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Insect olfactory receptors are heteromeric ligand-gated ion channels


In insects, each olfactory sensory neuron expresses between one and three ligand-binding members of the olfactory receptor (OR) gene family, along with the highly conserved and broadly expressed Or83b co-receptor1,2,3,4,5,6,7,8,9. The functional insect OR consists of a heteromeric complex of unknown stoichiometry but comprising at least one variable odorant-binding subunit and one constant Or83b family subunit10,11,12,13,14,15,16. Insect ORs lack homology to G-protein-coupled chemosensory receptors in vertebrates17 and possess a distinct seven-transmembrane topology with the amino terminus located intracellularly10,18. Here we provide evidence that heteromeric insect ORs comprise a new class of ligand-activated non-selective cation channels. Heterologous cells expressing silkmoth, fruitfly or mosquito heteromeric OR complexes showed extracellular Ca2+influx and cation-non-selective ion conductance on stimulation with odorant. Odour-evoked OR currents are independent of known G-protein-coupled second messenger pathways. The fast response kinetics and OR-subunit-dependent K+ ion selectivity of the insect OR complex support the hypothesis that the complex between OR and Or83b itself confers channel activity. Direct evidence for odorant-gated channels was obtained by outside-out patch-clamp recording of Xenopus oocyte and HEK293T cell membranes expressing insect OR complexes. The ligand-gated ion channel formed by an insect OR complex seems to be the basis for a unique strategy that insects have acquired to respond to the olfactory environment.

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Figure 1: Odorants activate a non-selective cation conductance in HeLa cells expressing multimeric insect ORs.
Figure 2: Insect OR activity is independent of G protein signalling.
Figure 3: Kinetic analysis of Ca 2+ and current responses of insect ORs in HeLa cells.
Figure 4: Excised outside-out patch-clamp recording of Or47a + Or83b currents measured in oocyte membranes.
Figure 5: Excised outside-out patch-clamp recording of insect OR currents measured in HEK293T membranes.


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K.S. and K.T. thank M. Tominaga, Y. Okamura and Y. Kubo for discussion. M.P. and L.B.V. thank D. Gadsby, and Gadsby laboratory members N. Vedovato, P. Artigas, P. Hoff and A. Kovacs. DNA clones were provided by R. Y. Tsien (mRFP), T.-Y. Chen (CNGs) and A. Kovacs (CFTR). This work was supported in part by grants from PROBRAIN and MEXT of Japan to K.T., by a grant from the Foundation for the National Institutes of Health to R. Axel and L.B.V. through the Grand Challenges in Global Health Initiative, and by a National Institutes of Health (NIH) grant to L.B.V., a postdoctoral fellowship from the Japan Society for the Promotion of Science (JSPS) to T.N., and an NIH US–Japan Brain Research Cooperative Program grant and Japan-US Cooperative Science Program funding from the JSPS to K.T. and L.B.V.

Author Contributions Experiments were performed by K.S. (Figs 1, 2a–d, 3 and 5, and Supplementary Figs 1, 2, 3a, 4, 5a, b, 6 and 8), M.P. (Fig. 4 and Supplementary Figs 3b–d, 5c and 7), Takao N. (Fig. 2e) and Tatsuro N. (Supplementary Fig. 5b). K.T. and L.B.V. conceived and supervised the experiments, and wrote the paper with K.S. and M.P.

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Correspondence to Kazushige Touhara.

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Sato, K., Pellegrino, M., Nakagawa, T. et al. Insect olfactory receptors are heteromeric ligand-gated ion channels. Nature 452, 1002–1006 (2008).

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