Three odorant-binding proteins from rabbit nasal mucosa.

Following the purification of an odorant-binding protein (OBP) from rabbit nasal mucosa, we have identified, purified and partially characterized two additional OBPs from the nasal tissue of the same animal species. OBP-II is a monomer of 21 kDa and isoelectric point 4.2; OBP-III is a dimer with subunits of 23 kDa and isoelectric point 4.8. Like OBP-I, both these new members bind the odorant 2-isobutyl-3-methoxypyrazine. The partial amino acid sequences of the three OBPs, determined by Edman degradation, confirm that they are members of the OBP family, but reveal poor similarity between them. However, higher similarity is found between each OBP and other members of the lipocalin family. In particular, OBP-I is most similar to bovine OBP (55% identity in the N-terminal region), OBP-II is > 50% identical, limited to its first 18 amino acids, to mouse OBP-I and porcupine OBP-II, while OBP-III shares 26 out of the first 40 amino acids with major urinary protein (MUP) 4, a member of the mouse salivary proteins. The possible role of these proteins in olfactory transduction is also discussed.

Microheterogeneity of odorant-binding proteins in the porcupine revealed by N-terminal sequencing and mass spectrometry.

Several odorant-binding proteins (OBP) have been previously purified from the nasal mucosa of the old world porcupine Hystrix cristata. In this paper, we report their N-terminal amino-acid sequences and accurate molecular weights, as measured by electrospray mass spectrometry. The partial amino acid sequences reveal significant similarity with OBPs of other mammalian species and segregate the eight proteins purified into two subclasses. Mass spectrometry has revealed microheterogeneity among the proteins belonging to each of these two groups, suggesting a total number of OBPs of at least nine. The molecular weight differences between OBPs cannot be readily accounted for by common post-translation modifications and indicate different gene products. Such a large number of different OBPs may represent further support to an odour discriminating role for these proteins.

Porcine VEG proteins and tear prealbumins.

Small soluble proteins, belonging to the lipocalin family are secreted in large amounts by tongue von Ebner's glands and lachrymal glands. In humans, the lingual protein, called VEG, and the lachrymal protein, called tear prealbumin, have shown identical cDNA sequences. In the pig, we have purified homodimeric proteins with subunits of 17 kDa, both from von Ebner's glands and from lachrymal glands. In both cases, the proteins can be resolved into two isoforms on a chromatofocusing column. Partial aminoacid sequences and full cDNA sequences have been obtained for the more abundant forms purified from both tissues. The two proteins appear to be identical, as in humans. The reason why the same protein is expressed in different tissues, as well as its physiological function, still remain to be clarified.

Multiple types and forms of odorant-binding proteins in the Old-World porcupine Hystrix cristata.

1. Eight new proteins have been identified and purified from the nasal tissue of the old-world porcupine. 2. All of them show good binding activity to tritiated 2-isobutyl-3-methoxypyrazine. 3. They show values of molecular mass, in denaturing conditions, between 18 and 23 kDa, and of isoelectric points between 4.2 and 4.6. 4. This represents the first example of more than two odorant-binding proteins (OBPs) found in the same animal species and could support a discriminating function of these proteins in the process of odour perception.