Protein herbicide-binding

Heptagold heteronuclear cluster compounds X-ray crystallography, 39 371-373 Heptasulfur imide, 2 161-164 Herbicide-binding protein, 33 224 Heteroallenes, cycloaddition to iminoboianes, 31 161... 

Still the identity, nature, and size of the herbicide-binding protein remained a puzzle. This putative protein was likely very hydrophobic. A methodology for isolating such membrane proteins was not at that time available. Even more difficult to comprehend was the orientation of such hydrophobic proteins in a membrane that had been a matter of discussion for many decades. The first X-ray structure of a membrane protein complex in 1985 suddenly solved this orientation question, as will be discussed below. 

The Three-Dimensional Orientation of the Triazines in the Herbicide-Binding Protein of PS II... 

Significance of the Rapid Turnover of the Herbicide-Binding Protein for the Mode of Action of Triazines 107... 

Erickson, J.M., M. Rahire, J.D. Rochaix, and L. Mets (1985). Herbicide resistance and cross-resistance Changes at three distinct sites in the herbicide-binding protein. Science, 228 204-207. 

Johanningmeier, U., U. Bodner, and G.F. Wildner (1987). A new mutation in the gene coding for the herbicide-binding protein in Chlamydomonas. Fed. European Biochem. Societies Lett., 211 221-224. 

Smeda, R.J., PM. Hasegawa, P.B. Goldsbrough, N.K. Singh, and S.C. Weller (1993). A serine-to-threonine substitution in the triazine herbicide-binding protein in potato cells results in atrazine resistance without impairing productivity. Plant Physiol., 103 911-917. 

Herbicides that inhibit photosynthetic electron flow prevent reduction of plastoquinone by the photosystem II acceptor complex. The properties of the photosystem II herbicide receptor proteins have been investigated by binding and displacement studies with radiolabeled herbicides. The herbicide receptor proteins have been identified with herbicide-derived photoaffinity labels. Herbicides, similar in their mode of action to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) bind to a 34 kDa protein, whereas phenolic herbicides bind to the 43-51 kDa photosystem II reaction center proteins. At these receptor proteins, plastoquinone/herbicide interactions and plastoquinone binding sites have been studied, the latter by means of a plastoquinone-deriv-ed photoaffinity label. For the 34 kDa herbicide binding protein, whose amino acid sequence is known, herbicide and plastoquinone binding are discussed at the molecular level. 

In 1979, the concept of a photosystem II herbicide binding protein with different but overlapping binding sites for the various photosystem II herbicides was simultaneously established by Trebst and Draber ( 5) and Pfister and Arntzen (6). This idea of a herbicide receptor protein proved to be extremely fruitful because the techniques of receptor biochemistry were now applicable. Tischer and Strotmann (7) were the first investigators to study binding of radiolabeled herbicides in isolated thylakoids. 

The phenolic photoaffinity label azidodinoseb (Figure 4) binds less specifically than either azidoatrazine or azidotriazinone (14). In addition to other proteins, it labels predominantly the photosystem II reaction center proteins (spinach 43 and 47 kDa Chlamydomo-nas 47 and 51 kDa) (17). Because of the unspecific binding of azidodinoseb, this can best be seen in photosystem II preparations (17). Thus, the phenolic herbicides bind predominantly to the photosystem II reaction center, which might explain many of the differences observed between "DCMU-type" and phenolic herbicides (9). The photosystem II reaction center proteins and the 34 kDa herbicide binding protein must be located closely to and interact with each other in order to explain the mutual displacement of both types of herbicides (8,12,21). Furthermore, it should be noted that for phenolic herbicides, some effects at the donor side of photosystem II (22) and on carotenoid oxidation in the photosystem II reaction center have been found (23). 

The 34 kDa herbicide binding protein is a plastid encoded protein. 

A schematic picture of the 34 kDa herbicide binding protein as it is thought to be located in the membrane is given in Figure 8. 

Figure 7. Hydropathy plot of the 34 kOa herbicide binding protein.

Iodolabeling studies on photosystem II particles from higher plants and cyanobacteria (221) and on a PSII complex (227) specifically labeled the herbicide-binding protein. As 1 is believed to donate electrons to Z, the secondary electron donor which is believed to accept electrons from the photosynthetic manganese complex, these experiments indicate a role for this protein on the oxidizing side of PSII. Consequently, Z must at least be located near, if not in, the herbicidebinding polypeptide (222). 

Stlamatellln. A qyxobacterlales species, Stiamatella aurontlaca. produces an antibiotic stigmatellln [76] which also has herbicldal properties (2721. This dimethoxychromone alters photosynthetic electron transport at the herbicide-binding protein and the cytochrome b f complex. 

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