THE 3-DIMENSIONAL STRUCTURE OF BOVINE ODORANT BINDING-PROTEIN AND ITSMECHANISM OF ODOR RECOGNITION

Odorant binding protein (OBP) is the major odorant binding component o f mammalian nasal mucosa. The two structures of bovine OBP reported in this paper (one crystallized as purified and one soaked in the presen ce of a selenium-containing odorant) show that: (i) the OBP dimer is c omposed of two compact domains related by an approximate two-fold axis of symmetry; (ii) between residues 122 and 123 the polypeptide chains cross from one domain to the other such that each domain is formed by residues from both monomers; (iii) purified OBP already contains two bound odorant molecules (one per monomer) - odorant binding occurs by replacement of these molecules with the added odorant; and (iv) the st ructure of the odorant binding site can explain OBP's extraordinarily broad odorant specificity.