Transmembrane Segment 3 of Drosophila melanogaster Odorant Receptor Subunit 85b Contributes to Ligand-Receptor Interactions

Abstract

The OR class insect odorant receptors are ligand-gated ion channels comprised of at least one common subunit (OR83b in Drosophila) and at least one putative odorant-binding subunit. However, little else is known about the molecular details of insect OR architecture. For example, nothing is known about how these receptors bind odorants, greatly limiting efforts to develop insect OR-targeted compounds for the control of insects involved in disease propagation and agricultural damage. Here we identify a portion of a Drosophila OR that is involved in odorant activation of the receptor. Using the substituted cysteine accessibility method, we identified residues 146 -150 of OR85b, located at the predicted interface between transmembrane segment 3 (TMS3) and extracellular loop 2 (ECL2), as playing a role in odorant (2-heptanone) activation. We found that occupation of the receptor by the competitive antagonist 2-nonanone protected the receptor from methanethiosulfonate action at position 148, placing this region close to the odorantbinding site. In addition, mutations at positions 142 and 143 within TMS3 altered odorant sensitivity. Our results identify the involvement of the extracellular half of TMS3 in Drosophila OR85b in odorant activation of the receptor. This finding can serve as a starting point for future detailed analysis of the molecular basis for odorant recognition by insect ORs, a novel class of ligand-gated channel.The accurate assessment of volatile chemicals in an environment requires an olfactory system to be both sensitive and broadly tuned. An organism can then quickly process new information about its surroundings and make behavioral decisions necessary for survival. To this end, the insect olfactory system employs a large array of chemosensory receptors for the detection of odorants and pheromones. These receptors are appealing targets for the control of insects involved in disease propagation and agricultural damage. Realizing this goal requires development of a detailed understanding of insect chemosensory receptor structure and function.

Highly sensitive and selective odorant sensor using living cells expressing insect olfactory receptors

“…S1). In our experiment, the EC 50 values of BmOR1, BmOR3, PxOR1, and DOr85b were 0.25, 0.38, 2.52, and 45.6 μM, respectively; these values are basically reasonable when compared to the reported data (24)(25)(26). For practical use, reproducible measurements will be achieved by construction of stable expression systems and generating a standard curve.…”

“…Although the mechanisms for the recognition of odorants are unclear, the oocytes expressing the insect olfactory receptor "sniff out" the odorants with high sensitivity. Our used receptors include the BmOR1, BmOR3, PxOR1, and DOr85b receptors, which come from the silkmoth (Bombyx mori), the diamondback moth (Plutella xylostella), and the fruit fly (Drosophila melanogaster) (23)(24)(25)(26). Especially, the availability of DOr85b implies that the system can be applied to detect odorants as well as pheromones.…”

Hemimetabolous genomes reveal molecular basis of termite eusociality

“…The smaller genomes of termites compared to the cockroach are in line with previous size estimations based on C-values 18 . The proteome of B. germanica (29,216 proteins) is also much larger than in the termites, where we find the proteome size in C. secundus (18,162) to be similar to those of the other two termites (M. natalensis: 16,140; Z. nevadensis: 15,459; Fig. 1).…”

“…3d). Such a variation in the transmembrane domain can be related to ligand-binding specificity, as has been shown for a polymorphism in the third transmembrane domain for an OR in D. melanogaster 28,29 , adding further support for an adaptive evolution of chemoreceptors, in line with the greater need for a sophisticated colony communication in the termites. Similar to IRs, a higher proportion of ORs were differentially expressed between workers and queens in the three termites than between nymphs and adults in the cockroach ( Fig.…”

“…B g e r ( 3 6 ) O th e r s ( 2 1 ) C s e c (9 ) Zn ev (2 0) Bg er (1 3) Rp ro (1 6) Tcas (12) Nvit (14) Oth ers (29 ) M n a t (9 ) TM1 TM2 TM3 TM4 TM5 TM6 TM7 Mnat C N T TM1 T T TM2 T T TM3 T T TM4 T T TM5 T T TM6 T TM7 …”