A deubiquitinating enzyme UBPY interacts with the Src homology 3 domain ofHrs-binding protein via a novel binding motif PX(V/I)(D/N)RXXKP

Hrs-binding protein (Hbp) is a Src homology 3 (SH3) domain-containing prote in that tightly associates with Hrs. Hbp together with Hrs is thought to pl ay a regulatory role in endocytic trafficking of growth factor-receptor com plexes through early endosomes. Association of Hbp with a binding partner(s ) via the SH3 domain seems to be essential for Hbp to exert its function. I n this study, we searched for Hbp-binding proteins by a far Western screeni ng and isolated a mouse cDNA clone encoding a deubiquitinating enzyme mUBPY as an Hbp SH3-binding protein, mUBPY has two Hbp-SH3 domain binding sites. Mutagenic analysis identified a consensus sequence PX(V/I)(D/N)RXXKP as th e Hbp-SH3 domain binding motif. It is a novel SH3-binding motif and does no t contain the canonical proline-rich consensus binding motif, PXXP. Ubiquit ination of growth factor receptors is thought to regulate their intracellul ar degradation. Thus, UBPY may play a regulatory role in the degradation by interaction with the SH3 domain of Hbp via the novel SH3-binding motif.