Fig. 2. The same PDZ domain can recognize two structurally distinct ligands. The 1-syntrophin PDZ domain is shown as a gray solvent-accessible surface. (A) The ligand is canonical peptide NH₂-VKESLV-COOH, shown as a red tube (Schultz et al., 1998). (B) The ligand is the nNOS PDZ domain with its distinctive ß-finger motif (indicated), shown as a red ribbon diagram. The internal peptide motif that mimics a C-terminal peptide is indicated (Hillier et al., 1999).