Discovery and biological characterization of a novel mesoionic insecticide fenmezoditiaz.

BACKGROUND: Many piercing-sucking insects have developed resistance or cross-resistance to many insecticides targeting insect neural nicotinic acetylcholine receptor (nAChR). Here we are aiming to present the discovery of a novel mesoionic insecticide, fenmezoditiaz, by BASF through structure-based drug design (SBDD) approaches. It has recently been added to the Insecticide Resistance Action Committee mode of classification (IRAC 4E). It is being developed for plant protection against piercing-sucking pests, especially rice hopper complex. RESULTS: The soluble acetylcholine binding protein (AChBP) from the sea slug Aplysia californica was modified using site-directed mutagenesis and based on putative aphid nAChR subunit sequences to create soluble insect-like AChBPs. Among them, insect-like ß1 AChBP and native aphid membrane preparation showed the highest correlated biochemical affinity toward structurally diverse ligands. This mutant AChBP was used to understand how insect nAChRs structurally interact with mesoionics, which was then utilized to design novel mesoionics including fenmezoditiaz. It is an excellent systemic insecticide with diverse application methods and has a broad insecticidal spectrum, especially against piercing/sucking insects. It lacks cross-resistance for neonicotinoid resistant plant hoppers. Field-collected brown plant hopper populations from Asian countries showed high susceptibility. CONCLUSIONS: Fenmezoditiaz is a systemic insecticide with a broad spectrum, lack of cross-resistance and it could be an additional tool for integrated pest management and insecticide resistance management, especially for the rice hopper complex. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A new herbicidal site of action: Cinmethylin binds to acyl-ACP thioesterase and inhibits plant fatty acid biosynthesis.

The prevalent occurrence of herbicide resistant weeds increases the necessity for new site of action herbicides for effective control as well as to relax selection pressure on the known sites of action. As a consequence, interest increased in the unexploited molecule cinmethylin as a new solution for the control of weedy grasses in cereals. Therefore, the mechanism of action of cinmethylin was reevaluated. We applied the chemoproteomic approach cellular Target Profiling™ from Evotec to identify the cinmethylin target in Lemna paucicostata protein extracts. We found three potential targets belonging to the same protein family of fatty acid thioesterases (FAT) to bind to cinmethylin with high affinity. Binding of cinmethylin to FAT proteins from Lemna and Arabidopsis was confirmed by fluorescence-based thermal shift assay. The plastid localized enzyme FAT plays a crucial role in plant lipid biosynthesis, by mediating the release of fatty acids (FA) from its acyl carrier protein (ACP) which is necessary for FA export to the endoplasmic reticulum. GC-MS analysis of free FA composition in Lemna extracts revealed strong reduction of unsaturated C18 as well as saturated C14, and C16 FAs upon treatment with cinmethylin, indicating that FA release for subsequent lipid biosynthesis is the primary target of cinmethylin. Lipid biosynthesis is a prominent target of different herbicide classes. To assess whether FAT inhibition constitutes a new mechanism of action within this complex pathway, we compared physiological effects of cinmethylin to different ACCase and VLCFA synthesis inhibitors and identified characteristic differences in plant symptomology and free FA composition upon treatment with the three herbicide classes. Also, principal component analysis of total metabolic profiling of treated Lemna plants showed strong differences in overall metabolic changes after cinmethylin, ACCase or VLCFA inhibitor treatments. Our results identified and confirmed FAT as the cinmethylin target and validate FAT inhibition as a new site of action different from other lipid biosynthesis inhibitor classes.

A single point mutation enhances hydroxynitrile synthesis by halohydrin dehalogenase.

The cyanide-mediated ring opening of epoxides catalyzed by halohydrin dehalogenases yields ß-hydroxynitriles that are of high interest for synthetic chemistry. The best studied halohydrin dehalogenase to date is the enzyme from Agrobacterium radiobacter, but this enzyme (HheC) exhibits only low cyanolysis activities. Sequence comparison between a pair of related halohydrin dehalogenases from Corynebacterium and Mycobacterium suggested that substitution of a threonine that interacts with the active site might be responsible for the higher cyanolytic activity of the former enzyme. Here we report that a variant of HheC in which this substitution (T134A) is adopted displays an up to 11-fold higher activity in cyanide-mediated epoxide ring-opening. The mutation causes removal of the hydrogen bond between residue 134 and the side chain O of the active site serine 132, which donates a hydrogen bond to the substrate oxygen. The mutation also increases dehalogenase rates with various substrates. Structural analysis revealed that the anion-binding site of the mutant enzyme remained unaltered, showing that the enhanced activity is due to altered interactions with the substrate oxygen rather than changes in the nucleophile binding site.

Quality matters: extension of clusters of residues with good hydrophobic contacts stabilize (hyper)thermophilic proteins.

Identifying determinant(s) of protein thermostability is key for rational and data-driven protein engineering. By analyzing more than 130 pairs of mesophilic/(hyper)thermophilic proteins, we identified the quality (residue-wise energy) of hydrophobic interactions as a key factor for protein thermostability. This distinguishes our study from previous ones that investigated predominantly structural determinants. Considering this key factor, we successfully discriminated between pairs of mesophilic/(hyper)thermophilic proteins (discrimination accuracy: ∼80%) and searched for structural weak spots in E. coli dihydrofolate reductase (classification accuracy: 70%).

A high heat of adsorption for hydrogen in magnesium formate.

The hydrogen adsorption and desorption properties of a microporous metal-organic framework, magnesium formate, are investigated. The material has channel-like pores of approximately 3.4 A diameter. The pore size is below the kinetic diameter of nitrogen and causes a breakdown of the linear relationship between maximum hydrogen uptake and specific surface area measured by nitrogen adsorption. From the experimental isotherms the isosteric heat of adsorption for hydrogen is calculated with very high accuracy over a wide range of surface coverage, up to 80 %. The isosteric heat of adsorption is 6.5-7 kJ mol(-1) which is one of the highest values ever observed over the whole range of surface coverage.

Structure determination of seven phases and solvates of Pigment Yellow 183 and Pigment Yellow 191 from X-ray powder and single-crystal data.

The crystal structures of two industrially produced laked yellow pigments, Pigment Yellow 183 [P.Y. 183, Ca(C16H10Cl2N4O7S2), alpha phase] and Pigment Yellow 191 [P.Y. 191, Ca(C17H13ClN4O7S2), alpha and beta phases], were determined from laboratory X-ray powder diffraction data. The coordinates of the molecular fragments of the crystal structures were found by means of real-space methods (simulated annealing) with the program DASH. The coordinates of the calcium ions and the water molecules were determined by combining real-space methods (DASH and MRIA) and repeated Rietveld refinements (TOPAS) of the partially finished crystal structures. TOPAS was also used for the final Rietveld refinements. The crystal structure of beta-P.Y. 183 was determined from single-crystal data. The alpha phases of the two pigments are isostructural, whereas the beta phases are not. All four phases exhibit a double-layer structure, built from nonpolar layers containing the C/N backbone and polar layers containing the calcium ions, sulfonate groups and water molecules. Furthermore, the crystal structures of an N,N-dimethylformamide solvate of P.Y. 183, and of P.Y. 191 solvates with N,N-dimethylformamide and N,N-dimethylacetamide were determined by single-crystal X-ray analysis.