scholarly journals Structural Basis of Cyanobacterial Photosystem II Inhibition by the Herbicide Terbutryn

2011 ◽  
Vol 286 (18) ◽  
pp. 15964-15972 ◽  
Author(s):  
Matthias Broser ◽  
Carina Glöckner ◽  
Azat Gabdulkhakov ◽  
Albert Guskov ◽  
Joachim Buchta ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Photosystem Ii ◽  
Purple Bacteria ◽  
Chloride Ion ◽  
Reaction Centers ◽  
Structural Basis ◽  
Photosynthetic Reaction Centers ◽  
Thermophilic Cyanobacterium ◽  
Herbicide Binding ◽  
Water Oxidizing Complex

Herbicides that target photosystem II (PSII) compete with the native electron acceptor plastoquinone for binding at the QB site in the D1 subunit and thus block the electron transfer from QA to QB. Here, we present the first crystal structure of PSII with a bound herbicide at a resolution of 3.2 Å. The crystallized PSII core complexes were isolated from the thermophilic cyanobacterium Thermosynechococcus elongatus. The used herbicide terbutryn is found to bind via at least two hydrogen bonds to the QB site similar to photosynthetic reaction centers in anoxygenic purple bacteria. Herbicide binding to PSII is also discussed regarding the influence on the redox potential of QA, which is known to affect photoinhibition. We further identified a second and novel chloride position close to the water-oxidizing complex and in the vicinity of the chloride ion reported earlier (Guskov, A., Kern, J., Gabdulkhakov, A., Broser, M., Zouni, A., and Saenger, W. (2009) Nat. Struct. Mol. Biol. 16, 334–342). This discovery is discussed in the context of proton transfer to the lumen.

Site-Directed Mutations of Two Histidine Residues in the D2 Protein Inactivate and Destabilize Photosystem II in the Cyanobacterium Synechocystis 6803

1987 ◽  
Vol 42 (7-8) ◽  
pp. 762-768 ◽  
Author(s):  
Wim F. J. Vermaas ◽  
John G. K. Williams ◽  
Charles J. Arntzen
Keyword(s):  
Low Temperature ◽  
Photosystem Ii ◽  
Purple Bacteria ◽  
Synechocystis 6803 ◽  
Ps Ii ◽  
Histidine Residues ◽  
Fluorescence Maximum ◽  
Herbicide Binding ◽  
Chlorophyll Protein ◽  
D2 Protein

Site-directed mutations were created in the cyanobacterium Synechocystis 6803 to alter specific histidine residues of the photosystem II (PS II) D2 protein. In one mutant (tyr-197). the his-197 residue was replaced by tyrosine, in another mutant (asn-214), his-214 was changed into asparagine. The tyr-197 mutant did not show any low-temperature fluorescence attributable to PS II. but contained a PS II chlorophyll-protein, CP-47, in significant quantities. Another PS II chlorophyll-protein, CP-43, was absent, as was PS II-related herbicide binding. The asn-214 mutant showed a blue-shifted low-temperature fluorescence maximum around 682 nm. but did not have a significant amount of membrane-incorporated CP-43 or CP-47. Herbicide binding was also absent in this mutant. These data indicate a very important role of the his-197 and his-214 residues in the D 2 protein, and are interpreted to support the hypothesis that the D2 protein and the M subunit from the photosynthetic reaction center of purple bacteria have analogous functions. According to this hypothesis, his-197 is involved in binding of P680. and his-214 forms ligands with Qᴀ and Fe2+. In absence of a functional D2 protein, the PS II core complex appears to be destabilized as evidenced by loss of chlorophyll-proteins in the mutants.

scholarly journals Acquirement of water-splitting ability and alteration of the charge-separation mechanism in photosynthetic reaction centers

2020 ◽  
Vol 117 (28) ◽  
pp. 16373-16382 ◽  
Author(s):  
Hiroyuki Tamura ◽  
Keisuke Saito ◽  
Hiroshi Ishikita
Keyword(s):  
Excitation Energy ◽  
Water Splitting ◽  
Charge Separation ◽  
Purple Bacteria ◽  
D1 Protein ◽  
Reaction Centers ◽  
Electronic Coupling ◽  
Separation Mechanism ◽  
Photosynthetic Reaction Centers ◽  
Charged Residues

In photosynthetic reaction centers from purple bacteria (PbRC) and the water-oxidizing enzyme, photosystem II (PSII), charge separation occurs along one of the two symmetrical electron-transfer branches. Here we report the microscopic origin of the unidirectional charge separation, fully considering electron–hole interaction, electronic coupling of the pigments, and electrostatic interaction with the polarizable entire protein environments. The electronic coupling between the pair of bacteriochlorophylls is large in PbRC, forming a delocalized excited state with the lowest excitation energy (i.e., the special pair). The charge-separated state in the active branch is stabilized by uncharged polar residues in the transmembrane region and charged residues on the cytochromec2binding surface. In contrast, the accessory chlorophyll in the D1 protein (ChlD1) has the lowest excitation energy in PSII. The charge-separated state involves ChlD1•+and is stabilized predominantly by charged residues near the Mn4CaO5cluster and the proceeding proton-transfer pathway. It seems likely that the acquirement of water-splitting ability makes ChlD1the initial electron donor in PSII.

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