scholarly journals The exchange of the fast substrate water in the S2 state of photosystem II is limited by diffusion of bulk water through channels – implications for the water oxidation mechanism

2021 ◽  
Author(s):  
Casper de Lichtenberg ◽  
Christopher J. Kim ◽  
Petko Chernev ◽  
Richard J Debus ◽  
Johannes Messinger
Keyword(s):  
Photosystem Ii ◽  
Molecular Oxygen ◽  
Water Oxidation ◽  
Oxidation Mechanism ◽  
Bulk Water ◽  
Oxygen Species ◽  
S2 State ◽  
Oxo Bridge

The molecular oxygen we breathe is produced from water-derived oxygen species bound to the Mn4CaO5 cluster in photosystem II (PSII). Present research points to the central oxo-bridge O5 as the...

scholarly journals Untangling the sequence of events during the S2→ S3transition in photosystem II and implications for the water oxidation mechanism

2020 ◽  
Vol 117 (23) ◽  
pp. 12624-12635 ◽  
Author(s):  
Mohamed Ibrahim ◽  
Thomas Fransson ◽  
Ruchira Chatterjee ◽  
Mun Hon Cheah ◽  
Rana Hussein ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Donor Site ◽  
Oxidation Mechanism ◽  
Oxygenic Photosynthesis ◽  
Acceptor Site ◽  
Oxygen Evolving Complex ◽  
Ps Ii ◽  
Sequence Of Events ◽  
Large Channel

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→ S3transition, 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 O2formation, we recorded diffraction and Mn X-ray emission spectroscopy (XES) data at several time points during the S2→ S3transition. At the electron acceptor site, changes due to the two-electron redox chemistry at the quinones, QAand QB, are observed. At the donor site, tyrosine YZand 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 of Mn1. This water, possibly a ligand of Ca, could be supplied via a “water wheel”-like arrangement of five waters next to the OEC that is connected by a large channel to the bulk solvent. XES spectra show that Mn oxidation (τ of ∼350 µs) during the S2→ S3transition mirrors the appearance of OXelectron density. This indicates that the oxidation state change and the insertion of water as a bridging atom between Mn1 and Ca are highly correlated.

scholarly journals Electron, proton and hydrogen–atom transfers in photosynthetic water oxidation

2002 ◽  
Vol 357 (1426) ◽  
pp. 1383-1394 ◽  
Author(s):  
Cecilia Tommos
Keyword(s):  
Photosystem Ii ◽  
Proton Transfer ◽  
Water Oxidation ◽  
Oxidation Mechanism ◽  
Bulk Solution ◽  
Hydrogen Atoms ◽  
Redox Active ◽  
Hydrogen Atom Transfers ◽  
Reduce Carbon Dioxide ◽  
Photosynthetic Water Oxidation

When photosynthetic organisms developed so that they could use water as an electron source to reduce carbon dioxide, the stage was set for efficient proliferation. Algae and plants spread globally and provided the foundation for our atmosphere and for O 2 –based chemistry in biological systems. Light–driven water oxidation is catalysed by photosystem II, the active site of which contains a redox–active tyrosine denoted Y Z , a tetramanganese cluster, calcium and chloride. In 1995, Gerald Babcock and co–workers presented the hypothesis that photosynthetic water oxidation occurs as a metallo–radical catalysed process. In this model, the oxidized tyrosine radical is generated by coupled proton/electron transfer and re–reduced by abstracting hydrogen atoms from substrate water or hydroxide–ligated to the manganese cluster. The proposed function of Y Z requires proton transfer from the tyrosine site upon oxidation. The oxidation mechanism of Y Z in an inhibited and O 2 –evolving photosystem II is discussed. Domino–deprotonation from Y Z to the bulk solution is shown to be consistent with a variety of data obtained on metal–depleted samples. Experimental data that suggest that the oxidation of Y Z in O 2 –evolving samples is coupled to proton transfer in a hydrogen–bonding network are described. Finally, a dielectric–dependent model for the proton release that is associated with the catalytic cycle of photosystem II is discussed.

scholarly journals The mechanism for proton–coupled electron transfer from tyrosine in a model complex and comparisons with Y Z oxidation in photosystem II

2002 ◽  
Vol 357 (1426) ◽  
pp. 1471-1479 ◽  
Author(s):  
Martin Sjödin ◽  
Stenbjörn Styring ◽  
Björn Åkermark ◽  
Licheng Sun ◽  
Leif Hammarström
Keyword(s):  
Electron Transfer ◽  
Photosystem Ii ◽  
Water Oxidation ◽  
Oxidation Mechanism ◽  
Model System ◽  
Proton Coupled Electron Transfer ◽  
Tyrosine Oxidation ◽  
Model Complex ◽  
Primary Donor ◽  
Mn Cluster

In the water–oxidizing reactions of photosystem II (PSII), a tyrosine residue plays a key part as an intermediate electron–transfer reactant between the primary donor chlorophylls (the pigment P 680 ) and the water–oxidizing Mn cluster. The tyrosine is deprotonated upon oxidation, and the coupling between the proton reaction and electron transfer is of great mechanistic importance for the understanding of the water–oxidation mechanism. Within a programme on artificial photosynthesis, we have made and studied the proton–coupled tyrosine oxidation in a model system and been able to draw mechanistic conclusions that we use to interpret the analogous reactions in PSII.

scholarly journals Crystallographic studies on Mn atoms in Photosystem II using K-edge wavelength

2014 ◽  
Vol 70 (a1) ◽  
pp. C350-C350
Author(s):  
Yasufumi Umena ◽  
Keisuke Kawakami ◽  
Jian-Ren Shen ◽  
Nobuo Kamiya
Keyword(s):  
Photosystem Ii ◽  
Molecular Oxygen ◽  
Electronic State ◽  
Absorption Edge ◽  
Water Oxidation ◽  
Catalytic Mechanism ◽  
Anomalous Scattering ◽  
Oxygen Evolving Complex ◽  
X Ray ◽  
Difference Fourier

Molecular oxygen on Earth is generated from photosynthesis by cyanobacteria, algae and plants, where water molecules are split by Photosystem II (PSII). PSII catalyzes light-induced water oxidation leading to the production of protons, electrons and molecular oxygen. The catalytic center of oxygen evolving complex (OEC) in PSII is composed of four Mn atoms and one Ca atom organized in a Mn4CaO5-cluster, which cycles through several different redox states to accomplish the catalytic process. Cyanobacterial PSII is a multi-subunits membrane protein complex composed of 17 membrane-spanning subunits, 3 membrane-extrinsic subunits and about 80 co-factor molecules with a total molecular weight of 350 kDa as a monomer. We reported the PSII structure at 1.9 Å resolution prepared from Thermosynechococcus vulcanus (PDB code: 3ARC)[1]. We determined unambiguously the positions of the atoms in OEC using the electron density map corresponding to each of five metal atoms and five oxygen atoms, for the first time. However, the valences of each of the four Mn atoms and their participation in the redox reactions in OEC are not fully understood. In order to uncover the catalytic mechanism of light-induced water oxidation by OEC, it is important to determine the valence of each Mn atom as well as to solve the detailed structure. In this study, we analyze the electronic state of each Mn atom in OEC by X-ray crystallographic analysis using Mn K-absorption edge wavelength. The Mn K-absorption edge depends on the oxidation number, and the anomalous scattering factor changes greatly for the Mn atoms in different oxidation states. We collected the anomalous difference data from PSII crystals using the wavelength (~1.8921 Å) on the Mn K-absorption edge at beamline BL38B1 and BL41XU of SPring-8 in Japan. The calculated anomalous difference Fourier map indicated different intensities among the four Mn atoms in OEC. This may suggest the different electronic state among the four Mn atoms in OEC. However, there is a possibility that these Mn atoms are reduced by X-ray exposures to some extent, and so the valences of these Mn atoms were not determined completely. We will discuss the relationship between peak heights of the anomalous difference Fourier map and the valence among the four Mn atoms in OEC.

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 Capturing structural changes of photosystem II using time-resolved serial femtosecond crystallography with proper flash excitations

2020 ◽  
Author(s):  
Honjie Li ◽  
Yoshiki Nakajima ◽  
Takashi Nomura ◽  
Michihiro Sugahara ◽  
Shinichiro Yonekura ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Structural Changes ◽  
Light Condition ◽  
Enzymatic Reactions ◽  
Time Resolved ◽  
Pump Probe ◽  
State Cycle ◽  
S2 State ◽  
Serial Femtosecond Crystallography

Abstract Photosystem II (PSII) catalyzes light-induced water oxidation through an Si-state cycle, leading to the generation of di-oxygen, protons, and electrons. Pump-probe time-resolved serial femtosecond crystallography (TR-SFX) has been used to capture intermediate states of light-driven enzymatic reactions. In this approach, it is crucial to avoid contamination of light into the samples when analyzing a particular reaction intermediate. Here, we describe a method for determining a proper light condition that avoids light contamination to the PSII microcrystals while minimizing the sample consumption in TR-SFX. With the proper illumination conditions determined, we analyzed the S2-state structure of PSII at room temperature, revealing the structural changes during the S1-to-S2 transition at an ambient temperature. By comparing with the previous studies performed at a low temperature or with a different delay time, we reveal the possible channels for water inlet and proton egress, as well as structural changes important for the water-splitting reaction.

Sign in / Sign up

Export Citation Format

Share Document