FIGURE 6.

Scheme of ligand and repellent binding to OBP1 and 4. In the absence of ligands OBP1 (light gray octagon) appears to exist predominantly as dimers, whereas OBP4 (dark gray) is a highly dynamic structure. Binding of odorants, including indole (black), leads to dissociation of OBP1 into monomers and a stabilization of the OBP4 structure that allows the two proteins to form heterodimers. Repellent molecules, like 6-MH (white square) can function either to compete for and displace the normal ligand or can bind at the same time as the native ligand and disrupt the formation of the OBP1-OBP4 complex.