Crystal structures and binding dynamics of Odorant-Binding Protein 3 from two aphid species Megoura viciae and Nasonovia ribisnigri

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 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

Thermodynamic studies of AgamOBP4 and AgamOBP5 from Anopheles gambiae with different semiochemicals

Mosquitoes and other arthropods may transmit infectious agents causing several diseases. In such a context, Anopheles gambiae is considered the primary mosquito vector responsible for the transmission of malaria causing more than 1 million deaths each year. The use of repellents is one of the strategies adopted to contrast the spread of such diseases as they reduce the contact frequency between vectors and human targets. Like for other insects, the olfactory system of mosquitoes is essential for finding food, mates and blood meals and Odorant-binding proteins (OBPs) are the first components of their odor detection unit. Specifically, semiochemicals are captured by OBPs after their interaction with insect\u2019s antennae and are delivered to odorant receptors. Therefore, given the crucial role of OBPs, they constitute promising targets for the design of new repellent or attractant molecules and may improve the effectiveness of mosquitos control strategies. Here we present a calorimetric study of the thermodynamic stability of AgamOBP4 and AgamOBP5 and their behaviour against several potential ligands. In spite of the great structural resemblance between these two proteins, nanoDSC investigation performed at different pH values (pH 5.0 and 8.0) revealed different pH-dependent thermodynamic profiles and stability. Moreover, AgamOBP5 and AgamOBP4 exhibited different binding affinities for certain molecules suggesting their ability to recognize different classes of odors and that they are likely involved in different pathways of host recognition. Specifically, among the potential ligands tested, AgamOBP4 preferentially binds to artemisia acetate, whereas AgamOBP5 prefers carvacrol, thymol and cuminaldehyde as binders

Amoebicidal activity of caffeine and maslinic acid by the induction of Programmed Cell Death in Acanthamoeba

International audienceFree-living amoebae of the genus Acanthamoeba are the causal agents of a sight-threatening ulceration of the cornea called Acanthamoeba keratitis, as well as the rare but usually fatal disease granulomatous amoebic encephalitis. Although there are many therapeutic options for the treatment of Acanthamoeba infections, they are generally lengthy and/or have limited efficacy. For the best clinical outcome, treatments should target both the trophozoite and the cyst stages, as cysts are known to confer resistance to treatment. In this study, we document the activities of caffeine and maslinic acid against both the trophozoite and the cyst stages of three clinical strains of Acanthamoeba These drugs were chosen because they are reported to inhibit glycogen phosphorylase, which is required for encystation. Maslinic acid is also reported to be an inhibitor of extracellular proteases, which may be relevant since the protease activities of Acanthamoeba species are correlated with their pathogenicity. We also provide evidence for the first time that both drugs exert their anti-amoebal effects through programmed cell death

Structural basis of the synergistic inhibition of glycogen phosphorylase a by caffeine and a potential antidiabetic drug

Journal URL: http://www.sciencedirect.com/science/journal/0003986