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Characterization of an enantioselective odorant receptor in the yellow fever mosquito Aedes aegypti.

Bohbot JD, Dickens JC - PLoS ONE (2009)

Bottom Line: Only recently were enantioselective odorant receptors demonstrated in mammals while their existence in insects has remained hypothetical.In addition to steric constraints, chain length and degree of unsaturation play important roles in this recognition process.This is the first characterization of an enantioselective odorant receptor in insects and the results demonstrate that an OR alone, without helper proteins, can account for chiral specificity exhibited by olfactory sensory neurons (OSNs).

View Article: PubMed Central - PubMed

Affiliation: United States Department of Agriculture, Agricultural Research Service, Henry A. Wallace Beltsville Agricultural Research Center, Plant Sciences Institute, Invasive Insect Biocontrol and Behavior Laboratory, Beltsville, Maryland, USA.

ABSTRACT
Enantiomers differ only in the left or right handedness (chirality) of their orientations and exhibit identical chemical and physical properties. In chemical communication systems, enantiomers can be differentially active at the physiological and behavioral levels. Only recently were enantioselective odorant receptors demonstrated in mammals while their existence in insects has remained hypothetical. Using the two-microelectrode voltage clamp of Xenopus oocytes, we show that the yellow fever mosquito, Aedes aegypti, odorant receptor 8 (AaOR8) acts as a chiral selective receptor for the (R)-(-)-enantiomer of 1-octen-3-ol, which in the presence of other kairomones is an attractant used by blood-sucking insects to locate their hosts. In addition to steric constraints, chain length and degree of unsaturation play important roles in this recognition process. This is the first characterization of an enantioselective odorant receptor in insects and the results demonstrate that an OR alone, without helper proteins, can account for chiral specificity exhibited by olfactory sensory neurons (OSNs).

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AaOR8 discriminates between the two enantiomers of 1-octen-3-ol.(A) The odorant 1-octen-3-ol occurs in two configurations: (R) and (S). Asterisk indicates the chiral center. (B) Response traces of AaOR8 to each enantiomer are recorded in nano-ampere (nA). For space considerations, time scales differ. (C) Concentration-response plots of AaOR8 to each enantiomer of 1-octen-3-ol (n = 6). Odorant concentrations were plotted on a logarithmic scale. Each point represents the mean and vertical current response; error bars are s.e.m. Responses to 10−5 M 1-octen-3-ol are highlighted in red.
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pone-0007032-g001: AaOR8 discriminates between the two enantiomers of 1-octen-3-ol.(A) The odorant 1-octen-3-ol occurs in two configurations: (R) and (S). Asterisk indicates the chiral center. (B) Response traces of AaOR8 to each enantiomer are recorded in nano-ampere (nA). For space considerations, time scales differ. (C) Concentration-response plots of AaOR8 to each enantiomer of 1-octen-3-ol (n = 6). Odorant concentrations were plotted on a logarithmic scale. Each point represents the mean and vertical current response; error bars are s.e.m. Responses to 10−5 M 1-octen-3-ol are highlighted in red.

Mentions: Racemic 1-octen-3-ol (CH3[CH2]4CH[OH]CH = CH2) is a mono-unsaturated 8-carbon alcohol with carbon 3 being the single stereogenic center (Fig. 1A), hence its composition of two optically active enantiomers, (R)-(—)-1-octen-3-ol and (S)-(+)-1-octen-3-ol. Octenol is a natural compound of plant [28] and animal origin [29], and has been identified from human sweat extracts [30]. (R)-(—)-1-octen-3-ol is the prevailing enantiomer in volatiles collected from cattle with a (R)/(S) ratio between 80% and 92% [29]. While both octenol enantiomers are equally active aggregation pheromones for several beetle species [31] and potent attractants to the tsetse fly, Glossina morsitans [29], many mosquito species exhibit a preference for the (R)-(—) form [32], [33]. This compound alone is an attractant for various hematophagous insects [29], [34] and its behavioral potency is increased when combined with CO2 [35]. OSNs located within the capitate peg sensilla on the maxillary palps of Aedes aegypti [36], Culex quinquefasciatus [33] and Anopheles gambiae [16] mediate the response to octenol and CO2. In the case of An. gambiae, the molecular basis of the octenol response has previously been attributed to An. gambiae OR8 (AgOR8) [16]. We recently identified the Or gene family of Ae. aegypti including the Ae. aegypti orthologue of AgOr8, AaOr8 [37]. In the current study, we establish that octenol is the preferred ligand of the AaOR8/AaOR7 protein complex, and investigate the structure-activity relationship between ligand and receptor, focusing on the enantiomeric discrimination of (R)- and (S)-octenol.


Characterization of an enantioselective odorant receptor in the yellow fever mosquito Aedes aegypti.

Bohbot JD, Dickens JC - PLoS ONE (2009)

AaOR8 discriminates between the two enantiomers of 1-octen-3-ol.(A) The odorant 1-octen-3-ol occurs in two configurations: (R) and (S). Asterisk indicates the chiral center. (B) Response traces of AaOR8 to each enantiomer are recorded in nano-ampere (nA). For space considerations, time scales differ. (C) Concentration-response plots of AaOR8 to each enantiomer of 1-octen-3-ol (n = 6). Odorant concentrations were plotted on a logarithmic scale. Each point represents the mean and vertical current response; error bars are s.e.m. Responses to 10−5 M 1-octen-3-ol are highlighted in red.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2737144&req=5

pone-0007032-g001: AaOR8 discriminates between the two enantiomers of 1-octen-3-ol.(A) The odorant 1-octen-3-ol occurs in two configurations: (R) and (S). Asterisk indicates the chiral center. (B) Response traces of AaOR8 to each enantiomer are recorded in nano-ampere (nA). For space considerations, time scales differ. (C) Concentration-response plots of AaOR8 to each enantiomer of 1-octen-3-ol (n = 6). Odorant concentrations were plotted on a logarithmic scale. Each point represents the mean and vertical current response; error bars are s.e.m. Responses to 10−5 M 1-octen-3-ol are highlighted in red.
Mentions: Racemic 1-octen-3-ol (CH3[CH2]4CH[OH]CH = CH2) is a mono-unsaturated 8-carbon alcohol with carbon 3 being the single stereogenic center (Fig. 1A), hence its composition of two optically active enantiomers, (R)-(—)-1-octen-3-ol and (S)-(+)-1-octen-3-ol. Octenol is a natural compound of plant [28] and animal origin [29], and has been identified from human sweat extracts [30]. (R)-(—)-1-octen-3-ol is the prevailing enantiomer in volatiles collected from cattle with a (R)/(S) ratio between 80% and 92% [29]. While both octenol enantiomers are equally active aggregation pheromones for several beetle species [31] and potent attractants to the tsetse fly, Glossina morsitans [29], many mosquito species exhibit a preference for the (R)-(—) form [32], [33]. This compound alone is an attractant for various hematophagous insects [29], [34] and its behavioral potency is increased when combined with CO2 [35]. OSNs located within the capitate peg sensilla on the maxillary palps of Aedes aegypti [36], Culex quinquefasciatus [33] and Anopheles gambiae [16] mediate the response to octenol and CO2. In the case of An. gambiae, the molecular basis of the octenol response has previously been attributed to An. gambiae OR8 (AgOR8) [16]. We recently identified the Or gene family of Ae. aegypti including the Ae. aegypti orthologue of AgOr8, AaOr8 [37]. In the current study, we establish that octenol is the preferred ligand of the AaOR8/AaOR7 protein complex, and investigate the structure-activity relationship between ligand and receptor, focusing on the enantiomeric discrimination of (R)- and (S)-octenol.

Bottom Line: Only recently were enantioselective odorant receptors demonstrated in mammals while their existence in insects has remained hypothetical.In addition to steric constraints, chain length and degree of unsaturation play important roles in this recognition process.This is the first characterization of an enantioselective odorant receptor in insects and the results demonstrate that an OR alone, without helper proteins, can account for chiral specificity exhibited by olfactory sensory neurons (OSNs).

View Article: PubMed Central - PubMed

Affiliation: United States Department of Agriculture, Agricultural Research Service, Henry A. Wallace Beltsville Agricultural Research Center, Plant Sciences Institute, Invasive Insect Biocontrol and Behavior Laboratory, Beltsville, Maryland, USA.

ABSTRACT
Enantiomers differ only in the left or right handedness (chirality) of their orientations and exhibit identical chemical and physical properties. In chemical communication systems, enantiomers can be differentially active at the physiological and behavioral levels. Only recently were enantioselective odorant receptors demonstrated in mammals while their existence in insects has remained hypothetical. Using the two-microelectrode voltage clamp of Xenopus oocytes, we show that the yellow fever mosquito, Aedes aegypti, odorant receptor 8 (AaOR8) acts as a chiral selective receptor for the (R)-(-)-enantiomer of 1-octen-3-ol, which in the presence of other kairomones is an attractant used by blood-sucking insects to locate their hosts. In addition to steric constraints, chain length and degree of unsaturation play important roles in this recognition process. This is the first characterization of an enantioselective odorant receptor in insects and the results demonstrate that an OR alone, without helper proteins, can account for chiral specificity exhibited by olfactory sensory neurons (OSNs).

Show MeSH
Related in: MedlinePlus