Gypsy Moth Pheromone Binding Proteins: Ligand Interactions and Antennal Mapping

Pheromone binding proteins (PBPs) are believed to be part of the transport of hydrophobic pheromone in the sensory hairs of insects. In this thesis, I have studied two gypsy moth (Lymantria dispar) PBPs for their interactions with the main sex attractant pheromone, (+)-disparlure, (7R,8S)-epoxy-2-methyloctadecane. I also studied interactions of the PBPs with the enantiomer of the pheromone, (-)-disparlure and both enantiomers of heteroatom substituted analogues. These studies were prompted by the fact that the interaction of these PBPs with these natural and artificial ligands is not completely understood. To address this problem, docking simulations of the protonated homology PBP models with the enantiomers of various ligands (disparlure, 5-oxadisparlure, 10-oxadisparlure, 5-thiadisparlure and 10-thiadisparlure) were performed together with a binding assay. A second question regarding the two PBPs of gypsy moth is how they are distributed on the moth’s antennae. Mapping the antennal PBP distribution on the moth was done through cutting the antennae into known sections and determination of PBPs by Western blotting. The result of molecular simulations revealed different amino acid residues in the binding sites of PBP, abrupt movement of specific amino acid residues at a certain pH and distinct amino acid-ligand interactions (sidechain donors/acceptors, H-arene bonding, backbone donors/ acceptors) of the best bound conformers of each protein-ligand complex. Overall, the results may correlate with the pKa values obtained from the binding assay, and explain the enantioselectivity of the gypsy moth PBPs. Mapping the antenna was accomplished and suggests that the two PBPs are present in similar general distributions. The symmetrical distribution of the PBPs is related to the number of sensilla found in the branches calculated by taking total and normalized PBP weights.