Identification of a third rat odorant-binding protein (OBP3)

From a rat olfactory epithelium cDNA library clones encoding a lipocalin we re isolated with sequence identity to the previously described salivary-spe cific alpha -2u globulin and the N-terminal region of mouse odorant-binding proteins OBP-III and OBP-IV In situ hybridization showed strong expression in nasal glands displaying a pattern equivalent to rat OBP1. Heterologousl y expressed protein was evaluated for its binding properties using spectros copic approaches. The recombinant protein interacted with two fluorescent p robes, 1-aminoanthracene (1-AMA) and 1,1'-bis(4-anilino-5-naphthalene)-sulf onic acid. 1-AMA binding was competed by several odorants with high affinit y. The thermodynamic parameters of the protein-odorant interaction were det ermined using isothermal titration calorimetry. Due to its nasal expression and odorant-binding characteristics this protein was designated OBP3.