NMR structure of the pheromone-binding protein from the silkworm Bombyx mori, BmPBP. Seven a-helices connected by linkers with nonregular secondary structure are shown in grey color and disulfide bonds are yellow. The core side chains are shown as bundles of 20 superimposed conformers, with red color for the side chains of the "regulatory" helix 7 and green color for all other core side chains.