Purification, cloning and characterisation of odorant- and pheromone-binding proteins from pig nasal epithelium

Two distinct classes of lipocalin isoforms (OBP-IIs and OBP-IIIs) were puri fied and identified from porcine nasal mucosa of male and female individual s. Using primers designed on their N-terminal sequence, the complete primar y structures of the mature polypeptides were determined. Mass spectrometry analysis confirmed the identity of the cDNA-derived sequences and provided information regarding their post-translational modifications. These species strongly resemble a lipocalin expressed by von Ebner's gland and salivary lipocalins carrying sex-specific pheromones secreted only by the boar's sub maxillary glands. Both OBP-IIs and OBP-IIIs present two cysteines paired in a disulphide bond; the remaining residues occur in a reduced form. In addi tion, OBP-IIIs are heavily glycosylated and markedly different in their gly can moiety from the salivary lipocalins. A three-dimensional model is propo sed based on protein species with known structure. Like salivary lipocalins , OBP-IIIs bind a number of odorant molecules, with highest affinity for th e specific pheromone 5 alpha -androst-16-en-3-one. The high similarity betw een OBPs from the nasal area and lipocalins from secretory glands suggests a common function in binding the same pheromonal ligands, the latter carryi ng chemical messages into the environment the former delivering them to spe cific receptors.