Understanding the Topography of the Photosystem II Herbicide Binding Niche: Does QSAR Help?

1993 ◽  
Vol 48 (3-4) ◽  
pp. 140-145 ◽  
Author(s):  
John L. Huppatz ◽  
Helen G. McFadden
Keyword(s):  
Photosystem Ii ◽  
Binding Site ◽  
Photosynthetic Electron Transport ◽  
Reaction Centre ◽  
Ps Ii ◽  
Qsar Analysis ◽  
Qsar Studies ◽  
Chemical Structures ◽  
Herbicide Binding ◽  
Inhibition Potency

Abstract For thirty years the study of Quantitative Structure Activity Relationships (QSAR) has been an active area of research aimed at developing an understanding of the interactions be­ tween inhibitors of photosynthetic electron transport and the herbicide binding site in the Photosystem II (PS II) reaction centre. Many QSAR studies of PS II inhibitors with diverse chemical structures have emphasized the hydrophobic nature of the binding domain, with lipophilicity being the dominant determinant of Hill inhibition activity. The cyanoacrylate classes of PS II inhibitors also show a diversity of active structures and considerable variation in inhibition potency with minor alterations to structure. QSAR analysis and examination of chirality in cyanoacrylate inhibitors has also shown the importance of steric factors in determining activity. Different modes of binding for different classes of cyanoacrylates have been identified; a classical urea-type relationship between activity and hydrophobicity and another type of interaction in which the lipophilicity or electronic nature of phenyl substituents plays little part and the size of the substituents is of primary importance. Because size and shape are parameters of great importance in determining the topography of a binding site, QSAR studies of flexible PS II inhibitors such as cyanoacrylates will continue to be important in elucidating the intricacies of inhibitor/PS II interactions.

Molecular Modelling of the Interaction between DCMU and the QB-Binding Site of Photosystem II

1993 ◽  
Vol 48 (3-4) ◽  
pp. 191-198 ◽  
Author(s):  
Simon P. Mackay ◽  
Patrick J. O ’Malley
Keyword(s):  
Hydrogen Bond ◽  
Photosystem Ii ◽  
Binding Site ◽  
Binding Sites ◽  
The Other ◽  
Reaction Centre ◽  
Protein Model ◽  
Intermolecular Energy ◽  
Herbicide Binding ◽  
Binding Orientations

Abstract The prefered binding orientations for the herbicide DCMU within the QB-binding site of the D 1 protein model from a photosystem II reaction centre have been determined. Calculation of the intermolecular energy between the herbicide and the binding site has been instrumental in obtaining optimum positions reinforced by experimental results from mutation studies and herbicide binding to analogous bacterial reaction centres. We have shown that two binding sites are possible, one involving a hydrogen bond to and the other to the Ser 264 residue. In both cases, which are more important for the stabilization of the interactions.

Synthesis and Use of Radiolabelled Cyanoacrylate Probes of the Photosystem II Herbicide Binding Site

1990 ◽  
Vol 45 (3-4) ◽  
pp. 196-202 ◽  
Author(s):  
Helen G. McFadden ◽  
John N. Phillips
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Binding Site ◽  
Active Site ◽  
Photosynthetic Electron Transport ◽  
Inhibitor Binding ◽  
Similar System ◽  
Weak Binding ◽  
Herbicide Binding ◽  
The Hill

Abstract Cyanoacrylates are potent inhibitors of photosynthetic electron transport (PET) and are potentially useful probes of the photosystem II herbicide binding site. A series of cyanoacrylates was synthesized and the Hill inhibition activities evaluated in order to select compounds suita­ble for radioactive synthesis. A cyanoacrylate, 2-(2-nitrophenoxy)ethyl 3-benzylamino-2-cyano-2-pentenoate, was found to displace diuron from the photosystem II herbicide binding site. For this compound the dissociation constant of the inhibitor/binding site complex was found to be 2 × 10-8 M with an active site concentration of 2 nmol/mg chlorophyll. In a similar system the corresponding figures for diuron were 1.2 × 10-8 m and 1.3 nmol/mg chlorophyll. Photoaffinity labelling of 1% II thylakoid proteins with 2-(2-azidophenoxy)ethyl 3-[7-14C]-benzylamino-2-cyano-2-pentenoate showed weak binding in the 32 and 28 kD mass regions, consistent with binding to the D, peptide.

N-Methylanilinocyanoacrylate Photosystem II Inhibitors. Structure-Activity Relationships

1993 ◽  
Vol 48 (3-4) ◽  
pp. 136-139 ◽  
Author(s):  
Wendy K. Banham ◽  
John L. Huppatz ◽  
John N . Phillips
Keyword(s):  
Photosystem Ii ◽  
Binding Site ◽  
Inhibitory Activity ◽  
Mixing Time ◽  
Position Effect ◽  
Photosynthetic Electron Transport ◽  
Ps Ii ◽  
Structure Activity ◽  
Equilibration Rate ◽  
Fluoro Derivatives

Abstract Many 3-N-methylanilino cyanoacrylate derivatives are potent inhibitors of photosynthetic electron transport at the PS II level in a thylakoid system isolated from Pisum sativum. These inhibitors are somewhat unusual in that they take more than 15 min to equilibrate with the binding site in contrast to most classical PS II inhibitors which tend to equilibrate rapidly i.e. within the mixing time of seconds. The effects of mono-and disubstituents in the aryl nucleus on inhibitory activity were studied. The nature and position of the substituent had no detectable influence on equilibration rate but a pronounced influence on inhibitory activity as measured by equilibrium pI50 values. Substituent position enhanced inhibitory activity in the order 3′ > 2′ ⋙ 4′ . As regards the nature of the substituent, size appeared to be the most important parameter -the smaller the substituent the greater the activity. Such influences were in contrast to those in analogous 3-anilino-and 3-benzylamino-2-cyano-acrylate series where the comparable order of substituent position effect was 3′ and 4′ ⋙ 2′ and where substituent hydro-phobicity rather than size was the most important factor. Disubstituted fluoro derivatives have given interesting insights into the preferred orientation of these inhibitors at the binding site with the 2′-and 5′-positions interacting positively, the 4′-position, negatively, and the 3′-position neutrally.

Photoinactivation of Photosynthetic Electron Transport under Anaerobic and Aerobic Conditions in Isolated Thylakoids of Spinach

1992 ◽  
Vol 47 (1-2) ◽  
pp. 63-68 ◽  
Author(s):  
Rekha Chaturvedi ◽  
M. Singh ◽  
P. V. Sane
Keyword(s):  
Electron Transport ◽  
Photosynthetic Electron Transport ◽  
Oxygen Evolving Complex ◽  
Reaction Centre ◽  
Ps Ii ◽  
Ps I ◽  
S2 State ◽  
The Stability ◽  
Oxygen Evolving ◽  
Spinach Thylakoids

Abstract The effect of exposure to strong white light on photosynthetic electron transport reactions of PS I and PS II were investigated in spinach thylakoids in the absence or presence of oxygen. Irrespective of the conditions used for photoinactivation, the damage to PS II was always much more than to PS I. Photoinactivation was severe under anaerobic conditions compared to that in air for the same duration. This shows that the presence of oxygen is required for prevention of photoinactivation of thylakoids. The susceptibility of water-splitting complex in photoinactivation is indicated by our data from experiments with chloride-deficient chloroplast membranes wherein it was observed that the whole chain electron transport from DPC to MV was much less photoinhibited than that from water. The data from the photoinactivation experiments with the Tris-treated thylakoids indicate another photodam age site at or near reaction centre of PS II. DCMU-protected PS II and oxygen-evolving complex from photoinactivation. DCMU protection can also be interpreted in terms of the stability of the PS II complex when it is in S2 state.

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.

X-Ray Structure Analysis of a Cyanoacrylate Inhibitor of Photosystem II Electron Transport

1991 ◽  
Vol 46 (1-2) ◽  
pp. 93-98 ◽  
Author(s):  
Helen G. McFadden ◽  
Donald C. Craig ◽  
John L. Huppatz ◽  
John N. Phillips
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Chlorophyll Concentration ◽  
Photosynthetic Electron Transport ◽  
Hill Reaction ◽  
Ps Ii ◽  
X Ray ◽  
High Affinity ◽  
Modelling Studies ◽  
Intramolecular Hydrogen

Abstract X-ray crystallographic data for the highly potent cyanoacrylate photosynthetic electron transport inhibitor, (Z)-ethoxyethyl 3-(4-chlorobenzylamino)-2-cyano-4-methylpent-2-enoate, are presented. This compound has a particularly high affinity for the photosystem II (PS II) herbicide receptor with a p I50 value of 9.5 (in the Hill reaction under uncoupled condi­tions with a chlorophyll concentration of 0.1 μg/ml). Data regarding the structure of small li­gands, such as this potent cyanoacrylate, which bind to the site with high affinity may be used to provide the basis for modelling studies of PS II/herbicide complexes. The X-ray data presented confirm the Z-stereochemistry of active cyanoacrylates and demonstrate the pres­ence of a planar core stabilized by an intramolecular hydrogen bond between the ester car­bonyl oxygen and a benzylamino hydrogen atom. In order to assess the importance of the benzylamino -NH -group in this type of cyanoacrylate, analogues containing a methylene group in its place were synthesized and found to be 100-and 1000-fold less active as Hill inhibitors.

Inhibition by Tetranitromethane of Photosynthetic Electron Transport from Water to Photosystem II in Chloroplasts

1980 ◽  
Vol 35 (3-4) ◽  
pp. 293-297 ◽  
Author(s):  
P. V. Sane ◽  
Udo Johanningmeier
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Electron Flow ◽  
Ph Dependence ◽  
Photosynthetic Electron Transport ◽  
Donor Side ◽  
Ps Ii ◽  
Diphenyl Carbazide ◽  
Low Concentrations ◽  
Sh Group

Abstract Low concentrations (10 µM) of tetranitromethane inhibit noncyclic electron transport in spinach chloroplasts. A study of different partial electron transport reactions shows that tetranitromethane primarily interferes with the electron flow from water to PS II. At higher concentrations the oxidation of plastohydroquinone is also inhibited. Because diphenyl carbazide but not Mn2+ ions can donate electrons efficiently to PS II in the presence of tetranitromethane it is suggested that it blocks the donor side of PS II prior to donation of electrons by diphenyl carbazide. The pH dependence of the inhibition by this protein modifying reagent may indicate that a functional-SH group is essential for a protein, which mediates electron transport between the water splitting complex and the reaction center of PS II.

The Molecular Mechanism of Photoinhibition — Facts and Fiction

1988 ◽  
Vol 15 (2) ◽  
pp. 27 ◽  
Author(s):  
C Critchley
Keyword(s):  
Photosystem Ii ◽  
Molecular Mechanism ◽  
Functional Group ◽  
Structure And Function ◽  
The Other ◽  
Proteolytic Degradation ◽  
Reaction Centre ◽  
Herbicide Binding ◽  
Recent Developments ◽  
And Function

In this paper, the evidence supporting two different models for the molecular mechanism of photoinhibition is discussed. One hypothesis centres around the suggestion that photoinhibition is due to the loss of the herbicide-binding Dl polypeptide of photosystem II. The other model suggests that damage to a functional group in the reaction centre is the primary cause of photoinhibition. In order to put the apparent controversy into context, recent developments in our understanding of the structure and function of the photosystem II reaction centre are described. Interpretation and judgement of all available evidence suggest primary photoinhibitory damage to be incurred by the reaction-centre chlorophyll P680 destabilising the apoprotein(s) and eventually resulting in their proteolytic degradation and removal from the photosystem II complex and the thylakoid membrane.

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