Fig. 3. Structures of related ‘PDZ-like’ domains. Proteins are shown in ribbon form; ß-strands are shown in turquoise, and 
-helices are shown in red. (A) A canonical metazoan PDZ domain exemplified by the third PDZ domain of PSD-95 (residues 306-394), shown with a bound peptide (dark blue) as in Fig. 1 (Doyle et al., 1996). (B) Interleukin 16 (IL-16), residues 25-119. Trp-99, shown in stick form, occludes the normal PDZ peptide-binding site (Mühlhahn et al., 1998). (C) The photosystem D1 protease (residues 157-249) from Scenedesmus obliquus. The structure is circularly permuted relative to the structures in (A) and (B), but the fold is essentially the same (Liao et al., 2000). Note that, in all structures, the N- and C-termini of the domains are close together.
