研究者詳細 - 沈　建仁

論文 - 沈　建仁

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Exploring reaction pathways for the structural rearrangements of the Mn cluster induced by water binding in the S-3 state of the oxygen evolving complex of photosystem II 査読

Hiroshi Isobe, Mitsuo Shoji, Takayoshi Suzuki, Jian-Ren Shen, Kizashi Yamaguchi

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 405 2021年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE SA

Photosynthetic oxidation of water to dioxygen is catalyzed by the Mn4CaO5 cluster in the protein-cofactor complex photosystem II. The light-driven catalytic cycle consists of four observable intermediates (S-0, S-1, S-2, and S-3) and one transient S-4 state. Recently, using X-ray free-electron laser crystallography, two experimental groups independently observed incorporation of one additional oxygen into the cluster during the S-2 to S-3 transition, which is likely to represent a substrate. The present study implicates two competing reaction routes encountered during the structural rearrangement of the catalyst induced by the water binding and immediately preceding the formation of final stable forms in the S-3 state. This mutually exclusive competition involves concerted versus stepwise conformational changes between two isomers, called open and closed cubane structures, which have different consequences on the immediate product in the S-3 state. The concerted pathway involves a one-step conversion between two isomeric hydroxo forms without changes to the metal oxidation and total spin (S-total = 3) states. Alternatively, in the stepwise process, the bound waters are oxidized and transformed into an oxyl-oxo form in a higher spin (S-total = 6) state. Here, density functional calculations are used to characterize all relevant intermediates and transition structures and demonstrate that the stepwise pathway to the substrate activation is substantially favored over the concerted one, as evidenced by comparison of the activation barriers (11.1 and 20.9 kcal mol(-1), respectively). Only after formation of the oxyl-oxo precursor can the hydroxo species be generated; this occurs with a slow kinetics and an activation barrier of 17.8 kcal mol(-1). The overall thermodynamic driving force is likely to be controlled by the movements of two glutamate ligands, D1-Glu189 and CP43-Glu354, in the active site and ranges from very weak (+0.4 kcal mol(-1)) to very strong (-23.5 kcal mol(-1)).

DOI： 10.1016/j.jphotochem.2020.112905

Molecular organizations and function of iron-stress-induced-A protein family in Anabaena sp. PCC 7120 査読国際誌

Ryo Nagao, Makio Yokono, Yoshifumi Ueno, Takehiro Suzuki, Koji Kato, Ka-Ho Kato, Naoki Tsuboshita, Tian-Yi Jiang, Naoshi Dohmae, Jian-Ren Shen, Shigeki Ehira, Seiji Akimoto

BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1862 ( 1 ) 148327 - 148327 2021年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER

Iron-stress-induced-A proteins (IsiAs) are expressed in cyanobacteria under iron-deficient conditions, and surround photosystem I (PSI) trimer with a ring formation. A cyanobacterium Anabaena sp. PCC 7120 has four isiA genes; however, it is unknown how the IsiAs are associated with PSI. Here we report on molecular organizations and function of the IsiAs in this cyanobacterium. A deletion mutant of the isiA1 gene was constructed, and the four types of thylakoids were prepared from the wild-type (WT) and Delta isiA1 cells under iron-replete (+Fe) and iron-deficient (-Fe) conditions. Immunoblotting analysis exhibits a clear expression of the IsiA1 in the WT-Fe. The PSI-IsiA1 supercomplex is found in the WT-Fe, and excitation-energy transfer from IsiA1 to PSI is verified by time-resolved fluorescence analyses. Instead of the IsiA1, both IsiA2 and IsiA3 are bound to PSI monomer in the Delta isiA1-Fe. These findings provide insights into multiple-expression system of the IsiA family in this cyanobacterium.

DOI： 10.1016/j.bbabio.2020.148327

Basic pH-induced modification of excitation-energy dynamics in fucoxanthin chlorophyll a/c-binding proteins isolated from a pinguiophyte, Glossomastix chrysoplasta 査読国際誌

Ryo Nagao, Makio Yokono, Yoshifumi Ueno, Ka-Ho Kato, Naoki Tsuboshita, Jian-Ren Shen, Seiji Akimoto

BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1862 ( 1 ) 148306 - 148306 2021年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER

Photosynthetic organisms have diversified light-harvesting complexes (LHCs) to collect solar energy efficiently, leading to an acquisition of their ecological niches. Herein we report on biochemical and spectroscopic characterizations of fucoxanthin chlorophyll a/c-binding protein (FCP) complexes isolated from a marine pinguiophyte Glossomastix chrysoplasta. The pinguiophyte FCP showed one subunit band in SDS-PAGE and one protein-complex band with a molecular weight at around 66 kDa in clear-native PAGE. By HPLC analysis, the FCP possesses chlorophylls a and c, fucoxanthin, and violaxanthin. To clarify excitation-energy-relaxation processes in the FCP, we measured time-resolved fluorescence spectra at 77 K of the FCP adapted to pH 5.0, 6.5, and 8.0. Fluorescence curves measured at pH 5.0 and 8.0 showed shorter lifetime components compared with those at pH 6.5. The rapid decay components at pH 5.0 and 8.0 are unveiled by fluorescence decay-associated (FDA) spectra; fluorescence decays occur in the 270 and 160-ps FDA spectra only at pH 5.0 and 8.0, respectively. In addition, energy-transfer pathways with time constants of tens of picoseconds are altered under the basic pH condition but not the acidic pH condition. These findings provide novel insights into pH-dependent energy-transfer and energy-quenching machinery in not only FCP family but also photosynthetic LHCs.

DOI： 10.1016/j.bbabio.2020.148306

Structural elucidation of vascular plant photosystem I and its functional implications 査読国際誌

Xiuxiu Li, Gongxian Yang, Xinyi Yuan, Fenghua Wu, Wenda Wang, Jian-Ren Shen, Tingyun Kuang, Xiaochun Qin

Functional Plant Biology 2021年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：CSIRO Publishing

In vascular plants, bryophytes and algae, the photosynthetic light reaction takes place in the thylakoid membrane where two transmembrane supercomplexes PSII and PSI work together with cytochrome b6f and ATP synthase to harvest the light energy and produce ATP and NADPH. Vascular plant PSI is a 600-kDa protein-pigment supercomplex, the core complex of which is partly surrounded by peripheral light-harvesting complex I (LHCI) that captures sunlight and transfers the excitation energy to the core to be used for charge separation. PSI is unique mainly in absorption of longer-wavelengths than PSII, fast excitation energy transfer including uphill energy transfer, and an extremely high quantum efﬁciency. From the early 1980s, a lot of effort has been dedicated to structural and functional studies of PSI-LHCI, leading to the current understanding of how more than 200 cofactors are kept at the correct distance and geometry to facilitate fast energy transfer in this supercomplex at an atomic level. In this review, we review the history of studies on vascular plant PSI-LHCI, summarise the present research progress on its structure, and present some new and further questions to be answered in future studies.

DOI： 10.1071/fp21077

Changes in excitation relaxation of diatoms in response to fluctuating light, probed by fluorescence spectroscopies 査読国際誌

Miyuki Tanabe, Yoshifumi Ueno, Makio Yokono, Jian-Ren Shen, Ryo Nagao, Seiji Akimoto

PHOTOSYNTHESIS RESEARCH 146 ( 1-3 ) 143 - 150 2020年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

A marine pennate diatom Phaeodactylum tricornutum (Pt) and a marine centric diatom Chaetoceros gracilis (Cg) possess unique light-harvesting complexes, fucoxanthin chlorophyll a/c-binding proteins (FCPs). FCPs have dual functions: light harvesting in the blue to green regions and quenching of excess energy. So far, excitation dynamics including FCPs have been studied by altering continuous light conditions. In the present study, we examined responses of the diatom cells to fluctuating light (FL) conditions. Excitation dynamics in the cells incubated under the FL conditions were analyzed by time-resolved fluorescence measurements followed by global analysis. As responses common to the Pt and Cg cells, quenching behaviors were observed in photosystem (PS) II with time constants of hundreds of picoseconds. The PSII -> PSI energy transfer was modified only in the Pt cells, whereas quenching in FCPs was suggested only in the Cg cells, indicating different strategy for the dissipation of excess energy under the FL conditions.

DOI： 10.1007/s11120-020-00720-3

Adaptation of light-harvesting and energy-transfer processes of a diatomPhaeodactylum tricornutumto different light qualities 査読国際誌

Kumiko Oka, Yoshifumi Ueno, Makio Yokono, Jian-Ren Shen, Ryo Nagao, Seiji Akimoto

PHOTOSYNTHESIS RESEARCH 146 ( 1-3 ) 227 - 234 2020年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

Fucoxanthin-chlorophyll (Chl)a/c-binding proteins (FCPs) are light-harvesting pigment-protein complexes found in diatoms and brown algae. Due to the characteristic pigments, such as fucoxanthin and Chlc, FCPs can capture light energy in blue-to green regions. A pennate diatomPhaeodactylum tricornutumsynthesizes a red-shifted form of FCP under weak or red light, extending a light-absorption ability to longer wavelengths. In the present study, we examined changes in light-harvesting and energy-transfer processes ofP. tricornutumcells grown under white- and single-colored light-emitting diodes (LEDs). The red-shifted FCP appears in the cells grown under the green, yellow, and red LEDs, and exhibited a fluorescence peak around 714 nm. Additional energy-transfer pathways are established in the red-shifted FCP; two forms (F713 and F718) of low-energy Chlawork as energy traps at 77 K. Averaged fluorescence lifetimes are prolonged in the cells grown under the yellow and red LEDs, whereas they are shortened in the blue-LED-grown cells. Based on these results, we discussed the light-adaptation machinery ofP. tricornutumcells involved in the red-shifted FCP.

DOI： 10.1007/s11120-020-00714-1

Adaptation of light-harvesting and energy-transfer processes of a diatom Chaetoceros gracilis to different light qualities 査読国際誌

Seiji Akimoto, Yoshifumi Ueno, Makio Yokono, Jian-Ren Shen, Ryo Nagao

PHOTOSYNTHESIS RESEARCH 146 ( 1-3 ) 87 - 93 2020年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

Diatoms are a major group of microalgae in marine and freshwater environments. To utilize the light energy in blue to green region, diatoms possess unique antenna pigment-protein complexes, fucoxanthin chlorophyll a/c-binding proteins (FCPs). Depending on light qualities and quantities, diatoms form FCPs with different energies: normal-type and red-shifted FCPs. In the present study, we examined changes in light-harvesting and energy-transfer processes of a diatom Chaetoceros gracilis cells grown using white- and single-colored light-emitting diodes (LEDs), by means of time-resolved fluorescence spectroscopy. The blue LED, which is harvested by FCPs, modified energy transfer involving CP47, and suppressed energy transfer to PSI. Under the red-LED conditions, which is absorbed by both FCPs and PSs, energy transfer to PSI was enhanced, and the red-shifted FCP appeared. The red-shifted FCP was also recognized under the green- and yellow-LEDs, suggesting that lack of the shorter-wavelength light induces the red-shifted FCP. Functions of the red-shifted FCPs are discussed.

DOI： 10.1007/s11120-020-00713-2

Effects of CO2 and temperature on photosynthetic performance in the diatom Chaetoceros gracilis 査読国際誌

Ryo Nagao, Yoshifumi Ueno, Seiji Akimoto, Jian-Ren Shen

PHOTOSYNTHESIS RESEARCH 146 ( 1-3 ) 189 - 195 2020年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

CO2 concentration and temperature for growth of photosynthetic organisms are two important factors to ensure better photosynthetic performance. In this study, we investigated the effects of CO2 concentration and temperature on the photosynthetic performance in a marine centric diatom Chaetoceros gracilis. Cells were grown under four different conditions, namely, at 25 degrees C with air bubbling, at 25 degrees C with a supplementation of 3% CO2, at 30 degrees C with air bubbling, and at 30 degrees C with the CO2 supplementation. It was found that the growth rate of cells at 30 degrees C with the CO2 supplementation is faster than those at other three conditions. The pigment compositions of cells grown under the different conditions are altered, and fluorescence spectra measured at 77 K also showed different peak positions. A novel fucoxanthin chlorophyll a/c-binding protein complex is observed in the cells grown at 30 degrees C with the CO2 supplementation but not in the other three types of cells. Since oxygen-evolving activities of the four types of cells are almost unchanged, it is suggested that the CO2 supplementation and growth temperature are involved in the regulation of photosynthetic light-harvesting apparatus in C. gracilis at different degrees. Based on these observations, we discuss the favorable growth conditions for C. gracilis.

DOI： 10.1007/s11120-020-00729-8

Regulation of photosystem I-light-harvesting complex I from a red algaCyanidioschyzon merolaein response to light intensities 査読国際誌

Lijing Chang, Lirong Tian, Fei Ma, Zhiyuan Mao, Xiaochi Liu, Guangye Han, Wenda Wang, Yanyan Yang, Tingyun Kuang, Jie Pan, Jian-Ren Shen

PHOTOSYNTHESIS RESEARCH 146 ( 1-3 ) 287 - 297 2020年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

Photosynthetic organisms use different means to regulate their photosynthetic activity in respond to different light conditions under which they grow. In this study, we analyzed changes in the photosystem I (PSI) light-harvesting complex I (LHCI) supercomplex from a red algaCyanidioschyzon merolae, upon growing under three different light intensities, low light (LL), medium light (ML), and high light (HL). The results showed that the red algal PSI-LHCI is separated into two bands on blue-native PAGE, which are designated PSI-LHCI-A and PSI-LHCI-B, respectively, from cells grown under LL and ML. The former has a higher molecular weight and binds more Lhcr subunits than the latter. They are considered to correspond to the two types of PSI-LHCI identified by cryo-electron microscopic analysis recently, namely, the former with five Lhcrs and the latter with three Lhcrs. The amount of PSI-LHCI-A is higher in the LL-grown cells than that in the ML-grown cells. In the HL-grown cells, PSI-LHCI-A completely disappeared and only PSI-LHCI-B was observed. Furthermore, PSI core complexes without Lhcr attached also appeared in the HL cells. Fluorescence decay kinetics measurement showed that Lhcrs are functionally connected with the PSI core in both PSI-LHCI-A and PSI-LHCI-B obtained from LL and ML cells; however, Lhcrs in the PSI-LHCI-B fraction from the HL cells are not coupled with the PSI core. These results indicate that the red algal PSI not only regulates its antenna size but also adjusts the functional connection of Lhcrs with the PSI core in response to different light intensities.

DOI： 10.1007/s11120-020-00778-z

Function of PsbO-Asp158 in photosystem II: effects of mutation of this residue on the binding of PsbO and function of PSII in Thermosynechococcus vulcanus 査読国際誌

Qingjun Zhu, Yanyan Yang, Yanan Xiao, Wenda Wang, Tingyun Kuang, Jian-Ren Shen, Guangye Han

PHOTOSYNTHESIS RESEARCH 146 ( 1-3 ) 29 - 40 2020年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

PsbO-D158 is a highly conserved residue of the PsbO protein in photosystem II (PSII), and participates in one of the hydrogen-bonding networks connecting the manganese cluster with the lumenal surface. In order to examine the role of PsbO-D158, we mutated it to E, N or K in Thermosynechococcus vulcanus and characterized photosynthetic properties of the mutants obtained. The growth rates of these three mutants were similar to that of the wild type, whereas the oxygen-evolving activity of the three mutant cells decreased to 60-64% of the wild type. Fluorescence kinetics showed that the mutations did not affect the electron transfer from Q(A) to Q(B), but slightly affected the donor side of PSII. Moreover, all of the three mutant cells were more sensitive to high light and became slower to recover from photoinhibition. In the isolated thylakoid membranes from the three mutants, the PsbU subunit was lost and the oxygen-evolving activity was reduced to a lower level compared to that in the respective cells. PSII complexes isolated from these mutants showed no oxygen-evolving activity, which was found to be due to large or complete loss of PsbO, PsbV and PsbU during the process of purification. Moreover, PSII cores purified from the three mutants contained Psb27, an assembly co-factor of PSII. These results suggest that PsbO-D158 is required for the proper binding of the three extrinsic proteins to PSII and plays an important role in maintaining the optimal oxygen-evolving activity, and its mutation caused incomplete assembly of the PSII complex.

DOI： 10.1007/s11120-020-00715-0

Role of PsbV-Tyr137 in photosystem II studied by site-directed mutagenesis in the thermophilic cyanobacterium Thermosynechococcus vulcanus 査読国際誌

Yanan Xiao, Qingjun Zhu, Yanyan Yang, Wenda Wang, Tingyun Kuang, Jian-Ren Shen, Guangye Han

PHOTOSYNTHESIS RESEARCH 146 ( 1-3 ) 41 - 54 2020年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

PsbV (cytochrome c(550)) is one of the three extrinsic proteins of photosystem II (PSII) and functions to maintain the stability and activity of the Mn4CaO5 cluster, the catalytic center for water oxidation. PsbV-Y137 is the C-terminal residue of PsbV and is located at the exit of a hydrogen-bond network mediated by the D1-Y161-H190 residue pair. In order to examine the function of PsbV-Y137, four mutants, PsbV-Y137A, PsbV-Y137F, PsbV-Y137G, and PsbV-Y137W, were generated with Thermosynechococcus vulcanus (T. vulcanus). These mutants showed growth rates similar to that of the wild-type strain (WT); however, their oxygen-evolving activities were different. At pH 6.5, the oxygen evolution rates of Y137F and Y137W were almost identical to that of WT, whereas the oxygen evolution rates of the Y137A, Y137G mutants were 64% and 61% of WT, respectively. However, the oxygen evolution in the latter two mutants decreased less at higher pHs, suggesting that higher pHs facilitated oxygen evolution probably by facilitating proton egress in these two mutants. Furthermore, thylakoid membranes isolated from the PsbV-Y137A, PsbV-Y137G mutants exhibited much lower levels of oxygen-evolving activity than that of WT, which was found to be caused by the release of PsbV. In addition, PSII complexes purified from the PsbV-Y137A and PsbV-Y137G mutants lost all of the three extrinsic proteins but instead bind Psb27, an assembly cofactor of PSII. These results demonstrate that the PsbV-Tyr137 residue is required for the stable binding of PsbV to PSII, and the hydrogen-bond network mediated by D1-Y161-H190 is likely to function in proton egress during water oxidation.

DOI： 10.1007/s11120-020-00753-8

Architecture of the photosynthetic complex from a green sulfur bacterium 査読国際誌

Jing-Hua Chen, Hangjun Wu, Caihuang Xu, Xiao-Chi Liu, Zihui Huang, Shenghai Chang, Wenda Wang, Guangye Han, Tingyun Kuang, Jian-Ren Shen, Xing Zhang

SCIENCE 370 ( 6519 ) 931 - + 2020年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER ASSOC ADVANCEMENT SCIENCE

The photosynthetic apparatus of green sulfur bacteria (GSB) contains a peripheral antenna chlorosome, light-harvesting Fenna-Matthews-Olson proteins (FMO), and a reaction center (GsbRC). We used cryo-electron microscopy to determine a 2.7-angstrom structure of the FMO-GsbRC supercomplex from Chlorobaculum tepidum. The GsbRC binds considerably fewer (bacterio) chlorophylls [(B)Chls] than other known type I RCs do, and the organization of (B)Chls is similar to that in photosystem II. Two BChl layers in GsbRC are not connected by Chls, as seen in other RCs, but associate with two carotenoid derivatives. Relatively long distances of 22 to 33 angstroms were observed between BChls of FMO and GsbRC, consistent with the inefficient energy transfer between these entities. The structure contains common features of both type I and type II RCs and provides insight into the evolution of photosynthetic RCs.

DOI： 10.1126/science.abb6350

Reply to "Comment on 'Acidic pH-Induced Modification of Energy Transfer in Diatom Fucoxanthin Chlorophyll a/c-Binding Proteins'" 査読国際誌

Ryo Nagao, Makio Yokono, Yoshifumi Ueno, Jian-Ren Shen, Seiji Akimoto

JOURNAL OF PHYSICAL CHEMISTRY B 124 ( 46 ) 10588 - 10589 2020年11月

High-resolution cryo-EM structure of photosystem II: Effects of electron beam damage

Koji Kato, Naoyuki Miyazaki, Tasuku Hamaguchi, Yoshiki Nakajima, Fusamichi Akita, Koji Yonekura, Jian-Ren Shen

2020年10月

出版者・発行元：Cold Spring Harbor Laboratory

Abstract

Photosystem II (PSII) plays a key role in water-splitting and oxygen evolution. X-ray crystallography has revealed its atomic structure and some intermediate structures. However, these structures are in the crystalline state, and its final state structure has not been solved because of the low efficiencies of the S-state transitions in the crystals. Here we analyzed the structure of PSII in solution at 1.95 Å resolution by single-particle cryo-electron microscopy (cryo-EM). The structure obtained is similar to the crystal structure, but a PsbY subunit was visible in the cryo-EM structure, indicating that it represents its physiological state more closely. Electron beam damage was observed at a high-dose in the regions that were easily affected by redox states, which was reduced by reducing the electron dose. This study will serve as a good indicator for determining damage-free cryo-EM structures of not only PSII but also all biological samples, especially redox-active metalloproteins.

DOI： 10.1101/2020.10.18.344648

Formation of the High-Spin S-2 State Related to the Extrinsic Proteins in the Oxygen Evolving Complex of Photosystem II 査読国際誌

Shota Taguchi, Liangliang Shen, Guangye Han, Yasufumi Umena, Jian-Ren Shen, Takumi Noguchi, Hiroyuki Mino

JOURNAL OF PHYSICAL CHEMISTRY LETTERS 11 ( 20 ) 8908 - 8913 2020年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

The high-spin S-2 state was investigated with photosystem II (PSII) from spinach, Thermosynechococcus vulcanus, and Cyanidioschyzon merolae. In extrinsic protein-depleted PSII, high-spin electron paramagnetic resonance (EPR) signals were not detected in either species, whereas all species showed g similar to 5 signals in the presence of a high concentration of Ca2+ instead of the multiline signal. In the intact and PsbP/Qdepleted PSII from spinach, the g = 4.1 EPR signal was detected. These results show that formation of the high-spin S-2 state of the manganese cluster is regulated by the extrinsic proteins through a charge located near the Mn4 atom in the Mn4CaO5 cluster but is independent of the intrinsic proteins. The shift to the g similar to 5 state is caused by tilting of the z-axis in the Mn4 coordinates through hydrogen bonds or external divalent cations. The structural modification may allow insertion of an oxygen atom during the S-2-to-S-3 transition.

DOI： 10.1021/acs.jpclett.0c02411

Structural basis for energy transfer in a huge diatom PSI-FCPI supercomplex 査読国際誌

Caizhe Xu, Xiong Pi, Yawen Huang, Guangye Han, Xiaobo Chen, Xiaochun Qin, Guoqiang Huang, Songhao Zhao, Yanyan Yang, Tingyun Kuang, Wenda Wang, Sen-Fang Sui, Jian-Ren Shen

NATURE COMMUNICATIONS 11 ( 1 ) 5081 - 5081 2020年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE RESEARCH

Diatom is an important group of marine algae and contributes to around 20% of the global photosynthetic carbon fixation. Photosystem I (PSI) of diatoms is associated with a large number of fucoxanthin-chlorophyll a/c proteins (FCPIs). We report the structure of PSI-FCPI from a diatom Chaetoceros gracilis at 2.38 angstrom resolution by single-particle cryo-electron microscopy. PSI-FCPI is a monomeric supercomplex consisting of 12 core and 24 antenna subunits (FCPIs), and 326 chlorophylls a, 34 chlorophylls c, 102 fucoxanthins, 35 diadinoxanthins, 18 beta -carotenes and some electron transfer cofactors. Two subunits designated PsaR and PsaS were found in the core, whereas several subunits were lost. The large number of pigments constitute a unique and huge network ensuring efficient energy harvesting, transfer and dissipation. These results provide a firm structural basis for unraveling the mechanisms of light-energy harvesting, transfer and quenching in the diatom PSI-FCPI, and also important clues to evolutionary changes of PSI-LHCI. Diatoms are marine algae with an important role in global photosynthetic carbon fixation. Here, the authors present the 2.38 angstrom cryo-EM structure of photosystem I (PSI) in complex with its 24 fucoxanthin chlorophyll a/c-binding (FCPI) antenna proteins from the diatom Chaetoceros gracilis, which provides mechanistic insights into light-energy harvesting, transfer and quenching of the PSI-FCPI supercomplex.

DOI： 10.1038/s41467-020-18867-x

Structural variations of photosystem I-antenna supercomplex in response to adaptations to different light environments 査読国際誌

Michihiro Suga, Jian-Ren Shen

CURRENT OPINION IN STRUCTURAL BIOLOGY 63 10 - 17 2020年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：CURRENT BIOLOGY LTD

Photosystem I (PSI) is one of the two photosystems in photosynthesis, and generates reducing power required for carbon dioxide fixation. PSI exists as a reaction center core in cyanobacteria but is surrounded by light-harvesting antenna complexes (LHCI) to form PSI-LHCI supercomplexes in eukaryotic organisms. The structures of PSI core and PSI-LHCI have been reported from various organisms. We compare these structures and highlight the differences among different organisms. While the PSI core is more conserved, there are differences in its subunit composition and organization. Larger differences are found in the subunit composition, organization, and pigment binding in LHCI. All these changes can be explained in the framework of better adaptation to different light environment that each photosynthetic organism inhabits.

DOI： 10.1016/j.sbi.2020.02.005

Spectral tuning of light-harvesting complex II in the siphonous alga Bryopsis corticulans and its effect on energy transfer dynamics 査読国際誌

Parveen Akhtar, Pawel J. Nowakowski, Wenda Wang, Thanh Nhut Do, Songhao Zhao, Giuliano Siligardi, Gyozo Garab, Jian-Ren Shen, Howe-Siang Tan, Petar H. Lambrev

BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1861 ( 7 ) 148191 - 148191 2020年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER

Light-harvesting complex II (LHCII) from the marine green macroalga Bryopsis corticulans is spectroscopically characterized to understand the structural and functional changes resulting from adaptation to intertidal environment. LHCII is homologous to its counterpart in land plants but has a different carotenoid and chlorophyll (Chl) composition. This is reflected in the steady-state absorption, fluorescence, linear dichroism, circular dichroism and anisotropic circular dichroism spectra. Time-resolved fluorescence and two-dimensional electronic spectroscopy were used to investigate the consequences of this adaptive change in the pigment composition on the excited-state dynamics. The complex contains additional Chl b spectral forms - absorbing at around 650 nm and 658 nm - and lacks the red-most Chl a forms compared with higher-plant LHCII. Similar to plant LHCII, energy transfer between Chls occurs on timescales from under hundred fs (mainly from Chl b to Chl a) to several picoseconds (mainly between Chl a pools). However, the presence of long-lived, weakly coupled Chl b and Chl a states leads to slower exciton equilibration in LHCII from B. corticulans. The finding demonstrates a trade-off between the enhanced absorption of blue-green light and the excitation migration time. However, the adaptive change does not result in a significant drop in the overall photochemical efficiency of Photosystem II. These results show that LHCII is a robust adaptable system whose spectral properties can be tuned to the environment for optimal light harvesting.

DOI： 10.1016/j.bbabio.2020.148191

Acidic pH-Induced Modification of Energy Transfer in Diatom Fucoxanthin Chlorophyll a/c-Binding Proteins 査読国際誌

Ryo Nagao, Makio Yokono, Yoshifumi Ueno, Jian-Ren Shen, Seiji Akimoto

JOURNAL OF PHYSICAL CHEMISTRY B 124 ( 24 ) 4919 - 4923 2020年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

pH influences excitation-energy-relaxation processes in photosynthetic light-harvesting complexes. Here, we report the excitation-energy dynamics by pH changes in fucoxanthin chlorophyll a/c-binding proteins (FCPs) isolated from a diatom Phaeodactylum tricornutum, probed by time-resolved fluorescence spectroscopy at 77 K. The fluorescence curve measured at pH 5.0 showed a shorter lifetime component than that measured at pH 6.5 and 8.0. The rapid decay component at pH 5.0 is supported by fluorescence decay-associated (FDA) spectra, where strong fluorescence decays relative to fluorescence rises appear in the pH-5.0 FDA spectrum with 70 ps. These results indicate that the diatom FCPs switch their function from light-harvesting to energy-quenching via arrangements of the energy-transfer pathways under acidic pHs. Based on the crystal structure of the diatom FCPs, we propose a model for the energy-quenching machinery through structural changes of the pigment environments, thus providing insights into the pH-dependent light-harvesting strategy in the diatom FCPs.

DOI： 10.1021/acs.jpcb.0c04231

Structural features of the diatom photosystem II-light-harvesting antenna complex 査読国際誌

Wenda Wang, Songhao Zhao, Xiong Pi, Tingyun Kuang, Sen-Fang Sui, Jian-Ren Shen

FEBS JOURNAL 287 ( 11 ) 2191 - 2200 2020年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY

In photosynthesis, light energy is captured by pigments bound to light-harvesting antenna proteins (LHC) that then transfer the energy to the photosystem (PS) cores to initiate photochemical reactions. The LHC proteins surround the PS cores to form PS-LHC supercomplexes. In order to adapt to a wide range of light environments, photosynthetic organisms have developed a large variety of pigments and antenna proteins to utilize the light energy efficiently under different environments. Diatoms are a group of important eukaryotic algae and possess fucoxanthin (Fx) chlorophyll a/c proteins (FCP) as antenna which have exceptional capabilities of harvesting blue-green light under water and dissipate excess energy under strong light conditions. We have solved the structure of a PSII-FCPII supercomplex from a centric diatom Chaetoceros gracilis by cryo-electron microscopy, and also the structure of an isolated FCP dimer from a pennate diatom Phaeodactylum tricornutum by X-ray crystallography at a high resolution. These results revealed the oligomerization states of FCPs distinctly different from those of LHCII found in the green lineage organisms, the detailed binding patterns of Chl c and Fxs, a huge pigment network, and extensive protein-protein, pigment-protein, and pigment-pigment interactions within the PSII-FCPII supercomplex. These results therefore provide a solid structural basis for examining the detailed mechanisms of the highly efficient energy transfer and quenching processes in diatoms.

DOI： 10.1111/febs.15183

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