Journal of Comparative Physiology A

, Volume 199, Issue 11, pp 897–909

The role of the coreceptor Orco in insect olfactory transduction

Authors

    • FB 10, Biology, Animal PhysiologyUniversity of Kassel
  • Nico W. Funk
    • FB 10, Biology, Animal PhysiologyUniversity of Kassel
Review

DOI: 10.1007/s00359-013-0837-3

Cite this article as:
Stengl, M. & Funk, N.W. J Comp Physiol A (2013) 199: 897. doi:10.1007/s00359-013-0837-3

Abstract

Insects sense odorants with specialized odorant receptors (ORs). Each antennal olfactory receptor neuron expresses one OR with an odorant binding site together with a conserved coreceptor called Orco which does not bind odorants. Orco is necessary for localization of ORs to dendritic membranes and, thus, is essential for odorant detection. It forms a spontaneously opening cation channel, activated via phosphorylation by protein kinase C. Thereafter, Orco is also activated via cyclic adenosine monophosphate (cAMP). Orco forms homo—as well as heteromers with ORs with unknown stoichiometry. Contradictory publications suggest different mechanisms of olfactory transduction. On the one hand, evidence accumulates for the employment of more than one G protein-coupled olfactory transduction cascade in different insects. On the other hand, results from other studies suggest that the OR–Orco complex functions as an odorant-gated cation channel mediating ionotropic signal transduction. This review analyzes conflicting hypotheses concerning the role of Orco in insect olfactory transduction. In conclusion, in situ studies in hawkmoths falsify the hypothesis that Orco underlies odorant-induced ionotropic signal transduction in all insect species. Instead, Orco forms a metabotropically gated, slow cation channel which controls odorant response threshold and kinetics of the sensory neuron.

Keywords

Insect olfaction Odorant receptor Pheromones Ionotropic receptor Metabotropic signal transduction cascade

Abbreviations

cAMP

Cyclic adenosine monophosphate

cGMP

Cyclic guanosine monophosphate

GR

Gustatory receptor

I i

Ionotropic current

I m

Metabotropic current

I t

Transduction current

IP3

Inositol 1,4,5-trisphosphate

IR

Ionotropic receptor

OR

Odorant receptor

Orco

Olfactory receptor coreceptor

ORN

Olfactory receptor neuron

PKC

Protein kinase C

PLCβ

Phospholipase Cβ

SNMP

Sensory neuron membrane protein

TM

transmembrane domain

Copyright information

© Springer-Verlag Berlin Heidelberg 2013