Gisriel, ChristopherShen, GaozhongKurashov, VasilyHo, Ming-YangZhang, ShangjiWilliams, DewightGolbeck, John H.Fromme, PetraBryant, Donald A.2020-06-092020-06-092020-02Gisriel, Christopher, Gaozhong Shen, Vasily Kurashov, Ming-Yang Ho, Shangji Zhang, Dewight Williams, John H. Golbeck, Petra Fromme, and Donald A. Bryant. "The structure of Photosystem I acclimated to far-red light illuminates an ecologically important acclimation process in photosynthesis." Science Advances 6, no. 6 (Feb 2020): eaay6415. DOI:10.1126/sciadv.aay6415.2375-2548https://scholarworks.montana.edu/handle/1/15943Phototrophic organisms are superbly adapted to different light environments but often must acclimate to challenging competition for visible light wavelengths in their niches. Some cyanobacteria overcome this challenge by expressing paralogous photosynthetic proteins and by synthesizing and incorporating ~8% chlorophyll f into their Photosystem I (PSI) complexes, enabling them to grow under far-red light (FRL). We solved the structure of FRL-acclimated PSI from the cyanobacterium Fischerella thermalis PCC 7521 by single-particle, cryo–electron microscopy to understand its structural and functional differences. Four binding sites occupied by chlorophyll f are proposed. Subtle structural changes enable FRL-adapted PSI to extend light utilization for oxygenic photosynthesis to nearly 800 nm. This structure provides a platform for understanding FRL-driven photosynthesis and illustrates the robustness of adaptive and acclimation mechanisms in nature.© This manuscript version is made available under the CC-BY 4.0 licensehttp://creativecommons.org/licenses/by/4.0/Article