International Union of Crystallography (IUCr) Acta Medica Okayama 2052-2525 12 5 2025 Illuminating DNA repair in action: structural insights into a photocaged glycosylase complex 513 514 EN Michihiro Suga Research Institute for Interdisciplinary Science, Okayama University No potential conflict of interest relevant to this article was reported.

Royal Society of Chemistry (RSC) Acta Medica Okayama 2041-6520 16 26 2025 Collective motions in the primary coordination sphere: a critical functional framework for catalytic activity of the oxygen-evolving complex of photosystem II 12024 EN Hiroshi Isobe Takayoshi Suzuki Research Institute for Interdisciplinary Science, Okayama University Michihiro Suga Research Institute for Interdisciplinary Science, Okayama University Jian-Ren Shen Research Institute for Interdisciplinary Science, Okayama University Kizashi Yamaguchi Center for Quantum Information and Quantum Biology, Osaka University Photosynthetic water oxidation, vital for dioxygen production and light energy conversion, is catalyzed by the oxygen-evolving complex of photosystem II, where the inorganic Mn4CaO5 cluster acts as the catalytic core. In this study, we investigate the functional significance of collective motions of amino acid side chains within the primary coordination sphere of the Mn cluster, focusing on their role in modulating the energetic demands for catalytic transformations in the S3 state. We applied regularized canonical correlation analysis to quantitatively correlate the three-dimensional arrangement of coordinating atoms with catalytic driving forces computed via density functional theory. Our analysis reveals that distinct collective side chain motions profoundly influence the energetic requirements for structural reconfigurations of the Mn cluster, achieved through expansion and contraction of the ligand cavity while fine-tuning its geometry to stabilize key intermediates. Complementary predictions from a neural network-based machine learning model indicate that the coordination sphere exerts a variable energetic impact on the catalytic transformations of the Mn cluster, depending on the S-state environment. Integrated computational analyses suggest that the extended lifetime of the S3YZ˙ state, consistently observed after three flash illuminations, may result from slow, progressive protein dynamics that continuously reshape the energy landscape, thereby shifting the equilibrium positions of rapid, reversible chemical processes over time. Overall, our findings demonstrate that collective motions in the primary coordination sphere constitute an active, dynamic framework essential for the efficient execution of multi-electron catalysis under ambient conditions, while simultaneously achieving a high selectivity with irreversible nature required for effective 3O2 evolution. No potential conflict of interest relevant to this article was reported.

American Chemical Society Acta Medica Okayama 2470-1343 9 50 2024 Conformational Flexibility of D1-Glu189: A Crucial Determinant in Substrate Water Selection, Positioning, and Stabilization within the Oxygen-Evolving Complex of Photosystem II 50041 50048 EN Hiroshi Isobe Research Institute for Interdisciplinary Science, Okayama University Takayoshi Suzuki Research Institute for Interdisciplinary Science, Okayama University Michihiro Suga Research Institute for Interdisciplinary Science, Okayama University Jian-Ren Shen Research Institute for Interdisciplinary Science, Okayama University Kizashi Yamaguchi Center for Quantum Information and Quantum Biology, Osaka University Photosynthetic water oxidation is a vital process responsible for producing dioxygen and supplying the energy necessary to sustain life on Earth. This fundamental reaction is catalyzed by the oxygen-evolving complex (OEC) of photosystem II, which houses the Mn4CaO5 cluster as its catalytic core. In this study, we specifically focus on the D1-Glu189 amino acid residue, which serves as a direct ligand to the Mn4CaO5 cluster. Our primary goal is to explore, using density functional theory (DFT), how the conformational flexibility of the D1-Glu189 side chain influences crucial catalytic processes, particularly the selection, positioning, and stabilization of a substrate water molecule within the OEC. Our investigation is based on a hypothesis put forth by Li et al. (Nature, 2024, 626, 670), which suggests that during the transition from the S2 to S3 state, a specific water molecule temporarily coordinating with the Ca ion, referred to as O6*, may exist as a hydroxide ion (OH-). Our results demonstrate a key mechanism by which the detachment of the D1-Glu189 carboxylate group from its coordination with the Ca ion allows the creation of a specialized microenvironment within the OEC that enables the selective attraction of O6* in its deprotonated form (OH-) and stabilizes it at the catalytic metal (MnD) site. Our findings indicate that D1-Glu189 is not only a structural ligand for the Ca ion but may also play an active and dynamic role in the catalytic process, positioning O6* optimally for its subsequent participation in the oxidation sequence during the water-splitting cycle. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 0028-0836 626 7999 2024 Oxygen-evolving photosystem II structures during S1–S2–S3 transitions 670 677 EN Hongjie Li Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Yoshiki Nakajima Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Eriko Nango Institute of Multidisciplinary Research for Advanced Materials, Tohoku University Shigeki Owada Japan Synchrotron Radiation Research Institute Daichi Yamada Department of Picobiology, Graduate School of Life Science, University of Hyogo Kana Hashimoto Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Fangjia Luo Japan Synchrotron Radiation Research Institute Rie Tanaka RIKEN SPring-8 Center Fusamichi Akita Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Koji Kato Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Jungmin Kang RIKEN SPring-8 Center Yasunori Saitoh Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Shunpei Kishi Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Huaxin Yu Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Naoki Matsubara Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Hajime Fujii Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Michihiro Sugahara Japan Synchrotron Radiation Research Institute Mamoru Suzuki Institute for Protein Research, Osaka University Tetsuya Masuda Division of Food and Nutrition, Faculty of Agriculture, Ryukoku University Tetsunari Kimura Department of Chemistry, Graduate School of Science, Kobe University Tran Nguyen Thao Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Shinichiro Yonekura Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Long-Jiang Yu Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Takehiko Tosha RIKEN SPring-8 Center Kensuke Tono Japan Synchrotron Radiation Research Institute Yasumasa Joti Japan Synchrotron Radiation Research Institute Takaki Hatsui Japan Synchrotron Radiation Research Institute Makina Yabashi Japan Synchrotron Radiation Research Institute Minoru Kubo Department of Picobiology, Graduate School of Life Science, University of Hyogo So Iwata RIKEN SPring-8 Center Hiroshi Isobe Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Kizashi Yamaguchi Center for Quantum Information and Quantum Biology, Osaka University Michihiro Suga Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Jian-Ren Shen Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Photosystem II (PSII) catalyses the oxidation of water through a four-step cycle of Si states (i = 0–4) at the Mn4CaO5 cluster1,2,3, during which an extra oxygen (O6) is incorporated at the S3 state to form a possible dioxygen4,5,6,7. Structural changes of the metal cluster and its environment during the S-state transitions have been studied on the microsecond timescale. Here we use pump-probe serial femtosecond crystallography to reveal the structural dynamics of PSII from nanoseconds to milliseconds after illumination with one flash (1F) or two flashes (2F). YZ, a tyrosine residue that connects the reaction centre P680 and the Mn4CaO5 cluster, showed structural changes on a nanosecond timescale, as did its surrounding amino acid residues and water molecules, reflecting the fast transfer of electrons and protons after flash illumination. Notably, one water molecule emerged in the vicinity of Glu189 of the D1 subunit of PSII (D1-E189), and was bound to the Ca2+ ion on a sub-microsecond timescale after 2F illumination. This water molecule disappeared later with the concomitant increase of O6, suggesting that it is the origin of O6. We also observed concerted movements of water molecules in the O1, O4 and Cl-1 channels and their surrounding amino acid residues to complete the sequence of electron transfer, proton release and substrate water delivery. These results provide crucial insights into the structural dynamics of PSII during S-state transitions as well as O–O bond formation. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 1083-351X 298 12 2022 Crystal structures of photosystem II from a cyanobacterium expressing psbA2 in comparison to psbA3 reveal differences in the D1 subunit 102668 EN Yoshiki Nakajima Research Institute for Interdisciplinary Science, Okayama University Natsumi Ugai-Amo Graduate School of Natural Science and Technology, Okayama University Naoki Tone Graduate School of Natural Science and Technology, Okayama University Akiko Nakagawa Proteo-Science Research Center, Ehime University Masako Iwai Graduate School and College of Arts and Sciences, The University of Tokyo Masahiko Ikeuchi Graduate School and College of Arts and Sciences, The University of Tokyo Miwa Sugiura Proteo-Science Research Center, Ehime University Michihiro Suga Research Institute for Interdisciplinary Science, Okayama University Shen Jian-Ren Research Institute for Interdisciplinary Science, Okayama University Three psbA genes (psbA1, psbA2, and psbA3) encoding the D1 subunit of photosystem II (PSII) are present in the ther-mophilic cyanobacterium Thermosynechococcus elongatus and are expressed differently in response to changes in the growth environment. To clarify the functional differences of the D1 protein expressed from these psbA genes, PSII dimers from two strains, each expressing only one psbA gene (psbA2 or psbA3), were crystallized, and we analyzed their structures at resolu-tions comparable to previously studied PsbA1-PSII. Our results showed that the hydrogen bond between pheophytin/D1 (PheoD1) and D1-130 became stronger in PsbA2-and PsbA3-PSII due to change of Gln to Glu, which partially explains the increase in the redox potential of PheoD1 observed in PsbA3. In PsbA2, one hydrogen bond was lost in PheoD1 due to the change of D1-Y147F, which may explain the decrease in stability of PheoD1 in PsbA2. Two water molecules in the Cl-1 channel were lost in PsbA2 due to the change of D1-P173M, leading to the narrowing of the channel, which may explain the lower efficiency of the S-state transition beyond S2 in PsbA2-PSII. In PsbA3-PSII, a hydrogen bond between D1-Ser270 and a sulfoquinovosyl-diacylglycerol molecule near QB dis-appeared due to the change of D1-Ser270 in PsbA1 and PsbA2 to D1-Ala270. This may result in an easier exchange of bound QB with free plastoquinone, hence an enhancement of oxygen evolution in PsbA3-PSII due to its high QB exchange efficiency. These results provide a structural basis for further functional examination of the three PsbA variants. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0010-8545 471 2022 Geometric, electronic and spin structures of the CaMn4O5 catalyst for water oxidation in oxygen-evolving photosystem II. Interplay between experiments and theoretical computations 214742 EN Kizashi Yamaguchi Center for Quantum Information and Quantum Biology, Osaka University Mitsuo Shoji Center of Computational Sciences, Tsukuba University Hiroshi Isobe Research Institute for Interdisciplinary Science, and Graduate School of Natural Science and Technology, Okayama University Takashi Kawakami RIKEN Center for Computational Science Koichi Miyagawa Center of Computational Sciences, Tsukuba University Michihiro Suga Research Institute for Interdisciplinary Science, and Graduate School of Natural Science and Technology, Okayama University Fusamichi Akita Research Institute for Interdisciplinary Science, and Graduate School of Natural Science and Technology, Okayama University Jian-Ren Shen Research Institute for Interdisciplinary Science, and Graduate School of Natural Science and Technology, Okayama University The aim of this review is to elucidate geometric structures of the catalytic CaMn4Ox (x = 5, 6) cluster in the Kok cycle for water oxidation in the oxygen evolving complex (OEC) of photosystem II (PSII) based on the high-resolution (HR) X-ray diffraction (XRD) and serial femtosecond crystallography (SFX) experiments using the X-ray free-electron laser (XFEL). Quantum mechanics (QM) and QM/molecular mechanics (MM) computations are performed to elucidate the electronic and spin structures of the CaMn4Ox (x = 5, 6) cluster in five states S-i (i = 0 similar to 4) on the basis of the X-ray spectroscopy, electron paramagnetic resonance (EPR) and related experiments. Interplay between the experiments and theoretical computations has been effective to elucidate the coordination structures of the CaMn4Ox (x = 5, 6) cluster ligated by amino acid residues of the protein matrix of PSII, valence states of the four Mn ions and total spin states by their exchange-couplings, and proton-shifted isomers of the CaMn4Ox (x = 5, 6) cluster. The HR XRD and SFX XFEL experiments have also elucidated the biomolecular systems structure of OEC of PSII and the hydrogen bonding networks consisting of water molecules, chloride anions, etc., for water inlet and proton release pathways in PSII. Large-scale QM/MM computations have been performed for elucidation of the hydrogen bonding distances and angles by adding invisible hydrogen atoms to the HR XRD structure. Full geometry optimizations by the QM and QM/MM methods have been effective for elucidation of the molecular systems structure around the CaMn4Ox (x = 5, 6) cluster in OEC. DLPNO-CCSD(T-0) method has been applied to elucidate relative energies of possible intermediates in each state of the Kok cycle for water oxidation. Implications of these results are discussed in relation to the blueprint for developments of artificial catalysts for water oxidation. No potential conflict of interest relevant to this article was reported.

Frontiers Media S.A. Acta Medica Okayama 1664-462X 13 2022 Structure and function of a silicic acid channel Lsi1 982068 EN Yasunori Saitoh Research Institute for Interdisciplinary Science, Okayama University Michihiro Suga Research Institute for Interdisciplinary Science, Okayama University Silicon is a beneficial element for plant growth and production, especially in rice. Plant roots take up silicon in the form of silicic acid. Silicic acid channels, which belong to the NIP subfamily of aquaporins, are responsible for silicic acid uptake. Accumulated experimental results have deepened our understanding of the silicic acid channel for its uptake mechanism, physiological function, localization, and other aspects. However, how the silicic acid channel efficiently and selectively permeates silicic acid remains to be elucidated. Recently reported crystal structures of the silicic acid channel enabled us to discuss the mechanism of silicic acid uptake by plant roots at an atomic level. In this mini-review, we focus on the crystal structures of the silicic acid channel and provide a detailed description of the structural determinants of silicic acid permeation and its transport mechanism, which are crucial for the rational creation of secure and sustainable crops. No potential conflict of interest relevant to this article was reported.

Nature Portfolio Acta Medica Okayama 2041-1723 12 1 2021 Structural basis for high selectivity of a rice silicon channel Lsi1 6236 EN Yasunori Saitoh Research Institute for Interdisciplinary Science, Okayama University Namiki Mitani-Ueno Institute of Plant Science and Resources, Okayama University Keisuke Saito Research Center for Advanced Science and Technology, The University of Tokyo Kengo Matsuki Graduate School of Natural Science and Technology, Okayama University Sheng Huang Institute of Plant Science and Resources, Okayama University Lingli Yang Research Institute for Interdisciplinary Science, Okayama University Naoki Yamaji Institute of Plant Science and Resources, Okayama University Hiroshi Ishikita Research Center for Advanced Science and Technology, The University of Tokyo Jian-Ren Shen Research Institute for Interdisciplinary Science, Okayama University Jian Feng Ma Institute of Plant Science and Resources, Okayama University Michihiro Suga Research Institute for Interdisciplinary Science, Okayama University Silicon (Si), the most abundant mineral element in the earth’s crust, is taken up by plant roots in the form of silicic acid through Low silicon rice 1 (Lsi1). Lsi1 belongs to the Nodulin 26-like intrinsic protein subfamily in aquaporin and shows high selectivity for silicic acid. To uncover the structural basis for this high selectivity, here we show the crystal structure of the rice Lsi1 at a resolution of 1.8 Å. The structure reveals transmembrane helical orientations different from other aquaporins, characterized by a unique, widely opened, and hydrophilic selectivity filter (SF) composed of five residues. Our structural, functional, and theoretical investigations provide a solid structural basis for the Si uptake mechanism in plants, which will contribute to secure and sustainable rice production by manipulating Lsi1 selectivity for different metalloids. No potential conflict of interest relevant to this article was reported.

SI Acta Medica Okayama 03044165 1864 2 2020 Time-resolved studies of metalloproteins using X-ray free electron laser radiation at SACLA 129466 EN Michihiro Suga Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Atsuhiro Shimada Graduate School of Applied Biological Sciences and Faculty of Applied Biological Sciences, Gifu University Fusamichi Akita Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Jian-Ren Shen Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Takehiko Tosha Synchrotron Radiation Life Science Instrumentation Team, RIKEN SPring-8 Center Hiroshi Sugimoto Synchrotron Radiation Life Science Instrumentation Team, RIKEN SPring-8 Center Background: The invention of the X-ray free-electron laser (XFEL) has provided unprecedented new opportunities for structural biology. The advantage of XFEL is an intense pulse of X-rays and a very short pulse duration (<10 fs) promising a damage-free and time-resolved crystallography approach.<br/> Scope of review: Recent time-resolved crystallographic analyses in XFEL facility SACLA are reviewed. Specifically, metalloproteins involved in the essential reactions of bioenergy conversion including photosystem II, cytochrome c oxidase and nitric oxide reductase are described.<br/> Major conclusions: XFEL with pump-probe techniques successfully visualized the process of the reaction and the dynamics of a protein. Since the active center of metalloproteins is very sensitive to the X-ray radiation, damage-free structures obtained by XFEL are essential to draw mechanistic conclusions. Methods and tools for sample delivery and reaction initiation are key for successful measurement of the time-resolved data.<br/> General significance: XFEL is at the center of approaches to gain insight into complex mechanism of structural dynamics and the reactions catalyzed by biological macromolecules. Further development has been carried out to expand the application of time-resolved X-ray crystallography. This article is part of a Special Issue entitled Novel measurement techniques for visualizing 'live' protein molecules. No potential conflict of interest relevant to this article was reported.

American Association for the Advancement of Science Acta Medica Okayama 0036-8075 366 6463 2019 An oxyl/oxo mechanism for dioxygen bond formation in PSII revealed by X-ray free electron lasers 334 338 EN Michihiro Suga Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Fusamichi Akita Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Keitaro Yamashita RIKEN SPring-8 Center Yoshiki Nakajima Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Go Ueno RIKEN SPring-8 Center Hongjie Li Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Takahiro Yamane Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Kunio Hirata RIKEN SPring-8 Center Yasufumi Umena Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Shinichiro Yonekura Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Long-Jiang Yu Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Hironori Murakami Japan Synchrotron Radiation Research Institute Takashi Nomura RIKEN SPring-8 Center Tetsunari Kimura Department of Chemistry, Graduate School of Science, Kobe University Minoru Kubo RIKEN SPring-8 Center Seiki Baba Japan Synchrotron Radiation Research Institute Takashi Kumasaka Japan Synchrotron Radiation Research Institute Kensuke Tono RIKEN SPring-8 Center Makina Yabashi RIKEN SPring-8 Center Hiroshi Isobe Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Kizashi Yamaguchi The Institute for Scientific and Industrial Research, Osaka University Masaki Yamamoto RIKEN SPring-8 Center Hideo Ago RIKEN SPring-8 Center Jian-Ren Shen Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Photosynthetic water oxidation is catalyzed by the Mn4CaO5 cluster of photosystem II (PSII) with linear progression through five S-state intermediates (S0 to S4). To reveal the mechanism of water oxidation, we analyzed structures of PSII in the S1, S2, and S3 states by x-ray free-electron laser serial crystallography. No insertion of water was found in S2, but flipping of D1 Glu189 upon transition to S3 leads to the opening of a water channel and provides a space for incorporation of an additional oxygen ligand, resulting in an open cubane Mn4CaO6 cluster with an oxyl/oxo bridge. Structural changes of PSII between the different S states reveal cooperative action of substrate water access, proton release, and dioxygen formation in photosynthetic water oxidation. No potential conflict of interest relevant to this article was reported.

American Society for Biochemistry and Molecular Biology Acta Medica Okayama 0021-9258 292 23 2017 Crystal structure and redox properties of a novel cyanobacterial heme protein with a His/Cys heme axial ligation and a Per-Arnt-Sim (PAS)-like domain 9599 9612 EN Taiki Motomura the Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Michihiro Suga the Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Rainer Hienerwadel the Laboratoire de Génétique et Biophysique des Plantes, UMR 7265, CNRS-CEA-Aix-Marseille Université, Faculté des Sciences de Luminy Akiko Nakagawa the Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Thanh-Lan Lai iBiTec-S Wolfgang Nitschke the Laboratoire de Bioénergétique et Ingénierie des Protéines Takahiro Kuma the Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Miwa Sugiura the Proteo-Science Research Center, Ehime University Alain Boussac iBiTec-S Jian-Ren Shen the Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University Photosystem II catalyzes light-induced water oxidation leading to the generation of dioxygen indispensable for sustaining aerobic life on Earth. The Photosystem II reaction center is composed of D1 and D2 proteins encoded by psbA and psbD genes, respectively. In cyanobacteria, different psbA genes are present in the genome. The thermophilic cyanobacterium Thermosynechococcus elongatus contains three psbA genes: psbA1, psbA2, and psbA3, and a new c-type heme protein, Tll0287, was found to be expressed in a strain expressing the psbA2 gene only, but the structure and function of Tll0287 are unknown. Here we solved the crystal structure of Tll0287 at a 2.0 Å resolution. The overall structure of Tll0287 was found to be similar to some kinases and sensor proteins with a Per-Arnt-Sim-like domain rather than to other c-type cytochromes. The fifth and sixth axial ligands for the heme were Cys and His, instead of the His/Met or His/His ligand pairs observed for most of the c-type hemes. The redox potential, E½, of Tll0287 was -255 ± 20 mV versus normal hydrogen electrode at pH values above 7.5. Below this pH value, the E½ increased by ≈57 mV/pH unit at 15 °C, suggesting the involvement of a protonatable group with a pKred = 7.2 ± 0.3. Possible functions of Tll0287 as a redox sensor under microaerobic conditions or a cytochrome subunit of an H2S-oxidizing system are discussed in view of the environmental conditions in which psbA2 is expressed, as well as phylogenetic analysis, structural, and sequence homologies. No potential conflict of interest relevant to this article was reported.

CURRENT BIOLOGY LTD Acta Medica Okayama 0959-440X 39 2016 Structure and energy transfer pathways of the plant photosystem I-LHCI supercomplex 46 53 EN Michihiro Suga Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Xiaochun Qin Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Tingyun Kuang Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences Jian-Ren Shen Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University Photosystem I (PSI) is one of the two photosystems in oxygenic photosynthesis, and absorbs light energy to generate reducing power for the reduction of NADP+ to NADPH with a quantum efficiency close to 100%. The plant PSI core forms a supercomplex with light-harvesting complex I (LHCI) with a total molecular weight of over 600 kDa. Recent X-ray structure analysis of the PSI-LHCI membrane-protein supercomplex has revealed detailed arrangement of the light-harvesting pigments and other cofactors especially within LHCI. Here we introduce the overall structure of the PSI-LHCI supercomplex, and then focus on the excited energy transfer (EET) pathways from LHCI to the PSI core and photoprotection mechanisms based on the structure obtained. No potential conflict of interest relevant to this article was reported.