Sexual attraction in the silkworm moth: structure of the pheromone-binding-protein-bombykol complex

Background: Insects use volatile organic molecules to communicate messages with remarkable sensitivity and specificity. In one of the most studied sys tems, female silkworm moths (Bombyx mori) attract male mates with the phero mone bombykol, a volatile 16-carbon alcohol. In the male moth's antennae, a pheromone-binding protein conveys bombykol to a membrane-bound receptor on a nerve cell. The structure of the pheromone-binding protein, its binding and recognition of bombykol, and its full role in signal transduction are n ot known. Results: The three-dimensional structure of the B. mori pheromone-binding p rotein with bound bombykol has been determined by X-ray diffraction at 1.8 Angstrom resolution. Conclusions: The pheromone binding protein of B. mori has six helices, and bombykol binds in a completely enclosed hydrophobic cavity formed by four a ntiparallel helices. Bombykol is bound in this cavity through numerous hydr ophobic interactions, and sequence alignments suggest critical residues for specific pheromone binding.