Structure of a photosystem I-ferredoxin complex from a marine cyanobacterium provides insights into far-red light photoacclimation
Journal
Journal of Biological Chemistry
Journal Volume
298
Journal Issue
1
Pages
101408
Date Issued
2022-01-01
Author(s)
Gisriel, Christopher J.
Flesher, David A.
Shen, Gaozhong
Wang, Jimin
Brudvig, Gary W.
Bryant, Donald A.
Abstract
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.
SDGs
Other Subjects
Antennas; Electron transitions; Medical imaging; Molecules; Binding-sites; Cyanobacteria Synechococcus; Cyanobacterium; Electron transfer; Far-red lights; High specificity; Isoforms; Marine cyanobacteria; Photosystems; Solar spectrum; Binding sites
Publisher
American Society for Biochemistry and Molecular Biology Inc.
Type
journal article