– WW Domain-Binding Protein 1 (WBP1) is widely expressed in many tissues, but it is lowly expressed in the lung, placenta, kidney, and liver. WBP1 contains two WW-binding motifs: WW-binding 1 and WW-binding 2 that are involved in mediating protein-protein interactions through the binding of polyproline ligands. The WW-binding domain is composed of 38 to 40 semi-conserved amino acids shared by proteins with diverse functions including structural, regulatory, and signaling proteins. In addition, WBP1 also encodes a ligand of the WW domain of the Yes kinase-associated protein. This function has not been determined.