Anopheles gambiae odorant binding protein crystal complex with the synthetic repellent DEET: implications for structure-based design of novel mosquito repellents

Abstract

Insect odorant binding proteins (OBPs) are the first components of the olfactory system to encounter and bind attractant and repellent odors emanating from various sources for presentation to olfactory receptors, which trigger relevant signal transduction cascades culminating in specific physiological and behavioral responses. For disease vectors, particularly hematophagous mosquitoes, repellents represent important defenses against parasitic diseases because they effect a reduction in the rate of contact between the vectors and humans. OBPs are targets for structure-based rational approaches for the discovery of new repellent or other olfaction inhibitory compounds with desirable features. Thus, a study was conducted to characterize the high resolution crystal structure of an OBP of Anopheles gambiae, the African malaria mosquito vector, in complex with N,N-diethyl-m-toluamide (DEET), one of the most effective repellents that has been in worldwide use for six decades. We found that DEET binds at the edge of a long hydrophobic tunnel by exploiting numerous non-polar interactions and one hydrogen bond, which is perceived to be critical for DEET's recognition. Based on the experimentally determined affinity of AgamOBP1 for DEET (K (d) of 31.3 μΜ) and our structural data, we modeled the interactions for this protein with 29 promising leads reported in the literature to have significant repellent activities, and carried out fluorescence binding studies with four highly ranked ligands. Our experimental results confirmed the modeling predictions indicating that structure-based modeling could facilitate the design of novel repellents with enhanced binding affinity and selectivity.

Applications of molecular modeling in the design of new insect repellents targeting the odorant binding protein of Anopheles gambiae

“…To perform the calculations in the present work, it was used the dimmeric 3D structure of AgOBP 1 , complexed with DEET and PEG (a 5 unit polyethylene glycol molecule) with resolution of 1.6 Å, available in the Protein Data Bank (PDB) 14 under the code 3N7H. This crystal structure presents one DEET molecule anchored in each subunit at sites located near the interface between the two monomers.…”

“…Next, these molecules are transported to the olfactory receptor neurons (ORN), located in the dendritic membranes at the antenna sensory bristles, driving the mosquito's attention to the potential meal. 3,9,[11][12][13][14] Studies by Biessmann et al 11 have proved the importance of OBP for smell recognition in the search for food, in mating and other activities. 3,12,14 Among the 60 types of OBP coded in the A. gambiae genoma, the Anopheles gambiae odorant binding protein (AgOBP 1 ) was found in higher levels in the antennas of females when compared to males and its levels were observed to reduce when the females feed on blood.…”

“…3,9,[11][12][13][14] Studies by Biessmann et al 11 have proved the importance of OBP for smell recognition in the search for food, in mating and other activities. 3,12,14 Among the 60 types of OBP coded in the A. gambiae genoma, the Anopheles gambiae odorant binding protein (AgOBP 1 ) was found in higher levels in the antennas of females when compared to males and its levels were observed to reduce when the females feed on blood. 14 Despite not having its mechanism of action well elucidated yet, N,N-diethyl-3-methylbenzamide (DEET) is the main repellent in use today against A. gambiae.…”

“…3,12,14 Among the 60 types of OBP coded in the A. gambiae genoma, the Anopheles gambiae odorant binding protein (AgOBP 1 ) was found in higher levels in the antennas of females when compared to males and its levels were observed to reduce when the females feed on blood. 14 Despite not having its mechanism of action well elucidated yet, N,N-diethyl-3-methylbenzamide (DEET) is the main repellent in use today against A. gambiae. 2,3,4,6,15 Tsitsanou et al 14 suggested that this molecule targets AgOBP 1 , blocking the binding site of the attractive molecules, and published the 3D structure of the AgOBP 1 -DEET complex as the first example of a repellent recognized by an OBP.…”

“…14 Despite not having its mechanism of action well elucidated yet, N,N-diethyl-3-methylbenzamide (DEET) is the main repellent in use today against A. gambiae. 2,3,4,6,15 Tsitsanou et al 14 suggested that this molecule targets AgOBP 1 , blocking the binding site of the attractive molecules, and published the 3D structure of the AgOBP 1 -DEET complex as the first example of a repellent recognized by an OBP. This achievement should give a significant impulse to the drug design of new repellents as it provides the first known target.…”