Crystal Structures and Binding Dynamics of Odorant-Binding Protein 3 from two aphid species Megoura viciae and Nasonovia ribisnigri

Abstract

Aphids use chemical cues to locate hosts and find mates. The vetch aphid Megoura viciae feeds exclusively on the Fabaceae, whereas the currant-lettuce aphid Nasonovia ribisnigri alternates hosts between the Grossulariaceae and Asteraceae. Both species use alarm pheromones to warn of dangers. For N. ribisnigri this pheromone is a single component (E)-β-farnesene but M. viciae uses a mixture of (E)-β-farnesene, (−)-α-pinene, β-pinene, and limonene. Odorant-binding proteins (OBP) are believed to capture and transport such semiochemicals to their receptors. Here, we report the first aphid OBP crystal structures and examine their molecular interactions with the alarm pheromone components. Our study reveals some unique structural features: 1) the lack of an internal ligand binding site; 2) a striking groove in the surface of the proteins as a putative binding site; 3) the N-terminus rather than the C-terminus occupies the site closing off the conventional OBP pocket. The results from fluorescent binding assays, molecular docking and dynamics demonstrate that OBP3 from M. viciae can bind to all four alarm pheromone components and the differential ligand binding between these very similar OBP3s from the two aphid species is determined mainly by the direct π-π interactions between ligands and the aromatic residues of OBP3s in the binding pocket.

Evolution and functional analysis of odorant‐binding proteins in three rice planthoppers: Nilaparvata lugens, Sogatella furcifera, and Laodelphax striatellus

“…All the ligands were located at hydrophobic pockets, surrounded by hydrophobic residues within 4 Å (Table and Fig. (A)–(F)), which is similar to the binding features of some other insect OBPs . In addition, Trp‐50, Leu‐67, and Phe‐113 are the three key residues that appeared most frequently, i.e.…”

“…7(A)-(F)), which is similar to the binding features of some other insect OBPs. [91][92][93] In addition, Trp-50, Leu-67, and Phe-113 are the three key residues that appeared most frequently, i.e. 12, 12, and 10 times, respectively, thus indicating their importance for binding.…”

Integrative transcriptomic and genomic analysis of odorant binding proteins and chemosensory proteins in aphids

“…Odorant binding proteins (OBPs) and chemosensory proteins (CSPs) are two families of small water-soluble proteins; they are highly concentrated (as high as 10 mm) in sensillum lymph of the antennal sensilla and believed to be involved in the initial chemosensory recognition of insects (Vogt and Riddiford, 1981;Calvello et al, 2003;Pelosi et al, 2006). Both OBPs and CSPs have small molecular weights, approximately 15 kDa for OBPs and 12 kDa for CSPs.…”

“…Both OBPs and CSPs have small molecular weights, approximately 15 kDa for OBPs and 12 kDa for CSPs. The common feature of insect OBPs is that they have six highly conserved cysteines that are paired to form interlocked disulphide bridges Northey et al, 2016). Insect CSPs, on other hand, have four conserved cysteines that are linked to form disulphide bridges .…”

“…The functional studies of aphid OBPs and CSPs in recognizing and discriminating the sex pheromones, the alarm pheromone and the host plant volatiles, however, are still limited. The OBP3 of A. pisum (Qiao et al, 2009), the OBP7 of S. avenae (Vandermoten et al, 2011;Zhong et al, 2012), the OBP3 of Megoura viciae and Nasonovia ribisnigri (Northey et al, 2016) and the OBP3 and OBP7 of Rhopalosiphum padi (Fan et al, 2017) have high binding affinities with the alarm pheromone Eβf. However, the in vivo evidence of OBP3 and OBP7 participating in Eβf recognition is still not conclusive.…”