Nature Portfolio Acta Medica Okayama 2041-1723 14 1 2023 Structure of a monomeric photosystem I core associated with iron-stress-induced-A proteins from Anabaena sp. PCC 7120 920 EN Ryo Nagao Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Koji Kato Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Tasuku Hamaguchi Biostructural Mechanism Laboratory, RIKEN SPring-8 Center Yoshifumi Ueno Graduate School of Science, Kobe University Naoki Tsuboshita Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Shota Shimizu Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Miyu Furutani Graduate School of Science, Kobe University Shigeki Ehira Department of Biological Sciences, Graduate School of Science, Tokyo Metropolitan University Yoshiki Nakajima Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Keisuke Kawakami Biostructural Mechanism Laboratory, RIKEN SPring-8 Center Takehiro Suzuki Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science Naoshi Dohmae Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science Seiji Akimoto Graduate School of Science, Kobe University Koji Yonekura Biostructural Mechanism Laboratory, RIKEN SPring-8 Center Jian-Ren Shen Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Iron-stress-induced-A proteins (IsiAs) are expressed in cyanobacteria under iron-deficient conditions. The cyanobacterium Anabaena sp. PCC 7120 has four isiA genes; however, their binding property and functional roles in PSI are still missing. We analyzed a cryo-electron microscopy structure of a PSI-IsiA supercomplex isolated from Anabaena grown under an iron-deficient condition. The PSI-IsiA structure contains six IsiA subunits associated with the PsaA side of a PSI core monomer. Three of the six IsiA subunits were identified as IsiA1 and IsiA2. The PSI-IsiA structure lacks a PsaL subunit; instead, a C-terminal domain of IsiA2 occupies the position of PsaL, which inhibits the oligomerization of PSI, leading to the formation of a PSI monomer. Furthermore, excitation-energy transfer from IsiAs to PSI appeared with a time constant of 55 ps. These findings provide insights into both the molecular assembly of the Anabaena IsiA family and the functional roles of IsiAs. No potential conflict of interest relevant to this article was reported.

eLIFE SCIENCES PUBL LTD Acta Medica Okayama 2050-084X 11 2022 Structural basis for the absence of low-energy chlorophylls in a photosystem I trimer from Gloeobacter violaceus e73990 EN Koji Kato Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Tasuku Hamaguchi Biostructural Mechanism Laboratory, RIKEN SPring-8 Center Ryo Nagao Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Keisuke Kawakami Biostructural Mechanism Laboratory, RIKEN SPring-8 Center Yoshifumi Ueno Graduate School of Science, Kobe University Takehiro Suzuki Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science Hiroko Uchida Research Center for Inland Seas, Kobe University Akio Murakami Graduate School of Science, Kobe University Yoshiki Nakajima Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Makio Yokono Institute of Low Temperature Science, Hokkaido University Seiji Akimoto Graduate School of Science, Kobe University Naoshi Dohmae Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science Koji Yonekura Biostructural Mechanism Laboratory, RIKEN SPring-8 Center Jian-Ren Shen Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Photosystem I (PSI) is a multi-subunit pigment-protein complex that functions in light-harvesting and photochemical charge-separation reactions, followed by reduction of NADP to NADPH required for CO2 fixation in photosynthetic organisms. PSI from different photosynthetic organisms has a variety of chlorophylls (Chls), some of which are at lower-energy levels than its reaction center P700, a special pair of Chls, and are called low-energy Chls. However, the sites of low-energy Chls are still under debate. Here, we solved a 2.04-& ANGS; resolution structure of a PSI trimer by cryo-electron microscopy from a primordial cyanobacterium Gloeobacter violaceus PCC 7421, which has no low-energy Chls. The structure shows the absence of some subunits commonly found in other cyanobacteria, confirming the primordial nature of this cyanobacterium. Comparison with the known structures of PSI from other cyanobacteria and eukaryotic organisms reveals that one dimeric and one trimeric Chls are lacking in the Gloeobacter PSI. The dimeric and trimeric Chls are named Low1 and Low2, respectively. Low2 is missing in some cyanobacterial and eukaryotic PSIs, whereas Low1 is absent only in Gloeobacter. These findings provide insights into not only the identity of low-energy Chls in PSI, but also the evolutionary changes of low-energy Chls in oxyphototrophs. No potential conflict of interest relevant to this article was reported.

Nature Portfolio Acta Medica Okayama 2041-1723 13 1 2022 Structural basis for different types of hetero-tetrameric light-harvesting complexes in a diatom PSII-FCPII supercomplex 1764 EN Ryo Nagao Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Koji Kato Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Minoru Kumazawa Graduate School of Biostudies, Kyoto University Kentaro Ifuku Graduate School of Agriculture, Kyoto University Makio Yokono Institute of Low Temperature Science, Hokkaido University Takehiro Suzuki Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science Naoshi Dohmae Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science Fusamichi Akita Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Seiji Akimoto Graduate School of Science, Kobe University Naoyuki Miyazaki Life Science Center for Survival Dynamics, Tsukuba Advanced Research Alliance (TARA), University of Tsukuba Jian-Ren Shen Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Fucoxanthin chlorophyll (Chl) a/c-binding proteins (FCPs) function as light harvesters in diatoms. The structure of a diatom photosystem II-FCPII (PSII-FCPII) supercomplex have been solved by cryo-electron microscopy (cryo-EM) previously; however, the FCPII subunits that constitute the FCPII tetramers and monomers are not identified individually due to their low resolutions. Here, we report a 2.5 angstrom resolution structure of the PSII-FCPII supercomplex using cryo-EM. Two types of tetrameric FCPs, S-tetramer, and M-tetramer, are identified as different types of hetero-tetrameric complexes. In addition, three FCP monomers, m1, m2, and m3, are assigned to different gene products of FCP. The present structure also identifies the positions of most Chls c and diadinoxanthins, which form a complicated pigment network. Excitation-energy transfer from FCPII to PSII is revealed by time-resolved fluorescence spectroscopy. These structural and spectroscopic findings provide insights into an assembly model of FCPII and its excitation-energy transfer and quenching processes. Fucoxanthin chlorophyll a/c-binding proteins (FCPs) harvest light energy in diatoms. The authors analyzed a structure of PSII-FCPII supercomplex at high resolution by cryo-EM, which identified each FCP subunit and pigment network in the supercomplex. No potential conflict of interest relevant to this article was reported.

Nature Portfolio Acta Medica Okayama 2041-1723 13 1 2022 Structure of a tetrameric photosystem I from a glaucophyte alga Cyanophora paradoxa 1679 EN Koji Kato Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Ryo Nagao Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Yoshifumi Ueno Graduate School of Science, Kobe University Makio Yokono Institute of Low Temperature Science, Hokkaido University Takehiro Suzuki Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science Jiang Tian-Yi Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Naoshi Dohmae Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science Fusamichi Akita Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Seiji Akimoto Graduate School of Science, Kobe University Naoyuki Miyazaki Life Science Center for Survival Dynamics, Tsukuba Advanced Research Alliance (TARA), University of Tsukuba Shen Jian-Ren Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Photosystem I (PSI) is one of the two photosystems functioning in light-energy harvesting, transfer, and electron transfer in photosynthesis. However, the oligomerization state of PSI is variable among photosynthetic organisms. We present a 3.8-angstrom resolution cryo-electron microscopic structure of tetrameric PSI isolated from the glaucophyte alga Cyanophora paradoxa, which reveals differences with PSI from other organisms in subunit composition and organization. The PSI tetramer is organized in a dimer of dimers with a C2 symmetry. Unlike cyanobacterial PSI tetramers, two of the four monomers are rotated around 90 degrees, resulting in a completely different pattern of monomer-monomer interactions. Excitation-energy transfer among chlorophylls differs significantly between Cyanophora and cyanobacterial PSI tetramers. These structural and spectroscopic features reveal characteristic interactions and excitation-energy transfer in the Cyanophora PSI tetramer, suggesting that the Cyanophora PSI could represent a turning point in the evolution of PSI from prokaryotes to eukaryotes. No potential conflict of interest relevant to this article was reported.

Nature Acta Medica Okayama 2399-3642 3 1 2020 Structure of a cyanobacterial photosystem I surrounded by octadecameric IsiA antenna proteins 232 EN Fusamichi Akita Graduate School of Natural Science and Technology, Okayama University Ryo Nagao Research Institute for Interdisciplinary Science, Okayama University Koji Kato Research Institute for Interdisciplinary Science, Okayama University Yoshiki Nakajima Graduate School of Natural Science and Technology, Okayama University Makio Yokono Nippon Flour Mills Co., Ltd., Innovation Center Yoshifumi Ueno Graduate School of Science, Kobe University Takehiro Suzuki Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science Naoshi Dohmae Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science Jian-Ren Shen Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Seiji Akimoto Graduate School of Science, Kobe University Naoyuki Miyazaki Life Science Center for Survival Dynamics, Tsukuba Advanced Research Alliance (TARA), University of Tsukuba Iron-stress induced protein A (IsiA) is a chlorophyll-binding membrane-spanning protein in photosynthetic prokaryote cyanobacteria, and is associated with photosystem I (PSI) trimer cores, but its structural and functional significance in light harvesting remains unclear. Here we report a 2.7-angstrom resolution cryo-electron microscopic structure of a supercomplex between PSI core trimer and IsiA from a thermophilic cyanobacterium Thermosynechococcus vulcanus. The structure showed that 18 IsiA subunits form a closed ring surrounding a PSI trimer core. Detailed arrangement of pigments within the supercomplex, as well as molecular interactions between PSI and IsiA and among IsiAs, were resolved. Time-resolved fluorescence spectra of the PSI-IsiA supercomplex showed clear excitation-energy transfer from IsiA to PSI, strongly indicating that IsiA functions as an energy donor, but not an energy quencher, in the supercomplex. These structural and spectroscopic findings provide important insights into the excitation-energy-transfer and subunit assembly mechanisms in the PSI-IsiA supercomplex. Akita et al. present the latest approach to solve IsiA-PSI supercomplex molecular structure with increased resolution using cryo-EM and time-resolved fluorescence studies. With 2.7 angstrom resolution, they reveal molecular interactions between PSI and IsiA subunits and that IsiA functions as an energy donor in the supercomplex. No potential conflict of interest relevant to this article was reported.

Nature Research Acta Medica Okayama 2041-1723 11 1 2020 Structural basis for assembly and function of a diatom photosystem I-light-harvesting supercomplex EN Ryo Nagao Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Koji Kato Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Kentaro Ifuku Graduate School of Biostudies, Kyoto University Takehiro Suzuki Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science Minoru Kumazawa Faculty of Agriculture, Kyoto University Ikuo Uchiyama National Institute for Basic Biology, National Institutes of Natural Sciences Yasuhiro Kashino Graduate School of Life Science, University of Hyogo Naoshi Dohmae Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science Seiji Akimoto Graduate School of Science,Kobe University Jian-Ren Shen Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Naoyuki Miyazaki Institute for Protein Research, Osaka University Fusamichi Akita Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Photosynthetic light-harvesting complexes (LHCs) play a pivotal role in collecting solar energy for photochemical reactions in photosynthesis. One of the major LHCs are fucoxanthin chlorophyll a/c-binding proteins (FCPs) present in diatoms, a group of organisms having important contribution to the global carbon cycle. Here, we report a 2.40-angstrom resolution structure of the diatom photosystem I (PSI)-FCPI supercomplex by cryo-electron microscopy. The supercomplex is composed of 16 different FCPI subunits surrounding a monomeric PSI core. Each FCPI subunit showed different protein structures with different pigment contents and binding sites, and they form a complicated pigment-protein network together with the PSI core to harvest and transfer the light energy efficiently. In addition, two unique, previously unidentified subunits were found in the PSI core. The structure provides numerous insights into not only the light-harvesting strategy in diatom PSI-FCPI but also evolutionary dynamics of light harvesters among oxyphototrophs. One of the major photosynthetic light-harvesting complexes (LHCs) are fucoxanthin chlorophyll a/c-binding proteins (FCPs), which are present in diatoms, a major group of algae. Here, the authors present the cryo-EM structure of the photosystem I-FCP (PSI-FCPI) supercomplex isolated from the marine centric diatom Chaetoceros gracilis that contains 16 FCPI subunits surrounding the PSI core and discuss possible excitation energy transfer pathways. No potential conflict of interest relevant to this article was reported.