Nature of binding of bombykol in Pheromone Binding Protein. An ab initio study

Vojtěch Klusák^{1, 2}, Zdeněk Havlas¹, Lubomír Rulíšek¹, Jiří Vondrášek¹, Aleš Svatoš³

Addresses: ¹Institute of Organic Chemistry and Biochemistry of the Academy of Sciences of the Czech Republic and Center for Complex Molecular Systems and Biomolecules, Flemingovo nám. 2, Praha 6, 166 10, Czech Republic. ²Charles University, Department of Physical and Macromolecular Chemistry, Albertov 6, Praha 2, 128 43, Czech Republic. ³Max-Planck-Institute for Chemical Ecology, Winzerlaer Str. 10, D-07745 Jena, Germany.

Interactions of insects with their surroundings are mostly based on chemical signals. One of the most remarkable communication systems known mediates sexual behavior of moths. Mature females ready to have offspring emit a sexual pheromone from their abdomen to attract conspecific males for mating. The ‘single-pheromone molecule’ tuned detection system of males is located in branches of male’s antennae. On these antennae olfactory hairs, sensila trichodea, are located. They are filled with sensilar liquor and house specialized dendritic cells, innervated to insect brain globular structures. Here, the signal received from the cell is proceeded and further recognized as a call for copulation.

The sensilar liquor contains a high concentration (10 mM) of water-soluble pheromone-binding-protein (PBP).

An analysis of the crystal structure of Bombyx mori PBP∙∙∙bombykol (pheromone) complex [1] identified nine amino acid residues involved in intermolecular hydrogen bonds, π∙∙∙π interactions, C-H∙∙∙π hydrogen bonds and weak interactions of purely van der Waals character. Using the model fragments as the representatives of each residue, the interaction energies of their complexes with bombykol were computed by ab initio calculations. The values were compared with literature and further discussed in terms of the method and basis set dependence, and the co-operative effect (influence of the neighboring groups on the interacting pair). It enabled us to explain quantitatively the nature of the binding forces in [BmPBP∙∙∙bombykol] complex in terms of contribution of the individual amino acids and individual types of interaction. It was observed that 70% of the stabilization is due to interactions other than classical hydrogen bonds.

1. Sandler, B.H., Nikonova, L., Leal, W.S., Clardy, J. (2000). Chemistry & Biology 7, 143-151. PDB code: 1DQE.