Enzymatic systems involved in peri-receptor events of olfaction in mammalian: evolutionary perspectives
Résumé
The olfactory epithelium is continuously exposed to exogenous chemicals, including compounds bearing odor activity. Organisms have developed multiple mechanisms for the protection of this epithelium, among which anti-microbial proteins, enzymes fighting the oxidative stress and xenobiotic metabolizing enzymes. Our approach consists in characterizing by immunohistochemistry and mass spectroscopy analysis the proteome of the nasal mucus in different mammals (currently including Harbour porpoise, Homo sapiens, Mus musculus, Oryctolagus cuniculus, Rattus norvegicus). These analyses reveal core some enzyme families in the different species investigated, including glutathione transferases (GSTs). GSTs represent a large family of enzymes comprising numerous members that appear ubiquitous in terrestrial organisms. GSTs operate in catalyzing the conjugation of glutathione (present in the nasal mucus) with various compounds including odorants, leading to their elimination and thus playing a role in the termination of the olfactory stimulus. Our results support the function of GSTs in the peripheral olfactory process, in terms of modulation of odorant availability for the olfactory receptors. We will explore the expression and function of the GST enzymes in different species of mammals and their redundant functions in the olfactory system. These results on mammalian GSTs will be discussed in an evolutionary perspective in comparison with insect GSTs. Despite insects have evolved a distinct olfactory system from mammals, their GSTs have a similar role in olfaction.