title: Molecular basis for odorant receptor tuning: a short C-terminal sequence is necessary and sufficient for selectivity of mosquito Or8.
abstract: A birth-and-death evolutionary model for odorant receptor gene repertoires presumes the creation of repertoires with the capacity for high-level diversity and rapid ligand specificity change. This changes the recognised odour space, directly affecting fitness-related behaviours and ultimately affecting adaptation to new environments and resources. The proximate molecular mechanisms underlying the tuning of odorant receptor repertoires, and thus peripheral olfaction, are unclear. In the present study, we report a concrete example of this model of odorant receptor evolution leading to rapid changes in receptor tuning that leave the peripheral neuronal circuitry intact. We identified a conserved odorant receptor gene in mosquitoes, Or8, which in Culex quinquefasciatus underwent a duplication and inversion event. The paralogues differ in only minor structural changes manifesting at the C-terminus. We assessed the specificity of the paralogous odorant receptors and receptor neurones. We found that the functional tuning of the receptor was indeed reflected in minor differences in amino acid structure. Specifically, we found that enantiomeric specificity of these mosquito Or8 paralogues relies on eight C-terminal amino acids encoded in the final exon of the gene; thus, the birth of a paralogous odorant receptor can change the tuning of the peripheral olfactory system.
authors.affiliation: Unit of Chemical Ecology, Department of Plant Protection Biology, Swedish University of Agricultural Sciences, Box 102, 230 52 Alnarp, Sweden.
authors.forename: S R
authors.initials: SR
authors.lastname: Hill
authors.affiliation: Unit of Chemical Ecology, Department of Plant Protection Biology, Swedish University of Agricultural Sciences, Box 102, 230 52 Alnarp, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Majeed
authors.affiliation: Unit of Chemical Ecology, Department of Plant Protection Biology, Swedish University of Agricultural Sciences, Box 102, 230 52 Alnarp, Sweden.
authors.forename: R
authors.initials: R
authors.lastname: Ignell
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D002460:Cell Line; D003465:Culex / Q000235:genetics*; D017344:Genes, Insect; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D017434:Protein Structure, Tertiary; D018035:Receptors, Odorant / Q000737:chemistry / Q000235:genetics*; D012903:Smell / Q000502:physiology
chemical_list: D019476:Insect Proteins; D018035:Receptors, Odorant
keywords: birth-and-death evolutionary model; chemical ecology; insects; olfaction; receptor-ligand interaction; selectivity