Gisriel, Christopher J.Christopher J.GisrielFlesher, David A.David A.FlesherShen, GaozhongGaozhongShenWang, JiminJiminWangMING-YANG HOBrudvig, Gary W.Gary W.BrudvigBryant, Donald A.Donald A.Bryant2022-01-222022-01-222022-01-010021-9258https://scholars.lib.ntu.edu.tw/handle/123456789/592946Far-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]SDG14Antennas; Electron transitions; Medical imaging; Molecules; Binding-sites; Cyanobacteria Synechococcus; Cyanobacterium; Electron transfer; Far-red lights; High specificity; Isoforms; Marine cyanobacteria; Photosystems; Solar spectrum; Binding sitesjournal article10.1016/j.jbc.2021.101408347938392-s2.0-85122070484https://api.elsevier.com/content/abstract/scopus_id/85122070484