Structure of Dunaliella Photosystem II reveals conformational flexibility of stacked and unstacked supercomplexes

Photosystem II (PSII) generates an oxidant whose redox potential is high enough to enable water oxidation, a substrate so abundant that it assures a practically unlimited electron source for life on earth. Our knowledge on the mechanism of water photooxidation was greatly advanced by high-resolution structures of prokaryotic PSII. Here we show high-resolution structures of eukaryotic PSII from the green algae Dunaliella salina at two distinct conformations. The conformers are also present in stacked PSII, exhibiting flexibility that is relevant to the grana formation in chloroplasts of the green lineage. CP29, one of PSII associated light harvesting antennae, plays a major role in distinguishing the two conformations of the supercomplex. We also show that the stacked PSII dimer, a form suggested to support the organization of thylakoid membranes, can appear in many different orientations providing a flexible stacking mechanism for the arrangement of grana stacks in thylakoids. Our findings provide a structural basis for the heterogenous nature of the eukaryotic PSII on multiple levels.

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High-resolution cryo-electron microscopy structure of photosystem II from the mesophilic cyanobacterium, Synechocystis sp. PCC 6803

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2116765118 ◽

2021 ◽

Vol 119 (1) ◽

pp. e2116765118

Author(s):

Christopher J. Gisriel ◽

Jimin Wang ◽

Jinchan Liu ◽

David A. Flesher ◽

Krystle M. Reiss ◽

...

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Photosystem Ii ◽

Water Oxidation ◽

Genetic Manipulation ◽

Water Channel ◽

Global Scale ◽

Cryo Electron Microscopy ◽

C Terminus ◽

Pcc 6803

Photosystem II (PSII) enables global-scale, light-driven water oxidation. Genetic manipulation of PSII from the mesophilic cyanobacterium Synechocystis sp. PCC 6803 has provided insights into the mechanism of water oxidation; however, the lack of a high-resolution structure of oxygen-evolving PSII from this organism has limited the interpretation of biophysical data to models based on structures of thermophilic cyanobacterial PSII. Here, we report the cryo-electron microscopy structure of PSII from Synechocystis sp. PCC 6803 at 1.93-Å resolution. A number of differences are observed relative to thermophilic PSII structures, including the following: the extrinsic subunit PsbQ is maintained, the C terminus of the D1 subunit is flexible, some waters near the active site are partially occupied, and differences in the PsbV subunit block the Large (O1) water channel. These features strongly influence the structural picture of PSII, especially as it pertains to the mechanism of water oxidation.

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Evidence for thylakoid membrane fusion during zygote formation in Chlamydomonas reinhardtii.

The Journal of Cell Biology ◽

10.1083/jcb.114.5.905 ◽

1991 ◽

Vol 114 (5) ◽

pp. 905-915 ◽

Cited By ~ 10

Author(s):

B Baldan ◽

J Girard-Bascou ◽

F A Wollman ◽

J Olive

Keyword(s):

Photosystem Ii ◽

Chlamydomonas Reinhardtii ◽

Photosystem I ◽

Thylakoid Membrane ◽

De Novo ◽

Electron Flow ◽

Thylakoid Membranes ◽

Structural Basis ◽

Zygote Formation ◽

Thin Sections

To understand whether fusions of thylakoid membranes from the parental chloroplasts occurred during zygote formation in Chlamydomonas reinhardtii, we performed an ultrastructural analysis of the zygotes produced by crossing mutants lacking photosystem I or II protein complexes, in the absence of de novo chloroplast protein synthesis. Thylakoid membranes from each parent could be distinguished on thin sections due to their organization in "supergrana" in mutants lacking photosystem I centers, by freeze-fracturing due to the absence of most of the exoplasmic-face (EF) particles in mutants lacking photosystem II centers, by immunocytochemistry using antibodies directed against photosystem II subunits. We demonstrate that a fusion of the thylakoid membranes occurred during zygote formation approximately 15 h after mating. These fusions allowed a lateral redistribution of the thylakoid membrane proteins. These observations provide the structural basis for the restoration of photosynthetic electron flow in the mature zygote that we observed in fluorescence induction experiments.

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Photosystem II: the engine of life

Quarterly Reviews of Biophysics ◽

10.1017/s0033583502003839 ◽

2003 ◽

Vol 36 (1) ◽

pp. 71-89 ◽

Cited By ~ 168

Author(s):

James Barber

Keyword(s):

High Resolution ◽

Photosystem Ii ◽

Water Oxidation ◽

Structural Models ◽

Reaction Centre ◽

Ps Ii ◽

X Ray ◽

X Ray Crystallography ◽

Redox Active ◽

Resolution Electron

1. Introduction 712. Electron transfer in PS II 723. (Mn)4cluster and mechanism of water oxidation 734. Organization and structure of the protein subunits 755. Organization of chlorophylls and redox active cofactors 816. Implications arising from the structural models 827. Perspectives 848. Acknowledgements 869. Addendum 8610. References 87Photosystem II (PS II) is a multisubunit membrane protein complex, which uses light energy to oxidize water and reduce plastoquinone. High-resolution electron cryomicroscopy and X-ray crystallography are revealing the structure of this important molecular machine. Both approaches have contributed to our understanding of the organization of the transmembrane helices of higher plant and cyanobacterial PS II and both indicate that PS II normally functions as a dimer. However the high-resolution electron density maps derived from X-ray crystallography currently at 3·7/3·8 Å, have allowed assignments to be made to the redox active cofactors involved in the light-driven water–plastoquinone oxidoreductase activity and to the chlorophyll molecules that absorb and transfer energy to the reaction centre. In particular the X-ray work has identified density that can accommodate the four manganese atoms which catalyse the water-oxidation process. The Mn cluster is located at the lumenal surface of the D1 protein and approximately 7 Å from the redox active tyrosine residue (YZ) which acts an electron/proton transfer link to the primary oxidant P680.+. The lower resolution electron microscopy studies, however, are providing structural models of larger PS II supercomplexes that are ideal frameworks in which to incorporate the X-ray derived structures.

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High resolution spot scan imaging of frozen, hydrated actin bundles with 400kV electrons

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100122964 ◽

1992 ◽

Vol 50 (1) ◽

pp. 512-513

Author(s):

J. Jakana ◽

M.F. Schmid ◽

P. Matsudaira ◽

W. Chiu

Keyword(s):

High Resolution ◽

Binding Proteins ◽

Actin Binding ◽

Eukaryotic Cells ◽

Dimensional Structure ◽

Structural Basis ◽

Actin Bundle ◽

Actin Bundles ◽

3 Dimensional ◽

Macromolecular Assembly

Actin is a protein found in all eukaryotic cells. In its polymerized form, the cells use it for motility, cytokinesis and for cytoskeletal support. An example of this latter class is the actin bundle in the acrosomal process from the Limulus sperm. The different functions actin performs seem to arise from its interaction with the actin binding proteins. A 3-dimensional structure of this macromolecular assembly is essential to provide a structural basis for understanding this interaction in relationship to its development and functions.

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Structural basis of the stereoselective formation of the spirooxindole ring in the biosynthesis of citrinadins

Nature Communications ◽

10.1038/s41467-021-24421-0 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Zhiwen Liu ◽

Fanglong Zhao ◽

Boyang Zhao ◽

Jie Yang ◽

Joseph Ferrara ◽

...

Keyword(s):

High Resolution ◽

Organic Synthesis ◽

Indole Alkaloids ◽

Site Directed Mutagenesis ◽

Structural Basis ◽

Directed Mutagenesis ◽

Computational Studies ◽

X Ray ◽

Evolutionary Branch ◽

Catalytic Mechanisms

AbstractPrenylated indole alkaloids featuring spirooxindole rings possess a 3R or 3S carbon stereocenter, which determines the bioactivities of these compounds. Despite the stereoselective advantages of spirooxindole biosynthesis compared with those of organic synthesis, the biocatalytic mechanism for controlling the 3R or 3S-spirooxindole formation has been elusive. Here, we report an oxygenase/semipinacolase CtdE that specifies the 3S-spirooxindole construction in the biosynthesis of 21R-citrinadin A. High-resolution X-ray crystal structures of CtdE with the substrate and cofactor, together with site-directed mutagenesis and computational studies, illustrate the catalytic mechanisms for the possible β-face epoxidation followed by a regioselective collapse of the epoxide intermediate, which triggers semipinacol rearrangement to form the 3S-spirooxindole. Comparing CtdE with PhqK, which catalyzes the formation of the 3R-spirooxindole, we reveal an evolutionary branch of CtdE in specific 3S spirocyclization. Our study provides deeper insights into the stereoselective catalytic machinery, which is important for the biocatalysis design to synthesize spirooxindole pharmaceuticals.

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Photosystem II Inhibition by Pyran-enamine Derivatives

Zeitschrift für Naturforschung C ◽

10.1515/znc-1993-3-409 ◽

1993 ◽

Vol 48 (3-4) ◽

pp. 163-167

Author(s):

Koichi Yoneyama ◽

Yoshihiro Nakajima ◽

Masaru Ogasawara ◽

Hitoshi Kuramochi ◽

Makoto Konnai ◽

...

Keyword(s):

Electron Transport ◽

Photosystem Ii ◽

Thylakoid Membranes ◽

Major Determinant ◽

Ps Ii ◽

Structure Activity Relationships ◽

Structure Activity

Abstract Through the studies on structure-activity relationships of 5-acyl-3-(1-aminoalkylidene)-4-hydroxy-2 H-pyran-2,6(3 H)-dione derivatives in photosystem II (PS II) inhibition, overall lipophilicity of the molecule was found to be a major determinant for the activity. In the substituted N -benzyl derivatives, not only the lipophilicity but also the electronic and steric characters of the substituents greatly affected the activity. Their mode of PS II inhibition seemed to be similar to that of DCMU , whereas pyran-enamine derivatives needed to be highly lipophilic to block the electron transport in thylakoid membranes, which in turn diminished the permeability through biomembranes.

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Singlet oxygen damages the function of Photosystem II in isolated thylakoids and in the green alga Chlorella sorokiniana

Photosynthesis Research ◽

10.1007/s11120-021-00841-3 ◽

2021 ◽

Author(s):

Faiza Bashir ◽

Ateeq Ur Rehman ◽

Milán Szabó ◽

Imre Vass

Keyword(s):

Photosystem Ii ◽

Singlet Oxygen ◽

Screening Method ◽

Physiological Role ◽

Thylakoid Membranes ◽

Chlorella Sorokiniana ◽

Dependent Manner ◽

Concentration Dependent Manner ◽

Intact Cells ◽

Green Alga Chlorella

AbstractSinglet oxygen (1O2) is an important damaging agent, which is produced during illumination by the interaction of the triplet excited state pigment molecules with molecular oxygen. In cells of photosynthetic organisms 1O2 is formed primarily in chlorophyll containing complexes, and damages pigments, lipids, proteins and other cellular constituents in their environment. A useful approach to study the physiological role of 1O2 is the utilization of external photosensitizers. In the present study, we employed a multiwell plate-based screening method in combination with chlorophyll fluorescence imaging to characterize the effect of externally produced 1O2 on the photosynthetic activity of isolated thylakoid membranes and intact Chlorella sorokiniana cells. The results show that the external 1O2 produced by the photosensitization reactions of Rose Bengal damages Photosystem II both in isolated thylakoid membranes and in intact cells in a concentration dependent manner indicating that 1O2 plays a significant role in photodamage of Photosystem II.

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