Selectivity of odorant-binding proteins from the southern house mosquito tested against physiologically relevant ligands

Abstract

As opposed to humans, insects rely heavily on an acute olfactory system for survival and reproduction. Two major types of olfactory proteins, namely, odorant-binding proteins (OBPs) and odorant receptors (ORs), may contribute to the selectivity and sensitivity of the insects' olfactory system. Here, we aimed at addressing the question whether OBPs highly enriched in the antennae of the southern house mosquito, Culex quinquefasciatus, contribute at least in part to the selective reception of physiologically relevant compounds. Using a fluorescence reporter and a panel of 34 compounds, including oviposition attractants, human-derived attractants, and repellents, we measured binding affinities of CquiOBP1, CquiOBP2, and CquiOBP5. Based on dissociation constants, we surmised that CquiOBP2 is a carrier for the oviposition attractant skatole, whereas CquiOBP1 and CquiOBP5 might transport the oviposition pheromone MOP, a human-derived attractant nonanal, and the insect repellent picardin. Binding of these three ligands to CquiOBP1 was further analyzed by examining the influence of pH on apparent affinity as well as by docking these three ligands into CquiOBP1. Our findings suggest that CquiOBP1 might discriminate MOP from nonanal/picaridin on the basis of the midpoint transition of a pH-dependence conformational change, and that MOP is better accommodated in the binding cavity than the other two ligands. These findings, along with previous experimental evidence suggesting that CquiOBP1 does not detect nonanal in vivo, suggest that OBP selectivity may not be clearly manifested in their dissociation constants.

New insights on repellent recognition by Anopheles gambiae odorant-binding protein 1

“…The results of our docking simulations directed at the hydrophobic channel formed between helices 4 and 5 are consistent with similar studies involving AgamOBP1 [ 53 ] as well as the highly homologous CquiOBP1 [ 54 ]. Ligand binding at the central cavity of AgamOBP1 is also possible as shown in simulations in which the docking grid was centred at it.…”

An Antennae-Specific Odorant-Binding Protein Is Involved in Bactrocera dorsalis Olfaction

“…Based on these results, we expect that the OBPs in subgroup I are most likely involved in odorant detection and are true OBPs that function directly in odorant perception and sensitivity. Here, for example, our data suggest that the Bdorobp20 is most enriched in the female antennae, and is perhaps involved with the detection of oviposition signals or reception of other attractants, which would be consistent with the similar OBPs that have been reported in other species (Biessmann et al, 2010;Mao et al, 2010;Pelletier et al, 2010;Xu et al, 2010;Yin et al, 2015). However, the specific role of Bdorobp20 in B. dorsalis olfaction needs to be continued exploring in future research.…”

Optimization of reverse chemical ecology method: false positive binding of Aenasius bambawalei odorant binding protein 1 caused by uncertain binding mechanism

“…Fluorescence competitive binding assays have been widely used to test the binding affinities of OBPs with ligands. The results may help to screen the potential behaviourally active compounds of insects (Yin et al, 2015;Ma et al, 2016;Sun et al, 2016). To assess lots of chemicals, the physiologically relevant binding and release mechanisms of OBP and ligands are considered as the essential theoretical basis to elicit a behavioural response (Klein, 1987;Brito et al, 2016).…”