The X-ray Structure of a Hemipteran Ecdysone Receptor Ligand-binding Domain

Abstract

The ecdysone receptor is a hormone-dependent transcription factor that plays a central role in regulating the expression of vast networks of genes during development and reproduction in the phylum Arthropoda. The functional receptor is a heterodimer of the two nuclear receptor proteins ecdysone receptor (EcR) and ultraspiracle protein. The receptor is the target of the environmentally friendly bisacylhydrazine insecticides, which are effective against Lepidoptera but not against Hemiptera or several other insect orders. Here we present evidence indicating that much of the selectivity of the bisacylhydrazine insecticides can be studied at the level of their binding to purified ecdysone receptor ligand-binding domain (LBD) heterodimers. We report the crystal structure of the ecdysone receptor LBD heterodimer of the hemipteran Bemisia tabaci (Bt, sweet potato whitefly) in complex with the ecdysone analogue ponasterone A. Although comparison with the corresponding known LBD structure from the lepidopteran Heliothis virescens (Hv) ecdysone receptor revealed the overall mode of ponasterone A binding to be very similar in the two cases, we observed that the BtEcR ecdysteroid-binding pocket is structured differently to that of HvEcR in those parts that are not in contact with ponasterone A. We suggest that these differences in the ligand-binding pocket may provide a molecular basis for the taxonomic order selectivity of bisacylhydrazine insecticides. The nuclear receptor (NR)1 family of proteins plays a crucial role in the regulation of transcription, and its members include the receptors for steroid hormones, vitamins, thyroid hormones, and bile acids (1). The human genome contains about 48 members of this family, and these have been studied extensively as therapeutic targets (2). The Arthropoda display a more limited suite of NRs (3) about 21 of which occur in Drosophila melanogaster. Among these is the receptor for the major arthropod steroid hormone, 20-hydroxyecdysone, which is involved in the regulation of insect molting, metamorphosis, and reproduction (4 -9). The receptor is absent from mammals and is thus potentially useful as a safe insecticide target. Indeed members of the bisacylhydrazine family exert their insecticidal activity by binding to the ecdysone receptor and exhibit remarkable taxonomic order selectivity (10, 11). These compounds act selectively on the Lepidoptera and certain Coleoptera (10) but are ineffective against insects of the hemipteran order and therefore cannot be used to control certain insect pests. A study (12) of two hemipteran insect predators (Geocoris punctipes and Orius insidiosus) showed that these beneficial (predatory) hemipterans are relatively insensitive to the bisacylhydrazine tebufenozide, whereas lepidopteran insect pests are susceptible. An improved understanding of variation in the structure of the ligand-binding pockets of ecdysone receptors and the basis of the specificity of these compounds at the atomic level of detail of their interaction with the receptor may aid ...

Critical Role of Desolvation in the Binding of 20-Hydroxyecdysone to the Ecdysone Receptor

“…The structure of Heliothis USP in the complex is almost identical to the structure of the monomer (root mean square deviation of 0.71 Å for 235 C ␣ atoms) (43), with a large hydrophobic ligandbinding pocket that is filled with a phospholipid molecule. A similar x-ray structure was also observed for Drosophila USP LBD, whereas a different structure was observed for Bemisia USP (14) and Tribolium USP (15).…”

“…The structure of EcR/USP in complex with ponA was previously solved for different insect species, the moth Heliothis (13), the silver whitefly Bemisia (14), and the beetle Tribolium (15). In their respective ligand bound ecdysone receptor crystal structures, 20E and ponA adopt almost identical chair conformations and similar positioning of their alkyl tail.…”

“…Unexpectedly, in Drosophila melanogaster, as in other species belonging to various insect orders, biological data indicate that the binding affinity of ponA is 1-2 orders of magnitude higher than the corresponding values for 20E (12). To date, four crystal structures of the heterodimer EcR/USP ligand-binding domains (LBDs) have been reported: two structures for the moth Heliothis virescens (Hv) EcR/USP, one bound to the phytoecdysteroid ponA and the other one to the synthetic dibenzoylhydrazine (DBH) agonist BYI06830 (13), and the EcR/USP structures of the silverleaf whitefly Bemisia tabaci (14) and of the red flour beetle Tribolium castaneum (15), both in complex with ponA. Remarkably, the crystal structures of HvEcR in complex with ponA and BYI06830, two chemically and structurally distinct compounds, were found to be markedly different.…”

Adrien Albert Award: How to Mine Chemistry Space for New Drugs and Biomedical Therapies

“…These methods have been used to design and optimise green pesticides [16][17][18][19][20] in collaboration with Du Pont and Schering Plough, have discovered new peptides and small molecules to control stem cells and cancers, [21][22][23][24][25][26][27] are accelerating the development of biomaterials for implantation and stem cell culture, [28][29][30][31][32][33] have provided new scientific insight into the potential adverse properties of nanomaterials, [34][35][36][37][38] have yielded clinical candidates for Australian SMEs and international companies, and were instrumental in the discovery of antibiotics [39,40] with a novel mode of action for the biotechnology spin off company, Betabiotics. Some of this research is discussed in more detail in the following sections.…”

Efeito letal e subletal de inseticidas reguladores de crescimento ao predador Ceraeochrysa cubana (Hagen, 1861) (Neuroptera: Chrysopidae) em condições de laboratório

“…Apesar de todos os insetos produzirem o 20E, esses ingredientes ativos se ligam a este complexo de receptores de forma específica em lepidópteros, conferindo a seletividade aos artrópodes de diferentes ordens (CARMICHAEL et al, 2005;DHADIALLA et al, 2005;ZOTTI et al, 2012). Diversos trabalhos conduzidos com a substância confirmam sua especificidade a lepidópteros como Spodoptera sp.…”