Therorical Studies Of The Target Features Of Insect Nicotinic Acetylcholine Receptor And Hexosaminidase

Two typical insecticide targets in insect, nicotinic acetylcholine receptor (nAChR) andβ-N-1,4-acetylhexosaminidase (Chitobiase/Hex) were studied in this thesis. nAChRs, an important ion channel in the insect central nervous system, are targets for neonicotinoids, the major insecticides used today, and therefore is a hot issue in the pesticide research field recently. Hexosaminidase, a chitin degrading enzyme, is physiologically important during the unique life cycle of insects and has been a potential species-specific target for novel green pesticide design. This thesis discussed the uses of theoretical methods, such as quantum chemistry, bioinformatics and molecular mechanics in tandem to elucidate the features of nAChR and hexosaminidase, including the sequences, structure and their ligand binding mode.Through quantum chemistry method, interactions between insect nAChR and neonicotinoids were studied and a novel binding model was proposed. Hydrogen bonds between neonicotinoids and the positively charged side chains of Arg/Lys in insect nAChR play essential roles in the binding, as well as theπ-πinteraction between the conjugate guanidine/amidine moiety of neonicotinoids and the indole ring of Trp. The mode well explained the action of neonicotinoids on insect nAChR, and was proved by the crystallographic experiment data subsequently.Based on large scale sequences data of nAChRs from insect and vertebrate, their differences between vertebrate and invertebrate were studied. The different subunit evolutionary trends, the different subunit clustering and the function divergence of nAChR in different phylum were discussed. The important function divergence sites were identified, and the divergence sites mainly occupied in the complementary subunits (LoopE-F). The results will be helpful to design novel molecules with phylum-specific selectivity.nAChRs from nilaparvata lugens and Apis mellifera, represented for beneficial and pest insects respectively, were selected to study their assembly and ligand binding features. It was found thatα8 subunit in nAChRs own two distinctive positive residues, which can form stronger hydrogen bonds with the negative tip of neonicotinoids. The results interpreted the experiments that nAChRs containingα8 subunit constitute the higher affinity binding site for imidacloprid in N. lugens.OfHexl, the hexosaminidase from the insect, Ostrinia furna, was studied.3D model of Oil lexl was build through the ligand-supported homology modeling approach (MOBILE). The binding modes of its substrate (diNAG) and inhibitor (2-ADN and allosamidin) were proposed through the docking and cluster analysis; two possible binding modes of allosamindin were proposed. Moreover, the multi-target characteristics of allosamidin which inhibits enzymes from different families, OfHexl (GH20) and chitinase (GH18) were discussed, which provide the possibility to develop allosamidin or its derivatives as a new type insecticide to "hit two birds with one stone" ,if possible, a novel strategy in pest control.