Three-dimensional structures of Drosophila melanogaster acetylcholinesterase and of its complexes with two potent inhibitors

Drosophila melanogaster as a model organism for screening acetylcholinesterase reactivators

The widely used insecticide chlorpyrifos (CP) is known to inhibit acetylcholinesterase (AChE) activity attributed to result in various neurological disorders and acetylcholine-dependent organ functions including heart, skeletal muscle, lung, gastrointestinal tract, and central nervous systems. Enzyme reactivators, such as oximes, are known to restore AChE activity and mitigate adverse effects. The identification of compounds that reactivate AChE constitute agents with important therapeutic beneficial effects in cases of pesticide poisoning. However, the screening of novel drugs using traditional models may raise ethical concerns. This study aimed to investigate the potential of Drosophila melanogaster as a model organism for screening AChE reactivators, with a focus on organophosphate poisoning. The efficacy of several oximes, including pralidoxime, trimedoxime, obidoxime, methoxime, HI-6, K027, and K048, against CP-induced AChE activity inhibition in D. melanogaster was determined in silico, in vitro, and in vivo experiments. Molecular docking studies indicated a strong interaction between studied oximes and the active-site gorge of AChE. Data showed that selected oximes (100 μM) are effective in the reactivation of AChE inhibited by CP (10 μM) in vitro. Finally, in vivo investigations demonstrated that selected oximes, pralidoxime and K048 (1.5 ppm), reversed the locomotor deficits, inhibition of AChE activity as well as lowered the mortality rates induced by CP (0.75 ppm). Our findings contribute to utilization of D. melanogaster as a robust model for determination of actions of identified new AChE inhibitory agents with more effective therapeutic properties that those currently in use in the clinical practice in treatment of AChE associated disorders.

Comparative toxicity and enzymatic detoxification responses in Spodoptera frugiperda (Lepidoptera: Noctuidae) to two insecticides

The fall armyworm (FAW), Spodoptera frugiperda Smith (Lepidoptera: Noctuidae), poses a significant threat to food security, necessitating effective management strategies. While chemical control remains a primary approach, understanding the toxicity and detoxification mechanisms of different insecticides is crucial. In this study, we conducted leaf-dipping bioassays to assess the toxicity of quinalphos and beta-cypermethrin·emamectin benzoate (β-cyp·EMB) on S. frugiperda larvae. Additionally, we assessed the response of alterations in CarE, GST, MFO, and AChE activities to sublethal concentrations of these insecticides over various treatment durations. Results indicated that β-cyp·EMB exhibited higher toxicity than quinalphos in S. frugiperda. Interestingly, the highest activities of GST, CarE, MFO, and AChE were observed at 6 h exposure to LC10 and LC25 of β-cyp·EMB, surpassing equivalent sublethal concentrations of quinalphos. Subsequently, GST and CarE activities exposure to β-cyp·EMB steadily decreased, while MFO and AChE activities exposure to both insecticides was initially decreased then increased. Conversely, two sublethal concentrations of quinalphos notably enhanced GST activity across all exposure durations, with significantly higher than β-cyp·EMB at 12-48 h. Similarly, CarE activity was also increased at various durations. Our research has exhibited significant alterations in enzyme activities exposure to both concentration and duration. Furthermore, Pearson correlation analysis showed significant correlations among these enzyme activities at different treatment durations. These findings contribute to a better understanding of detoxification mechanisms across different insecticides, providing valuable insights for the rational management of S. frugiperda populations.

Sequence analysis, homology modeling, tissue expression, and potential functions of seven putative acetylcholinesterases in the spider Cupiennius salei

Acetylcholine esterases (AChEs) are essential enzymes in cholinergic synapses, terminating neurotransmission by hydrolysing acetylcholine. While membrane bound AChEs at synaptic clefts efficiently perform this task, soluble AChEs are less stable and effective, but function over broader areas. In vertebrates, a single gene produces alternatively spliced forms of AChE, whereas invertebrates often have multiple genes, producing both enzyme types. Despite their significance as pesticide targets, the physiological roles of invertebrate AChEs remain unclear. Here, we characterized seven putative AChEs in the wandering spider, Cupiennius salei, a model species for neurophysiological studies. Sequence analyses and homology modeling predicted CsAChE7 as the sole stable, membrane-bound enzyme functioning at synaptic clefts, while the others are likely soluble enzymes. In situ hybridization of sections from the spider's nervous system revealed CsAChE7 transcripts co-localizing with choline acetyltransferase in cells that also exhibited AChE activity. CsAChE7 transcripts were also found in rapidly adapting mechanosensory neurons, suggesting a role in precise and transient activation of postsynaptic cells, contrasting with slowly adapting, also cholinergic, neurons expressing only soluble AChEs, which allow prolonged activation of postsynaptic cells. These findings suggest that cholinergic transmission is influenced not only by postsynaptic receptors but also by the enzymatic properties regulating acetylcholine clearance. We also show that acetylcholine is a crucial neurotransmitter in the spider's visual system and sensory and motor pathways, but absent in excitatory motor neurons at neuromuscular junctions, consistent with other arthropods. Our findings on sequence structures may have implications for the development of neurological drugs and pesticides.

Lemongrass essential oil and its major component citronellol: evaluation of larvicidal activity and acetylcholinesterase inhibition against Anopheles sinensis

Mosquito-borne diseases, such as malaria, dengue fever, and the Zika virus, pose significant global health challenges, affecting millions annually. Due to increasing insecticide resistance, there is a growing interest in natural alternatives for mosquito control. Lemongrass essential oil, derived from Cymbopogon citratus, has shown promising repellent and larvicidal properties against various mosquito species. In this study, we investigated the larvicidal effect of lemongrass oil and its major compounds on Anopheles sinensis, the primary malaria vector in China. GC-MS analysis identified the major compounds of lemongrass oil as ( +)-citronellal (35.60%), geraniol (21.84%), and citronellol (13.88%). Lemongrass oil showed larvicidal activity against An. sinensis larvae, with an LC50 value of 119.20 ± 3.81 mg/L. Among the major components, citronellol had the lowest LC50 value of 42.76 ± 3.18 mg/L. Moreover, citronellol demonstrated inhibitory effects on acetylcholinesterase (AChE) activity in An. sinensis larvae, assessed by homogenizing larvae at different time points following treatment. Molecular docking studies further elucidated the interaction between citronellol and AChE, revealing the formation of hydrogen bonds and Pi-Sigma bonds. Aromatic amino acid residues such as Tyr71, Trp83, Tyr370, and Tyr374 played a pivotal role in these interactions. These findings may contribute to understanding lemongrass oil's larvicidal activity against An. sinensis and the mechanisms underlying these effects.

Analysis of Chemical Composition, Antioxidant Activity, and Toxicity of Essential Oil from Virola sebifera Aubl (Myristicaceae)

Volatile oils or essential oils (EOs) were extracted from three V. sebifera samples (labeled as A, B, and C) in September 2018 and February 2019; the extraction process involved hydrodistillation of the leaves. The chemical compositions of the EOs were analyzed using gas chromatography-mass spectrometry (GC/MS). The volatile components were identified by comparing their retention indices and mass spectra with standard substances documented in the literature (ADAMS). The antioxidant activity of the EOs was evaluated using 2, 2-diphenyl-1-picrylhydrazyl (DPPH), while their toxicity was assessed using Artemia salina Leach. Molecular docking was utilized to examine the interaction between the major constituents of V. sebifera EO and acetylcholinesterase (AChE), a molecular target linked to toxicity in A. salina models. The EO obtained from specimen A, collected in September 2018, was characterized by being primarily composed of (E,E)-α-farnesene (47.57%), (E)-caryophyllene (12.26%), and α-pinene (6.93%). Conversely, the EO from specimen A, collected in February 2019, was predominantly composed of (E,E)-α-farnesene (42.82%), (E)-caryophyllene (16.02%), and bicyclogermacrene (8.85%), the EO from specimen B, collected in September 2018, primarily contained (E,E)-α-farnesene (47.65%), (E)-caryophyllene (19.67%), and α-pinene (11.95%), and the EO from the leaves collected in February 2019 was characterized by (E,E)-α-farnesene (23.57%), (E)-caryophyllene (19.34%), and germacrene D (7.33%). The EO from the leaves collected in September 2018 contained (E,E)-α-farnesene (26.65%), (E)-caryophyllene (15.7%), and germacrene D (7.72%), while the EO from the leaves collected in February 2019 was primarily characterized by (E,E)-α-farnesene (37.43%), (E)-caryophyllene (21.4%), and α-pinene (16.91%). Among these EOs, sample B collected in February 2019 demonstrated the highest potential for inhibiting free radicals, with an inhibition rate of 34.74%. Conversely, the EOs from specimen A exhibited the highest toxic potentials, with an lethal concentration 50 (LC50) value of 57.62 ± 1.53 µg/mL, while specimen B had an LC50 value of 74.72 ± 2.86 µg/mL. Molecular docking results suggested that hydrophobic interactions significantly contributed to the binding of the major compounds in the EO from sample B to the binding pocket of AChE.

Identification of a Novel Inhibitor of Cimex lectularius Acetylcholinesterase

Acetylcholinesterase (AChE) stands as a primary target of commercial insecticides, notably organophosphates and carbamates. Despite their widespread use in agricultural and indoor pest control, concerns over their high toxicity and the emergence of resistance have restricted their efficacy. In this study, we conducted high-throughput virtual screening against both wild-type (WT) and resistant Cimex lectularius AChE utilizing a library encompassing 1 270 000 compounds. From this screening, we identified 100 candidate compounds and subsequently assessed their inhibitory effects on purified AChE enzymes. Among these candidates, AE027 emerged as a potent inhibitor against both WT and resistant AChE, exhibiting IC50 values of 10 and 43 μM, respectively. Moreover, the binding of AE027 significantly stabilized AChE, elevating its melting temperature by approximately 7 °C. Through molecular docking and molecular dynamics simulation, we delineated the binding mode of AE027, revealing its interaction with a site adjacent to the catalytic center, which is distinct from known inhibitors, with differing poses observed between WT and resistant AChE. Notably, the resistance mutation F348Y, positioned at a site directly interfacing with AE027, impedes ligand binding through steric hindrance. Furthermore, we evaluated the toxicity and pharmacokinetic properties of AE027 utilizing bioinformatics tools. These findings lay a crucial foundation for the development of a novel generation of insecticides that can combat both WT and resistant pest populations effectively and safely.

Exploring the Larvicidal and Adulticidal Activity against Aedes aegypti of Essential Oil from Bocageopsis multiflora

This study investigates the chemical composition of the essential oil obtained from the leaves of Bocageopsis multiflora (Mart.) R.E.Fr (Annonaceae), examining its effectiveness in combating both the larvae and adult forms of Aedes aegypti mosquitoes. Additionally, for a deeper understanding of the insecticidal activity, toxicity properties and molecular docking calculations were conducted using the main compounds of this essential oil. GC/MS analysis revealed the presence of 26 constituents, representing 95.2% of the essential oil, with the major components identified as the sesquiterpenes α-selinene, β-selinene, and β-elemene. Larvicidal assays demonstrated potent activity of this essential oil with significant LC50 values of 40.8 and 39.4 μg/mL at 24 and 48 h, respectively. Adulticidal assessments highlighted strong efficacy with LC50 of 12.5 µg/mL. Molecular docking analysis identified optimal interaction activities of α-selinene and β-selinene with key Aedes proteins. The in silico studies comparing synthetic insecticides with the major sesquiterpenes of the essential oil revealed that β-selinene exhibited a significantly higher binding affinity compared to the other two sesquiterpenes. Also, ADMET studies of the three main sesquiterpenes indicated acceptable drug-like properties. In these findings, safety evaluations showed low toxicity and skin sensitization for the main sesquiterpenes, contrasting with commercial synthetic insecticides. Therefore, in silico analyses suggest promising interactions with Aedes proteins, indicating its potential as an effective alternative to conventional insecticides These results show the larvicidal and adulticidal potential of the essential oil from Bocageopsis multiflora against Aedes aegypti, supported by its predominant constituents, α-selinene, β-selinene and β-elemene.

Connectivity between surface and interior in catalytic subunits of acetylcholinesterases inferred from their X-ray structures

Catalytic activity and function of acetylcholinesterase (AChE; EC 3.1.1.7) have been recognized and studied for over a century and its quaternary and primary structures for about half a century, and its tertiary structure has been known for about 33 years. Clear understanding of relationships between the structure and the function is still pending for this enzyme. Hundreds of crystallographic, static snapshots of AChEs from different sources reveal largely one general backbone conformation with narrow entry into the active center gorge, tightly fit to accept one acetylcholine (ACh) molecule, in contrast to its high catalytic turnover. This short review of available X-ray structures of AChEs from electric ray Torpedo californica, mouse and human, finds some limited, yet consistent deviations in conformations of selected secondary structure elements of AChE relevant for its function. The observed conformational diversity of the acyl pocket loop of AChE, unlike the large Ω-loop, appears consistent with structurally dynamic INS data and solution-based SAXS experiments to explain its dominant role in controlling the size of the active center gorge opening, as well as connectivity between the immediate surroundings of the buried active Ser, and catalytically relevant sites on the AChE surface.

Noncovalent binding of carbofuran to acetylcholinesterase from Homo sapiens, Danio rerio, Apis mellifera and Caenorhabditis elegans: Homology modelling, molecular docking and dynamics, and quantum biochemistry description

Although various regulatory agencies have banned or severely restricted the use of carbofuran (CAR), recent reports indicate the presence of CAR residues in both cultivated and wild areas. This pesticide is a potent inhibitor of acetylcholinesterase (AChE), which acts by preventing the hydrolysis of acetylcholine (ACh). Given the critical role of AChE::ACh in the proper functioning of the nervous system, we thought it appropriate to investigate the binding of CAR to AChEs from Homo sapiens, Danio rerio, Apis mellifera, and Caenorhabditis elegans using homology modelling, molecular docking, molecular dynamics, and quantum biochemistry. Molecular docking and dynamics results indicated peculiar structural behavior in each AChE::CAR system. Quantum biochemistry results showed similar affinities for all complexes, confirming the description of carbofuran as a broad-spectrum pesticide, and have a limited correlation with IC50 values. We found the following decreasing affinity order of AChE species: H. sapiens > A. mellifera > C. elegans > D. rerio. The computational results suggest that CAR occupies different pockets in the AChEs studied. In addition, our results showed that CAR binds to hsAChE and ceAChE in a very similar manner: it has high affinities for the same subsites in both species and forms hydrogen bonds with residues (hsTYR124 and ceTRP107) occupying homologous positions in the peripheral site. This suggests that this nematode is a potential model to evaluate the toxicity of carbamates, even though the sequence identity between them is only 41 %. Interestingly, we also observed that the catalytic histidines of drAChE and amAChE exhibited favorable contacts with carbofuran, suggesting that the non-covalent binding of carbofuran to these proteins may promote faster carbamylation rates than the binding modes to human and worm acetylcholinesterases. Our computational results provide a better understanding of the binding mechanisms in these complexes, as well as new insights into the mechanism of carbamylation.

Involvement of functional senescence in efavirenz-induced toxicity in fruit fly

Background

We aimed in this article to assess the likeliness of efavirenz to induce functional senescence in Drosophila melanogaster (fruit fly).

Methods

Ten different concentrations of EFV were mixed with fly food and fed to 3-day-old flies orally for a 7 day LC50 calculation. Drug concentrations from LC50 were selected for a 28 day survival to determine the duration of treatment for behavioral and biochemical assays. A 5day feeding plan was used to investigate the effects of the drug on organismal, neuromuscular, reproductive, and metabolic senescence. An in silico study was executed to decipher a molecular interaction of Drosophila enzymes glutathione-s-transferase (GST) or acetylcholinesterase (AChE) with EFV.

Results

The calculated LC50 of EFV was 118 mg/10-g fly diet. The test drug induced a significant (P < 0.05) increase in fly mortality, climbing difficulty, and procreative deficits after a 5 day oral exposure. Similarly, there were significant (P < 0.05) biochemical alterations, which suggested in vivo biochemical damage against total thiols (T-SH), SOD (superoxide dismutase), CAT (catalase), GST, AChE, and MDA (malondialdehyde) in the test flies compared to the control groups. In silico study revealed a significantly (P < 0.05) higher binding energy between EFV and the active amino acids of fly AChE and GST when compared to the substrates or standard inhibitors respectively.

Conclusion

EFV exhibited ecotoxic potentials evidenced by age-related deficits in the fly's functional integrity such as sluggish movement, procreative deficiency, increased mortality, and oxidant-antioxidant inequality. Results from in silico study suggested antagonism against GST and AChE activities as a likely mechanism of EFV-induced toxicity in the fruit fly.

A chromosome-scale genome assembly of the grape powdery mildew pathogen Erysiphe necator reveals its genomic architecture and previously unknown features of its biology

Erysiphe necator is an obligate fungal pathogen that causes grape powdery mildew, globally the most important disease on grapevines. Previous attempts to obtain a quality genome assembly for this pathogen were hindered by its high repetitive DNA content. Here, chromatin conformation capture (Hi-C) with long-read PacBio sequencing was combined to obtain a chromosome-scale assembly and a high-quality annotation for E. necator isolate EnFRAME01. The resulting 81.1 Mb genome assembly is 98% complete and consists of 34 scaffolds, 11 of which represent complete chromosomes. All chromosomes contain large centromeric-like regions and lack synteny to the 11 chromosomes of the cereal PM pathogen Blumeria graminis. Further analysis of their composition showed that repeats and transposable elements (TEs) occupy 62.7% of their content. TEs were almost evenly interspersed outside centromeric and telomeric regions and massively overlapped with regions of annotated genes, suggesting that they could have a significant functional impact. Abundant gene duplicates were observed as well, particularly in genes encoding candidate secreted effector proteins. Moreover, younger in age gene duplicates exhibited more relaxed selection pressure and were more likely to be located physically close in the genome than older duplicates. A total of 122 genes with copy number variations among six isolates of E. necator were also identified and were enriched in genes that were duplicated in EnFRAME01, indicating they may reflect an adaptive variation. Taken together, our study illuminates higher-order genomic architectural features of E. necator and provides a valuable resource for studying genomic structural variations in this pathogen. IMPORTANCE Grape powdery mildew caused by the ascomycete fungus Erysiphe necator is economically the most important and recurrent disease in vineyards across the world. The obligate biotrophic nature of E. necator hinders the use of typical genetic methods to elucidate its pathogenicity and adaptation to adverse conditions, and thus comparative genomics has been a major method to study its genome biology. However, the current reference genome of E. necator isolate C-strain is highly fragmented with many non-coding regions left unassembled. This incompleteness prohibits in-depth comparative genomic analyses and the study of genomic structural variations (SVs) that are known to affect several aspects of microbial life, including fitness, virulence, and host adaptation. By obtaining a chromosome-scale genome assembly and a high-quality gene annotation for E. necator, we reveal the organization of its chromosomal content, unearth previously unknown features of its biology, and provide a reference for studying genomic SVs in this pathogen.

In Vitro and Molecular Docking Evaluation of Larvicidal Effects of Essential Oils of Five Aromatic Plants on the Fall Armyworm Spodoptera frugiperda JE. Smith (Lepidoptera: Noctuidae) from Ivory Coast

Faced with the serious consequences resulting from the abusive and repeated use of synthetic chemicals, today rethinking crop protection is more than necessary. It is in this context that the essential oils of the Lamiaceae Ocimum gratissimum and Ocimum canum, the Poaceae Cymbopogon citratus and nardus and a Rutaceae Citrus sp. of known chemical compositions were experimented. The evaluation of the larvicidal potential of the essential oils was done by the method of topical application of the test solutions, on the L1-L2 stage larvae from the first generation of S. frugiperda obtained after rearing in an air-conditioned room. Lethal concentrations (LC10 , LC50 and LC90 ) were determined after 48 h. After assessing the larvicidal potential of essential oils, molecular docking was carried out to study protein-ligand interactions and their propensity to bind to insect enzyme sites (AChE). The essential oil of O. gratissimum was the most effective with the lowest lethal concentrations (LC10 =0.91 %, LC50 =1.91 % and LC90 =3.92 %). The least toxic oil to larvae was Citrus sp. (LC10 =5.44 %, LC50 =20.50 % and LC90 =77.41 %). Molecular docking revealed that p-cymene and thymol from O. gratissimum essential oil are structurally similar and bind to the AChE active site via predominantly hydrophobic interactions and a H-bond with Tyr374 in the case of thymol. The essential oil of O. gratissimum constitutes a potential candidate for the development of biological insecticides for the fight against insect pests and for the protection of the environment.

Structure of an antennally-expressed carboxylesterase suggests lepidopteran odorant degrading enzymes are broadly tuned

Insects rely on the detection of chemical cues present in the environment to guide their foraging and reproductive behaviour. As such, insects have evolved a sophisticated chemical processing system in their antennae comprised of several types of olfactory proteins. Of these proteins, odorant degrading enzymes are responsible for metabolising the chemical cues within the antennae, thereby maintaining olfactory system function. Members of the carboxyl/cholinesterase gene family are known to degrade odorant molecules with acetate-ester moieties that function as host recognition cues or sex pheromones, however, their specificity for these compounds remains unclear. Here, we evaluate expression levels of this gene family in the light-brown apple moth, Epiphyas postvittana, via RNAseq and identify putative odorant degrading enzymes. We then solve the apo-structure for EposCCE24 by X-ray crystallography to a resolution of 2.43 Å and infer substrate specificity based on structural characteristics of the enzyme's binding pocket. The specificity of EposCCE24 was validated by testing its ability to degrade biologically relevant and non-relevant sex pheromone components and plant volatiles using GC-MS. We found that EposCCE24 is neither capable of discriminating between linear acetate-ester odorant molecules of varying chain length, nor between molecules with varying double bond positions. EposCCE24 efficiently degraded both plant volatiles and sex pheromone components containing acetate-ester functional groups, confirming its role as a broadly-tuned odorant degrading enzyme in the moth olfactory organ.

Insecticidal activity of essential oils from American native plants against Aedes aegypti (Diptera: Culicidae): an introduction to their possible mechanism of action

Searching for new bioactive molecules to design insecticides is a complex process since pesticides should be highly selective, active against the vector, and bio-safe for humans. Aiming to find natural compounds for mosquito control, we evaluated the insecticidal activity of essential oils (EOs) from 20 American native plants against Aedes aegypti larvae using bioassay, biochemical, and in silico analyses. The highest larvicide activity was exhibited by EOs from Steiractinia aspera (LC₅₀ = 42.4 µg/mL), Turnera diffusa (LC₅₀ = 70.9 µg/mL), Piper aduncum (LC₅₀ = 55.8 µg/mL), Lippia origanoides (chemotype thymol/carvacrol) (LC₅₀ = 61.9 µg/mL), L. origanoides (chemotype carvacrol/thymol) (LC₅₀ = 59.8 µg/mL), Hyptis dilatata (LC₅₀ = 61.1 µg/mL), Elaphandra quinquenervis (LC₅₀ = 61.1 µg/mL), and Calycolpus moritzianus (LC₅₀ = 73.29 µg/mL) after 24 h. This biological activity may be related to the disruption of the electron transport chain through the mitochondrial protein complexes. We hypothesized that the observed EOs' effect is due to their major components, where computational approaches such as homology modeling and molecular docking may suggest the possible binding pose of secondary metabolites that inhibit the mitochondrial enzymes and acetylcholinesterase activity (AChE). Our results provided insights into the possible mechanism of action of EOs and their major compounds for new insecticide designs targeting the mitochondria and AChE activity in A. aegypti for effective and safe insecticide.

Dynamic Roles of Insect Carboxyl/Cholinesterases in Chemical Adaptation

Insects have evolved several intricate defense mechanisms to adapt to their chemical environment. Due to their versatile capabilities in hydrolytic biotransformation, insect carboxyl/cholinesterases (CCEs) play vital roles in the development of pesticide resistance, facilitating the adaptation of insects to their host plants, and manipulating insect behaviors through the olfaction system. CCEs confer insecticide resistance through the mechanisms of qualitative or quantitative changes of CCE-mediated enhanced metabolism or target-site insensitivity, and may contribute to the host plant adaptation. CCEs represent the first odorant-degrading enzymes (ODEs) discovered to degrade insect pheromones and plant odors and remain the most promising ODE candidates. Here, we summarize insect CCE classification, currently characterized insect CCE protein structure characteristics, and the dynamic roles of insect CCEs in chemical adaptation.

Jatamansinol from Nardostachys jatamansi: a multi-targeted neuroprotective agent for Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial progressive and irreversible neurodegenerative disorder characterized by severe memory impairment and cognitive disability in the middle and old-aged human population. There are no proven drugs for AD treatment and prevention. In Ayurveda, medhya plants are used to prepare Rasayana, and its consumption improves memory and cognition. Nardostachys jatamansi (D.Don) DC is a medhya plant used in traditional medicine to treat neurological disorders, and its unique pyranocoumarins can be a potential drug candidate for AD. Given its traditional claims, this study aims to find the multi-target potential efficacy of the ligands (drug molecules) against the AD from N. jatamansi pyranocoumarins using computational drug discovery techniques. Drug likeliness analysis confirms that pyranocoumarins of N. jatamansi, such as seselin, jatamansinol, jatamansine, jatamansinone, and dihydrojatamansin are probable drug candidates for AD. Molecular docking, molecular dynamic simulations, and Molecular Mechanics/Generalized Born Surface Area (MM-GBSA) analysis confirm that dihydrojatamansin inhibits acetylcholinesterase (AChE), and jatamansinol inhibits butyrylcholinesterase (BuChE), glycogen synthase kinase 3β (GSK3β), and kelch-like ECH-associating protein 1 (Keap1) AD therapeutic targets. Therefore, this study provides potential multi-target inhibitors that would further validate experimental studies, leading to new treatments for AD.Communicated by Ramaswamy H. Sarma.

Structural fractal analysis of the active sites of acetylcholinesterase from various organisms

Acetylcholinesterase (AChE) is the object of many studies due to the fact that it plays an important role in the vital activity of organisms. In particular, when new AChE inhibitors are developed, much attention is paid to the specificity of their action. One of the approaches used to study the specificity is to compare AChE taken from various organisms. In this work, crystallographic data are used to investigate the active sites of AChE (ASAs) in the free (uncomplexed) state for the following five organisms: Homo sapiens (HS), Mus musculus (MM), Torpedo californica (TC), Electrophorus electricus (EE), and Drosophila melanogaster (DM). The structural fractal analysis (SFA) proposed by us earlier is used as a research method. This method is based on the calculation and comparison of the fractal dimensions of molecular structures. SFA demonstrates that there are no significant structural differences between the active sites of human AChE and other AChEs. However, differences are found for the MM/EE pair. Further analysis of individual AARs has revealed two different areas of active sites. Ser203, Trp236, Phe338, and Tyr341 are found to belong to a variable region, and the remaining AARs belong to a conservative region of the ASAs. The fraction of "variability" is low, 0.8%.

Non-covalent acetylcholinesterase inhibitors: In vitro screening and molecular modeling for novel selective insecticides

Insecticides represent the most crucial element in the integrated management approach to malaria and other vector-borne diseases. The evolution of insect resistance to long-used substances and the toxicity of organophosphates (OPs) and carbamates are the main factors contributing to the development of new, environmentally safe pesticides. In our work, fourteen compounds of 7-methoxytacrine-tacrine heterodimers were tested for their insecticidal effect. Compounds were evaluated in vitro on insect acetylcholinesterase from Anopheles gambiae (AgAChE) and Musca domestica (MdAChE). The evaluation was executed in parallel with testing on human erythrocyte acetylcholinesterase (HssAChE) and human butyrylcholinesterase (HssBChE) using a modified Ellman's method. Compound efficacy was determined as IC₅₀ values for the respective enzymes and selectivity indexes were expressed to compare the interspecies selectivity. Docking studies were performed to predict the binding modes of selected compounds. K1328 and K1329 provided high HssAChE/AgAChE selectivity outperforming standard pesticides (carbofuran and bendiocarb), and thus can be considered as suitable lead structure for novel anticholinesterase insecticides.

Screening for insecticide resistance in Australian field populations of Bemisia tabaci (Hemiptera: Aleyrodidae) using bioassays and DNA sequencing

BACKGROUND

Species within the Bemisia tabaci cryptic species complex can cause significant crop damage. We used high-throughput amplicon sequencing to identify the species composition and resistance allele genotypes in field populations from cotton fields in Australia. For selected populations, the resistance phenotype was determined in bioassays and compared with sequencing data.

RESULTS

A metabarcoding approach was used to analyse the species composition in 144 field populations collected between 2013 and 2021. Two mixed AUS I and MEAM1 populations were detected, whereas the remaining 142 populations consisted of MEAM1 only. High-throughput sequencing of organophosphate and pyrethroid resistance gene amplicons showed that the organophosphate resistance allele F331W was fixed (> 99%) in all MEAM1 populations, whereas the pyrethroid resistance allele L925I in the voltage-gated sodium channel gene was detected at varying frequencies [1.0%-7.0% (43 populations); 27.7% and 42.1% (two populations); 95%-97.5% (three populations)]. Neither organophosphate nor pyrethroid resistance alleles were detected in the AUS I populations. Pyrethroid bioassays of 85 MEAM1 field-derived populations detected no resistance in 51 populations, whereas 32 populations showed low frequency resistance, and 2 populations were highly resistant.

CONCLUSIONS

We demonstrate that high-throughput sequencing and bioassays are complementary approaches. The detection of target site mutations and the phenotypic provides a comprehensive analysis of the low-level resistance to pyrethroids that is present in Australian cotton farms. By contrast, a limited survey of whitefly populations from horticulture found evidence of high-level resistance against pyrethroids. Furthermore, we found that the F331W allele (linked to organophosphate resistance) is ubiquitous in Australian MEAM1. © 2022 Commonwealth of Australia. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Role of Bmal1 in mediating the cholinergic system to regulate the behavioral rhythm of nocturnal marine molluscs

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The circadian differential expression of AchE was identified using TMT quantitative proteomics;

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It was found that the Ach concentration and the expression levels of AchE and Bmal1 exhibit circadian cosine rhythm;

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The full-length sequences of AchE and nAchR were obtained by cloning technique and made available for phylogenetic analysis;

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The movement distance and duration of abalone increased after the injection of neostigmine methylsulfate as the AchE inhibitor;

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Bmal1 as the core circadian clock gene was proven to bind to AchE and nAchR, thereby regulating the movement behavior of abalone.

The circadian rhythm is one of the most general and important rhythms in biological organisms. In this study, continuous 24-h video recordings showed that the cumulative movement distance and duration of the abalone, Haliotis discus hannai, reached their maximum values between 20:00–00:00, but both were significantly lower between 08:00–12:00 than at any other time of day or night (P < 0.05). To investigate the causes of these diel differences in abalone movement behavior, their cerebral ganglia were harvested at 00:00 (group D) and 12:00 (group L) to screen for differentially expressed proteins using tandem mass tagging (TMT) quantitative proteomics. Seventy-five significantly different proteins were identified in group D vs. group L. The differences in acetylcholinesterase (AchE) expression levels between day- and nighttime and the key role in the cholinergic nervous system received particular attention during the investigation. A cosine rhythm analysis found that the concentration of acetylcholine (Ach) and the expression levels of AchE tended to be low during the day and high at night, and high during the day and low at night, respectively. However, the rhythmicity of the diel expression levels of acetylcholine receptor (nAchR) appeared to be insignificant (P > 0.05). Following the injection of three different concentrations of neostigmine methylsulfate, as an AchE inhibitor, the concentration of Ach in the hemolymph, and the expression levels of nAchR in the cerebral ganglia increased significantly (P < 0.05). Four hours after drug injection, the cumulative movement distance and duration of abalones were significantly higher than those in the uninjected control group, and the group injected with saline (P < 0.05). The expression levels of the core diurnal clock Bmal1 over a 24-h period also tended to be high during the day and low at night. First, a co-immunoprecipitation assay demonstrated the binding between Bmal1 and AchE or nAchR. A dual-luciferase gene test and electrophoretic mobility shift assay showed that Bmal1 bound to the promoter regions of AchE and nAchR. Twenty-four hours after silencing the Bmal1 gene, the expression levels of AchE and nAchR decreased significantly compared to those of the dsEGFP and PBS control groups, further showing that Bmal1 mediates the cholinergic system to regulate the behavioral rhythm of abalone. These findings shed light on the endocrine mechanism regulating the rhythmic behavior of abalone, and provide a reference for understanding the life history adaptation strategies of nocturnal organisms and the proliferation and protection of bottom dwelling economically important organisms.

Response of xenobiotic biodegradation and metabolic genes in Tribolium castaneum following eugenol exposure

Eugenol, a plant-derived component possessing small side effects, has an insecticidal activity to Tribolium castaneum; however, the underlying molecular mechanisms of eugenol acting on T. castaneum are currently unclear. Here, a nerve conduction carboxylesterase and a detoxifying glutathione S-transferase were significantly inhibited after eugenol exposure, resulting in the paralysis or death of beetles. Then, RNA-sequencing of eugenol-exposed and control samples identified 362 differentially expressed genes (DEGs), containing 206 up-regulated and 156 down-regulated genes. RNA-seq data were validated further by qRT-PCR. GO analysis revealed that DEGs were associated with 1308 GO terms of which the most enriched GO terms were catalytic activity, and integral component of membrane; KEGG pathway analysis showed that these DEGs were distributed in 151 different pathways, of which some pathways associated with metabolism of xenobiotics or drug were significantly enriched, which indicated that eugenol most likely disturbed the processes of metabolism, and detoxication. Moreover, several DEGs including Hexokinase type 2, Isocitrate dehydrogenase, and Cytochrome b-related protein, might participate in the respiratory metabolism of eugenol-exposed beetles. Some DEGs encoding CYP, UGT, GST, OBP, CSP, and ABC transporter were involved in the xenobiotic or drug metabolism pathway, which suggested that these genes of T. castaneum participated in the response to eugenol exposure. Additionally, TcOBPC11/ TcGSTs7, detected by qRT-PCR and RNA-interference against these genes, significantly increased the mortality of eugenol-treated T. castaneum, providing further evidence for the involvement of OBP/GST in eugenol metabolic detoxification in T. castaneum. These results aid eugenol insecticidal mechanisms and provide the basis of insect control.

Larvicidal activity against Aedes aegypti and molecular docking studies of compounds extracted from the endophytic fungus Aspergillus sp. isolated from Bertholletia excelsa Humn. & Bonpl

Endophytic fungi are microorganisms capable of colonizing the interior of plant tissues without causing damage to them. The study of the secondary metabolites produced by their vast biodiversity fungal is relevant for the discovery of new products for biotechnological and agrochemical applications. In addition, extract of the endophytic fungus Aspergillus sp., isolated from the almonds of Bertholletia excelsa Humn & Bonlp collected in the Brazilian Amazon, oviposition deterrent, and larvicidal activity of against Aedes aegypti. In the oviposition deterrence test was observed that females able to lay eggs preferred the control oviposition sites (46.6%). Furthermore, the extract showed larvicidal activity with LC50 26.86 µg/mL at 24 h and 18.75 µg/mL at 48 h. Molecular docking studies showed the compound Aspergillol B a potent larvicide by to inhibit the acetylcholinesterase enzyme (- 7.74 kcal/mol). These results indicate that compounds from secondary metabolites of Aspergillus sp., isolated from almonds of B. excelsa, are useful biological potential against vectors A. aegypti.

Insecticide resistance in Australian Spodoptera frugiperda (J.E. Smith) and development of testing procedures for resistance surveillance

Spodoptera frugiperda (J.E. Smith) is a highly invasive noctuid pest first reported in northern Australia during early 2020. To document current status of resistance in S. frugiperda in Australia, insecticide toxicity was tested in field populations collected during the first year of establishment, between March 2020 and March 2021. Dose-response was measured by larval bioassay in 11 populations of S. frugiperda and a susceptible laboratory strain of Helicoverpa armigera. Emamectin benzoate was the most efficacious insecticide (LC50 0.023μg/ml) followed by chlorantraniliprole (LC50 0.055μg/ml), spinetoram (LC50 0.098μg/ml), spinosad (LC50 0.526μg/ml), and methoxyfenozide (1.413μg/ml). Indoxacarb was the least toxic selective insecticide on S. frugiperda (LC50 3.789μg/ml). Emamectin benzoate, chlorantraniliprole and methoxyfenozide were 2- to 7-fold less toxic on S. frugiperda compared with H. armigera while spinosyns were equally toxic on both species. Indoxacarb was 28-fold less toxic on S. frugiperda compared with H. armigera. There was decreased sensitivity to Group 1 insecticides and synthetic pyrethroids in S. frugiperda compared with H. armigera: toxicity was reduced up to 11-fold for methomyl, 56 to 199-fold for cyhalothrin, and 44 to 132-fold for alpha cypermethrin. Synergism bioassays with metabolic inhibitors suggest involvement of mixed function oxidase in pyrethroid resistance. Recommended diagnostic doses for emamectin benzoate, chlorantraniliprole, spinetoram, spinosad, methoxyfenozide and indoxacarb are 0.19, 1.0, 0.75, 6, 12 and 48μg/μl, respectively.

Potential implications of vouacapan compounds for insecticidal activity: an in silico study

BACKGROUND

From the fruits and seeds of the species of Pterodon, it is possible to obtain two main products: the essential oil and oleoresin. In oleoresin, numerous vouacapan compounds have been demonstrated to have biological potential, including insecticidal activity.

OBJECTIVE

In silico studies were performed to identify potential candidates for natural insecticides among the vouacapans present in the genus Pterodon.

MATERIALS AND METHODS

Molecular docking and molecular dynamics studies were performed to analyze the interaction of vouacapan compounds with acetylcholinesterase of Drosophila melanogaster. Pharmacokinetic parameters regarding physicochemical properties, plasma protein binding, and activity in the central nervous system were evaluated. The toxicological properties of the selected molecules were predicted using Malathion as the reference compound.

RESULTS

6α,7β-dimethoxivouacapan-17-ene (15) showed a high number of interactions and scores in molecular docking studies. This result suggests that this compound exhibits an inhibitory activity of the enzyme acetylcholinesterase. Regarding physicochemical properties, this compound showed the best results, besides presenting low cutaneous permeability values, suggesting null absorption. Molecular dynamics studies demonstrated few conformational changes in the structure of the complex formed by compound 4 and acetylcholinesterase enzyme throughout the simulation time.

CONCLUSION

It was determined that compound 4 (vouacapan 6α,7β,17β,19-tetraol) is an excellent candidate for usage as a natural insecticide.

Atividade da Metilxantina em pó aplicada na cama de frango sobre adultos de Alphitobius diaperinus (Panzer, 1797) (Coleoptera: Tenebrionidae)

Resumo Uma das pragas que mais afetam e comprometem a produção avícola no mundo é o inseto Alphitobius diaperinus, conhecido como cascudinho. Este inseto é vetor de doenças que comprometem não só a produção de frangos como também a saúde humana. Objetivou-se com esse trabalho avaliar a eficácia e determinar a dose adequada de Metilxantina (MTX), inseticida natural extraído da cafeína, para o controle da população adulta de cascudinhos em cama de frango. Foram utilizados 2.500 cascudinhos adultos distribuídos em delineamento inteiramente casualizado, cinco tratamentos, 10 repetições com 50 insetos por repetição. Os tratamentos consistiram de grupo controle e quatro concentrações 14 g/m2, 16 g/m2, 18 g/m2, 20 g/m2 de MTX espalhadas em recipientes plásticos contendo cama de frango reutilizada e ração, alocados em um galpão de frangos de corte a fm de simular a condição de granja. Período experimental foi de 18 dias e realizadas cinco leituras nos dias dois, quatro, seis, 10 e 18. A MTX afetou (P<0,05) a taxa de mortalidade acumulada de cascudinhos, grupos de insetos alojados em caixas tratadas com 16 g/m2 de MTX apresentaram maior mortalidade acumulada (86,6%) ao final do período experimental. Conclui-se que MTX tem ação inseticida sobre adultos de cascudinho, podendo ser utilizada sobre a cama de frango para o controle da população deste inseto em galpões de criação de frangos, a concentração 16 g/MTX/m2 demonstrou maior efetividade.

Activity of powdered methylxanthine applied to poultry litter on adults of Alphitobius diaperinus (Panzer, 1797) (Coleoptera: Tenebrionidae)

Abstract One of the pests that most affect and compromise poultry production worldwide is the insect Alphitobius diaperinus, known as the lesser mealworm. This insect is a vector of diseases that compromise not only chicken production but also human health. This study proposes to examine the efficacy and determine the appropriate rate of methylxanthine (MTX), a natural insecticide extracted from cafeine, for the control of an adult population of lesser mealworms in poultry litter. A total of 2,500 adult mealworms were distributed into five treatments in a completely randomized design using 10 replications with 50 insects per replication. The treatments consisted of a control group and four concentrations of MTX (14, 16, 18, and 20 g/m2) spread in plastic boxes containing reused poultry litter and feed, allocated in a broiler shed, to simulate the farm condition. The experimental period was 18 days, and five readings were performed on days 2, 4, 6, 10, and 18. Methylxanthine affected (P<0.05) the mealworms’ cumulative mortality rate, with the groups of insects housed in boxes treated with 16 g /m2 MTX showing the highest cumulative mortality (86.6%) at the end of the experimental period. In conclusion, MTX has insecticidal action on adults of lesser mealworm and can be used on chicken litter to control the population of this insect in poultry sheds. The MTX concentration of 16 g/m2 showed the greatest effectiveness.

Synthesis, computational and nanoencapsulation studies on eugenol-derived insecticides

A new set of alkoxy alcohols were synthesised by reaction of eugenol oxirane with aliphatic and aromatic alcohols. These eugenol derivatives were evaluated against their effect upon the viability of...

Biochemical evaluation and molecular docking assessment of Cymbopogon citratus as a natural source of acetylcholine esterase (AChE)- targeting insecticides

Acetylcholinesterase (AChE) has been an effective target for insecticide development which is a very important aspect of the global fight against insect-borne diseases. The drastic reduction in the sensitivity of insects to AChE-targeting insecticides like organophosphates and carbamates have increased the need for insecticides of natural origin. In this study, we used Drosophila melanogaster as a model to investigate the insecticidal and AChE inhibitory potentials of Cymbopogon citratus and its bioactive compounds. Flies were exposed to 100 and 200 mg/mL C. citratus leaf extract for a 3-h survival assay followed by 45 min exposure for negative geotaxis and biochemical assays. Molecular docking analysis of 45 bioactive compounds of the plant was conducted against Drosophila melanogaster AChE (DmAChE). Exposure to C. citratus significantly reduced the survival rate of flies throughout the exposure period and this was accompanied by a significant decrease in percentage negative geotaxis, AChE activity, catalase activity, total thiol level and a significant increase in glutathione-S-transferase (GST) activity. The bioactive compounds of C. citratus showed varying levels of binding affinities for the enzyme. (+)-Cymbodiacetal scored highest (−9.407 kcal/mol) followed by proximadiol (−8.253 kcal/mol), geranylacetone (−8.177 kcal/mol), and rutin (−8.148 kcal/mol). The four compounds occupied the same binding pocket and interacted with important active site amino acid residues as the co-crystallized ligand (1qon). These compounds could be responsible for the insecticidal and AChE inhibitory potentials of C. citratus and they could be further explored in the development of AChE-targeting insecticides.

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Cymbopogon citratus reduced the AChE activity, catalase activity, total thiol level in Drosophilia melanogaster.

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The bioactive compounds of Cymbopogon citratus displayed considerable binding affinities for Drosophila melanogaster AChE and the four top-scoring compounds are (+)-Cymbodiacetal, proximadiol, geranylacetone, and rutin.

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(+)-Cymbodiacetal showed the highest binding affinity to AChE (DmAChE).

New carvacrol and thymol derivatives as potential insecticides: synthesis, biological activity, computational studies and nanoencapsulation

New compounds with potential insecticide activity were synthesized by structural modifications performed in the monoterpenoid phenolic moieties of carvacrol and thymol, resulting in a set of derivatives with the ether function containing the propyl, chloropropyl or hydroxypropyl chains, as well as a bicyclic ether with an unsaturated chain containing a carboxylic acid terminal. In addition, an analogue of carvacrol and thymol isomers bearing methoxyl, 1-hydroxyethyl and (3-chlorobenzoyl)oxy, instead of the three original methyl groups, was also synthesized. Several structural changes that resulted in diminished insecticide activity have been identified, but two significantly active molecules have been synthesized, one of them being less toxic to human cells than the naturally-derived starting materials. Structure-based inverted virtual screening and molecular dynamics simulations demonstrate that these active molecules likely target the insect odorant binding proteins and/or acetylcholinesterase and are able to form stable complexes. For the most promising compounds, nanoencapsulation assays were carried out in liposomes of egg phosphatidylcholine/cholesterol (7 : 3) prepared by both thin film hydration and ethanolic injection methods. The compound-loaded liposomes were generally monodisperse and with sizes smaller than or around 200 nm. The thin film hydration method allowed high encapsulation efficiencies (above 85%) for both compounds and a delayed release, while for the systems prepared by ethanolic injection the encapsulation efficiency is lower than 50%, but the release is almost complete in two days.

Rational Multitargeted Drug Design Strategy from the Perspective of a Medicinal Chemist

The development of multitarget-directed ligands (MTDLs) has become a widely focused research topic, but rational design remains as an enormous challenge. This paper reviews and discusses the design strategy of incorporating the second activity into an existing single-active ligand. If the binding sites of both targets share similar endogenous substrates, MTDLs can be designed by merging two lead compounds with similar functional groups. If the binding sites are large or adjacent to the solution, two key pharmacophores can be fused directly. If the binding regions are small and deep inside the proteins, the linked-pharmacophore strategy might be the only way. The added pharmacophores of second targets should not affect the binding mode of the original ones. Moreover, the inhibitory activities of the two targets need to be adjusted to achieve an optimal ratio.

Acetylcholinesterase target sites for developing environmentally friendly insecticides against Tetranychus urticae (Acari: Tetranychidae)

The non-target toxicity and resistance problems of acetylcholinesterase (AChE) insecticides, such as organophosphates and carbamates, are of growing concern. To explore the potential targets for achieving inhibitor selectivity, the AChE structures at or near the catalytic pocket of Tetranychus urticae (TuAChE), honey bees, and humans were compared. The entrances to the AChE catalytic pocket differ significantly because of their different peripheral sites. The role of these potential mite-specific sites in AChE function was further elucidated by site-directed mutagenesis of these sites and then examining the catalytic activities of TuAChE mutants. The spider mite E₃₁₆, H₃₆₉, and V₁₀₅ active sites are important for AChE function. By further analyzing their physostigmine inhibitory properties and the detailed interaction between physostigmine and TuAChE, the peripheral site H₃₆₉ locating near the gorge entrance, and S₁₅₄ at the oxyanion hole, affects substrate and inhibitor trafficking. The discovery of conserved mite-specific residues in Tetranychus will enable the development of safer, effective pesticides that target residues present only in mite AChEs, potentially offering effective control against this important agricultural pest.

Enhancement of Temephos and Deltamethrin Toxicity by Petroselinum crispum Oil and its Main Constituents Against Aedes aegypti (Diptera: Culicidae)

Previous work presented the profound antimosquito potential of Petroselinum crispum essential oil (PEO) against either the pyrethroid-susceptible or resistant strains of Aedes aegypti. This plant oil also inhibited the activity of acetylcholinesterase and mixed-function oxidases significantly, thus suggesting its potential as a synergist for improving mosquitocidal efficacy of insecticidal formulations. This study investigated the chemical composition, larvicidal activity, and potential synergism with synthetic insecticides of PEO and its main compounds for the purpose of interacting with insecticide resistance in mosquito vectors. The chemical profile of PEO, obtained by GC-MS analysis, showed a total of 17 bioactive compounds, accounting for 99.09% of the whole oil, with the most dominant constituents being thymol (74.57%), p-cymene (10.73%), and γ-terpinene (8.34%). All PEO constituents exhibited promising larvicidal effects, with LC50 values ranging from 19.47 to 59.75 ppm against Ae. aegypti, in both the pyrethroid-susceptible and resistant strains. Furthermore, combination-based bioassays revealed that PEO, thymol, p-cymene, and γ-terpinene enhanced the efficacy of temephos and deltamethrin significantly. The most effective synergist with temephos was PEO, which reduced LC50 values to 2.73, 4.94, and 3.28 ppb against MCM-S, PMD-R, and UPK-R, respectively, with synergism ratio (SR) values of 1.33, 1.38, and 2.12, respectively. The best synergist with deltamethrin also was PEO, which reduced LC50 values against MCM-S, PMD-R, and UPK-R to 0.008, 0.18, and 2.49 ppb, respectively, with SR values of 21.25, 9.00, and 4.06, respectively. This research promoted the potential for using essential oil and its principal constituents as not only alternative larvicides, but also attractive synergists for enhancing efficacy of existing conventional insecticides.

In Silico Studies of Lamiaceae Diterpenes with Bioinsecticide Potential against Aphis gossypii and Drosophila melanogaster

Background: The growing demand for agricultural products has led to the misuse/overuse of insecticides; resulting in the use of higher concentrations and the need for ever more toxic products. Ecologically, bioinsecticides are considered better and safer than synthetic insecticides; they must be toxic to the target organism, yet with low or no toxicity to non-target organisms. Many plant extracts have seen their high insecticide potential confirmed under laboratory conditions, and in the search for plant compounds with bioinsecticidal activity, the Lamiaceae family has yielded satisfactory results. Objective: The aim of our study was to develop computer-assisted predictions for compounds with known insecticidal activity against Aphis gossypii and Drosophila melanogaster. Results and conclusion: Structure analysis revealed ent-kaurane, kaurene, and clerodane diterpenes as the most active, showing excellent results. We also found that the interactions formed by these compounds were more stable, or presented similar stability to the commercialized insecticides tested. Overall, we concluded that the compounds bistenuifolin L (1836) and bistenuifolin K (1931), were potentially active against A. gossypii enzymes; and salvisplendin C (1086) and salvixalapadiene (1195), are potentially active against D. melanogaster. We observed and highlight that the diterpenes bistenuifolin L (1836), bistenuifolin K (1931), salvisplendin C (1086), and salvixalapadiene (1195), present a high probability of activity and low toxicity against the species studied.

Comparative mapping of selected structural determinants on the extracellular domains of cholinesterase-like cell-adhesion molecules

Cell adhesion generally involves formation of homophilic or heterophilic protein complexes between two cells to form transcellular junctions. Neural cell-adhesion members of the α/β-hydrolase fold superfamily of proteins use their extracellular or soluble cholinesterase-like domain to bind cognate partners across cell membranes, as illustrated by the neuroligins. These cell-adhesion molecules currently comprise the synaptic organizers neuroligins found in all animal phyla, along with three proteins found only in invertebrates: the guidance molecule neurotactin, the glia-specific gliotactin, and the basement membrane protein glutactin. Although these proteins share a cholinesterase-like fold, they lack one or more residues composing the catalytic triad responsible for the enzymatic activity of the cholinesterases. Conversely, they are found in various subcellular localisations and display specific disulfide bonding and N-glycosylation patterns, along with individual surface determinants possibly associated with recognition and binding of protein partners. Formation of non-covalent dimers typical of the cholinesterases is documented for mammalian neuroligins, yet whether invertebrate neuroligins and their neurotactin, gliotactin and glutactin relatives also form dimers in physiological conditions is unknown. Here we provide a brief overview of the localization, function, evolution, and conserved versus individual structural determinants of these cholinesterase-like cell-adhesion proteins. This article is part of the special issue entitled 'Acetylcholinesterase Inhibitors: From Bench to Bedside to Battlefield'.

Estimating the ligand-binding affinity via λ-dependent umbrella sampling simulations

The umbrella sampling (US) approach has been demonstrated to be a very efficient method for estimating the ligand-binding affinity. However, most of the calculated values overestimate experimental ones that are probably caused by the inaccurate representation of the interaction between the ligand and the surrounding molecules. The issue can be resolved via the implementation aspects of λ-alteration simulation into the US approach, which we call the λ-dependent umbrella sampling (λUS) scheme. In particular, the electrostatic and van der Waals interactions were simultaneously changed by using the coupling parameter λ during λUS simulations. The mean value of obtained results, ∆ G US λ = 0.20 = - 11.59 ± 1.51 kcal mol^-1 , is in good fitting to the mean value of respective experiments, ∆G_EXP =  - 11.26 ± 0.89 kcal mol^-1 . Moreover, the correlation between the proposed approach and experiment is quite good with a value of R US λ = 0.20 = 0.82 ± 0.10 . The λUS scheme significantly enhances the calculated accuracy since the RMSE of the proposed scheme is smaller than traditional US simulations, RMSE US λ = 0.20 = 2.99 ± 0.82 kcal mol^-1 versus RMSE US λ = 0.00 = 5.48 ± 0.81 kcal mol^-1 . Furthermore, the precision is increased since the computed error via λUS approach, δ US λ = 0.20 = 1.51 kcal mol^-1 , was smaller than those of the US simulation, δ US λ = 0.00 = 1.78 kcal mol^-1 . Overall, the proposed approach perhaps provides an efficient way to accurately and precisely estimate the ligand-binding free energy.

QSAR modelling of larvicidal phytocompounds against Aedes aegypti using index of ideality of correlation

Aedes aegypti is the primary vector of several infectious viruses that cause yellow, dengue, chikungunya, and Zika fevers. Recently, plant-derived products have been tested as safe and eco-friendly larvicides against Ae. aegypti. The present study aimed to improve QSAR models for 62 larvicidal phytocompounds against Ae. aegypti via the Monte Carlo method based on the index of the ideality of correlation (IIC) criterion. The representation of structures was done with SMILES. Three splits were prepared randomly and three QSAR models were constructed using IIC target function. The molecular descriptors were selected from SMILES descriptors and the hydrogen-filled molecular graphs. The predictability of three models was evaluated on the validation sets, the r ² of which was 0.9770, 0.8660, and 0.8565 for models 1 to 3, respectively. The statistical results of three randomized splits indicated that robust, simple, predictive, and reliable models were obtained for different sets. From the modelling results, important descriptors were identified to enhance and reduce the larvicidal activity of compounds. Based on the identified important descriptors, some new structures of larvicidal compounds were proposed. The larvicidal activity of novel molecules designed further was supported by docking studies. Using the simple QSAR model, one can predict pLC₅₀ of new similarity larvicidal phytocompounds.

Effects of Sublethal Doses of Methyl Benzoate on the Life History Traits and Acetylcholinesterase (AChE) Activity of Aphis gossypii

Safer alternatives to synthetic pesticides are essential for sustainable agriculture. Methyl benzoate (MB) is a volatile essential oil found in several plants. Recent reports of the toxicity of MB to arthropod pests suggest that MB may be a useful alternative insecticide. The present study assessed the effects of a sublethal concentration of MB (LC30, 0.22%) on the life history and reproductive characteristics of the cotton aphid, Aphis gossypii Glover, in both a treated parental generation (F0) and untreated progeny (F1). MB treatment significantly decreased longevity and fecundity in both the F0 and F1 generations, and prolonged the developmental duration of each immature instar of the F1 generations, compared with controls. The intrinsic rate of increase (r), finite rate of increase (λ), and net reproductive rate (R0) of the F1 generation were significantly reduced, compared to controls. The mode of action of MB is not known, but in aphids treated with LC30 MB, the activity of the enzyme acetylcholinesterase (AChE) decreased by more than 65%, compared with untreated controls. AChE activity was rapidly inhibited within 1 h, and remained inhibited for 6 h after in vivo exposure to MB. Moreover, molecular docking analysis revealed that MB had a strong affinity with the catalytic site of AChE, with a binding energy value of −6.2 kcal/mole. Our results suggest that MB targets AChE, and that a sublethal dose of MB can have adverse transgenerational effects on cotton aphids.

Monitoring of Target-Site Mutations Conferring Insecticide Resistance in Spodoptera frugiperda

Simple Summary

Fall armyworm, Spodoptera frugiperda, is an invasive moth species and one of the most destructive pests of maize. It is native to the Americas but recently invaded (sub)tropical regions in Africa, Asia and Oceania. Fall armyworm larvae feeding on maize plants cause substantial economic damage and are usually controlled by the application of insecticides and genetically modified (GM) maize expressing Bacillus thuringiensis (Bt) proteins, selectively targeting fall armyworm. It has developed resistance to many different classes of insecticides and Bt proteins as well; therefore, it is important to check field populations for the presence of mutations in target proteins conferring resistance. Here, we developed molecular diagnostic tools allowing us to test the frequency of resistance alleles in field-collected populations, either alive or preserved in alcohol. We tested 34 different populations collected on four different continents for the presence of mutations conferring resistance to common classes of insecticides and Bt proteins. We detected resistance mutations which are quite widespread, whereas others are restricted to certain geographies or even completely absent. The established molecular methods show robust results in samples collected across a broad geographical range and can be used to support decisions for sustainable fall armyworm control and applied resistance management.

Abstract

Fall armyworm (FAW), Spodoptera frugiperda, a major pest of corn and native to the Americas, recently invaded (sub)tropical regions worldwide. The intensive use of insecticides and the high adoption of crops expressing Bacillus thuringiensis (Bt) proteins has led to many cases of resistance. Target-site mutations are among the main mechanisms of resistance and monitoring their frequency is of great value for insecticide resistance management. Pyrosequencing and PCR-based allelic discrimination assays were developed and used to genotype target-site resistance alleles in 34 FAW populations from different continents. The diagnostic methods revealed a high frequency of mutations in acetylcholinesterase, conferring resistance to organophosphates and carbamates. In voltage-gated sodium channels targeted by pyrethroids, only one population from Indonesia showed a mutation. No mutations were detected in the ryanodine receptor, suggesting susceptibility to diamides. Indels in the ATP-binding cassette transporter C2 associated with Bt-resistance were observed in samples collected in Puerto Rico and Brazil. Additionally, we analyzed all samples for the presence of markers associated with two sympatric FAW host plant strains. The molecular methods established show robust results in FAW samples collected across a broad geographical range and can be used to support decisions for sustainable FAW control and applied resistance management.

Disentangling the ecotoxicological selectivity of clove essential oil against aphids and non-target ladybeetles

The plant-based biopesticides have been proposed as insect pest control tools that seem to be safer for the environment and human health when compared to synthetic conventional molecules. However, such assumptions are generally made without considering the absence of detrimental effects on sublethally-exposed non-target organisms or showing the physiological basis of the selective action of such botanical products. Thus, by using in silico-based and in vivo toxicological approaches, the present investigation aimed to disentangle the ecotoxicological selectivity of clove, Syzygium aromaticum, essential oil against the aphid Rhopalosiphum maidis and the non-target ladybeetle, Coleomegilla maculata. We also investigated whether the sublethal exposure to clove essential oil would affect the locomotory and predatory abilities of C. maculata. We found that the clove essential oil concentration estimated to kill 95% (LC₉₅: 0.17 μL/cm²) of the aphids was lethal to <18% of C. maculata. Indeed, our in silico results reinforced such differential susceptibility, as it predicted that eugenol and β-caryophyllene (i.e., the clove essential oil major components) bound to three potential molecular targets (i.e., transient receptor potential (TRP) channels, octopamine, and gamma-aminobutyric acid (GABA) receptors) of the aphids but only to the octopamine receptors of the ladybeetles. Additionally, the ladybeetles that were exposure to the clove essential oil exhibited unaffected abilities to locomote and to prey upon R. maidis aphids when compared to unexposed ladybeetles. Thus, by displaying lower toxicity against the ladybeetles, the clove essential oil represents a safer alternative tool to be integrated into programs aiming to manage aphid infestations.

Quantitative Structure-Activity Relationship Modeling and Docking of Monoterpenes with Insecticidal Activity Against Reticulitermes chinensis Snyder and Drosophila melanogaster

The goal of this study was to perform in silico identification of bioinsecticidal potential of 42 monoterpenes against Drosophila melanogaster and Reticulitermes chinensis Snyder. Quantitative structure-activity relationship (QSAR) modeling was performed for both organisms, while docking and molecular dynamics were used only for Drosophila melanogaster. Neryl acetate has the lowest interaction energy (-87 kcal/mol) against active site of acetylcholinesterase, which is comparable to the ones of methiocarb and pirimicarb (-90 kcal/mol) and reported PDB binder 9-(3-iodobenzylamino)-1,2,3,4-tetrahydroacridine (-112.67 kcal/mol). Interaction stability was verified by molecular dynamics simulations and showed that the stability of ACHE active site complexes with three selected terpenes is comparable to the one of the pirimicarb and methiocarb. Overall, our results suggest that pulegone, citronellal, carvacrol, linalyl acetate, neryl acetate, citronellyl acetate, and geranyl acetate may be considered as a potential pesticide candidates.

Arylaminopropanone Derivatives as Potential Cholinesterase Inhibitors: Synthesis, Docking Study and Biological Evaluation

Neurodegenerative diseases in which the decrease of the acetylcholine is observed are growing worldwide. In the present study, a series of new arylaminopropanone derivatives with N-phenylcarbamate moiety (1–16) were prepared as potential acetylcholinesterase and butyrylcholinesterase inhibitors. In vitro enzyme assays were performed; the results are expressed as a percentage of inhibition and the IC₅₀ values. The inhibitory activities were compared with reference drugs galantamine and rivastigmine showing piperidine derivatives (1–3) as the most potent. A possible mechanism of action for these compounds was determined from a molecular modelling study by using combined techniques of docking, molecular dynamics simulations and quantum mechanics calculations.

A Second Look at the Crystal Structures of Drosophila melanogaster Acetylcholinesterase in Complex with Tacrine Derivatives Provides Insights Concerning Catalytic Intermediates and the Design of Specific Insecticides

Over recent decades, crystallographic software for data processing and structure refinement has improved dramatically, resulting in more accurate and detailed crystal structures. It is, therefore, sometimes valuable to have a second look at "old" diffraction data, especially when earlier interpretation of the electron density maps was rather difficult. Here, we present updated crystal structures of Drosophila melanogaster acetylcholinesterase (DmAChE) originally published in [Harel et al., Prot Sci (2000) 9:1063-1072], which reveal features previously unnoticed. Thus, previously unmodeled density in the native active site can be interpreted as stable acetylation of the catalytic serine. Similarly, a strong density in the DmAChE/ZA complex originally attributed to a sulfate ion is better interpreted as a small molecule that is covalently bound. This small molecule can be modeled as either a propionate or a glycinate. The complex is reminiscent of the carboxylate butyrylcholinesterase complexes observed in crystal structures of human butyrylcholinesterases from various sources, and demonstrates the remarkable ability of cholinesterases to stabilize covalent complexes with carboxylates. A very strong peak of density (10 σ) at covalent distance from the Cβ of the catalytic serine is present in the DmAChE/ZAI complex. This can be undoubtedly attributed to an iodine atom, suggesting an unanticipated iodo/hydroxyl exchange between Ser238 and the inhibitor, possibly driven by the intense X-ray irradiation. Finally, the binding of tacrine-derived inhibitors, such as ZA (1DX4) or the iodinated analog, ZAI (1QON) results in the appearance of an open channel that connects the base of the active-site gorge to the solvent. This channel, which arises due to the absence of the conserved tyrosine present in vertebrate cholinesterases, could be exploited to design inhibitors specific to insect cholinesterases. The present study demonstrates that updated processing of older diffraction images, and the re-refinement of older diffraction data, can produce valuable information that could not be detected in the original analysis, and strongly supports the preservation of the diffraction images in public data banks.

The acid-base-nucleophile catalytic triad in ABH-fold enzymes is coordinated by a set of structural elements

The alpha/beta-Hydrolases (ABH) are a structural class of proteins that are found widespread in nature and includes enzymes that can catalyze various reactions in different substrates. The catalytic versatility of the ABH fold enzymes, which has been a valuable property in protein engineering applications, is based on a similar acid-base-nucleophile catalytic mechanism. In our research, we are concerned with the structure that surrounds the key units of the catalytic machinery, and we have previously found conserved structural organizations that coordinate the catalytic acid, the catalytic nucleophile and the residues of the oxyanion hole. Here, we explore the architecture that surrounds the catalytic histidine at the active sites of enzymes from 40 ABH fold families, where we have identified six conserved interactions that coordinate the catalytic histidine next to the catalytic acid and the catalytic nucleophile. Specifically, the catalytic nucleophile is coordinated next to the catalytic histidine by two weak hydrogen bonds, while the catalytic acid is directly involved in the coordination of the catalytic histidine through by two weak hydrogen bonds. The imidazole ring of the catalytic histidine is coordinated by a CH-π contact and a hydrophobic interaction. Moreover, the catalytic triad residues are connected with a residue that is located at the core of the active site of ABH fold, which is suggested to be the fourth member of a “structural catalytic tetrad”. Besides their role in the stability of the catalytic mechanism, the conserved elements of the catalytic site are actively involved in ligand binding and affect other properties of the catalytic activity, such as substrate specificity, enantioselectivity, pH optimum and thermostability of ABH fold enzymes. These properties are regularly targeted in protein engineering applications, and thus, the identified conserved structural elements can serve as potential modification sites in order to develop ABH fold enzymes with altered activities.

Cysteine-Targeted Insecticides against A. gambiae Acetylcholinesterase Are Neither Selective nor Reversible Inhibitors

Acetylcholinesterase cysteine-targeted insecticides against malaria vector Anopheles gambia and other mosquitos have already been introduced. We have applied the olefin metathesis for the preparation of cysteine-targeted insecticides in high yields. The prepared compounds with either a succinimide or maleimide moiety were evaluated on Anopheles gambiae and human acetylcholinesterase with relatively high irreversible inhibition of both enzymes but poor selectivity. The concept of cysteine binding was not proved by several methods, and poor stability was observed of the chosen most potent/selective compounds in a water/buffer environment. Thus, our findings do not support the proposed concept of cysteine-targeted selective insecticides for the prepared series of succinimide or maleimide compounds.