Differences In The Effects Of Insecticide And Zebrafish GABA_A And Drosophila RDL Receptors

y-aminobutyirc acid receptor (GABA receptor) is the major inhibitoryneurotransmitter receptor in the central nervous system(CNS) of vertebrate andperipheral nervous system of insects. It is modulated by endogenous ligandy-aminobutyric acid and some important pharmacology and clinical drugs, and italso associated with a vairety of human neurological diseases, y-aminobutyric acidtype A receptor (GABAa receptor) is one of the most important recepors in GABAreceptor which was the target of picrotoxinin and a variety of pesticides such aslindane, endosulfan, ifpronil and avermectin. These compounds are noncompetitiveantagonists when bind with GABAa receptors, and blocked the receptor channels.Insect GABA receptors located in central nervous system of insects and the joints ofmuscles，and it is an important target of some pesticides. Radioligand binding assayand electrophysiological techniques were applied in entomology, which indicatedthat RDL subunit of insect could form a functional GABA ligand-gated ion channels,but there were many differences in pharmacology with vertebrate GABAa receptors.Up to now, the crystal structures of Zebrafish and insect GABA receptors havenot been reported yet. In this work, the three dimensional structures of ZebraifshGABAa receptor and Fruitfly RDL receptor, the interaction modes between the twoGABA receptors and small molecules and the stability in both receptor-ligandcomplexes were compared by using the technology of computational simulation. Ingeneral, three parts were included:1.The three-dimensional models of the transmembrane domain of Zebraifsh(Danio rerio) aip2y2GABAa receptor and Fruitfly (Drosophila melanogaster) RDLreceptor were constructed by homology modeling based on the nicotinicacetylcholine receptor. The receptor structures were optimized by using moleculardynamics and the rationality of the two models were evaluated by ramachandran plot.The sequence identity of the second transmembrane (M2) domain in ZebrafishGABAa receptor and Fruitlfy RDL receptor was high, but the structures of the tworeceptors are different. The structure of Ala301in RDL receptor whichcorresponding to Zebrafish GABAa receptor al subunit Val284and y2subunit Ser306，the conformation difference between these amino acids is much larger.2.Molecular docking and Molecular dynamics were used to investigate thedifferent interactions between Fipronil and the two receptors. In Zebraifsh GABAareceptor, Fipronil located at the bottom of the transmembrane domain, while inFruitlfy RDL receptor，Fipronil located within the region from Ala301to Leu308.The two receptor-Fipronil complexes were stable atfer molecular dynamicssimulation. There were4hydrogen bonds formed between Fipronil and ZebraifshGABAa receptor, two of them whose frequency were higher than60%. There were6hydrogen bonds in Fruitlfy RDL receptor-Fipronil complex, only one of them whosefrequency was higher than50%. It is clear the stability of Fruitfly RDL receptor-Fipronil complex was lower than that of Zebrafish GABAa receptor-Fipronilcomplex.3.Molecular docking was used to investigate the interaction between somefipronil metabolites and the two GABA receptors，and we analyzed the relationshipbetween the cdockeri_nteraction_energy of fipronil and its metabolites with theirbiological activity data. It was found that the cdockeri一nteraction一energy of fipronilmetabolites in Zebraifsh GABAa receptor were higher than fipronil itself, whichindicating that the toxicity of fipronil metabolites are much higher than fipronil toZebraifsh and the environment. In Fruitlfy RDL receptor， thecdockeri一nteraction一energy of ifpronil metabolites was as high as ifpronil, whichindicated that ifpronil metabolites also had insecticidal activity.