Proteína ligadora de odor 17 (RproOBP17) de Rhodnius prolixus como alvo molecular para o controle populacional do vetor da doença de Chagas

Abstract

Chagas disease is considered a neglected tropical disease which still affects around 7 million people worldwide. Its etiological agent is the protozoan Trypanosoma cruzi, transmitted by triatomine insects known as kissing bugs, amongst which Rhodnius prolixus is a major vector, especially in the Andean region of South America and in Central America. Seeing that there is no vaccine for Chagas disease, vector control has been the most effective means for preventing infection. However, population management of triatomine vectors using chemicals has been repeatedly unsuccessful. A while ago, insecticide resistance of triatomines was considered unlikely due to their long life-cycle and low genetic variability. Nonetheless, several studies have reported the resistance of different species to various insecticides, essentially the most commonly used pyrethroids. Classic repellents shown to be useful for protection against mosquito populations such as DEET, IR3535 and picaridin were also proven ineffective when dealing with triatomines. Since it is well established that interpretation of chemical signals from the environment is essential for insect survival, the molecular mechanism underlying their olfactory system has become an area of interest for research aiming to develop new strategies for vector control capable of interfering in olfaction-mediated behavioral responses. After reaching the antennae, semiochemicals penetrate the cuticle through pores in the sensilla and arrive at the aqueous environment of the sensillar lymph, rich in soluble proteins. Several proteins take part in insect olfaction, including odorant-binding proteins (OBPs), responsible for binding and transporting hydrophobic odorants across the sensillar lymph until they reach sensory dendrites and activate membrane-bound odorant receptors (ORs), initiating the transduction of the olfactory signal that will evoke a behavioral response. OBPs are small soluble proteins secreted by accessory cells into the sensillar lymph. Given that no odorant comes to ORs except through OBPs, they can be used as molecular targets for the screening of new insect behaviorally active compounds (attractants or repellents) through a reverse chemical ecology approach. In order to use OBPs as molecular targets in that kind of study, it is essential to focus on functional OBPs, namely, the ones actually involved in chemical communication. Therefore, the purpose of this study was to use OBP17 from R. prolixus (RproOBP17) as a molecular target aiming at the development of novel strategies for population management of this vector. Results revealed that RproOBP17 is antennae-specific and non-dependent of the insects’ nutritional state. Combining experimental analysis and in silico studies, we were able to hypothesize a role for RproOBP17 in detecting Brindley’s glands volatiles, like 2- phenylethyl 2-methylpropanoate, 2-phenylethanol, 2-methylpropyl 2-methylpropanoate. We have also been able to successfully express and purify RproOBP17. Finally, virtual screening for potential behaviorally active compounds using RproOBP17 suggested high binding affinity for ligands such as cedrol, α-humulene, β-caryophyllene and β-damascenone.