Photosystem II: the engine of life

2003 ◽  
Vol 36 (1) ◽  
pp. 71-89 ◽  
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.

Electron microscopy of rabbit FC crystals

1983 ◽  
Vol 41 ◽  
pp. 730-731
Author(s):  
Robert A. Grant ◽  
Laura L. Degn ◽  
Wah Chiu ◽  
John Robinson
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Molecular Replacement ◽  
X Ray ◽  
X Ray Crystallography ◽  
Resolution Electron ◽  
Replacement Technique ◽  
Hydrated Crystal ◽  
Molecular Structure Analysis

Proteolytic digestion of the immunoglobulin IgG with papain cleaves the molecule into an antigen binding fragment, Fab, and a compliment binding fragment, Fc. Structures of intact immunoglobulin, Fab and Fc from various sources have been solved by X-ray crystallography. Rabbit Fc can be crystallized as thin platelets suitable for high resolution electron microscopy. The structure of rabbit Fc can be expected to be similar to the known structure of human Fc, making it an ideal specimen for comparing the X-ray and electron crystallographic techniques and for the application of the molecular replacement technique to electron crystallography. Thin protein crystals embedded in ice diffract to high resolution. A low resolution image of a frozen, hydrated crystal can be expected to have a better contrast than a glucose embedded crystal due to the larger density difference between protein and ice compared to protein and glucose. For these reasons we are using an ice embedding technique to prepare the rabbit Fc crystals for molecular structure analysis by electron microscopy.

scholarly journals High-resolution cryo-EM structure of photosystem II reveals damage from high-dose electron beams

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Koji Kato ◽  
Naoyuki Miyazaki ◽  
Tasuku Hamaguchi ◽  
Yoshiki Nakajima ◽  
Fusamichi Akita ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Physiological State ◽  
High Dose ◽  
Final State ◽  
X Ray ◽  
Redox States ◽  
X Ray Crystallography ◽  
Cryo Electron Microscopy ◽  
Redox Active ◽  
Beam Damage

AbstractPhotosystem 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. 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, and reducing the beam dosage by reducing frames from 50 to 2 yielded a similar resolution but reduced the damage remarkably. 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.

Isolation and Partial Characterization of a Manganese Requiring ʟ-Arginine Metabolizing Enzyme Being Present in Photosystem II Complexes of Spinach and Tobacco

1995 ◽  
Vol 50 (9-10) ◽  
pp. 638-651 ◽  
Author(s):  
Achim E. Gau ◽  
Hubert H. Thole ◽  
Elfriede K. Pistorius
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Cation Binding ◽  
Active Group ◽  
Anion Exchange Column ◽  
Ps Ii ◽  
Cation Binding Site ◽  
Redox Active ◽  
Metabolizing Enzyme ◽  
Ph Range

Abstract A low ʟ-arginine metabolizing enzyme (L-AME) activity leading to ornithine, urea and additional products not identified so far could be detected in photosystem II (PS II) membranes of spinach and of the chlorophyll deficient tobacco mutant Su/su. The detectable L-AME activity was very low in untreated PS II membranes, but increased significantly (about 10 fold) when the extrinsic peptides (psbO, P and Q gene products) were removed - suggesting that the L-AME is exposed at the lumen side of PS II. It was possible to isolate the detergent-solubilized protein from CaCl2-washed PS II membranes of spinach by a combination of anion and cation exchange columns. On the basis of SDS PAGE the protein was homogenous and had an apparent molecular mass of 7 kDa. N-terminal sequencing of the polypeptide gave a contiguous sequence of 20 amino acids showing no homologies to PS II polypeptides as yet sequenced. After chromatography of the L-AME on an anion exchange column at pH 9.5 (last purification step) a completely inactive enzyme was obtained. Maximal reactivation was achieved by dialyzing the protein against Hepes-NaOH buffer in the pH range of 6.5 to 7.5 containing 100 mᴍ chloride or sulfate (being the most effective anions). The L-AME activity was totally dependent on manganese added to the reaction mixture. Moreover, there were indications of a second cation binding site being more sequestered and requiring bound Ca2+ or Mn2+ for activity (Sr2+ was less effective and Mg2+ was ineffective). There are indications that the protein contains a redox active group - possibly an aminoacid- derived quinonoid (based on a redox cycling assay with glycine and nitroblue tetrazolium). The capability of this PS II associated protein to bind the cofactors of water oxidation and having a redox active group (preliminary results) suggests that this protein might be functional in photosynthetic water oxidation. This is further supported by the fact that the isolated L-AME has a low catalase activity

scholarly journals Water oxidation chemistry of photosystem II

2007 ◽  
Vol 363 (1494) ◽  
pp. 1211-1219 ◽  
Author(s):  
Gary W Brudvig
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Oxidation Mechanism ◽  
Intermediate Species ◽  
X Ray ◽  
Redox Active ◽  
Ca Ions ◽  
Oxidation Chemistry ◽  
Chemical Problem ◽  
Mechanism Of The Reaction

Photosystem II (PSII) uses light energy to split water into protons, electrons and O 2 . In this reaction, nature has solved the difficult chemical problem of efficient four-electron oxidation of water to yield O 2 without significant amounts of reactive intermediate species such as superoxide, hydrogen peroxide and hydroxyl radicals. In order to use nature's solution for the design of artificial catalysts that split water, it is important to understand the mechanism of the reaction. The recently published X-ray crystal structures of cyanobacterial PSII complexes provide information on the structure of the Mn and Ca ions, the redox-active tyrosine called Y Z and the surrounding amino acids that comprise the O 2 -evolving complex (OEC). The emerging structure of the OEC provides constraints on the different hypothesized mechanisms for O 2 evolution. The water oxidation mechanism of PSII is discussed in the light of biophysical and computational studies, inorganic chemistry and X-ray crystallographic information.

scholarly journals Organization of transmembrane helices in photosystem II: comparison of plants and cyanobacteria

2002 ◽  
Vol 357 (1426) ◽  
pp. 1329-1335 ◽  
Author(s):  
J. Barber ◽  
J. Nield
Keyword(s):  
Electron Microscopy ◽  
Photosystem Ii ◽  
3D Structure ◽  
Structural Data ◽  
Reaction Centre ◽  
Transmembrane Helices ◽  
Light Harvesting Complex ◽  
X Ray ◽  
X Ray Crystallography ◽  
Light Harvesting Complex Ii

Electron microscopy and X–ray crystallography are revealing the structure of photosystem II. Electron crystallography has yielded a 3D structure at sufficient resolution to identify subunit positioning and transmembrane organization of the reaction–centre core complex of spinach. Single–particle analyses are providing 3D structures of photosystem II–light–harvesting complex II supercomplexes that can be used to incorporate high–resolution structural data emerging from electron and X–ray crystallography. The positions of the chlorins and metal centres within photosystem II are now available. It can be concluded that photosystem II is a dimeric complex with the transmembrane helices of CP47/D2 proteins related to those of the CP43/D1 proteins by a twofold axis within each monomer. Further, both electron microscopy and X–ray analyses show that P 680 is not a 'special pair‘ and that cytochrome b 559 is located on the D2 side of the reaction centres some distance from P 680 . However, although comparison of the electron microscopy and X–ray models for spinach and Synechococcus elongatus show considerable similarities, there seem to be differences in the number and positioning of some small subunits.

Nano-probe x-ray analysis and high-resolution imaging on planar defects in high-pressure synthesized infinite-layer superconductor

1994 ◽  
Vol 52 ◽  
pp. 728-729
Author(s):  
Y. Y. Wang ◽  
H. Zhang ◽  
V. P. Dravid ◽  
H. Zhang ◽  
L. D. Marks ◽  
...  
Keyword(s):  
High Pressure ◽  
High Resolution ◽  
Atomic Structure ◽  
Emission Spectra ◽  
High Resolution Electron Microscopy ◽  
Planar Defects ◽  
X Ray ◽  
Infinite Layer ◽  
Resolution Electron ◽  
Resolution Imaging

Azuma et al. observed planar defects in a high pressure synthesized infinitelayer compound (i.e. ACuO2 (A=cation)), which exhibits superconductivity at ~110 K. It was proposed that the defects are cation deficient and that the superconductivity in this material is related to the planar defects. In this report, we present quantitative analysis of the planar defects utilizing nanometer probe xray microanalysis, high resolution electron microscopy, and image simulation to determine the chemical composition and atomic structure of the planar defects. We propose an atomic structure model for the planar defects.Infinite-layer samples with the nominal chemical formula, (Sr1-xCax)yCuO2 (x=0.3; y=0.9,1.0,1.1), were prepared using solid state synthesized low pressure forms of (Sr1-xCax)CuO2 with additions of CuO or (Sr1-xCax)2CuO3, followed by a high pressure treatment.Quantitative x-ray microanalysis, with a 1 nm probe, was performed using a cold field emission gun TEM (Hitachi HF-2000) equipped with an Oxford Pentafet thin-window x-ray detector. The probe was positioned on the planar defects, which has a 0.74 nm width, and x-ray emission spectra from the defects were compared with those obtained from vicinity regions.

Characterisation of planar crystal defects in Y2Fe17Cx (0.6 ≤ x ≤ 1.6) magnetic material by High Resolution Electron Microscopy

1990 ◽  
Vol 48 (4) ◽  
pp. 774-775
Author(s):  
W. Coene ◽  
F. Hakkens ◽  
T.H. Jacobs ◽  
K.H.J. Buschow
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Permanent Magnets ◽  
Annealing Treatment ◽  
High Resolution Electron Microscopy ◽  
Crystal Defects ◽  
Ordered Structure ◽  
X Ray ◽  
Planar Crystal ◽  
Resolution Electron

Intermetallic compounds of the type RE2Fe17Cx (RE= rare earth element) are promising candidates for permanent magnets. In case of Y2Fe17Cx, the Curie temperature increases from 325 K for x =0 to 550 K for x = 1.6 . X ray and electron diffraction reveal a carbon - induced structural transformation in Y2Fe17Cx from the hexagonal Th2Ni17 - type (x < 0.6 ) to the rhombohedral Th2Zn17 - type ( x ≥ 0.6). Planar crystal defects introduce local sheets of different magnetic anisotropy as compared with the ordered structure, and therefore may have an important impact on the coercivivity mechanism .High resolution electron microscopy ( HREM ) on a Philips CM30 / Super Twin has been used to characterize planar crystal defects in rhombohedral Y2Fe17Cx ( x ≥ 0.6 ). The basal plane stacking sequences are imaged in the [100] - orientation, showing an ABC or ACB sequence of Y - atoms and Fe2 - dumbbells, for both coaxial twin variants, respectively . Compounds resulting from a 3 - week annealing treatment at high temperature ( Ta = 1000 - 1100°C ) contain a high density of planar defects.

scholarly journals Base-enhanced catalytic water oxidation by a carboxylate–bipyridine Ru(II) complex

2015 ◽  
Vol 112 (16) ◽  
pp. 4935-4940 ◽  
Author(s):  
Na Song ◽  
Javier J. Concepcion ◽  
Robert A. Binstead ◽  
Jennifer A. Rudd ◽  
Aaron K. Vannucci ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Proton Transfer ◽  
Water Oxidation ◽  
Proton Acceptor ◽  
Half Time ◽  
X Ray ◽  
X Ray Crystallography ◽  
Buffer Base ◽  
Electron Proton Transfer ◽  
C Nmr

In aqueous solution above pH 2.4 with 4% (vol/vol) CH3CN, the complex [RuII(bda)(isoq)2] (bda is 2,2′-bipyridine-6,6′-dicarboxylate; isoq is isoquinoline) exists as the open-arm chelate, [RuII(CO2-bpy-CO2−)(isoq)2(NCCH3)], as shown by 1H and 13C-NMR, X-ray crystallography, and pH titrations. Rates of water oxidation with the open-arm chelate are remarkably enhanced by added proton acceptor bases, as measured by cyclic voltammetry (CV). In 1.0 M PO43–, the calculated half-time for water oxidation is ∼7 μs. The key to the rate accelerations with added bases is direct involvement of the buffer base in either atom–proton transfer (APT) or concerted electron–proton transfer (EPT) pathways.

Three-dimensional crystallization of membrane proteins

1988 ◽  
Vol 21 (4) ◽  
pp. 429-477 ◽  
Author(s):  
W. Kühlbrandt
Keyword(s):  
High Resolution ◽  
Membrane Proteins ◽  
Membrane Protein ◽  
Protein Complexes ◽  
Three Dimensional ◽  
Biological Macromolecules ◽  
X Ray ◽  
X Ray Crystallography ◽  
Membrane Protein Complexes ◽  
Essential Prerequisite

As recently as 10 years ago, the prospect of solving the structure of any membrane protein by X-ray crystallography seemed remote. Since then, the threedimensional (3-D) structures of two membrane protein complexes, the bacterial photosynthetic reaction centres of Rhodopseudomonas viridis (Deisenhofer et al. 1984, 1985) and of Rhodobacter sphaeroides (Allen et al. 1986, 1987 a, 6; Chang et al. 1986) have been determined at high resolution. This astonishing progress would not have been possible without the pioneering work of Michel and Garavito who first succeeded in growing 3-D crystals of the membrane proteins bacteriorhodopsin (Michel & Oesterhelt, 1980) and matrix porin (Garavito & Rosenbusch, 1980). X-ray crystallography is still the only routine method for determining the 3-D structures of biological macromolecules at high resolution and well-ordered 3-D crystals of sufficient size are the essential prerequisite.

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