D3415: Deorphanization of odorant binding proteins in the mosquito maxillary palp

The first step in insect olfaction is facilitated by odorant binding proteins (OBPs). Insect OBPs are small cysteine stabilized proteins that bind to and solubilize hydrophobic odorants within the aqueous sensillar lymph and release them near the dendrites of olfactory receptor neurons. In mosquitoes, the maxillary palp is relatively simple compared to other olfactory appendages; it contains one sensillar type, the capitate peg sensillum. Each sensillum contains three sensory neurons, labeled “A”, “B”, and “C”. In Aedes aegypti these express Gustatory Receptors (GRs), Olfactory Receptor 8 (OR8), and OR49, which bind to CO2, 1-octen-3-ol, and Camphor respectively. We hypothesized that the most highly expressed OBPs in the maxillary palps would bind to the ligands which activate the receptors from neurons “A”, “B”, and “C”. We evaluated the maxillary palp OBP transcription profiles from Aedes aegypti, Anopheles gambiae, and Toxorhynchites amboinensis. We decided to produce the four most highly expressed maxillary palp OBPs from each of these species as recombinant proteins, to elucidate their structures by NMR analysis, and to deorphanize them using fluorescent binding assays. Surprisingly, we found that among the four OBPs with the highest maxillary palp expression, the amino acid sequence of two were highly conserved across all three species. Here, we discuss our findings of structure and function, drawing conclusions about olfaction across diverse species of mosquitoes.