Spyridon E. Zographos

Odorant-binding proteins (OBPs) play central roles in insect chemoreception and represent attractive molecular targets for the discovery of novel behavior-modifying compounds. We report two crystal structures of Anopheles gambiae OBP4: one complexed with the fluorescent probe N-phenyl-1-naphthylamine and a second containing two indole molecules simultaneously bound within the ligand-binding cavity. Structural comparison revealed two binding subsites accommodating the aromatic moieties of 1-NPN or two indole molecules, while identifying Thr58 and Thr70 as key residues in ligand recognition. A structure-based virtual screening campaign was performed against a volatility-filtered library from DrugBank, FooDB, BioNet, and natural-volatiles datasets. Twenty-three ligands were selected for fluorescence competitive binding assays, identifying four AgamOBP4 binders with micromolar affinities ( K i = 2.4-21.8 μM). Among them were benzoyl peroxide, an active anti-acne ingredient, Avex-73 (blarcamesine), a clinical-stage drug candidate, and 2-phenylethyl benzoate, a food- and fragrance-associated ester. Additional candidates include o,p′-DDE, a metabolite of the insecticide DDT, and fluorene, a polycyclic aromatic hydrocarbon detected in foods as environmental or processing-derived contaminants. Seven selected compounds were subsequently evaluated against Aedes albopictus in in-vivo behavioral assays, with benzoyl peroxide displaying the highest repellency (RI = 81.8% at 0.2 mg cm ^-2 ). AI-based protein-ligand modeling provided insights into ligand recognition and suggested relationships among binding mode, binding affinity, and bioactivity. Collectively, these findings establish the structural basis of ligand recognition by AgamOBP4, highlight the potential of drug-repurposing and food-derived chemical space as sources of next-generation mosquito repellents, and open new opportunities for the development of OBP4-based biosensors for food-quality and environmental monitoring applications. Highlights: Novel AgamOBP4 crystal complexes revealed a dual aromatic-recognition binding site Structure-based virtual screening of >139,000 compounds from DrugBank, FooDB, and BioNet uncovered novel AgamOBP4 ligands from drug-repurposing and food-derived chemical spaces In vitro validation identified the clinical-stage candidate Avex-73 and the anti-acne agent benzoyl peroxide as novel low-micromolar AgamOBP4 ligands. Binding of the DDT metabolite o,p′-DDE suggests a possible involvement of AgamOBP4 in insecticide recognition. Recognition of food-associated fragrances and environmental contaminants highlights the potential for the development of AgamOBP4-based biosensors for food quality and environmental monitoring. Behavioral bioassays have identified benzoyl peroxide as a potent repellent against the Asian tiger mosquito Aedes albopictus . AI-based protein-ligand modeling provided insight into binding-mode, affinity, and bioactivity relationships

Motivation: Insect odorant receptors (iORs) essential for olfaction function as 7-transmembrane-domain (7TM) ion channels. iORs form tetrameric complexes that include a highly conserved odorant receptor co-receptor (Orco). Functional Orco homotetramers have also known to form ex vivo. Blocking Orco ex vivo and in vivo disrupts olfactory signalling, making it a promising target for functional intervention. Understanding its gating behaviour is critical for developing strategies to disrupt odour-guided behaviours in disease-vector insects. Thus, insights into the dynamic gating of the Anopheles gambiae Orco have implications on the rational design of vector-control strategies against malaria. We studied molecular dynamics (MD) simulations on homotetrameric AgamOrco models generated using template-based modelling (TBM) and AlphaFold3 (AF3), to investigate ligand-dependent pore dynamics. Agonist and antagonist bound systems were analysed to understand the ligand-dependent gating. Results: Our results show that apo and antagonistic IPC-bound AgamOrco homotetramer models remain in a stable, closed, and non-conductive state across both models. TBM, but not AF3, successfully captures agonistic VUAA1-induced activation, consistent with experimental observations, exhibiting asymmetric pore widening and conformational changes. Antagonist displacement simulations confirm IPC-mediated pore closure. Overall, the TBM AgamOrco model provides a reliable framework for structure-guided discovery of novel agents for control of insect pests and vector diseases.

Although it is reported that the protein tyrosine phosphatase gene of baculovirus (group I nucleopolyhedrovirus) can induce enhanced locomotory activity (ELA) in caterpillars, our understanding of the host factors that are involved in the regulation of the behavioral change is still limited. Previously, single-nucleus RNA sequencing (snRNA-seq) was used to identify 19 distinct clusters representing Kenyon cell, glial cell, olfactory projection neuron, optic lobes neuron, hemocyte, muscle cell types and other unannotated cells in the silkworm larvae brains. Analysis of viral transcriptomes in each brain cell subset revealed that all brain cells could be infected by Bombyx mori nucleopolyhedrovirus (BmNPV) at 96 hours post infection but infection occurred at low levels. Furthermore, we found that chemosensory protein 3 ( CSP3 ), encoding a small secreted protein that is possibly implicated in the transport of semiochemicals, was significantly up-regulated after BmNPV infection in most of the brain cell clusters. Knockdown of BmCSP3 resulted in significantly reduced ELA in BmNPV-infected silkworm larvae. In parallel, targeted metabolomics revealed significant shifts in the abundance of specific lipids and neurotransmitters. Subsequently, structural modeling and molecular dynamics experiments indicated that CSP3 has a large hydrophobic pocket that manifests significant flexibility and likely can accommodate divergent ligand structures or mixtures of them, including known neurotransmitters of the brain and (lyso)glycerophospholipids from larval head samples. In vitro binding assays have confirmed the interaction of several neurotransmitters and an eicosanoid to purified BmCSP3 protein. Our study provides insights into the regulation of insect behavior following analysis of viral infection at the single-cell transcriptome level and reveals an unexpected function for CSP proteins in the insect brain.

Toward the discovery of novel efficient repellents, protein‐directed dynamic combinatorial chemistry (pdDCC) coupled to saturation‐transfer difference (STD) NMR spectroscopy was initially employed to identify modulators of the malaria vector Anopheles gambiae Odorant Binding Protein 1 (AgamOBP1). A library of potential binders of AgamOBP1 (secondary amines) generated from two amines and seven aldehydes was designed aiming to enable interactions with critical amino acids at the DEET‐site and to bridge the DEET‐ and Icaridin sIC‐binding pockets, both implicated in repellents recognition. Solubility issues hindered the clear identification of binders among the DCL members, except for one sublibrary, leading us to shift our strategy towards the synthesis of the designed amines, followed by direct evaluation of their binding to AgamOBP1 using ¹ H STD NMR spectroscopy. The identified binders were further validated in vitro by fluorescence competition assays, and the most potent compounds which also possessed suitable vapor pressure were evaluated as repellents in arm‐in‐cage behavioral assays against Aedes albopictus . Amines 2A , 3A , 4A , and 6A showed significant repellent activity. The most potent was compound 4A (4‐methyl‐ N ‐(pyridin‐4‐ylmethyl)aniline) which acted as a a DEET‐like repellent at 0.4 μL cm ^{− 2} dose. Thus, our strategy showcased a promising scaffold for further optimization toward efficient mosquito repellents.

Insect olfactory receptors are heteromeric ligand-gated cation channels composed of an obligatory receptor subunit, ORco, and one of many variable subunits, ORx, in as yet undefined molar ratios. When expressed alone ex vivo , ORco forms homotetrameric channels gated by ORco-specific ligands acting as channel agonists. Using an insect cell-based system as a functional platform for expressing mosquito odorant receptors ex vivo, we identified small molecules of natural origin acting as specific ORco channel antagonists, orthosteric or allosteric relative to a postulated ORco agonist binding site, and causing severe inhibition of olfactory function in mosquitoes. In the present communication, we are reporting on the compilation of common structural features of such orthosteric antagonists and development of a ligand-based pharmacophore whose properties are deemed necessary for binding to the agonist binding site and inhibition of ORco’s biological function. In silico screening of an available collection of natural volatile compounds with this pharmacophore resulted in identification of several ORco antagonist hits. Cell-based functional screening of the same compound collection resulted in the identification of several compounds acting as orthosteric and allosteric antagonists of ORco channel function ex vivo and inducing anosmic behaviors to Aedes albopictus mosquitoes in vivo. Comparison of the in silico screening results with those of the functional assays revealed that the pharmacophore predicted correctly 7 out of the 8 confirmed orthosteric antagonists and none of the allosteric ones. Because the pharmacophore screen also produced additional hits that did not cause inhibition of the ORco channel function, we generated a Support Vector Machine (SVM) model based on two descriptors of all pharmacophore hits. Training of the SVM on the ex vivo validated compound collection resulted in the selection of the confirmed orthosteric antagonists with a very low cross-validation out-of-sample misclassification rate. Employment of the combined pharmacophore-SVM platform for in silico screening of a larger collection of olfaction-relevant volatiles produced several new hits. Functional validation of randomly selected hits and rejected compounds from this screen confirmed the power of this virtual screening platform as convenient tool for identifying novel vector control agents. To the best of our knowledge, this study is the first one that combines a pharmacophore with a SVM model for identification of AgamORco antagonists and specifically orthosteric ones.