CHARACTERIZATION OF A NOVEL PROTEIN-BINDING MODULE - THE WW DOMAIN

We have identified, characterized and cloned human, mouse and chicken cDNA of a novel protein that binds to the Src homology domain 3 (SH3) of the Yes proto-oncogene product, We subsequently named it YAP for Ye s-associated protein. Analysis of the YAP sequence revealed a protein module that was found in various structural, regulatory and signaling molecules, Because one of the prominent features of this sequence moti f is the presence of two conserved tryptophans (W), we named it the WW domain. Using a functional screen of a cDNA expression library, we ha ve identified two putative ligands of the WW domain of YAP which we na med WBP-1 and WBP-2. Peptide sequence comparison between the two parti al clones revealed a homologous proline-rich region, Binding assays an d site-specific mutagenesis have shown that the proline-rich motif bin ds with relatively high affinity and specificity to the WW domain of Y AP, with a preliminary consensus that is different from the SH3-bindin g PXXP motif, This suggests that the WW domain has a role in mediating protein-protein interactions via proline-rich regions, similar but di stinct from Src homology 3 (SH3) domains, Based on this finding, we hy pothesize that additional protein modules exist and that they could be isolated using proline-rich peptides as functional probes.