replacement of six photosystem I (PSI) subunits with isoforms that confer the binding of chlorophyll (Chl) f molecules that absorb far-red light (FRL). However, the exact sites at which Chl f molecules are bound are still challenging to determine. To aid in the identification of Chl f-binding sites, we solved the cryo-EM structure of PSI from far-red light-acclimated cells of the cyanobacterium Synechococcus sp. PCC 7335. We identified six sites that bind Chl f with high specificity and three additional sites that are likely to bind Chl f at lower specificity. All of these binding sites are in the core-antenna regions of PSI, and Chl f was not observed among the electron transfer cofactors. This structural analysis also reveals both conserved and non-conserved Chl f-binding sites, the latter of which exemplify the diversity in FRL-PSI among species. We found that the FRL-PSI structure also contains a bound soluble ferredoxin, PetF1, at low occupancy, which suggests that ferredoxin binds less transiently than expected according to the canonical view of ferredoxin-binding to facilitate electron transfer. We suggest that this may result from structural changes in FRL-PSI that occur specifically during FRL photoacclimation.
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