Structureactivity relationships for a new family of sulfonylurea herbicides (original) (raw)
Related papers
Molecular Basis of Sulfonylurea Herbicide Inhibition of Acetohydroxyacid Synthase
Journal of Biological Chemistry, 2002
Acetohydroxyacid synthase (AHAS) (acetolactate synthase, EC 4.1.3.18) catalyzes the first step in branchedchain amino acid biosynthesis and is the target for sulfonylurea and imidazolinone herbicides. These compounds are potent and selective inhibitors, but their binding site on AHAS has not been elucidated. Here we report the 2.8 Å resolution crystal structure of yeast AHAS in complex with a sulfonylurea herbicide, chlorimuron ethyl. The inhibitor, which has a K i of 3.3 nM, blocks access to the active site and contacts multiple residues where mutation results in herbicide resistance. The structure provides a starting point for the rational design of further herbicidal compounds.
Elucidating the Specificity of Binding of Sulfonylurea Herbicides to Acetohydroxyacid Synthase
Biochemistry, 2005
Acetohydroxyacid synthase (AHAS, EC 2.2.1.6) is the target for the sulfonylurea herbicides, which act as potent inhibitors of the enzyme. Chlorsulfuron (marketed as Glean) and sulfometuron methyl (marketed as Oust) are two commercially important members of this family of herbicides. Here we report crystal structures of yeast AHAS in complex with chlorsulfuron (at a resolution of 2.19 Å), sulfometuron methyl (2.34 Å), and two other sulfonylureas, metsulfuron methyl (2.29 Å) and tribenuron methyl (2.58 Å). The structures observed suggest why these inhibitors have different potencies and provide clues about the differential effects of mutations in the active site tunnel on various inhibitors. In all of the structures, the thiamin diphosphate cofactor is fragmented, possibly as the result of inhibitor binding. In addition to thiamin diphosphate, AHAS requires FAD for activity. Recently, it has been reported that reduction of FAD can occur as a minor side reaction due to reaction with the carbanion/enamine of the hydroxyethyl-ThDP intermediate that is formed midway through the catalytic cycle. Here we report that the isoalloxazine ring has a bent conformation that would account for its ability to accept electrons from the hydroxyethyl intermediate. Most sequence and mutation data suggest that yeast AHAS is a high-quality model for the plant enzyme.
Crystal structure of yeast acetohydroxyacid synthase: a target for herbicidal inhibitors1
Journal of Molecular Biology, 2002
Acetohydroxyacid synthase (AHAS; EC 4.1.3.18) catalyzes the ®rst step in branched-chain amino acid biosynthesis. The enzyme requires thiamin diphosphate and FAD for activity, but the latter is unexpected, because the reaction involves no oxidation or reduction. Due to its presence in plants, AHAS is a target for sulfonylurea and imidazolinone herbicides. Here, the crystal structure to 2.6 A Ê resolution of the catalytic subunit of yeast AHAS is reported. The active site is located at the dimer interface and is near the proposed herbicide-binding site. The conformation of FAD and its position in the active site are de®ned. The structure of AHAS provides a starting point for the rational design of new herbicides.
Crystal structure of plant acetohydroxyacid synthase, the target for several commercial herbicides
The FEBS journal, 2017
Acetohydroxyacid synthase (AHAS, E.C. 2.2.1.6) is the first enzyme in the branched-chain amino acid biosynthesis pathway. Five of the most widely used commercial herbicides (i.e. sulfonylureas, imidazolinones, triazolopyrimidines, pyrimidinyl-benzoates and sulfonylamino-cabonyl-triazolinones) target this enzyme. Here we have determined the first crystal structure of a plantAHAS in the absence of any inhibitor (2.9 Å resolution) and itshows that the herbicide-binding site adopts a folded state even in the absence of an inhibitor. This is unexpected because the equivalent regions for herbicide bindingin uninhibited Saccharomyces cerevisiae AHAS crystal structures are either disordered,or adopt a different fold when the herbicide is not present. In addition, the structure provides anexplanation as to why some herbicides are more potent inhibitorsofArabidopsis thaliana AHAS compared to AHASs from other species (e.g.Saccharomyces cerevisiae). The elucidation of the native structure of pl...
Herbicide-binding sites revealed in the structure of plant acetohydroxyacid synthase
Proceedings of the National Academy of Sciences, 2006
The sulfonylureas and imidazolinones are potent commercial herbicide families. They are among the most popular choices for farmers worldwide, because they are nontoxic to animals and highly selective. These herbicides inhibit branched-chain amino acid biosynthesis in plants by targeting acetohydroxyacid synthase (AHAS, EC 2.2.1.6). This report describes the 3D structure of Arabidopsis thaliana AHAS in complex with five sulfonylureas (to 2.5 Å resolution) and with the imidazolinone, imazaquin (IQ; 2.8 Å). Neither class of molecule has a structure that mimics the substrates for the enzyme, but both inhibit by blocking a channel through which access to the active site is gained. The sulfonylureas approach within 5 Å of the catalytic center, which is the C2 atom of the cofactor thiamin diphosphate, whereas IQ is at least 7 Å from this atom. Ten of the amino acid residues that bind the sulfonylureas also bind IQ. Six additional residues interact only with the sulfonylureas, whereas there...
Acta Crystallographica Section D Biological Crystallography, 2003
Acetohydroxyacid synthase (AHAS; EC 2.2.1.6) catalyses the formation of 2-acetolactate and 2-aceto-2-hydroxybutyrate as the ®rst step in the biosynthesis of the branched-chain amino acids valine, leucine and isoleucine. The enzyme is inhibited by a wide range of substituted sulfonylureas and imidazolinones and many of these compounds are used as commercial herbicides. Here, the crystallization and preliminary X-ray diffraction analysis of the catalytic subunit of Arabidopsis thaliana AHAS in complex with the sulfonylurea herbicide chlorimuron ethyl are reported. This is the ®rst report of the structure of any plant protein in complex with a commercial herbicide. Crystals diffract to 3.0 A Ê resolution, have unitcell parameters a = b = 179.92, c = 185.82 A Ê and belong to space group P6 4 22. Preliminary analysis indicates that there is one monomer in the asymmetric unit and that these are arranged as pairs of dimers in the crystal. The dimers form a very open hexagonal lattice, with a high solvent content of 81%.
Biochemistry, 2010
O-Acetylserine sulfhydrylase is a pyridoxal 5 0 -phosphate (PLP)-dependent enzyme that catalyzes the final step in the cysteine biosynthetic pathway in enteric bacteria and plants, the replacement of the βacetoxy group of O-acetyl-L-serine (OAS) by a thiol to give L-cysteine. Previous studies of the K41A mutant enzyme showed L-methionine bound in an external Schiff base (ESB) linkage to PLP as the enzyme was isolated. The mutant enzyme exists in a closed form, optimizing the orientation of the cofactor PLP and properly positioning active site functional groups for reaction. The trigger for closing the active site upon formation of the ESB is thought to be interaction of the substrate R-carboxylate with the substrate-binding loop comprised of T68, S69, G70, and N71, and Q142, which is positioned above the cofactor as one looks into the active site. To probe the contribution of these residues to the active site closing and orientation of PLP in the ESB, T68, S69, N71, and Q142 were changed to alanine. Absorbance, fluorescence, near UV-visible CD, and 31 P NMR spectral studies and pre-steady state kinetic studies were used to characterize the mutant enzymes. All of the mutations affect closure of the active site, but to differing extents. In addition, the site appears to be more hydrophilic given that the ESBs do not exhibit a significant amount of the enolimine tautomer. No buildup of the R-aminoacrylate intermediate (AA) is observed for the T68A and Q142A mutant enzymes. However, pyruvate is produced at a rate much greater than that of the wild-type enzyme. Data suggest that T68 and Q142 play a role in stabilizing the AA. Both residues donate a hydrogen bond to one of the carboxylate oxygens of the methionine ESB and may also be responsible for the proper orientation of the ESB to generate the AA. The S69A and N71A mutants exhibit formation of the AA, but the rate constant for its formation from the ESB is decreased by 1 order of magnitude compared to that of the wild type. S69 donates a hydrogen bond to the substrate carboxylate in the ESB, while N71 donates hydrogen bonds to O3 0 of the cofactor and the carboxylate of the ESB; these side chains may also affect the orientation of the ESB. Data suggest that interaction of intermediates with the substrate-binding loop and Q142 gives a properly aligned Michaelis complex and facilitates the β-elimination reaction.
Design of O -Acetylserine Sulfhydrylase Inhibitors by Mimicking Nature
Journal of Medicinal Chemistry, 2010
The inhibition of cysteine biosynthesis in prokaryotes and protozoa has been proposed to be relevant for the development of antibiotics. Haemophilus influenzae O-acetylserine sulfhydrylase (OASS), catalyzing L-cysteine formation, is inhibited by the insertion of the C-terminal pentapeptide (MNLNI) of serine acetyltransferase into the active site. 400 MNXXI pentapeptides were generated, docked into OASS active site using GOLD and scored with HINT. The terminal P5 Ile accounts for about 50% of the binding energy. Glu or Asp at position P4, and to a lesser extent, at position P3, also significantly contribute to the binding interaction. The predicted affinity of 14 selected pentapeptides correlated well with the experimentally determined dissociation constants. The X-ray structure of three high affinity pentapeptides-OASS complexes were compared with the docked poses. These results, combined with a GRID analysis of the active site, allowed us to define a pharmacophoric scaffold for the design of peptidomimetic inhibitors.