title: Combined roles of loops C and D in the interactions of a neonicotinoid insecticide imidacloprid with the alpha4beta2 nicotinic acetylcholine receptor.
abstract: Neonicotinoid insecticides are widely used for crop protection based on their selective actions on insect nicotinic acetylcholine receptors (insect nAChRs). Loops C and D in insect nAChRs have been shown to possess structural features favorable for neonicotinoid-nAChR interactions. However, it remains to be resolved whether such features serve either co-operatively, or independently, to enhance neonicotinoid sensitivity of nAChRs. We therefore examined using voltage-clamp electrophysiology the effects on the response to imidacloprid of combinatorial substitutions of residues in loops C and D of the chicken alpha4beta2 nAChR by those present in insect nAChRs. The E219P mutation in loop C of the alpha4 subunit resulted in enhanced responses to imidacloprid of alpha4beta2, whereas E219S and E219T mutations barely influenced its actions. On the other hand, mutations in loop D (T77R; E79V and T77N; E79R) alone shifted the imidacloprid concentration-response curve to the left (lower concentrations). Interestingly, all three mutations did, however, further enhance the agonist efficacy of imidacloprid when combined with the mutations in loop D. Such synergistic effects of the two loops on the interactions with imidaclprid were observed irrespective of subunit stoichiometry. Computational modeling of the ligand binding domain of the wild-type and mutant alpha4beta2 nAChRs using the crystal structure of the acetylcholine binding protein from Lymnaea stagnalis also indicated that interactions with loop F of loops C and D may contribute to determining the response to imidacloprid.
authors.affiliation: Department of Agricultural Chemistry, Faculty of Agriculture, Kinki University, 3327-204 Nakamachi, Nara 631-8505, Japan.
authors.forename: Kayoko
authors.initials: K
authors.lastname: Toshima
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kanaoka
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yamada
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Tarumoto
authors.forename: Miki
authors.initials: M
authors.lastname: Akamatsu
authors.forename: David B
authors.initials: DB
authors.lastname: Sattelle
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Matsuda
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D007093:Imidazoles / Q000494:pharmacology*; D007306:Insecticides / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D008845:Microinjections / Q000379:methods; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000494:pharmacology*; D009865:Oocytes; D018408:Patch-Clamp Techniques; D020836:Protein Structure, Quaternary; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
chemical_list: D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; D011978:Receptors, Nicotinic; C403531:nicotinic receptor alpha4beta2; C082359:imidacloprid; D000109:Acetylcholine