THE WW DOMAIN OF YES-ASSOCIATED PROTEIN BINDS A PROLINE-RICH LIGAND THAT DIFFERS FROM THE CONSENSUS ESTABLISHED FOR SRC HOMOLOGY 3-BINDING MODULES

The WW domain has previously been described as a motif of 38 semiconse rved residues found in seemingly unrelated proteins, such as dystrophi n, Yes-associated protein (YAP), and two transcriptional regulators, R sp-5 and FE65. The molecular function of the WW domain has been unknow n until this time. Using a functional screen of a cDNA expression libr ary, we have identified two putative ligands of the WW domain of YAP, which we named WBP-1 and WBP-2. Peptide sequence comparison between th e two partial clones revealed a homologous region consisting of a prol ine-rich domain followed by a tyrosine residue (with the shared sequen ce PPPPY), which we shall call the PY motif. Binding assays and site-s pecific mutagenesis have shown that the PY motif binds with relatively high affinity and specificity to the WW domain of YAP, with the preli minary consensus XPPXY being critical for binding. Herein, we have imp licated the WW domain with a role in mediating protein-protein interac tions, as a variant of the paradigm set by Src homology 3 domains and their proline-rich ligands.