Olfaction in the gypsy moth, Lymantria dispar - Effect of pH, ionic strength, and reductants on pheromone transport by pheromone-binding proteins

The pheromone-binding proteins (PBPs) are 16-kDa abundant proteins in speci alized olfactory hairs in insects. The mechanism by which the PBPs remove t he pheromone from the inner surface of sensory hairs and deliver it to the sensory cell remains unclear. Existing qualitative models postulate that ph eromone is released near the dendrite by a decrease in pH or by a reduced f orm of the PBP. This study focuses on the two PBPs from the gypsy moth and the enantiomers of the pheromone cis-2-methyl-7,8-epoxyoctadecane. The pH d ependence of pheromone binding has revealed three ionizations that are impo rtant. The type of ligand influences two of these ionizations. We propose t hat the (-)-enantiomer of the pheromone interacts with one of the ionizable residues on the protein while the (+)-enantiomer does not. Simultaneous va riation of pH and KCl concentration in the physiological range or reduction of disulfide bridges does not change the affinity of PBP for pheromone. We propose a revised model of pheromone transport from the inner surface of t he sensory hair to the sensory neuron.