Oxygen evolving complex in Photosystem II: Better than excellent (original) (raw)
Related papers
Structural Changes of the Oxygen-evolving Complex in Photosystem II during the Catalytic Cycle
Journal of Biological Chemistry, 2013
Background: Mn 4 CaO 5 cluster catalyzes water oxidation in photosystem II. Results: Mn-Mn/Ca/ligand distances and changes in the structure of the Mn 4 CaO 5 cluster are determined for the intermediate states in the reaction using x-ray spectroscopy. Conclusion: Position of one bridging oxygen and related geometric changes may be critical during catalysis. Significance: Knowledge about structural changes during catalysis is crucial for understanding the O-O bond formation mechanism in PSII.
Photosystem II: The Reaction Center of Oxygenic Photosynthesis*
Annual Review of Biochemistry, 2013
Photosystem II (PSII) uses light energy to split water into chemical products that power the planet. The stripped protons contribute to a membrane electrochemical potential before combining with the stripped electrons to make chemical bonds and releasing O 2 for powering respiratory metabolisms. In this review, we provide an overview of the kinetics and thermodynamics of water oxidation that highlights the conserved performance of PSIIs across species. We discuss recent advances in our understanding of the site of water oxidation based upon the improved (1.9-Å resolution) atomic structure of the Mn 4 CaO 5 wateroxidizing complex (WOC) within cyanobacterial PSII. We combine these insights with recent knowledge gained from studies of the biogenesis and assembly of the WOC (called photoassembly) to arrive at a proposed chemical mechanism for water oxidation.
The water-oxidation complex in photosynthesis
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2004
Studies of the photosynthetic water-oxidation complex of photosystem II (PS II) using spectroscopic techniques have characterized not only important structural features, but also changes that occur in oxidation state of the Mn(4) cluster and in its internal organization during the accumulation of oxidizing equivalents leading to O(2) formation. Combining this spectroscopic information with that from the recently published relatively low-resolution X-ray diffraction studies, we have succeeded in limiting the range of likely cluster arrangements. This evidence strongly supports several options proposed earlier by DeRose et al. [J. Am. Chem. Soc. 116 (1994) 5239] and these can be further narrowed using compatibility with electron paramagnetic resonance (EPR) data.
The inorganic biochemistry of photosynthetic oxygen evolution/water oxidation
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2001
At the request of the organizer of this special edition, we have attempted to do several things in this manuscript: (1) we present a mini-review of recent, selected, works on the light-induced inorganic biogenesis (photoactivation), composition and structure of the inorganic core responsible for photosynthetic water oxidation ; (2) we summarize a new proposal for the evolutionary origin of the water oxidation catalyst which postulates a key role for bicarbonate in formation of the inorganic core; (3) we summarize published studies and present new results on what has been learned from studies of`inorganic mutants' in which the endogenous cofactors (Mn n , Ca 2 , Cl 3 ) are substituted; (4) the first vpH changes measured during the photoactivation process are reported and used to develop a model for the stepwise photo-assembly process; (5) a comparative analysis is given of data in the literature on the kinetics of substrate water exchange and peroxide binding/ dismutation which support a mechanistic model for water oxidation in general; (6) we discuss alternative interpretations of data in the literature with a view to forecast new avenues where progress is needed. ß
Search for intermediates of photosynthetic water oxidation
Photosynthesis Research, 2005
Photosystem II of cyanobacteria and plants incorporates the catalytic centre of water oxidation. Powered and clocked by quanta of light the centre accumulates four oxidising equivalents before oxygen is released. The first three oxidising equivalents are stored on the Mn(4)Ca-cluster, raising its formal oxidation state from S0 to S3 and the third on YZ, producing S3 YZ ox. From there on water oxidation proceeds in what appears as a single reaction step (S3 YZ ox(H2O)2 <==>O2 + 4H+ + S0. Intermediate oxidation products of bound water had not been detected, until our recent report on the stabilisation of such an intermediate by high oxygen pressure (NATURE 430, 2004, 480-483). Based on the oxygen titration (half-point 2.3 bar) the standard free-energy profile of a reaction sequence with a single intermediate was calculated. It revealed a rather small difference (-3 kJ mol-1) between the starting state [S3YZ OX(H2O2) and the product state S0YZ + O2 + 4H+ . Here we describe the tests for side effects of exposing core particles to high oxygen pressure. We found the reduction of P680 +* in ns and the reduction/dismutation of quinones at the acceptor side of PSII both unaffected, and the inhibition of the oxygen evolving reaction by exposure to high O2-pressure was fully reversible by decompression to atmospheric conditions.
Proceedings of the National Academy of Sciences
In oxygenic photosynthesis, light-driven oxidation of water to molecular oxygen is carried out by the oxygen-evolving complex (OEC) in photosystem II (PS II). Recently, we reported the room-temperature structures of PS II in the four (semi)stable S-states, S1, S2, S3, and S0, showing that a water molecule is inserted during the S2 → S3 transition, as a new bridging O(H)-ligand between Mn1 and Ca. To understand the sequence of events leading to the formation of this last stable intermediate state before O2 formation, we recorded diffraction and Mn X-ray emission spectroscopy (XES) data at several time points during the S2 → S3 transition. At the electron acceptor site, changes due to the two-electron redox chemistry at the quinones, QA and QB, are observed. At the donor site, tyrosine YZ and His190 H-bonded to it move by 50 µs after the second flash, and Glu189 moves away from Ca. This is followed by Mn1 and Mn4 moving apart, and the insertion of OX(H) at the open coordination site o...
Indian journal of biochemistry & biophysics, 2012
The redox active component of oxygenic photosynthetic reaction center II contains metal cluster Mn4-Ca, where two H2O are oxidized to O2 and four H+ ions are liberated. A binuclear Mn-Ca metal center binding one substrate H2O on each ion is proposed to be the minimal unit of the redox center. A model for the water oxidizing metal cluster is built with molecular modeling software (HyperChem 8.0 Pro). Mn, being a transitional metal with variable valency is redox active, while Ca is redox inert. Formation and deprotonation of H2O+ on MnIII may be favorable compared to Ca. Deprotonation of H2O+ yields a stable species HO(-) on MnIV by transfer of one electron from MnIII as a consequence of first photoact. Similarly, during second photoact, it may lead to formation of MnV = O. The O-O bond may be formed in the third photoact between O on Mn and H2O on Ca. Subsequently, HO2*(-) may be formed, leading to formation of O2. Molecular models are built for each transition states.
Biochemistry, 2012
As a light-driven water-plastoquinone oxidoreductase, Photosystem II produces molecular oxygen as an enzymatic product. Additionally, under a variety of stress conditions, reactive oxygen species are produced at or near the active site for oxygen evolution. In this study, Fouriertransform ion cyclotron resonance mass spectrometry was used to identify oxidized amino acid residues located in several core Photosystem II proteins (D1, D2, CP43 and CP47) isolated from spinach Photosystem II membranes. While the majority of these oxidized residues (81%) are located on the oxygenated solvent-exposed surface of the complex, several residues on the CP43 protein (354 E, 355 T, 356 M and 357 R) which are in close proximity (<15 Å) to the Mn 4 CaO 5 active site are also modified. These residues appear to be associated with putative oxygen/reactive oxygen species exit channel(s) in the photosystem. These results are discussed within the context of a number of computational studies which have identified putative oxygen channels within the photosystem. Photosystem II (PS II) functions as a light-driven, water-plastoquinone oxidoreductase. In higher plants and cyanobacteria at least six intrinsic proteins appear to be required for O 2 evolution. These are CP47, CP43, D1, D2, and the α and β subunits of cytochrome b 559. Deletion of these subunits uniformly results in the loss of PS II function and assembly (1, 2). Additionally, in higher plants, three extrinsic proteins, PsbO, PsbP and PsbQ are also required for maximal rates of O 2 evolution under physiological inorganic cofactor concentrations (3). Of these three proteins, the PsbO protein appears to play a central role in the stabilization of the manganese cluster, is essential for efficient and stable O 2 evolution and is required, along with PsbP, for photoautotrophic growth and PS II assembly in higher plants propagated under normal growth conditions (4-6). Under low light growth conditions the PsbQ component is also required for photoautotrophy (7). Over the past eleven years, moderate resolution crystal structures of cyanobacterial PS II have significantly enhanced our understanding of the molecular organization of the constituent polypeptides of the photosystem and the active site for oxygen evolution, the Mn 4 O 5 Ca cluster (8-12). Recently, a high resolution 1.9 Å crystal structure of cyanobacterial PS II has been presented
Photoactivation: The Light-Driven Assembly of the Water Oxidation Complex of Photosystem II
Frontiers in plant science, 2016
Photosynthetic water oxidation is catalyzed by the Mn4CaO5 cluster of photosystem II. The assembly of the Mn4O5Ca requires light and involves a sequential process called photoactivation. This process harnesses the charge-separation of the photochemical reaction center and the coordination environment provided by the amino acid side chains of the protein to oxidize and organize the incoming manganese ions to form the oxo-bridged metal cluster capable of H2O-oxidation. Although most aspects of this assembly process remain poorly understood, recent advances in the elucidation of the crystal structure of the fully assembled cyanobacterial PSII complex help in the interpretation of the rich history of experiments designed to understand this process. Moreover, recent insights on the structure and stability of the constituent ions of the Mn4CaO5 cluster may guide future experiments. Here we consider the literature and suggest possible models of assembly including one involving single Mn(2+...
Oxidation of water in photosynthesis
Bioelectrochemistry and Bioenergetics, 1984
A model for the oxidation of water in chloroplasts is suggested. This model is based on certain physico-chemical principles and it accommodates the experimental results associated with the O,-evolving system. The model consists of two pools of heterogeneously bound manganese. Two manganese ions are bound to an enzyme system containing a water-splitting site and four manganese ions are bound to another protein system which connects the reaction centre of photosystem II to the water-splitting enzyme. The latter pool of manganese acts as an electron carrier and an electron trap. It is proposed that water is oxidised in the enzyme system to form H202 and 0; as transient species, and finally liberates 0,. This pathway is energetically feasible. The model explains the flash yield kinetics of O,-evolution and the action of various artificial electron donors and inhibitors of photosystem II. It gives a molecular picture and the quantum requirements of the redox reactions associated with the process of Os-evolution.