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: 9.67). 10/2010; 107(44):19102-7. DOI: 10.1073/pnas.1012274107
Source: PubMed


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 · 3.53 Impact Factor
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    • "The following NMR structure proved that the C-terminal dodecapeptide segment of the acidic form of BmorPBP (pH 4.5) formed an additional helix in the protein core, occupied the corresponding pheromone-binding site and released ligands [3]. Aside from the above long-chain OBPs structures, there are several structures of medium-chain OBPs reported, including Anopheles gambia OBP1 (AgamOBP1) [4], AgamOBP7 [5] and Culex quinquefasciatus OBP1 (CquiOBP1) [6], in which the C-terminal extensions are locked by a hydrogen bond triad composed of the last residue and two other residues (Tyr and His). The hydrogen bond triad would be disrupted at lower pH, leading to the C-terminal loop move away from the binding pocket and the ''lid'' open. "
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    ABSTRACT: Locusta migratoria (Lmig) causes enormous losses to agricultural products, especially because it often infests the world with great swarms as locust plagues. Locusts find their plant hosts on which they feed through their olfactory system, in which odorant binding proteins (OBPs) play an important role. Previous study indicated that the amino acid sequences of LmigOBP showed low similarity to OBPs from other insect orders and we speculated that it might perform unique binding behavior. Here, we solved the first LmigOBP1 structure at 1.65 Å, which is a monomer in solution and disulfide bonds play a key role in maintaining its function. We show that LmigOBP1 possesses a unique seventh α-helix, which is located at the surface with strong interactions with the LmigOBP1 scaffold consisting of other six α-helices. Moreover, the seventh α-helix forms a wall of an "L" shaped internal hydrophobic cavity to accommodate linear ligands, which is consistent with the binding experiments. We also demonstrate that the ligand-binding pocket in LmigOBP1 is greatly different from that in the closest homologs mosquito OBPs. Taken together, this study provides a structural basis for designing small inhibitors to control locust. Copyright © 2014. Published by Elsevier Inc.
    Biochemical and Biophysical Research Communications 12/2014; 456(3). DOI:10.1016/j.bbrc.2014.12.048 · 2.30 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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