Binding Characterization of Recombinant Odorant-binding Proteins from the Parasitic Wasp, Microplitis mediator (Hymenoptera: Braconidae)

Chemoreception in insects is mediated by small odorant-binding proteins (OBPs) that are believed to carry lipophilic stimuli to the olfactory receptor cells through the aqueous sensillar lymph. Binding experiments and recent structural studies of OBPs have illustrated their versatility and ability to accommodate ligands of different shapes and chemical structures. We expressed and purified seven recombinant OBPs (MmedOBP1-MmedOBP7) from the parasitic wasp, Microplitis mediator (Hymenoptera: Braconidae) in a prokaryotic expression system. With 4,4'-dianilino- 1,1'-binaphthyl-5,5'-sulfonic acid (bis-ANS) as a fluorescent probe, the ligand-binding specificities of these seven MmedOBPs with 50 small organic compounds were investigated in vitro. The results revealed that all of the M. mediator OBPs can bind a wide variety of odorant molecules with different binding affinities. The best ligand for all seven MmedOBPs was beta-ionone. MmedOBP2 showed affinity for some aromatic compounds, whereas MmedOBP4 and MmedOBP6 bound several terpenoids. MmedOBP5 bound beta-ionone, but did not bind any of the other potential ligands that we tested.