Figure 6.

A, crystal structures of HER1 (blue and red for HER1 and EGF, respectively; PDB code 3NJP; 36) and HER4 (gray and green for HER4 and neuregulin, respectively; PDB code 3U7U; 22) ligand-induced dimers, superimposed, show that the dimerization interface is solely made of subdomains II (the area within the blue dotted rectangle). B, superimposition of either of those homodimers with the 39S Fab-HER2 structure shows that 39S causes steric hindrance and prevents homo- and heterodimerization of HER molecules. The area of clash is shown by the black circle.