title: A determinant of odorant specificity is located at the extracellular loop 2-transmembrane domain 4 interface of an Anopheles gambiae odorant receptor subunit.
abstract: To explore the structural basis for odorant specificity in odorant receptors of the human malaria vector mosquito, Anopheles gambiae, odorant-binding subunits (Agam\Ors) expressed in Xenopus oocytes in combination with Agam\Orco (coreceptor subunit) were assayed by 2-electrode voltage clamp against 25 structurally related odorants. Agam\Or13 and Agam\Or15 display 82% amino acid identity and had similar, but somewhat distinct odorant response profiles. The ratio of acetophenone to 4-methylphenol responses was used in a mutation-based analysis of Agam\Or15, interchanging 37 disparate residues between Agam\Or15 and Agam\Or13. Eleven mutations caused significant changes in odorant responsiveness. Mutation of alanine 195 resulted in the largest shift in response ratio from Agam\Or15 toward Agam\Or13. Concentration-response analysis for a series of mutations of residue 195 revealed a large effect on acetophenone sensitivity, with EC50 values varying by >1800-fold and correlating with residue side chain length. Similar results were obtained for propiophenone and benzaldehyde. But, for other odorants, such as 4-methylphenol, 4-methylbenzaldehyde, and 4-methylpropiophenone, the effect of mutation was much smaller (EC50 values varied by ≤16-fold). These results show that alanine 195, putatively located at the second extracellular loop/fourth transmembrane domain interface, plays a critical role in determining the odorant response specificity of Agam\Or15.
authors.affiliation: Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL 33101, USA and Present address: University of Colorado School of Medicine, 13001 E. 17th Place, Aurora, CO 80045, USA.
authors.forename: David T
authors.initials: DT
authors.lastname: Hughes
authors.affiliation: Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA Present address: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100101, China.
authors.forename: Guirong
authors.initials: G
authors.lastname: Wang
authors.affiliation: Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA.
authors.forename: Laurence J
authors.initials: LJ
authors.lastname: Zwiebel
authors.affiliation: Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL 33101, USA and cluetje@med.miami.edu.
authors.forename: Charles W
authors.initials: CW
authors.lastname: Luetje
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000852:Anopheles / Q000737:chemistry / Q000502:physiology*; D002478:Cells, Cultured; D015870:Gene Expression; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D009812:Odorants / Q000032:analysis; D017434:Protein Structure, Tertiary; D018035:Receptors, Odorant / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012903:Smell; D014981:Xenopus
chemical_list: D019476:Insect Proteins; D018035:Receptors, Odorant
keywords: Xenopus oocytes; electrophysiology; insect; olfaction; receptor; structure