Mechanisms of Olfaction in Insects - ResearchSpace@Auckland ...
Mechanisms of Olfaction in Insects - ResearchSpace@Auckland ...
Mechanisms of Olfaction in Insects - ResearchSpace@Auckland ...
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General Introduction 7<br />
1.5 Components <strong>of</strong> the olfactory system<br />
The identification <strong>of</strong> several prote<strong>in</strong> components <strong>of</strong> the olfactory system <strong>in</strong> <strong>in</strong>sects<br />
such as fruit flies and moths has paved the way for further detailed study <strong>of</strong> these<br />
prote<strong>in</strong>s and the peripheral events <strong>in</strong>volved <strong>in</strong> signal transduction. The identification,<br />
isolation and functional analysis <strong>of</strong> these prote<strong>in</strong>s are described below.<br />
1.5.1 Prote<strong>in</strong>s found <strong>in</strong> the sensillum lymph<br />
Abundant <strong>in</strong> the sensillum lymph are small, soluble prote<strong>in</strong>s, rang<strong>in</strong>g <strong>in</strong> size from 14–<br />
16 kDa called odorant b<strong>in</strong>d<strong>in</strong>g prote<strong>in</strong>s (OBP). These prote<strong>in</strong>s are produced <strong>in</strong> the<br />
sensillum support cells and secreted <strong>in</strong>to the lymph (Vogt and Riddiford, 1981). The<br />
first OBP to be identified was a 15 kDa male antennal specific prote<strong>in</strong>, unique to the<br />
pheromone sensitive sensilla, that bound sex pheromones <strong>in</strong> the wild silkmoth<br />
Antheraea polyphemus (Vogt and Riddiford, 1981). Due to its close association with<br />
sex pheromones, it was called a pheromone b<strong>in</strong>d<strong>in</strong>g prote<strong>in</strong> (PBP). PBPs are generally<br />
found at high concentrations (10 mM) <strong>in</strong> male <strong>in</strong>sect antennae (Kle<strong>in</strong>, 1987), but<br />
some PBPs have also been identified <strong>in</strong> female moth antennas (Callahan et al., 2000).<br />
Low levels <strong>of</strong> PBP have been identified <strong>in</strong> some Lepidoptera species while high<br />
expression levels <strong>of</strong> PBPs have been shown <strong>in</strong> members <strong>of</strong> the Noctuoidea (Kle<strong>in</strong>,<br />
1987; Callahan et al., 2000). It was not until 1991 when the first evidence <strong>of</strong><br />
multigene families <strong>of</strong> OBPs emerged with the identification <strong>of</strong> two groups <strong>of</strong> general<br />
odorant b<strong>in</strong>d<strong>in</strong>g prote<strong>in</strong>s (GOBP), namely GOBP1 and GOBP2; prote<strong>in</strong>s that are not<br />
sex-biased and have highly conserved regions with<strong>in</strong> members <strong>of</strong> the groups (Vogt et<br />
al., 1991; Krieger et al., 1993; Krieger et al., 1996). Most PBPs were identified and<br />
characterised by their b<strong>in</strong>d<strong>in</strong>g to radio-labelled versions <strong>of</strong> known sex pheromone<br />
components. GOBPs on the other hand have been less studied <strong>in</strong> terms <strong>of</strong> their<br />
b<strong>in</strong>d<strong>in</strong>g partners. In 1997, Feng and Prestwich deduced the ligand <strong>of</strong> GOBP2 from<br />
Manduca sexta by competitive displacement <strong>of</strong> tritium-labelled diazoacetate<br />
pheromone analog, [ 3 H]-6E,11Z-16:Dza, by the plant odorants (Z)-3-hexen-1-ol,<br />
geraniol, geranyl acetate and limonene (Feng and Prestwich, 1997). In a recent study<br />
<strong>of</strong> OBPs from B. mori, GOBP2 was shown to b<strong>in</strong>d the sex pheromone <strong>of</strong> B. mori,<br />
bombykol and also to be able to discrim<strong>in</strong>ate it from its antagonist, bombykal (Zhou<br />
et al., 2009). The specific function <strong>of</strong> OBPs is still unclear but several roles <strong>of</strong> OBPs