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Title: MUTATIONAL CHARACTERIZATION OF BINDING-SITES FOR QUINOL-OXIDATION INHIBITORS IN THE CYTOCHROME BF COMPLEX OF SYNECHOCOCCUS SP. PCC 7002

Author
item LEE, T - UNIV WISCONSIN OSHKOSH WI
item METZGER, S - PLANT BIOLOGY UOFI URBANA
item CHO, Y - PLANT BIOLOGY UOFI URBANA
item WHITMARSH, CLIFFORD
item KALLAS, T - UNIV WISCONSIN OSHKOSH WI

Submitted to: Biochimica et Biophysica Acta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Photosynthesis depends on a series of reactions that use light energy to produce carbohydrate from atmospheric carbon dioxide. When plants are exposed to full sunlight, the slowest component of the electron transport chain is the cytochrome bf complex. The cytochrome bf complex contains iron atoms, which serve to transfer electrons from a molecule that carries hydrogen atoms to a molecule that carries a single electron. Several photosynthetic inhibitors are known to block electron transfer through the cytochrome bf complex. To understand the molecular basis of the inhibition we created site specific mutations in the cytochrome bf complex. By measuring electron transport in the mutants in the presence of different inhibitors, we have identified key amino acids that are important in controlling herbicide binding, and therefore the amount of herbicide necessary for inhibition. This information makes it possible to design plants that are resistant to specific inhibitors, which can be useful in the use of herbicides to eliminate weeds without damaging crop plants.

Technical Abstract: The cytochrome bf complex, which links electron transfer from photosystem II to photosystem I in oxygenic photosynthesis, has not been amenable to site-directed mutagenesis in cyanobacteria. Using the cyanobacterium Synechococcus sp. we have successfully modified the cytochrome b6 subunit of the complex. Single amino acid substitutions at the position's D148, A154, and S159 revealed altered binding of the quinol-oxidation inhibitors 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), myxothiazol, and stigmatellin. Cytochrome bf and mitochondrial-type cytochrome bc complexes are related, but exhibit different inhibitor specificity. Cytochrome bf complexes are insensitive to myxothiazol and sensitive to DBMIB whereas cytochrome bc complexes are sensitive to myxothiazol and relatively insensitive to DBMIB. These mutations made the cytochrome bf complex more like the cytochrome bc complex. This work demonstrates that cyanobacteria can be used as effective models to investigate structure-function relationships in the cytochrome bf complex.