Homology modeling and molecular docking studies of Drosophila and Aedes sex peptide receptors.

The Drosophila melanogaster sex peptide receptor (DrmSPR), which is a G protein-coupled receptor (GPCR), is known as the specific receptor for sex peptide (SP). It is responsible for the reproductive behavior in the Drosophila model system; in particular, it is involved in the post-mating responses such as the increase in egg-laying ability and decrease in receptivity in females. In a previous study, we discovered a small molecule agonist of DrmSPR for the first time, which could not, however, activate Aedes aegypti SPR (AedesSPR). To investigate the binding mechanism of the small molecule agonist of DrmSPR, the ensemble structures of low-lying packing structures of DrmSPR and AedesSPR were assembled using the GEnSeMBLE (GPCR Ensemble of Structures in Membrane BiLayer Environment) method. The generated homology models exhibited the typical pattern of inter-helical interactions of the class A GPCRs. The docking experiments of the small molecule agonist suggest that Tyr(5.35) and Phe(2.67) residues may be involved in a hydrophobic interaction and that Ser(3.25) forms a hydrogen bond with the agonist. Additionally, we found that the docking results were consistent with the experimental data of the reference compounds with variable agonistic activities. Moreover, a potential distinction of the putative binding sites in two GPCR models of DrmSPR and AedesSPR, which was determined in this study, can explain the selective action of the agonist for DrmSPR but not for AedesSPR.

Discovery and structure-activity relationships of pyrazolodiazepine derivatives as the first small molecule agonists of the Drosophila sex peptide receptor.

In behavioral research, the sex peptide receptor in Drosophila melanogaster (DrmSPR) is the most interesting G protein-coupled receptor (GPCR) and is involved in post-mating responses such as increased egg-laying and decreased receptivity of the female; during these responses, the receptors are activated by a specific natural peptide agonist (sex peptide, SP). To discover small molecule agonists for DrmSPR, a compound library based on a pyrazolodiazepine scaffold, which was previously reported as a potential privileged structure, was screened. Structure-activity relationship (SAR) studies of the hit compounds, which exhibited weak agonistic effects (69-72% activation at 100µM), were explored through the synthesis of various analogs with substituents at the R1, R2, R3 and R4 positions of the pyrazolodiazepine skeleton. As a result, compounds 21 and 31 of the 6-benzyl pyrazolodiazepine derivative series were found to be small molecule agonists for DrmSPR with EC50 values of 3-4µM.