Disulfide pairing and secondary structure of ASP1, an olfactory-binding protein from honeybee (Apis mellifera L)

In insects, the transport of airborne, hydrophobic odorants and pheromones through the sensillum lymph is accomplished by olfactory-binding proteins (OBPs). We report the structural characterization of a honeybee OBP called ASP1 found in workers and drones, previously observed to bind queen pheromone components. A novel method based on ion-spray mass spectrometry analysis of cyanylation-induced cleavage products of partially reduced protein with Tris(2-carboxyethyl)phosphine was needed to determine the recombinant ASP1 disulfide bond pairing. It was observed to Cys(I)-Cys(III), Cys(Il)-Cys(V), Cys(IV)-Cys(VI), similar to those already described for other OBPs from honeybee and Bombyx mori suggesting that this pattern occurs commonly the diverse family of insect OBPs. Circular dichroism revealed that ASP1 is an all-alpha protein in accordance with NMR preliminary data, but unlike lipocalin-like vertebrate OBPs.