Origin of the herbicide binding site of acetolactate synthase

Schloss, John V.; Ciskanik, L M; Dyk, Drew E. Van

doi:10.1038/331360a0

Cited by 176 publications

(114 citation statements)

References 24 publications

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“…The imr and csrl (10) mutations cause high levels of AHAS resistance to either the imidazolinones or the sulfonylureas, but not to both. Assuming that both classes of herbicides bind the active site of AHAS as suggested (16)(17)(18)22), then imr and csri mutations probably cause amino acid substitutions at the active site that prevent the binding ofonly one herbicide class. That such discrimination could occur is not surprising considering how chemically distinct sulfonylurea compounds are from imidazolinone compounds.…”

Section: Genetic Analysis Of Gh90mentioning

confidence: 99%

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A Mutation Causing Imidazolinone Resistance Maps to the Csr1 Locus of Arabidopsis thaliana

Haughn

Somerville²

1990

Plant Physiol.

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A mutant of Arabidopsis thaliana, two hundred times more resistant to the imidazolinone herbicide imazapyr than wild-type plants, was isolated by direct selection of seedlings from a mutagenized population. Genetic analysis showed that resistance is due to a single dominant nuclear mutation that could not be separated by recombination from a mutation in the CSR1 gene encoding acetohydroxy acid synthase. Acetohydroxy acid synthase activity in extracts isolated from the mutant was 1000-fold more resistant to inhibition by imazapyr than that of the wild type. The resistant enzyme activity cosegregated with whole plant resistance. These data strongly suggest that the mutation is an allele of CSR1 encoding an imazapyr-resistant AHAS.

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Section: Genetic Analysis Of Gh90mentioning

confidence: 99%

“…First, enzyme kinetics data have shown that the imidazolinones, like the sulfonylureas, inhibit AHAS activity by binding noncompetitively to a common site on the enzyme (17). Second, a number of variant cell lines of Datura innoxia resistant to sulfonylurea herbicides showed crossresistance to imidazolinone herbicides (16).…”

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confidence: 99%

A Mutation Causing Imidazolinone Resistance Maps to the Csr1 Locus of Arabidopsis thaliana

Haughn

Somerville²

1990

Plant Physiol.

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“…Saturated ammonium sulfate was added to the supernatant to a final concentration of 50%, and the mixture was stirred and kept in an ice bath for 10 min. The protein pelleting at 50% ammonium sulfate was collected by centrifugation at 20,000g for 20 (3) were performed using graphical methods described by Webb (27). Experiments were repeated two to six times using different extracts.…”

Section: Materials and Methods Cell Suspension Culturesmentioning

confidence: 99%

“…Schloss et al (20) proposed that the herbicide-specific site of ALS is an evolutionary vestige of the quinone binding site of pyruvate oxidase. They also indicated the possibility that the quinone/herbicide binding site of ALS has some, as yet, undiscovered regulatory or mechanistic role (20 …”

Section: Determination Of Kmp For Pyruvatementioning

confidence: 99%

Herbicide Resistance in Datura innoxia

Rathinasabapathi

King²

1991

Plant Physiol.

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Acetolactate synthase (ALS, EC 4.1.3.18), the first enzyme in the biosynthesis of branched-chain amino acids, was isolated from wild-type and sulfonylurea-resistant Datura innoxia cell variants and characterized. Apparent Km values of the ALS for pyruvate from three sulfonylurea-resistant variants (CSR2, CSR6, and CSR10) were manyfold greater than that of the wild type. The inhibition of wild-type and herbicide-resistant ALS activity by chlorsulfuron (CS), a sulfonylurea herbicide, and L-leucine (LLeu), one of the feedback inhibitors of the enzyme, was examined. ALS from two CS-resistant variants exhibited severalfold greater resistance to CS than did the wild-type enzyme. Inhibition of ALS by L-Leu fitted a partially competitive pattern most closely.It is proposed that the herbicide resistance mutation accentuated the partial inhibition characteristics of ALS by L-Leu. ALS from one of the two CS-resistant variants (CSR6) had a Ki for L-Leu an order of magnitude greater than that of the wild-type enzyme. The alterations in kinetic properties observed in the ALS from sulfonylurea-resistant variants are discussed in relation to the possible evolutionary significance of the herbicide binding site of this enzyme, the physiological effects of such biochemical alterations, and their practical utility in genetic studies.ALS3 (EC 4.1.3.18, also known as acetohydroxy acid synthase) is the first enzyme in the biosynthesis of Val, Leu, and Ile. This enzyme catalyzes the condensation of an acetaldehyde moiety derived from pyruvate either with another molecule of pyruvate to form 2-acetolactate or with 2-ketobutyrate to form 2-aceto-2-hydroxybutyrate.ALS is feedback inhibited by the end products Val and Leu in both micro-organisms and in plants (5,11,26). Recently, it has been discovered that ALS is the target of several structurally diverse herbicidal compounds such as SUs, IZs, and TPs (9,16,22,24). The In our laboratory, a number of SU-resistant and IZ-resistant variants of Datura innoxia have been isolated, and ALS from these variants exhibits different degrees of cross-resistance to SUs and IZs. The lack of cross-resistance in some of the variants has been used to support the hypothesis that there are two separable binding domains for SUs and IZs on the ALS molecule (18,19). ALS from several of these variants has also been found to be altered in feedback sensitivity to Val, Leu, and Ile (14). In this report, the properties of ALS from SU-resistant variants are compared with that ofthe wild type. We report the mechanism of inhibition of ALS from D. innoxia by the feedback inhibitor, Leu. The implications of the altered kinetic constants of the ALS from SU-resistant variants are discussed in relation to our current understanding of the herbicide binding site of ALS and the regulation of branched-chain amino acid biosynthesis in higher plants. MATERIALS AND METHODS Cell Suspension CulturesMaintenance and isolation of SU-resistant cell variants of Datura innoxia from a predominantly haploid (>90%) cell culture we...

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“…However, in contrast to microorganisms, for purified KARI from higher plants no data with respect to inhibition by the experimental herbicides Hoe 704 or IpOHA are available. Because of the dramatic difference in herbicidal potency between ALS inhibitors (2-75 g ha-' in the case of sulfonylureas) and Hoe 704 and IpOHA (approximately 2000 g ha-'; Schloss, 1989a), it appeared necessary to investigate more closely the inhibition behavior of purified plant KARI. Additionally, values of both substrate affinity and inhibition by Hoe 704 strongly depend on the extent of purification of KARI (Dumer et al, 1993).…”

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confidence: 99%

Ketol-Acid Reductoisomerase from Barley (Hordeum vulgare) (Purification, Properties, and Specific Inhibition)

1993

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Ketol-acid reductoisomerase (KARI, EC 1.1.1.86) was purified to homogeneity from etiolated barley shoots (Hordeum vulgare) using anion exchange, Red-Sepharose, hydrophobic interaction, and chromatofocusing steps. Purification yielded 0.25 to 0.27 mg of pure KARl per 100 g fresh weight of starting material. l h e specific activity of the purified enzyme was 6 pmol of NADPH oxidized min-' mg-' with acetohydroxybutyrate as substrate. The native enzyme had an apparent molecular weight of 115,000 as estimated by gel filtration and appeared to be a homodimer with a subunit molecular weight of 59,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. l h e K,,, values of the purified KARl for acetolactate, acetohydroxybutyrate, and NADPH (determined with acetohydroxybutyrate) were 11, 38, and 4.3 p~, respectively. l h e V,,, obtained with acetohydroxybutyrate was 1.8 pmol min-' mg-'; the corresponding value for acetolactate was 0.16 pmol min-' mg-'. l h e enzyme showed optimum activity at pH 7.5. When either acetolactate or acetohydroxybutyrate was used as substrate, the experimental herbicidal compound 2-dimethylphosphinoyl-2-hydroxyacetic acid inhibited the purified KARl in a time-dependent and reversible manner. l h e initial inhibition was strictly competitive. l h e inhibition constant values were 0.46 (using acetolactate as substrate) and 0.19 p~ (acetohydroxybutyrate), respectively.

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Origin of the herbicide binding site of acetolactate synthase

Cited by 176 publications

References 24 publications

A Mutation Causing Imidazolinone Resistance Maps to the Csr1 Locus of Arabidopsis thaliana

A Mutation Causing Imidazolinone Resistance Maps to the Csr1 Locus of Arabidopsis thaliana

Herbicide Resistance in Datura innoxia

Ketol-Acid Reductoisomerase from Barley (Hordeum vulgare) (Purification, Properties, and Specific Inhibition)

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