TAILIEUCHUNG - Báo cáo khoa học: Systematic characterization of mutations in yeast acetohydroxyacid synthase

Acetohydroxyacid synthase (AHAS, EC ) catalyses the first step in branched-chain amino acid biosynthesis and is the target for sulfonylurea and imidazolinone herbicides, which act as potent and specific inhibitors. Mutants of the enzyme have been identified that are resistant to particular , the selectivityof thesemutants towards various sulfonylureas and imidazolinones has not been determined systematically. Now that the structure of the yeast enzyme isknown, both in theabsenceandpresenceof a bound herbicide, a detailed understanding of the molecular interactions between the enzyme and its inhibitors becomes possible. . | Eur. J. Biochem. 270 2895-2904 2003 FEBS 2003 doi Systematic characterization of mutations in yeast acetohydroxyacid synthase Interpretation of herbicide-resistance data Ronald G. Duggleby Siew Siew Pang Hongqi Yu and Luke W. Guddat Department of Biochemistry and Molecular Biology The University of Queensland Brisbane QLD 4072 Australia Acetohydroxyacid synthase AHAS EC catalyses the first step in branched-chain amino acid biosynthesis and is the target for sulfonylurea and imidazolinone herbicides which act as potent and specific inhibitors. Mutants of the enzyme have been identified that are resistant to particular herbicides. However the selectivity of these mutants towards various sulfonylureas and imidazolinones has not been determined systematically. Now that the structure of the yeast enzyme is known both in the absence and presence of a bound herbicide a detailed understanding of the molecular interactions between the enzyme and its inhibitors becomes possible. Here we construct 10 active mutants of yeast AHAS purify the enzymes and determine their sensitivity to six sulfonylureas and three imidazolinones. An additional three active mutants were constructed with a view to increasing imidazolinone sensitivity. These three variants were purified and tested for their sensitivity to the imida-zolinones only. Substantial differences are observed in the sensitivity of the 13 mutants to the various inhibitors and these differences are interpreted in terms of the structure of the herbicide-binding site on the enzyme. Keywords acetohydroxyacid synthase herbicide inhibition herbicide-resistance mutations imidazolinone sulfonylurea. The inability of higher animals to synthesize branched-chain amino acids makes these compounds essential in the diet. In contrast plants and many microorganisms do not require a supply of these amino acids and contain all of the enzymes for their biosynthesis Fig. 1A . As a result these enzymes .

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