Odorant-binding proteins: expression and function.

Odorant-binding proteins (OBPs) are a major constituent of the aqueous perireceptor compartment in vertebrates and in insects. Although different in primary structure, they are supposed to serve similar functions in both animal groups: (i) OBPs may act as solubilizers and carriers of the lipophilic odorants in the aqueous mucus or sensillum lymph; (ii) OBPs may act in addition as peripheral filters in odor discrimination by selectively binding certain classes of odorants; (iii) OBPs may present the stimulus molecule in a particular way to the receptor proteins to facilitate signal transduction; (iv) OBPs may clean the perireceptor space from unwanted and toxic compounds; (v) OBPs may rapidly deactivate odorants after stimulation of the receptors. Experimental evidence in favor of this multiple role of OBPs is reviewed.