Fig. 6. Ligand (worm structures)–receptor (yellow structures) models of: VEGF–Flt-1, SCF–Kit and PDGF–PDGF receptor. The VCAM-1 structure (PDB code: 1vca) was used, without any modification, to approximate the receptor models. Receptor models are presented as yellow surfaces. Background portions of ligands are colored light blue for one protomer and green for the other; receptor-interacting residues identified from site-directed mutagenesis experiments [VEGF (Muller et al., 1997), PDGF (Fenstermaker et al., 1993)] and other experimental data (SCF; see text) are colored magenta. Figures were drawn by GRASP (Nicholls et al., 1991).