title: The crystal structure of the AgamOBP1•Icaridin complex reveals alternative binding modes and stereo-selective repellent recognition.
abstract: Anopheles gambiae Odorant Binding Protein 1 in complex with the most widely used insect repellent DEET, was the first reported crystal structure of an olfactory macromolecule with a repellent, and paved the way for OBP1-structure-based approaches for discovery of new host-seeking disruptors. In this work, we performed STD-NMR experiments to directly monitor and verify the formation of a complex between AgamOBP1 and Icaridin, an efficient DEET alternative. Furthermore, Isothermal Titration Calorimetry experiments provided evidence for two Icaridin-binding sites with different affinities (Kd = 0.034 and 0.714 mM) and thermodynamic profiles of ligand binding. To elucidate the binding mode of Icaridin, the crystal structure of AgamOBP1•Icaridin complex was determined at 1.75 Å resolution. We found that Icaridin binds to the DEET-binding site in two distinct orientations and also to a novel binding site located at the C-terminal region. Importantly, only the most active 1R,2S-isomer of Icaridin's equimolar diastereoisomeric mixture binds to the AgamOBP1 crystal, providing structural evidence for the possible contribution of OBP1 to the stereoselectivity of Icaridin perception in mosquitoes. Structural analysis revealed two ensembles of conformations differing mainly in spatial arrangement of their sec-butyl moieties. Moreover, structural comparison with DEET indicates a common recognition mechanism for these structurally related repellents. Ligand interactions with both sites and binding modes were further confirmed by 2D1H-15N HSQC NMR spectroscopy. The identification of a novel repellent-binding site in AgamOBP1 and the observed structural conservation and stereoselectivity of its DEET/Icaridin-binding sites open new perspectives for the OBP1-structure-based discovery of next-generation insect repellents.
authors.affiliation: Institute of Biology, Medicinal Chemistry and Biotechnology, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, 11635, Athens, Greece.
authors.forename: Christina E
authors.initials: CE
authors.lastname: Drakou
authors.affiliation: Institute of Biology, Medicinal Chemistry and Biotechnology, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, 11635, Athens, Greece.
authors.forename: Katerina E
authors.initials: KE
authors.lastname: Tsitsanou
authors.affiliation: Institute of Biology, Medicinal Chemistry and Biotechnology, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, 11635, Athens, Greece.
authors.forename: Constantinos
authors.initials: C
authors.lastname: Potamitis
authors.affiliation: Department of Food, Environmental and Nutritional Sciences (DeFENS), Università degli Studi di Milano, Via Celoria 2, 20133, Milan, Italy.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Fessas
authors.affiliation: Institute of Biology, Medicinal Chemistry and Biotechnology, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, 11635, Athens, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Zervou
authors.affiliation: Institute of Biology, Medicinal Chemistry and Biotechnology, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, 11635, Athens, Greece. sez@eie.gr.
authors.forename: Spyros E
authors.identifier: 0000-0001-8455-2352
authors.initials: SE
authors.lastname: Zographos
mesh_terms: D000818:Animals; D000852:Anopheles / Q000378:metabolism*; D002151:Calorimetry; D018360:Crystallography, X-Ray; D003671:DEET / Q000737:chemistry / Q000378:metabolism; D005453:Fluorescence; D006860:Hydrogen Bonding; D007302:Insect Repellents / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D010880:Piperidines / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization; D066244:Proton Magnetic Resonance Spectroscopy; D018035:Receptors, Odorant / Q000737:chemistry* / Q000378:metabolism*; D012996:Solutions; D055672:Static Electricity; D013237:Stereoisomerism
chemical_list: D007302:Insect Repellents; D010880:Piperidines; D018035:Receptors, Odorant; D012996:Solutions; D003671:DEET; C483506:picaridin
keywords: Anopheles gambiae; DEET; Icaridin; Odorant binding protein; Repellents; Stereoselectivity