J Integr Plant Biol.

• Research Articles •    

A unique photosystem I reaction center from a chlorophyll d-containing cyanobacterium Acaryochloris marina

Caihuang Xu1† , Qingjun Zhu2,3† , Jing‐Hua Chen1,4† , Liangliang Shen2,3 , Xiaohan Yi1 , Zihui Huang1 , Wenda Wang2 , Min Chen5 , Tingyun Kuang2 , Jian‐Ren Shen2,6* , Xing Zhang1,4* and Guangye Han2 *   

  1. 1 Department of Biophysics and Department of Pathology of Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou 310058, China
    2 Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, The Chinese Academy of Sciences, Beijing 100093, China
    3 College of Life Sciences, University of Chinese Academy of Science, Beijing 100049, China
    4 Center of Cryo‐Electron Microscopy, Zhejiang University School of Medicine, Hangzhou 310058, China
    5 School of Life and Environmental Science, Faculty of Science, University of Sydney, Sydney NSW2006, Australia
    6 Division of Photosynthesis and Structural Biology, Institute for Interdisciplinary Science, and Graduate School of Natural Science and Technology, Okayama University, Okayama 700‐8530, Japan

    These authors contributed equally to this work.
    *Correspondences: Jian-Ren Shen (shen@cc.okayama-u.ac.jp); Xing Zhang (xzhang1999@zju.edu.cn); Guangye Han (hanguangye@ibcas.ac.cn, Dr. Han is responsible for the distribution of the materials associated with this article)
  • Received:2021-02-26 Accepted:2021-05-12 Online:2021-05-17

Abstract: Photosystem I (PSI) is a large protein supercomplex that catalyzes the light-dependent oxidation of plastocyanin (or cytochrome c6) and the reduction of ferredoxin. This catalytic reaction is realized by a transmembrane electron transfer chain consisting of primary electron donor (a special chlorophyll (Chl) pair) and electron acceptors A0, A1, and three Fe4S4 clusters, FX, FA, and FB. Here we report the PSI structure from a Chl d-dominated cyanobacterium Acaryochloris marina at 3.3 Å resolution obtained by single-particle cryo-electron microscopy. The A. marina PSI exists as a trimer with three identical monomers. Surprisingly, the structure reveals a unique composition of electron transfer chain in which the primary electron acceptor A0 is composed of two pheophytin a rather than Chl a found in any other well-known PSI structures. A novel subunit Psa27 is observed in the A. marina PSI structure. In addition, 77 Chls, 13 α-carotenes, two phylloquinones, three Fe-S clusters, two phosphatidyl glycerols, and one monogalactosyl-diglyceride were identified in each PSI monomer. Our results provide a structural basis for deciphering the mechanism of photosynthesis in a PSI complex with Chl d as the dominating pigments and absorbing far-red light.

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