3 ODORANT-BINDING PROTEINS FROM RABBIT NASAL-MUCOSA

Following the purification of an odorant-binding protein (OBP) from ra bbit nasal mucosa, we have identified, purified and partially characte rized two additional OBPs from the nasal tissue of the same animal spe cies. 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 OB P-I, both these new members bind the odorant 2-isobutyl-3-methoxypyraz ine. The partial amino acid sequences of the three OBPs, determined by Edman degradation, confirm that they are members of the OBP family, b ut reveal poor similarity between them. However, higher similarity is found between each OBP and other members of the lipocalin family In pa rticular, OBP-I is most similar to bovine OBP (55% identity in the N-t erminal region), OBP-II is >50% identical, limited to its first 18 ami no acids, to mouse OBP-I and porcupine OBP-II, while OBP-II 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 prot eins in olfactory transduction is also discussed.