Sexual attraction in the silkworm moth. Nature of binding of bombykol in pheromone binding protein--an ab initio study.

An analysis of the crystal structure of [BmPBP...bombykol] complex identified nine amino acid residues involved in a variety of intermolecular interactions binding the ligand. Using simple model fragments as the representatives of the residues, the interaction energies of their complexes with bombykol were calculated using high-level ab initio methods. The results were discussed in terms of the method and basis set dependence and were further corrected to account for their pair nonadditivities. This enabled us to describe quantitatively the nature and origin of the binding forces in terms of contribution of the individual amino acids and individual types of interaction to the overall stability. All of these interactions are well defined and cannot be considered as nonspecific hydrophobic interactions, one of the major conclusions of this work.