Abstract
The diversity of olfactory binding proteins (OBPs) is a key point to understand their role in molecular olfaction. Since only few different sequences were characterized in each mammalian species, they have been considered as passive carriers of odors and pheromones. We have explored the soluble proteome of pig nasal mucus, taking benefit of the powerful tools of proteomics. Combining two-dimensional electrophoresis, mass spectrometry, and western-blot with specific antibodies, our analyses revealed for the first time that the pig nasal mucus is mainly composed of secreted OBP isoforms, some of them being potentially modified by O-GlcNAcylation. An ortholog gene of the glycosyltransferase responsible of the O-GlcNAc linking on extracellular proteins in Drosophila and Mouse (EOGT) was amplified from tissues of pigs of different ages and sex. The sequence was used in a phylogenetic analysis, which evidenced conservation of EOGT in insect and mammalian models studied in molecular olfaction. Extracellular O-GlcNAcylation of secreted OBPs could finely modulate their binding specificities to odors and pheromones. This constitutes a new mechanism for extracellular signaling by OBPs, suggesting that they act as the first step of odor discrimination.
Highlights
Olfaction is generally considered as a minor, primitive sense for human beings, and the study of this sense in mammals has been neglected
The proteomic analysis of pig nasal mucus described above brought important novelty at several aspects: SOLUBLE PROTEOME OF PIG NASAL MUCUS IS MAINLY COMPOSED OF olfactory binding proteins (OBPs), VEG, AND SAL ISOFORMS The composition of the pig nasal mucus has never been investigated by 2-DE
The human saliva did not contain any SAL isoform, as the encoding gene SAL1 is a pseudogene in this species [48]
Summary
Olfaction is generally considered as a minor, primitive sense for human beings, and the study of this sense in mammals has been neglected. Many odor-guided behaviors are involved in the establishment of biological functions: reproduction via the choice of mate partner, establishment of the mother–young bond, maintenance of the social hierarchy, and to a less extent choice of food. This dialog between partners of the same species is driven by pheromones. A general scheme of olfactory coding hypothesized that pheromones are detected by sensory neurons of the vomeronasal organ (VNO), while other odors are detected by the main olfactory epithelium (MOE) sensory neurons [reviewed in Ref. Mouse VNO neurons can be stimulated by odorants emitted by other species, such as floral and woody smelling compounds [9]
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