Crystal and solution structures of an odorant-binding protein from the southern house mosquito complexed with an oviposition pheromone

Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 10/2010; 107(44):19102-7. DOI: 10.1073/pnas.1012274107
Source: PubMed

ABSTRACT Culex mosquitoes introduce the pathogens responsible for filariasis, West Nile virus, St. Louis encephalitis, and other diseases into humans. Currently, traps baited with oviposition semiochemicals play an important role in detection efforts and could provide an environmentally friendly approach to controlling their populations. The odorant binding proteins (OBPs) in the female's antenna play a crucial, if yet imperfectly understood, role in sensing oviposition cues. Here, we report the X-ray crystallography and NMR 3D structures of OBP1 for Culex quinquefasciatus (CquiOBP1) bound to an oviposition pheromone (5R,6S)-6-acetoxy-5-hexadecanolide (MOP). In both studies, CquiOBP1 had the same overall six-helix structure seen in other insect OBPs, but a detailed analysis revealed an important previously undescribed feature. There are two models for OBP-mediated signal transduction: (i) direct release of the pheromone from an internal binding pocket in a pH-dependent fashion and (ii) detection of a pheromone-induced conformational change in the OBP·pheromone complex. Although CquiOBP1 binds MOP in a pH-dependent fashion, it lacks the C terminus required for the pH-dependent release model. This study shows that CquiOBP binds MOP in an unprecedented fashion using both a small central cavity for the lactone head group and a long hydrophobic channel for its tail.

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Available from: Yuko Ishida, Jul 01, 2014
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    • "The position of the polar moiety of MOP in the binding pocket matched that observed in the crystal structure. As previously described, MOP has its long lipid " tail " bound in a hydrophobic tunnel formed between helices 4 and 5 and only its lactone/acetate head is housed in the central cavity (Mao et al., 2010). There was a slight difference between the position of the hydrophobic moiety of MOP in the simulated and crystal structures, but this part of the molecule is flexible and different conformations could be accommodated in the hydrophobic tunnel. "
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    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.
    Frontiers in Physiology 02/2015; 6:56. DOI:10.3389/fphys.2015.00056 · 3.50 Impact Factor
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    • "Furthermore, a second mutant, where C-terminus one (Lys123) of the three lysine residues was replaced by methionine showed reduced affinity to pheromone components, as well as to their analogues due to less hydrogen bonds formation affinity [4]. pH-dependent ligand-release mechanisms were reported in Culex quinquefasciatus, CquiOBP1 [57], Aedes aegypti, AaegOBP1 [27] and Anopheles gambiae, AgamOBP1 [58], in which a decrease in pH, disrupts the hydrogen bond between the C-terminal loop and the rest of the protein, and then opens the loop to release the ligands [50]. "
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    ABSTRACT: Odorant binding proteins (OBPs) play a central role in transporting odorant molecules from the sensillum lymph to olfactory receptors to initiate behavioral responses. In this study, the OBP of Macrocentrus cingulum McinOBP1 was expressed in Escherichia coli and purified by Ni ion affinity chromatography. Real-time PCR experiments indicate that the McinOBP1 is expressed mainly in adult antennae, with expression levels differing by sex. Ligand-binding experiments using N-phenyl-naphthylamine (1-NPN) as a fluorescent probe demonstrated that the McinOBP1 can bind green-leaf volatiles, including aldehydes and terpenoids, but also can bind aliphatic alcohols with good affinity, in the order trans-2-nonenal>cis-3-hexen-1-ol>trans-caryophelle, suggesting a role of McinOBP1 in general odorant chemoreception. We chose those three odorants for further homology modeling and ligand docking based on their binding affinity. The Val58, Leu62 and Glu130 are the key amino acids in the binding pockets that bind with these three odorants. The three mutants, Val58, Leu62 and Glu130, where the valine, leucine and glutamic residues were replaced by alanine, proline and alanine, respectively; showed reduced affinity to these odorants. This information suggests, Val58, Leu62 and Glu130 are involved in the binding of these compounds, possibly through the specific recognition of ligands that forms hydrogen bonds with the ligands functional groups.
    PLoS ONE 04/2014; 9(4):e93501. DOI:10.1371/journal.pone.0093501 · 3.23 Impact Factor
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    • "Three-dimensional modelling of the antennal OBP of B. dorsalis was developed using an online protein threading (PHYRE 2) and homology modelling (SWISS-MODEL) online programs. AgamOBP1, a female odorant binding protein from Anopheles gambiae (PDB code: 2ERB) [34], CquiOBP1, a female-dominant odorant binding protein from Culex quinquefasciatus (PDB code: 3OGN) [35,36] and AaegOBP1, a major female- enriched odorant-binding protein from Aedes aegypti (PDB code: 3K1E) [6] were suggested as templates by the program. Multiple sequence alignment of the OBPs was carried out using Clustal O (see Additional file 3). "
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    ABSTRACT: Semiochemical is a generic term used for a chemical substance that influences the behaviour of an organism. It is a common term used in the field of chemical ecology to encompass pheromones, allomones, kairomones, attractants and repellents. Insects have mastered the art of using semiochemicals as communication signals and rely on them to find mates, host or habitat. This dependency of insects on semiochemicals has allowed chemical ecologists to develop environment friendly pest management strategies. However, discovering semiochemicals is a laborious process that involves a plethora of behavioural and analytical techniques, making it expansively time consuming. Recently, reverse chemical ecology approach using odorant binding proteins (OBPs) as target for elucidating behaviourally active compounds is gaining eminence. In this scenario, we describe a "computational reverse chemical ecology" approach for rapid screening of potential semiochemicals. We illustrate the high prediction accuracy of our computational method. We screened 25 semiochemicals for their binding potential to a GOBP of B. dorsalis using molecular docking (in silico) and molecular dynamics. Parallely, compounds were subjected to fluorescent quenching assays (Experimental). The correlation between in silico and experimental data were significant (r2 = 0.9408; P < 0.0001). Further, predicted compounds were subjected to behavioral bioassays and were found to be highly attractive to insects. The present study provides a unique methodology for rapid screening and predicting behaviorally active semiochemicals. This methodology may be developed as a viable approach for prospecting active semiochemicals for pest control, which otherwise is a laborious process.
    BMC Genomics 03/2014; 15(1):209. DOI:10.1186/1471-2164-15-209 · 4.04 Impact Factor
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