title: Photoaffinity labeling of insect nicotinic acetylcholine receptors with a novel [(3)H]azidoneonicotinoid.
abstract: The nicotinic acetylcholine receptor (nAChR) is a ligand-gated ion channel in the insect CNS and a target for major insecticides. Here we use photoaffinity labeling to approach the functional architecture of insect nAChRs. Two candidate 5-azido-6-chloropyridin-3-yl photoaffinity probes are evaluated for their receptor potencies: azidoneonicotinoid (AzNN) with an acyclic nitroguanidine moiety; azidodehydrothiacloprid. Compared to their non-azido parents, both probes are of decreased potencies at Drosophila (fruit fly) and Musca (housefly) receptors but AzNN retains full potency at the Myzus (aphid) receptor. [(3)H]AzNN was therefore radiosynthesized at high specific activity (84 Ci/mmol) as a novel photoaffinity probe. [(3)H]AzNN binds to a single high-affinity site in Myzus that is competitively inhibited by imidacloprid and nicotine and further characterized as to its pharmacological profile with various nicotinic ligands. [(3)H]AzNN photoaffinity labeling of Myzus and Homalodisca (leafhopper) detects a single radiolabeled peak in each case displaceable with imidacloprid and nicotine and with molecular masses corresponding to approximately 45 and approximately 56 kDa, respectively. The photoaffinity-labeled receptor in both Drosophila and Musca has imidacloprid- and nicotine-sensitive profiles and migrates at approximately 66 kDa. These photoaffinity-labeled polypeptides are considered to be the insecticide-binding subunits of native insect nAChRs.
authors.affiliation: Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720-3112, USA.
authors.forename: M
authors.initials: M
authors.lastname: Tomizawa
authors.forename: Z
authors.initials: Z
authors.lastname: Wen
authors.forename: H L
authors.initials: HL
authors.lastname: Chin
authors.forename: H
authors.initials: H
authors.lastname: Morimoto
authors.forename: H
authors.initials: H
authors.lastname: Kayser
authors.forename: J E
authors.initials: JE
authors.lastname: Casida
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D007093:Imidazoles / Q000378:metabolism; D007313:Insecta / Q000378:metabolism*; D000073943:Neonicotinoids; D009538:Nicotine / Q000378:metabolism; D009539:Nicotinic Acids / Q000378:metabolism; D009574:Nitro Compounds; D019920:Photoaffinity Labels; D011978:Receptors, Nicotinic / Q000378:metabolism*; D014316:Tritium
chemical_list: D007093:Imidazoles; D000073943:Neonicotinoids; D009539:Nicotinic Acids; D009574:Nitro Compounds; D019920:Photoaffinity Labels; D011978:Receptors, Nicotinic; C437283:azidobenzoylneonicotinoid; C437264:azidoneonicotinoid; D014316:Tritium; C082359:imidacloprid; D009538:Nicotine