Fig. 1. A WW-like sequence on the DRß chain. (A) Sequence alignment of MHCII ß chain sequences. A list of sequences from HLA-D ß allo- and isotypes and of MHCII ß chain orthologs from several species is shown. The positions of conserved Y and W residues are labeled in black. Conserved amino acid residues are colored in gray. (B) A potential proline-binding sequence of the DRß chain is adjacent to the proline-rich sequence of Ii. The X-ray structure of HLA-DR3 loaded with CLIP is shown. The YWD residues of WWCII are indicated (pdb accession 1A6A). Amino acid residues DRßW153 and DRßY123 form a hydrophobic cluster that is exposed to a potential position of the proline-rich region of Ii. Residues DRßW131 and DRßY171 form a cluster that is imprinted in the sequence of other members of the Ig super gene family. The P87 residue of CLIP is resolved in the X-ray structure. The X-ray structure was modified with Swiss-Deep view3.7 and visualized with Viewer Lite5.0 (right).