Amino acids within loops D, E and F of insect nicotinic acetylcholine receptor beta subunits influence neonicotinoid selectivity.
Nicotinic acetylcholine (ACh) receptors (nAChRs) are ligand-gated ion channels which mediate fast cholinergic synaptic transmission in insect and vertebrate nervous systems. The nAChR agonist-binding site is present at the interface of adjacent subunits and is formed by loops A-C present in alpha subunits together with loops D-F present in either non-alpha subunits or homomer-forming alpha subunits. To investigate the mechanism of neonicotinoid selectivity, we have examined the effects of altering insect-specific loops D, E and F in hybrid nAChRs containing insect and mammalian subunits (Nlalpha1 from the brown planthopper Nilaparvata lugens and beta2 from rat). Introduction of the insect-specific loops D, E and F, singly or together, into rat beta2 subunit resulted in a leftward shift of the imidacloprid dose-response curves for nAChRs Nlalpha1-beta2 chimeras, reflecting decreases in EC(50), compared to wildtype nAChRs Nlalpha1-beta2. By contrast, the influences on ACh potency were minimal or negligible. The effects of loop D could be interpreted by the earlier findings of Shimomura et al. [2006. Role in the selectivity of neonicotinoids of insect-specific basic residues in loop D of the nicotinic acetylcholine receptor agonist-binding site. Mol. Pharmacol. 70, 1255-1263.], in which T77R and E79V were shown to be responsible for neonicotinoid selectivity. In the present study, S131Y(R) and D133N in loop E and T191W and P192K in loop F were found to contribute to the neonicotinoid selectivity of insect-specific loops E and F. These results indicated the insect-specific loops D, E and F each play important roles in neonicotinoids selectivity. This study contributes to our understanding of the molecular mechanism underlying selectivity of neonicotinoids against insects over vertebrates.
Yao
Xiangmei
X
Key Laboratory of Monitoring and Management of Plant Disease and Insect, Ministry of Agriculture, Nanjing Agricultural University, Tongwei Road 6, Nanjing 210095, PR China.
Song
Feng
F
Chen
Fajun
F
Zhang
Yixi
Y
Gu
Jianhua
J
Liu
Shuhua
S
Liu
Zewen
Z
D000595:Amino Acid Sequence; D000818:Animals; D001042:Aphids; D018679:Cholinergic Agonists / Q000493:pharmacokinetics*; D004330:Drosophila; D006430:Hemiptera / Q000737:chemistry / Q000187:drug effects*; D007093:Imidazoles / Q000493:pharmacokinetics*; D008969:Molecular Sequence Data; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000493:pharmacokinetics*; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D054730:Protein Interaction Domains and Motifs; D051381:Rats; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014981:Xenopus
D018679:Cholinergic Agonists; D007093:Imidazoles; D000073943:Neonicotinoids; D009574:Nitro Compounds; D011978:Receptors, Nicotinic; D011993:Recombinant Fusion Proteins; C082359:imidacloprid