Evidence of an odorant-binding protein in the human olfactory mucus: location, structural characterization, and odorant-binding properties.
Odorant-binding proteins (OBPs) are small abundant extracellular proteins belonging to the lipocalin superfamily. They are thought to participate in perireceptor events of odor detection by carrying, deactivating, and/or selecting odorant molecules. Putative human OBP genes (hOBP) have recently been described [Lacazette et al. (2000) Hum. Mol. Genet. 9, 289-301], but the presence of the corresponding proteins remained to be established in the human olfactory mucus. This paper reports the first evidence of such expression in the mucus covering the olfactory cleft, where the sensory olfactory epithelium is located. On the contrary, hOBPs were not observed in the nasal mucus covering the septum and the lower turbinate. To demonstrate the odorant binding activity of these proteins, a corresponding recombinant protein variant, hOBP(IIa)(alpha), was secreted by the yeast Pichia pastoris and thoroughly characterized. It appears as a monomer with one disulfide bond located between C59 and C151, a conservative feature of all other vertebrate OBPs. By measuring the displacement of several fluorescent probes, we show that hOBP(IIa)(alpha) is able to bind numerous odorants of diverse chemical structures, with a higher affinity for aldehydes and large fatty acids. A computed 3D model of hOBP(IIa)(alpha) is proposed and reveals that two lysyl residues of the binding pocket may account for the increased affinity for aldehydes. The relatively limited specificity of hOBP(IIa)(alpha) suggests that other human OBPs are expected to take into account the large diversity of odorant molecules.
Briand
Loïc
L
Biochimie et Structure des Protéines, Unité de recherches INRA 477, Domaine de Vilvert, F-78352, Jouy-en-Josas Cedex, France.
Eloit
Corinne
C
Nespoulous
Claude
C
Bézirard
Valérie
V
Huet
Jean-Claude
JC
Henry
Céline
C
Blon
Florence
F
Trotier
Didier
D
Pernollet
Jean-Claude
JC
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D001483:Base Sequence; D001667:Binding, Competitive; D004591:Electrophoresis, Polyacrylamide Gel; D005456:Fluorescent Dyes / Q000378:metabolism; D005822:Genetic Vectors; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D009093:Mucus / Q000737:chemistry / Q000378:metabolism; D009812:Odorants / Q000032:analysis*; D009831:Olfactory Mucosa / Q000737:chemistry* / Q000378:metabolism*; D010843:Pichia / Q000235:genetics; D020033:Protein Isoforms / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D018035:Receptors, Odorant / Q000096:biosynthesis / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D020539:Sequence Analysis, Protein; D013050:Spectrometry, Fluorescence; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D005456:Fluorescent Dyes; D008024:Ligands; D020033:Protein Isoforms; D018035:Receptors, Odorant; D011994:Recombinant Proteins; C045648:odorant-binding protein